17-F1MM

kiRCHIVES

612_ FISHERIES RESEARCH BOARD OF CANADA

Translation Series No. 812

Ecological studies on the common squid, Todarodes pacificus Steenstrup, mainly in the southwestern waters of the Sea of Japan

By Mototsugu Hamabe and Torao Shimizu

Original title: Nihonkai Seinan Kaiiki o shuni shita Surumeika no Seitaigakuteki Kenkyu.

From: Bulletin of the Japan Sea Regional Fisheries Research Laboratory, No. 16, pp. 13-55. 1966.

Translated by the Translation Bureau (GN) Foreign Languages Division

Department of the Secretary of State of Canada

Fisheries Research Board of Canada Biological Station, St. John's, Nfld.

1967

FISHERIES AND OCEAKI:,, LIBRARY 'BIBLIOTHÈQUE PÊCHES ET OCÉANS OrFAWA, ONTARIO KlA 0E6 CANADA

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Bull. Jap. Sea Reg. Fish, Res. Lab., (16): 13-55, 1966

ECOLOGICAL STUDIES ON THE COMMON SQUID, TODARODES PACIFICUS

STEENSTRUP, MAINLY IN THE SOUTHWESTERN WATERS OF THE SEA OF JAPAN

By Mototsugu Hamabe l and Torao Shimizu

Abstract (published in làlglish)

Experiments and observations on the common squid in the South-western part of the Japan Sea undertaken at the Oki Islands and their neighborhood was described in a previous report (Hamabe, 1962b). The description of the squid included copulation, spawning behavior, hatching, and metamorphosis of its larvae. As a continuation of these studies, efforts have been made to persue the reproduction process, migration, and feeding habits of them, and the results are given in this report.

1) Among a batch of the squid ground under identical environments as to time and place, a biologically minimum size is about 20 cm on the average in the mantle length, before the members of the batch begin activities for reproduction (Hamabe and Shimizu, 1959). As the gonad of the male gets mature earlier than that of the female, the former leads the latter in mating activity. In copu-lation, the sperm-bulb containing the inactive sperms is delivered from the male to the female. About three months later, the sperms in the capsules of the female become active and move into the seminal receptacle, being kept there prior to fertilization. After a while the ovary and oviduct become full of the ova. When the weight of the ovary and oviduct reaches more than one tenth of that of the body, the female deposits the eggs independently of the male.

Although the end of the mating period overlaps with the beginning of the spawning period, the peak of one activity seems to take place separately from that of the other at around the middle of the respective period. As the male gets mature earlier than female, the reproductive and nutritive organs of male are exhausted in their functions earlier than the female. It is conceivable, therefore, that in the latter half of the reproductive period there would be cases where the male dies of exhaustion and becomes fewer than the female in number in the same group. Sometimes, however, the decrease of the male from one group may be attributed to those which come to live, as often seen, in isolation from the female. When the female survives after the male died, the sperms kept in the body of the female become fully active. At that stage, the female staying near the bottom of the sea laye a large number of fertilized eggs in batches (egg-mass), each of which looks something like a football (Hamabe, 1961b). Upon completion of the spawning, the female dies, possibly due to exhaustion, some-where nearby her spawning niche (Hamabe, 1963b).

(13)

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2) Uhtil the squid reaches about 20 cm in the mantle length, the young squid grows at the rate of 3 to 4 cm per month. After that period, the growth rate slows down to about 1 cm per month (Idamabe, 1956). From the study of the mantle length, sex ratio, and migratory patterns to be described below, the squid found in the Japan Sea can be classified into three groups with their life span being respectively estimated at about one year long.

3) A number of the recoveries from tagging experiments conducted so far along the coast of the Japan Sea brought to light the migratory patterns that the squids likely follow in their travel from north or south to the southwestern part across the Sea in different seasons of the year. It is inferred that the first group found in the waters of the Oki Islands possibly comes

1. Now at the Nankai Regional Fisheries Research Laboratory.

2

from the offshore close to the center of the Japan Sea in October and November. This group takes the carne route similar to the southward migration of the second group e she spawning small amounts of eggs on the way. The second group (winter squid) is the main one of the southward migrators. They visit the East China Sea in December and January and pass through the Tsushima Straits, continuing mating on the may. Evidences indicate that sometime around March considerable members of the third group immigrate from the south to the southwestern part of the Sea. They stay there and assume spawning during the months from May to August.

Ecological patterns related to water temperatures revealed that the squids prefer to live in warmer waters as their gonad gets ribe. Consequently the range of water temperatures suitable for them becomes increasingly narrow with the pre7ess of maturation. These observations lead to an assumption as follows; Although the squids live in the sea along chains of warm water masses, they may become adapted to an environment which may be more suitable for their gonad development, passing from one ecologically favorable chain to another adjacent one, the squid may migrate toward warmer waters.

4) The squids are known to form a huge throng under certain circa:instances in the winter, and to rush together onto the beach of regions swept by the Tsushima Warm Stream. According to the informations from these regions, such aggregations are usually taken place at five localities. That is, aggregations are seen at Kunashiri e south Kurile Islands; Hakodate, Hokkaido; Ofunato Bay, Iwata Prefecture; Oki Islands, Shimane prefecture; and the east coast of the Tsushima Islands, Nagasaki Prefecture. In search of the key to the phenomena occurring at these Cifferent places, oceanographic and topographical conditions of the localities were compared with one another. The results disclosed the following. i) The aggregation occurs in December and January when the Warm Stream prevails over the coastal waters of the island where the counter current of the warm water is notably developed. Naturally the area of the counter current forms a terminal point of the whirling chains flowing from the offshore. Under these circumstances the squids accumulate there as a throng and are driven up to the beachdong with a rapid tide or a wind-driven current. ii) They belong to the second group following actively the southward migration. On the moonlight night, they emerge to the surface to copulate and move from place to place, whereas they become moveless and sink for food when it becomes dark. Observations show that these activities are inversely correlated with each other (Namabe, 1964).

5) On the basis of morphometric data and spawning experiments, it was recognized that the winter squid in the region under consideration belongs mainly to the second group of the southward migrators. It reaches its height of copulation in December and Jaauary. Considerable members of the adult squids which occur in the region in spring and summer are the third group of the northward migrator. Apparently they come there to spawn. The first group passes through the region and spawns a little in October and November on its way to the south.

I ,

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6) Efforts have been made to determine factors which participate in providing a spawning ground for the squid. The data were obtained by observing the spawning groups, ment individuals and larvae, as well as environmental con-ditions. The evidences proved that the third northward migrators usually spawn on reefs located in a warm water mass at the depth of 70 to 150 m along the coast under the influence of the warm stream with a temperature of 10-20°C, and chlorinity of over 19.0e.

In addition, there are reasons to believe that the second group spawn (15) from January to March at such localities as the northeastern part of the East China Sea including the Tsushima Straits.

7) Stomach content analyses of the squid indicated that the young members prey not only on plankton but also on fish and various species of their own kind, as well. Particularly those which attain 15 - 20 cm in mantle length seem to devour any kind of food without selectivity. As a result they grow fast. After reaching that stage, however, as they become ready to spawn, the fish and squid are more frequently found in their stomachs than before. In the subsequent period of their life, they tend to eat only their fellow members but apparently with a falling appetite. Reflecting this tendency an empty stomach occurs with a higher frequency, especially in the male sampled in summer months.

Comparing with the individuals sampled at the bottom in the daytime, those caught on the surface water at night were remarkable in leaving a stomach lighter in weight or empty with 0.1-4;.j1rfrequency of occurrences. The adult squids stay at the bottom in the feeding period. From these evidences it is inferred that the adult squids copulate mainly at night on the surface and eat in the daytime at the bottom.

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TABLE OF CONTENTS

AbStraet 00000oo00coo0OoppOoogob00000000oopoeou0...O... , ........ 00....ee 13

I . Prefae0000000500.0041so0000000000.0000000000o 0 0.0 0000000000000000000 16

Physical Dimension Datao.01.00000.000npopop000p000 ,200.0ooeop0000000.0 16

III Growth and 17

1. Hypothesis concerning the growth of different genealogical groups .. 17

(1) 1st southward migratory group..................................... 18

(2) 2nd southward migratory group..................................... 18

(3) 3rd northward migratory gr0UP000000000000110000000000000.0000000000 18

2 Discussion0 Q O Q Q Q O Q O Q Q O Q Q QQ Q Q O Q Q O O Q Q Q Q O O Q S O Q O Q Q Q Q O Q Q O O O O Q Q O Q O O • ... • 19

IV . MOVeMentp.Opopoopn 0 ao0000000900000000c0000p000o00 030000o00000000000 20

1. Past observations.......................•........................... 20

2. Migration - tagged release surveys.................................. 20

(1)Material and MethOdp000000000000000 000000.0o000000000000000001,0 OOOOO 20

(2)Release and recovery5000000000000Q.O.000QOQ00000000000QQ000Q00000000 20

(3) Discussion.......................................................... 21

A. Movement of the 1st southward migratory group..................... 21

B. Movement of the 2nd southward migratory group in the Oki

Island WaterS000000O.O000000000000000000000000000000000.00000091100 21

C. Movement of the winter fishing season terminal group in the

Oki Island waters Opecroop0000...00g000peo0p7On/boo"opOo000o00000000 22

D. Migration of the 2nd southward migratory group to Shimane

Peninsula, Tsushima and Goto Island waters, and migration

of the winter fishing season terminal group to the Tamma

and Wakasa coasts.•.............................••.•...........•.. 23

E. Proof that the winter fishing season terminal group caught in

March in the Oki Islands is the forerunner of the 3rd northward

migratory group...........,...................................... 23

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3 . Swarming Phen0Menapp000pppoopm..p0O0000.000000000000000000000p0O000000000 26

(1) Past, observation.s. 0000.0opOoopp00000o1“00000rootr00000000 ,30P0001700o0Opop 26

(2) Swarming phenomena at Akashima and Ashigaura near Kamoiso-cho

on the east coast of Tsushima in Nagasaki Prefecture................... 26

(3) Swarming phenomena in the Oki Islands in Shimane Prefecture............ 27

(4) Recapitulation and discusnion 27

(5) SUMMarY000000000000000000000000000000000 0 000000000000000 0 00000000000.0. 30

V. Sexual Maturation Process................................................ 30

1 0 Principal mating season of the nocturnal surface layer squid group

of the coastal region seen in the case of the Oki Islands............... 31

2. Principal spawning season of the nocturnal surface layer squid group

of the coastal region seen in the case of the Oki Islands............... 31

3. Principal mating season and principal spawning season of the nocturnal

surface layer squid group in the southwcstorn offing region of the

Sea of JaPan000000000000000000001.00000000000000000000000000000000000000 33

4 0 Principal mating season and principal spawning season of the diurnal

bottom layer squid group in the dredging-net fishing grounds of the

southwestern waters of the Sea of JaPan00p0000000000000000000b00000000. 34

5 , Discussion............................................................. 34

VI . SpawningGrounds. 0 000 0 00000 0 000000000000000000000000000000000000000000. 35

1. Distribution of the spawning group..................................... 35

(1) Collection results in the nocturnal surface layer...................... 35

(2) Collection results in the diurnal bottom layer......................... 36

2. Distribution of squid weakened by spawning and squid dead from spawning. 37

(1)Collection results in the nocturnal surface layer...................... 37

(2)Collection results in the diurnal bottom layer......................... 37

(3)Name of the so-called "dead common squid" collected in the

.. 37 diurnal bottom laYer0000.0000oro

3 0 Distribution of juvenile 0.D000000DD00000D00000DDDD000D0000DDDDDDDD00000 39

(1) Collection results in the nocturnal surface layor..................... 39

(2) Collection results in the diurnal bottom layer........................ 40

4. Spawning 40

5 0 DiSCUSSi011 00o0000000000oon0000a0o000000004,000000000000000000o00000000000 41 (16)

VII . Feeding HabitS00000000000000000000000000000000000000000000000000000000 42

Pas b observations... c000n 0000000000 0 0 0 00 00 0 000 0 0• 11 000 . 0000 . 000000000 . 0 42

2. Stomach content composition and stomach weight of nocturnal surface

layer squids of different mantle lengths....0000..................0.0 43

3. Stomach content composition and stomach weight of diurnal bottom

layer squids of different mantlo longths............................. 44

4- Discussion0017000DopoOpoppOnoOD.GOOD000000“00o000000000•0009000000000 45

VIII . Siirirnary. O D O D D O O O O D O O O O D O 0 0 0 D O D D O D D D O O D O O D D O O D 0 0 0 0 D O D C Q D D 0 G D D D Q 0 0 0 47

49

Appended Tablos and Appended FigUr05000000009000000000000000000000000$1.0000 52

I. PREFACE

With regard to the ecology of the common squid, owing to the lack of

developmental information and the difficulty of breeding observations, apart from

limited knowledge euch as information on the mattor of migration, complote infor-

mation has not been obtained on a number of important ecological mattors. Among

them, nevertheless, the subject of development has hitherto commanded the interest

and concorn of a largo number of individuals, there being the contributions of

Sasaki (1921; 1929a), Ishii (1924), Soeda (1952; 1954 1956), Hayushi & Iizuka -

(1953; 1957), Hayashi (1957; 1960), and Soeda, Aratani,, Otsuki & Machinaka (1958),

among others. In addition, Hamabe has reported the results of ecological studios

concerning the propagation of the common squid conducted in the Oki Islands (1960a,

1.

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1962a), and also the results of developmental studies (1962b) which amplified and

corrected the foregoing.

In this report, a collective discussion has been presented of all the

ecological matters that in spite of having a profound correlation with tho afore-

mentioned studies on the ecology of propagation and development, were reluctantly

omitted by necessity from previous reports.

Additionally, while a number of important reports was published together

prior to this report by the authors, including those of Okiyama (1965a; 1965b),

Ito, Okiyama & Kasahara (1965), Okutani (1965), and Hamabe (1965), the inter-

correlation with these was loft for discussion at a later date and has not been

taken up in this report.

Deep appreciation is expresr,ed to Dr. Kiyoshi Uchihashi, former chief of tho

Japan Sea Regional Fisheries Research Laboratory, and present chief, Dr. Senji

Tanita, for their advice in pursuing this study, and also to engineer Genji Kato,

chief of the Laboratory's Resources Section, who undertook the revising.

Additionally, as one of the authors, Hamabe, put this report together after

being transferred to tho Nankai Regional Fisheries Research Laboratory, much kind

assistaaco was received from many superiors and friends at both the Japan Sea

Regional and Nankai Regional Fisheries Research Laboratories, including their

chiefs. In particular, warm assistance, both material and otherwise was received

from Dr. Tadahiko Asami, chief of the First Laboratory of the Coastal Resources

Section of the Nankai Regional Fisheries Research Laboratory, as well as the members

of the staff of this section. Tho arrangement of the material and figures was done

by throe gentlemen, Gunsoi Kodaira, Fisheries Science student in the Faculty of

Agriculture, Miyazaki University, Kenzo Muraoka, - KOChiTrefectural Fisheries Indus-

trial Improvement and Propagation staff member, and Hiroyuki Suzuki, Tokushima

Prefectural Fisheries Industrial Improvement and Propagation staff member. To all

of these, an expression of sincere gratitude is recorded.

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II. PHYSICAL DIMENSION DATA

With regard to dimensional data, in the female they include tho mantle

length and thickness, body weight, oviduct weight, ovary weight, egg gland length

and weight, gonad maturity, number of sperm sacs on the outer labia of the oral

bulb, number of milky sommai receptacles on the circumoral membrane, stomach

weight and content variety, liver weight, and number of parasites, while in the

male, the reproductive organs replace those of the female and the 11 items exclud-

ing the traces of mating are included. The dimensional data in respect of each of

the aforementioned items were collected from (1) 14,613 nocturnal surface layer

squids (common squids caught by single lino, stationary net, purso-not, and picking

up swarming squids) in the Oki Islands during 1954-1963 (comprised of 6,617 juveniles

9 cm and under in mantle length, 1,949 immature squids 10 - 19 cm in mantle

length, and 6,047 adults 20 cm or over in mantle length); (2) 674 adult nocturnal

surface layer squids and diurnal bottom layer squids (common squids caught by

dredging-nets from bottom layers less than 500 m deep) at Tsushima and Goto Island

during 1960-1963; (3) 2,992 nocturnal surface layer squids (539 juveniles, 1,135

immature squids, and 1,318 adults) at Tama during 1962-1963; and (4) 8 5 058 diurnal

bottom layer squids (687 juveniles, 4,523 immature squids, and 2,848 adults) at (17)

the dredging-not fishing grounds in the southwestern waters of the Soa of Japan

during 1961-1963. These dimensional data are intended to be tabulated and published

in a separate report.

Among the items of measurement, it has traditionally been problematical to

ascertain the degree of maturity of the gonads with the naked eye. As a result of

a series of developmental studios conducted in the Oki Islands (Hamabe, 1961a; 1962a;

1962b), the standards adopted by the authors in determining the degree of maturity

of the gonads of female squids were that, those in which all the internal incubatory

organs (the ovary and left and right oviducts) were full of mature eggs, the weight

• •:

of which was 10% or more of the body weight, were considered fully mature females,

those likewise between 9% and 2% with only a few mature eggs in the oviduct and

thought to require some timo before spawning wore considered mature females, and

those likewise 2% or loss with no mature eggs whatover were takon to be immature

femalos. In addition, those whose skin was strippod and in which a striking docroase

in the content weight of the incubatory organs and liyor was notod along with a

shruhken mantle (Hamabe, 1963a), were deemed to be spent femalos in the process of

dying from post-spawning exhaustion.

In the classification of males, using the formation or non-formation of

spormatophoros in Needham's sac as the basis of difforentiation, those unformed were

taken to be immature males and thoso so equipped were considerod mature males,

while those possessing spormatophores but whose features and internal organs were

doomed to be in a state of debility similar to that of the spont fomalos were

classified as spent males.

III. GROWTH AND LIFE-SPAN

1. Hypothesis concerning the growth of differont genealogical groups

With regard to growth, ago-class, and life-span, there are the reports of

Sasaki (1921), Ishii (1924), Tanouchi (1941), Ito (1952), Yasui & Ishibe (1955),

Sooda (1956), Hamabo & Shimizu (1956), Sooda, Aratani, Otsuki & Plachinaka (1958),

and Hamabo (1963a).

While Tanouchi (1941) reported that the age-class of common squids goes as

high as 4 years, Ito (1952) calculatod the rate of growth to be approximately 2.5

cm per month-and surmised that they die ii about 1 yoar and a half. In the reports

of Sasaki (1921), Ishii (1924), Soeda (1956), and Sooda, Aratani, Otsuki & igachi-

naka (1958), it has been ostimatod that mature growth to a mantlo length of 25 cm

takes 1 year, and giant squids of 30 cm or more in mantle length require something

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over 1 year. In addition, Yasui & Ishibe (1955) reported that maturity is reached

in 1 year at a growth rate of 3 - 4 cm per month during the first - 6 months after

hatching and 2 cm per month after that Hamabe & Shimizu (1956) estimated the

growth rate to be 3 - 4 cm per month up to a mantle length of 20 cm and 1 cm per

month above 20 cm, and that 1 year is required to attain standard size adulthood

(winter squid).

On the other hand, in the isolated island waters of the Sea of Japan, there

ha s over the years existed one genealogical group known as the isolated island

stationary group, or the summer remnant group (Soeda, 1950), which had been believed

to follow a stationary existence with the isolated island waters as its sphere of

life. While this group had been looked upon with considerable interest as a conve-

nient isolated group for learning the complete life history and tracing the growth

of squids, as a result of a full year's survey by the authors on the common squid

groups that appear in the Oki Island waters, its existence is thought to be doubt-

ful, and instead, it is felt that it might have been more correct to take the view .

of overlapping migration times between several genealogical groups that commonly

migrate with the season.

For all the shortness of the life-span of common squids, they are pelagic

marine animals that engage in long range migration, and moreover, judging from the

fact that they appear to comprise several genealogical groups, their spawning

season and spawning grounds are seen to be long and extensive, and the distribution

and expansion of newly developed groups are also deemed to be quite complex. Even

by simply taking a look ab the juveniles developed in one genealogical group,

judging from the differences in their ecological characteristics due to such

environmental variables as the abundance of food and the extensiveness of the

feeding ground at the places they visited, it is felt to be certain that they split

into a number of different groups, but the big question is how to distinguish the

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various groups of cannon squids. In thinking about the group separation cf common

squids, since no clearly distinctive qualities have so far boon dotocted in such

characteristic features as bone structure and sucking-disk tooth, in a strict senso

the concept of groups romaine rather difficult. Accordingly, as tho next best (18)

policy, the idea was evolved whereby groups would be distinguished on the bai s of

their forming soparate colloctive groups when caught, with different spawning and

mantle length ranges, and being unrelated to other groups in the gonad maturity

stage and the corresponding group sox ratio, and also of groups that could not be

deemed to have any genoalogical connection with other groups from the results of

tagged release surveys. This takes the conceptual view that tho genealogical groups

would have homogeneous life cycles and developmental stages, consisting of units

subject to substantial numerical variation, and should not necessarily be meaning-

less under the prosent circumstances.

Looking at it from the foregoing viewpoints, the presence of tho 1st south-

ward migratory group, 2nd southward migratory group, and 3rd northward migratory

group described below can be considered in the southwestern waters of the Sea of

Japan. Those aro known respectively as autumn squid, winter squid, and summor

squid, and the differences in their arrival soason, volume of catch, characteristic

features and sex ratio are familiar to squid handlers.

(1) 1st southward migratory group

This is a group of largo-size common squids having a mature mantic length

of 27 - 33 cm or even greator, with a life-span estimated to be 1 year or more.

This group consists of common squids that inhabit the 3rd tributary of tho Tsushima

warm current or the central part of the Sea of Japan influenced by the East Korean

warm current (Fisheries Agency Investigative Rescarch Section, 1962), and thoir

distribution is surmised to extend oven as far as the cold continontal wators beyond

the polar front and tho coastal waters of the continent. The period when this group

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arrives in the southwestern waters of the Soa of Japan is Septembor-Novembor, and

in the group that appears in the coastal region there are many females. This is a

spawning group in which tho gonads of the femalos arc oithor maturo or fully mature,

while the gonads of the males are all in a stage of maturity, and is what is known

as the autumn squid in the Oki Islands, Tama and Imban coasts, and as the equinoc-

tial squid at Tsushima and Goto Island. This group is surmised to cross the Tsushima

Channel and leave the Sea of Japan by Docembor.

(2) 2nd southward migratory group

This is a group of standard size common squids having a maturo mantle length

of 24 - 27 cm, with an estimated life-span said to be approximately I year. Common-

ly known as the winter squid or cold squid anywhere on tho Soa of 42 an coast, these

squids constitute the main group that is caught mn the wintor soason. This group

inhabits the 2nd tributary region of the Tsushima warm current, and distributes

itself mainly over the entire coast of Hokkaido including tho Sea of Okhot*, and

the Sanriku coast. This northern group enters the Sea of Japan by crossing the

Soya and Tsugara Straits around October and Hovomber, moves into southward migration

on masse around December, and leavos the Soa of Japan from Tsushima Strait about

:Larch. This group has traditionally been known as the northern winter spawning

group (Hokkaido :Fish. Exp. Station, 1931a), or the common group (Yasui & Ishibo,

1955), and the sexual characteristic of this group at the time of its visit to the

southwestc,rn waters of the Sea of Japan (Docember-March) is that initially there

are many malos, with a gradual equalization lacing soon in the number of malos and

females. The maturity of the gonads is remarkably close to 100% maturity in tho

males, but the females vary largely with the year, and while at timos as many as

20% of tho total are seen to be maturo, oven in those cases almost none is fully

mature, the greater majority of the females generally boing of the immature mating

group.

1

1 1

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(3) 3rd northward migratory group

This is a group of small-size common squids having a mature mantle length

of 15 - 23 am, with an estimated life-span seen to be approximately 1 year. Since

the arrival period of this group is after April, its forerunners intermingle with

the terminal group of the 2nd southward migratory group, and after April they inter-

mingle with the northbound group of the new-born . generation (commonly called juveniles)

produced by the spawning of the 1st and 2nd southward migratory groups, and because

of their resemblance to those among the new-born group that grow particularly

rapidly, differentiation is difficult. However, under natural conditions, the

2nd southward migratory group and the 3rd northward migratory group, as well as the

3rd northward migratory group and the new-born group, separate from each other to

form their own groups, and the distribution area of each is also inherently differ-

ent. This group makes the southwestern waters of the Sea of Japan as its main

distribution area, the eastern limit of which extends to the west coast of Not°

Peninsula with the western limit extending beyond Tsushima Channel into the East

China Sea, and its center of distribution is the 1st coastal tributary of the

Tsushima warm current, particularly the coastal frontal zone.

What warrants attention here is the fact that,judging from the results of

the tagged release surveys described later, the forerunners of this 3rd northward

migratory group (small-size spawning group) which constitutes the summer squids

(Hamabe, 1963b) of the eastern Sanin area, especially the Tamma coast, arrive in

the Oki Islands coast as early as mid-March. The special characteristic of the

forerunners of the 3rd northward migratory group is that the range of mantle lengths

is smaller than the 2nd southward migratory group, and that they are a pre-mating

group with a low degree of group maturity (males and females are almost equal in

number, with a mixture of mature and immature gonads in the males, while the

females are largely immature and unmated). (19)

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Apart from this, two squids that were released in the spring at Pusan in

Korea were recovered in the eastern Sanin area, and judging from the fact that they

possessed the special characteristics of the small-size summer spawning group,

together with the fact that the "group unrelated to migration" at Tsushima (Tanaka &

Iizuka, 1956), the summer spawning group of the SanrIku coast (Yasui & Ihibe, 1955),

and the female squids of the Hokkaido coast or the southern mmer spawning group

(Hokkaido Fish. Exp. Station, 1931a) are all thought to be close in genealogy to

this group, it is surmised that there are many local groups within what the authors

have summarily called the 3rd northward migratory group. In addition, with regard

• o its migration direction as well, such diversity can be surmised that it cannot

be deemed as being simply northward or southward. On these points, there is a need

for further investigation in the future.

2. Discussion

While the life-span of the standard size common squids is generally estimated

to be about 1 year, because among the common squids there are such large-size groups

as the autumn squids of the southwestern waters of the Sea of Japan, regarding the

origin and age-class of this large-size group, there had hitherto been the 1 year-

class theory (Soeda, Aratani, Otsuki & Machinaka, 1958; Kato, 1959; 1960) and the

2 year-class theory (Hayashi & Iizuka , 1957; Hamabe & Shimizu, 1956).

The authors, in a previous report (Hamabe & Shimizu, 1956), emphasized such

ecological characteristics as the fact that, in the giant squid group whose mantle

length measures 33 cm or more, there is a large number of females in the group, and

the maturity state of the gonade of the females is considerably advanced, and with

these facts in mind, the following manner of thinking was done. That is, while

those squids of common standard size aged 1 full year to a mantle length of around

27 cm almost all die for reasons of reproductive exhaustion (Hamabe, 1963a), the

few that survive for some unknown reason were surmised to continue growing even

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beyond the first full year and become so-called mold-timere. This supposition,

however, has not been supported by any observed examples of the survival phenomenon

of the common squid in natural waters, nor has it been verified experimentally, and

1st group J pan

the 1st group L',ea of J pan

-3rd groups H

H

S-vmbol 2' 211

2nd group

e 3rd group f Japan

so it has the weakness of being rejected as

Fig. 1. ilyroth:Dtical growth curvo of the 3 genealogical groups of common squids.

J 1 - 3 ... Juvenile group of the lot 1 1 - 3'... Immature group of

\a" - 3" • liating group of ilm' -3".. Spawnirg group of

Loca2 name of the catch-group r-Sanriku and ISol±aido summer

ti il .winter .2,ntire Japan Sea coaSt; Sanin summer s-1uid _

A . . . 3pawning_ . volume and seas on of in the fwestern part of the

' )2a.st China. Sea 13...Spawning- volume and season of the

in -U:le L'a f3 1; China Sea C,.,Spawning volume and season of th

in the western part of the : ._,et.t o

The black areas indicato the relative size of the quantity produced, while the white or shaded areas are unrelated to quantity.

an unsubstantiated conjecture. On this

point, the authors tentatively

founded their hypothesis on

such phenomenal similarities

as the fact that the fresh-water

sweet-fish, which is a short-

lived marine animal with a one

year life-span similar to the

common squid, aImost all die

after spawning, and the excep-

tional few that do survive

enter the second year of life

the following spring as biennial

sweet-fish or old-timers (Ishi-

kawa, 1930), along with the •

fact that among these old-timers

'there are many females whose

gonad maturity state is consid-

erably advanced, and also that

in the pond-smelt as well,

there are many large-size

mature females among second

year specimens (private corres-

pondence with Matsubara, 1963).

I I

sciuid squid

1 qu t e e yri

- 15 -

However, looking at the tagged release surveys discussed later, and (20)

particularly the continuity pattern of the gonad maturity state investigated as

a means of deducing the genealogical continuity, these 3 groups are mutually ide-

pendent groups, and the occurrence period of each group overlaps and intermingles

in their initial and final stages depending on the year, while quantitative varia-

tions are also involved to make the situation rather complex. Neverthe less, it can

be thought that the 1st group appears in the autumn, the 2nd group inlinter,md

the 3rd group in summer, that the mating and spawning seasons of each group occur

at respectively different times, and that it seems proper to view the growth dif-

ference seen as age-class difference to result from variations in the birth period

and environmental effects on growth.

Among the 3 genealogical groups, no clear, ecologically distinctive features

can be discerned, and particularly since the life process from the youngling stage

to the spawning stage cannot be separately traced, any depiction of their growth

curve is rather difficult, but judging from the fact that the life-span in all

groups is about 1 year or so, that their growth rate as a species is generally

3 - 4 cm (mantle length) per month, and that during the mating and spawning periods

there occurs a reduction in feeding as will be mentioned later, hypothetical growth

curves were drawn on the assumption that all 3 groups had the same growth rate and

that the lengths of their mating and spawning seasons were respectively different.

It is anticipated that the growth rate of the respective groups might be clarified

in the near future.

IV. MOVESUŒ.IT

1. Past observations

The important and fundamental aspects of the movement patterns of the common

squid are the diurnal vertical movements and the seasonal horizontal migrations.

- 16 -

On the diurnal vertical movements of the common squid, there are the reports

of Sasaki (1921; 1929a) and Ishii (1924), while with regard to the seasonal hori-

zontal migrations, there are many reports based on assumed migratory routes derived

by joining the release points and recovery points of tagged release surveys (Sasaki,

1921; Ishii, 1924; Soeda, 1950; Hoshino & Mon, 1951; Hamabe & Shimizu, 1957b;

Soeda, Aratani, • tsuki & Machinaka, 1958; Màchinaka, 1957; 1959; Kojima, 1959;

Yasui, 1961; Aratani gc. Kawasaki, 1962; Fisheries Agency Investigative Research

Section, 1962).

The migration survey conducted by the authors in the southwestern waters

of the Sea of Japan aimed not only at determining the migratory routes, but also

at ascertaining the changes in the maturity state of the gonads that take place in

transit, by means of contrasting the physical dimension values of released squids

and recovered squids. In addition, upon observing the movements of the common

squids in the Oki Islands, a peculiar group movement describable as a "swarming

phenomenon" was discerned. This group movement entailed the phenomenon of a large

mass of common squids advancing into Saigo Bay and Urago Bay from the outer offing,

pushing deep into the narrow reaches of the bay, and leaping upon the shallows and

the beach so that people could pick them up, and the authors studied this swarming

phenomenon in considerable detail (Hamabe & Shimizu, 1955; 1956; 1959).

2. Migration - tagged release surveys

(1) Material and method

For the tagged release surveys, squids caught by single line and squids

caught by stationary net were used. Nickel clip-on tags stamped with symbol and

number were attached to the fins of these squids, and the unit of survey was 1,000

squids at a time. The release point was the Oki Islands in -winter-spring and the

Tamma coast in the spring-summer season. In carrying out the surveys, emphasis was

placed on studying the southward and northward migrations of the common squid groups

-17-

in the southwestern waters of the Sea of Japan, and particularly the pattern of the

apparent reversal in the migratory direction of the squid groups in these waters in

spring, whilst also bearing the relationships with the genealogical groups in mind.

With these objectives in mind, simultaneously with the release, accurate

physical dimension measurements were taken on the squid group corresponding to those

released, while accurate measurements of the recovered squids and of the group caught

at the same time were requested of the prefectural fisheries experimental stations

and fishing cooperative unions in the expected recovery areas, thus providing the

data for ascertaining the maturity state of the gonads and its continuity pattern.

(2) Release and recovery

A summary of the 17,282 releases and 500 recoveries carried out between (21)

1950 - 1960, and of the 7,850 releases and 35 recoveries made in 1962 and 1963 has

been provided in Appended Table 1. Combining these tagged release survey results

with the results of tagged release surveys conducted in the offing of the Sea of

Japan in 1962 (Fisheries Agency Investigative Research Section, 1962), the assumed

migratory routes in the 'waters near the Oki Islands and the southwestern waters of

the Sea of Japan have been depicted as shown in Fig. 2.

(3) Discussion

The common seuid fishing season in the southwestern waters of the Sea of

Japan is divided into the fall fishing season involving the 1st southward migratory

group during the autumn months of September-November, the winter fishing season

involving the 2nd southward migratory group in December-January, and the summer

fishing season involving the 3rd northward migratory group during May-August. It

had not been clear whether those traditionally caught in the 3-month period of

February-April between the winter fishing season and the summer fishing season,

were really confined only to the remnants of the 2nd southward migratory group or

were replaced or overlapped by another group, namely the 3rd northward migratory

-18-

Fig. 2.

groupe Thus, in order to

clarify the relationship

of the genealogical conti-

nuity of the groups, tagged

releases were carried out

in the Oki Islands with

the 2nd southward migratory

group of December-January

and the winter fishing

season terminal group of

March, and emphasis was

placed on clarifying the

relationships between these

two groups and the 3rd north-

ward migratory group of the

summer season which was

tagged and released at the

same time on the eastern

Sanin coast.

A. Movement of the 1st

southward migratory group

It had hitherto been

surmised that ono group of

large-size squids known as the autumn squids in the Oki Islands and on the Tamma

coast and as the equinoctial squids at Tsushima, seemed to conter its distribution

in the polar frontal zone that forms near Yamato Bank in the central part of the

Sea of Japan, and from the results of tagged releases involving the offing group

- 19 -

in the vicinity of Yamato Bank (Fisheries Agency Investigative Research Section,

1962), judging from the fact that the recovery points were found to be on Tsushima

and the Tottori coast, as well as the fact that their recovery periods corresponded

to the respective fishing seasons for equinoctial squids and autumn squids, it was

verified that this assumption was largely factual.

B. Movement of the 2nd southward migratory group in the Oki Island waters

Owing to the northwesterly monsoon that predominates in the winter season,

and the topography of the Oki Islands which becomes a frontal barrier to this, a

coastal reflux zone is formed paralleling the leeward southeastern coast of the Oki

Islands. This reflux zone extends from the Saigo offing of Dogo on the east to the

Hakashima offing adjacent to Chiburi Island of Dozen on the west, and while it con-

stantly changes with the weather and sea conditions, generally speaking it exhibits

a long elliptical shape with a major east-west axis of 30 km and a minor north-south

axis of 10 km. (22)

The common squid group inhabiting the warm water mass that moves shoreward

from the offing of the Oki Islands in the fall and winter, moves shoreward together

with the warm water mass and intensifies in density (Sasaki, 1921; Ishii, 1924;

Hamabe & Shimizu, 1955). In the Oki Island waters, as the wind-blown currents of

the surface waters of the Tsushima warm current become stronger, the rising of the

characteristically stationary cold water of the bottom layer is intensified, and

both the warm water mass and the squid group are driven from the north-northeastern

region of rising cold water.

It is the 2nd southward migratory group that arrives in the Oki Island waters

around December-January, and upon extracting and studying the tagged release results

for this group from Appended Table 1, in the 2nd southward migratory group there

were 165 recoveries for 10,810 releases, making the recovery rate approximately 1.5%.

Among these, looking at the daily breakdown of recoveries up to the 160th recovery,

-20-

excluding the 5 recovered at remote points, there were 22 recoveries on the day of

release, 80 on the lot day after release, 5 on the 2nd day, 17 on the 3rd day, 21

on the 4th day, 3 on the 5th day, 1 on the 6th day, 2 on the 8th day, 1 on the 9th

day, 7 on the 35th day, and 1 on the 61st day, and judging from the fact that re-

covery was continuous up to a week after release, and that there were recoveries

occurring after 35 days and 61 days, it can be deemed that one section of the squid

group becomes "resident squid" within this reflux vortex zone and hibernates there.

On the offing side of the reflux vortex zone inside of the tidal ridge,

there is a weak current that flows westward, while on the coastal side there is a

weak current flowing eastward. The fact that the recovery results were poor in the

tagged releases involving squids surfacing nocturnally outside the tidal ridge in

the offing of this vortex zone, is seen to suggest that the squids in this area

ride along on the wind-blown surface current and thus leave the Oki Island waters

to commence migration to the Japanese mainland coast and the northwestern waters of

Kyushu. On the other hand, in the tagged releases involving the squid group that

had crossed the tidal ridge on the offing side and had entered the vortex zone, the

released squids were recovered in the process of moving progressively westward riding

on the westerly flow, and in a large number of cases bunched recoveries were made in

the resting grounds at Hakashima and Misaki offing on the western edge of the vortex

zone, while on the coast the released squids riding and moving eastward with the

easterly flow were successively recovered from the west, and the recovery points

were discerned to be shifting towards the Saigo offing on the eastern edge of the

vortex zone. In addition, possibly because the Toyota and Toman vicinities influenced

by small drift currents flowing in from Oki Channel are used as assembling and rest-

ing grounds by the squid group inside the coastal reflux zone, there is a tendency

for the recoveries to bunch up in these localities.

C. Movement of the winter fishing season terminal group in the Oki Island waters

Among the common squid groups that arrive in the Oki Islands, the group seen

- 21 -

around March towards the end of the winter fishing season is smaller in sise and

more retarded in the degree of gonad maturity in both males and females as compared

to the 2nd southward migratory group of December-January. For this reason, it is

necessary to clarify whether this group seen at the end of the fishing season around

March should be looked upon as a poorly developed trailing group belonging to the

2nd southward migratory group, or as an intermixture or replacement involving another

different group (3rd northward migratory group). In the tagged release surveys in-

volving the fishing season terminal group of March, emphasis was placed more upon

clarifying its genealogical continuity relationship with the 3rd northward migratory

group appearing in the southwestern waters of the Sea of Japan in summer, rather

than upon its relationship with the 2nd southward migratory group. Since the 3rd

northward migratory group of the summer is a small-size spawning group, in objective

terms it would be sufficient to verify whether the fishing season terminal group,

that is the small-size pre-mating group, in the Oki Island in March is related with

the small-size spawning group of summer squids on the eastern Sanin coast in June,

both genealogically as well as in terms of its gonad maturity state continuity pat-

tern, and thus determine whether the fishing season terminal group of March is a

forerunner of the 3rd northward migratory group or not.

The coastal reflux zone in the southeastern coastal offing of the Oki Islands

gradually becomes obscure in outline because of a weakening in the monsoon and a

resultant deterioration in the vortex action around March-April when the Tsushima

warm current shrinks up, while on the other hand, as a result of being enveloped in

a cold water mass, the Oki Islands vicinity reveals a super-cooled phenomenon (23)

(Sasaki, 1921), and thus becomes unfavourable for the habitation of squid groups.

Consequently, the squids released at Urago Bay during this period almost all loft

directly for the outer -waters following the west coast of Urago Bay, and there is

no eastward movement along the foot of the islands as seen with the 2nd southward

- 92 -

migratory group. There were 10,472 releases involving tho fishing season terminal

group in the reflux zone, from which 338 recoveries were made (recovery rate of

approximately 3%). Of these, the daily breakdown of recoveries up to the 336th

recovery, excluding the 2 recovered at remote points, was 330 after I day, 3 after

3 days, 2 after 4 days, and 1 after 5 days, generally indicating a tendency for a

relatively short time lapse until recovery, and thus differing from the movement

of the 2nd southward migratory group inthis respect.

D. Migration of the 2nd southward migratory group to Shimane Peninsula, Tsushima

and Goto Island waters, and migration of the winter fishing season terminal

group to the Tamma and Wàkasa coasts

Extracting the remote recovery cases from the results of tagged release

surveys carried out in the Oki Islands and on the Tamma coast from 1950 to 1963 (in-

volving a total number of 25,132 releases), and also adding to those the results of

similar surveys at Yamato Bank in 1962 (Fisheries Agency Investigative Research

Section, 1962), the migratory routes during the period from the autumn-winter season

to the summer season were hypothesized (Fig. 2). According to fig. 2, the recovery

points of tagged squids of the 1st southward migratory group were noted on the

Shimane Prefecture coast and the east coast of Tsushima, and the recovery points

of tagged squids of the 2nd southward migratory group occurred in 3 cases on the

east coast of Tsushima and in 2 cases on Shimane Peninsula, while the recovery points

of tagged squids of the winter fishing season terminal group occurred in 1 case at

Goto Island and in 5 cases on the Tamma and Wakasa coasts. Looking at the monthly

directional frequencies with respect to such remote recovery cases, among the Oki

island releases there were 6 cases of southward movement in January, 1 case of south-

ward movement in February, 1 case of southward movement in March and 2 cases of

northward movement in March, while in the Tamma releases there were 3 cases of north-

ward movement in June. This suggests that, assuming the Oki Islands to be the base,

-23-

the common squids move southward along the coast around January-Màrch and reverse

northward in March-June, and in the squid groups arriving in the southwestern waters

of tho Sea of Japan in winter, the presence can be noted of a group which stays for

a long period in the waters between the west coast of Noto Peninsula on the east

and Tsushima Channel on the west, and spreads out over the coastal region in the

spring and summer, quite distinct from the one that passes through Tsushima Channel

and leaves for the East China Sea.

E. Proof that the winter fishing season terminal group caught in March in the

Oki Islands is the forerunner of the 3rd northward migratory group

As made clear from the results of tagged release surveys discussed thus far,

there is a reversal in the migratory direction of the common squids in the south-

western waters of the Sea of Japan, and the alternation or replacement of groups

can be surmised to take place internally. Whether this is true or not can be ascer-

tained by the tendency in the shifting of fishing grounds as well as by the monthly

variation in the volume of catch in the spring and summer season in the various

coastal prefectures adjoining these waters. Since the tagged release surveys ran

from 1950 to 1963, the 1955-1956 period corresponding to their mid-point was taken

Table 1. Monthly volume of catch of common squids in the 11 prefectures adjoining the western Sea of Japan and :East China Sea areas (1955-1956).

(unit: ton)

- 24 - (24)

and the monthly volume of catch of common squids in the 11 prefectures on the west

coast of the Sea of Japan was examined as shown in Table 1.

As can be seen in Table 1, the volume of catch in the 11 prefectures is

given in the ratio of 3:1 between that of December-January in winter and that of

June-July in summer. The volume of catch in Shimane Prefecture including the Oki

Island fishing grounds is minimal in March-April and increases from May onwards,

and since this trend is the same everywhere east of Shimane Prefecture, there is

no doubt that a northward reversal of the common snuids takes place in the waters

west of Shimane Prefecture. What poses a problem here is the fact that the group

caught in summer is a mixed group consisting of a spring-bred group and a spawning

group containing females with a highly advanced state of gonad maturity, and also

the fact that there is a wide variation in the compositional ratio. In order to

clarify this situation, a compositional survey was carried out of the summer squids

landed at Kasumi harbour in 1962-1963, whereupon it was found that adult squids

consisting mainly of the fully mature spawning variety were predominant, comprising

6040% of the daily volume of catch, and that it reversed the composition of the

record catch years (1950-1952) comprised mainly of immature squids. In actual fact,

while it is risky to generalize on the basis of the composition of 1962-1963, the

mixture rate of adult squids in the composition of normal harvest years is high,

being in many cases as high as 1/2 - 1/3 of the total volume of catch, and it becomes

clear that the summer souids in the southwestern waters of the Sea of Japan cannot

be considered without taking the presence of adult snuids into account.

What was most anticipated by the authors in carrying out the tagged release

surveys was the clarification of the time lapse between the release and recovery,

and the corresponding change in the maturity state of the gonads. Accordingly, the

maturity state of the gonads of the common squids was examined in the release area

and the recovery area during the months of release and recovery. This is shown by

1 - 25 -

items A-E in the following table.

Release area

A Oki Islands; March 1960: males (im-mature and mature mixed); females immature

B Oki Islands; January 1959: males mature; females immature (a few mature and fully mature mixed)

C Oki Islands; February 1958: males mature; females immature (a few mature and fully mature mixed)

D Oki Islands; March 1957: males (im-mature and mature mixed); females immature

E Oki Islands; March 1957: males (im-mature and mature mixed); females immature

Recovery area

Goto Island, Nagasaki Prefecture; April 1960: males mature; females fully mature

Tsushima, Nagasaki Prefecture; February 1959: males mature; females immature (a few mature and fully mature mixed)

Shimane Peninsula, Shimane Prefecture; Feb. 1958: males mature; females immature (a few mature and fully mature mixed)

Kanjin-cho, Kyoto Prefecture; May 1957: males mature; females fully mature

Etsuzen Promontory, Fukui Prefecture; Jure 1957: males mature; females fully mature

The general tendency that can be noted from items A-E in the foregoing

table is that the maturity state of the gonads in the squid group of January-March

released in the Oki Islands, changes from mature males with a small mixture of

immature ones and immature females with a small mixture of mature and fully mature

ones, to mature males and fully mature females in all cases 1-3 months later at

the recovery points of Goto Island, Kyoto and Fukui, indicating that the sexual

maturity of the squid group advances rapidly in the spring-early summer season.

In addition, in the case of items D and E in the above table, the physical

dimension measurements of the recovered squids themselves were obtained to enable

comparison with the dimension measurements taken at the release point. With regard

to item D, from among the 500 squids released on March 22, 1957, 1 female was caught

by single line on May 7, 1957, in the offing 4 nautical miles NNE of Kanjin, Tango-

cho, Takeno-gun, Kyoto Prefecture, while in the case of E, 1 other female was re-

covered on June 4, 1957, at the Takasa stationary grounds, Etsuzen-cho, Tansei-gun,

Fukui Prefecture. The former measured 25.0 cm in mantle length, 315.0 g in body

- 26

weight, 34.0 g in incubatory organ (ovary and oviducts) weight, 11.5 cm in nidamental

gland length and 21.5 g in egg gland weight, while the latter measured 22.8 cm in

mantle length, 275.0 g in body weight, 27.5 g in incubatory organ weight, 9.7 cm

in nidamental gland length and 13.3 g in nidamental gland weight, both being fully

mature females. While it is difficult to let these 2 examples alone represent the

entire group, at least they can be emphasized as being actual cases which possibly

show sonie genealogical continuity and continuity pattern in the gonad maturity state

between the souid group in the release area and in the recovery area. From this

viewpoint, the authors surmised the fishing season terminal group of March in the

Oki Islands to be the small-size spawning group, that is the forerunner of the 3rd

northward migratory group, traditionally caught intermixed with the summer squids

of the Sanin and Wakasa coasts around May-June, or a mixed group composed mainly of the

forerunners of the 3rd northward migratory groupe

Upon combining the results of migratory surveys conducted by other re- (25)

searchers in the Sea of Japan with the results of migratory surveys carried out

in the southwestern waters of the Sea of Japan by the authors on this occasion,

the following phenomenal points can be discerned concerning the migration of the

common squids. That is, the 1st southward migratory group is surmised to move

southward in autumn while spawning along the southwestern coastal waters of the Sea

of Japan, with the final group passing through Tsushima Channel around December to

leave for the East China Sea, while the 2nd southward migratory group is believed

to have its peak mating season in the southwestern waters of the Sea of Japan in

winter, and passing through Tsushima Channel around January-February, it is assumed

to group for spawning in the eastern part of the East China Sea including Tsushima

Channel to carry out its main spawning. One section of this group can also be

thought to remain and pass the winter: in the southwestern waters of the Sea of Japan,

reversing northward in the spring-summer season while spawn-grouping, but its number

- 27 -

is deemed to be extremely small. The 3rd northward migratory group shows a dense

distribution as the main group in the southwestern waters of the Sea of Japan in the

spring-summer season, and on this point, it serves as a valuable squid resource in

the southwestern waters of the Sea of Japan. The forerunners of this group, however,

are seen to be in the Oki Island waters as early as the end of the winter fishing

season around March.

While it is just as important to carry out tagged release surveys involving

the juveniles as with adult souids, because of a number of technical difficulties

in addition to environmental and ecological disadvantages, this has not been con-

ducted either effectively or sufficiently. As a substitute fer this, there is no

other means but to analogize the movement patterns of the juvenile group from the

relationship between the catch conditions of common squid juveniles in stationary

nets in the Oki Islands vicinity and Tamma coast, and the variation in the sea

conditions. While the distribution of the natantly feeble new-born group of spring

is seen to occur largely in the strong current zone of the Tsushima warm current

which is its conveyer current, the eventual distribution is believed to break up

into 3 distinct groups. First of all, it is thought that the coastal water mass in

the birth area containing the new-born group is swallowed up by the Tsushima warm

current, and the juveniles accompany the flow of the water mass thus torn away, so

to speak. Then, due to subsequent fluctuations in the strength of the warm current,

the juvenile group drawn into the warm water mass splits up into 3 groups consist-

ing of those that enter the flow axis of the Tsushima warm current, those that

remain in the vortex zone in the central part of the Sea of Japan, and those that

remain in the coastal waters. These 3 groups are presumed to be the origins of

the 3 genealogical groups of adult migrators that differ in their mature mantle

lengths in the reproductive stage due to differences in development caused by varia-

tions in their respective time of birth and environmental variances. This sort of

- 28 -

he new-born group and adult group has been

3 0

Juvenile-immature group • Mating group Spawning group Migratory direction

Fig. 3. Hypothetical diagram concerning the migration and distribution of the 3 genealogical groups of common squids in the Sea of Japan.

Ag Central growth area 1: 1st southward group Bg Northern growth area 2: 2nd southward group C: Coastal growth area 3 3rd northward group

hypothetical relationship between t

diagrammatically presented in Fig.

The problem with regard

to Fig. 3 is that the spawning

group (1) of the 1st southward

migratory group is, in actual

fact, intermixed with the mating

group (1") which has not reached

a state of full maturity, with

the coastal visitation group

being highly mature in contrast

to the low degree of maturity of

the offing group, and also that

the same 1st southward migratory

group annually appears at Goto

Island around October, which is

approximately 1 month earlier

than in the Oki Islands. While further studies will also be required in the future

concerning these two points, at the present stage the authors have taken the follow-

ing viewpoint. That is to say, the migratory movements of the common squids general-

ly appear to start with well developed squids of early gonad maturation, and even in

the 2nd southward migratory group given most attention to date, the tendency noted

between the southward preparatory group staying in Hokkaido waters and the southward

migratory group seems to be towards diversity in gonad maturity and uniformity in

high degree of maturity as seen between the offing group and coastal group of the

1st southward migratory group. Upon examining this further, in the assembly area (26)

used until migratory movements are commenced, there are many shoals varying widely

- 29 -

in the gonad maturity state, and among these, those above a certain limit are pre-

sumed to selectively assemble and group with other shoals of nearly the same matu-

rity, thus separating into a number of groups for movement and migration. For this

reason, at the destination points of their movement and migration, the concentration

of a highly mature group of any genealogical group can be seen, while in the assembly

area from which the movement and migration originate, the retention of a low maturity

group can be seen.

In actually looking at the corresponding relationship between the fishing

ground environment, particularly the seasonal variation in water temperature, and

the catch conditions of common squids along with the maturity state of the gonads,

the water temperature range of the fishing grounds for immature squids is 5-27°C

(Hokkaido Fish. Exp. Station, 1928a; 1929a; 1931b), the water temperature range of

the fishing grounds for adult mating souids is 13-18°C (Hamabe, 1961a; 1963b),

and the water temperature range of the fishing grounds for adult spawning souids is

15-20°C (Hamabe, 1961b; c). In general, as the maturity of the gonads advances,

a change in the water temperature adaptibility of the squids seems to take place,

with the relatively wide temperature band of the immature stage becoming a narrow

temperature band favouring warmer temperatures, and the area of distribution thus

seems to incline towards a warm water environment.

In the winter-spring season during which the 2nd southward migratory group

enters its reproductive stage, the Tsushima warm current in the Sea of Japan becomes

concentrated in the coastal region and the cold water region expands in the offing

so that the common squids which envelop themselves in the warm water mass are carried

along toward the coast together with this, entering the biological circulation system

of the water mass (Uchihashi, 1960a; b). ,The sauids within this circulation system

most likely transfer to a water mass with an ecologically more favourable water

temperature range suitable to the maturity stage of their own gonads, or else move

Single line fishing ground Sea-bed reef zone

Stationary squid net

Fig. 4. Diagram showing the occurrence of swarming phenomena near Kamoise-cho on the east coast of Tsushima in Nagasaki Prefecture, 1: Akashima, 2: Okinoshima, 3: Kuroshima.

IS A- 0:

,

-30-

II in the opposite direction and migrate towards extinction.

In the southwestern waters of the Sea of Japan as well, the reason that the

appearance of the 1st southward migratory group is earlier at Tsushima than in the

Oki Islands, and earlier still at Goto Island than at Tsushima, is probably because

the cold water tongue of the north Korean cold current system located in the northern

part of the Sea of Japan moves southward along the Korean east coast from the coastal

provinces on the continental sicle, driving and intensifying the squid groups to the

Tsushima and Goto Island waters earlier than to other waters.

3. Swarming phenomena

(1) Past observations

Examining the occurrence

sites and actual cases of swarming

phenomena that have taken place

within the Tsushima warm current

system, mention can be made of

Kunashir Island in the southern

Kuriles (Hokkaido Fish. Exp, Sta-

tion, 1928c; 1929b; c), Hakodate

harbour in Hokkaido (Hokkaido Fish.

Exp. Station, 1928b), Ofunato Bay,

Kisen-gun, Iwate Prefecture (Hok-sites

kaido Fish. Exp, Station, 1930),

Oki Islands in Shimane Prefecture

1. Fukaura; 2. Shichikamaura; 3. Mloteura; (Hàmabe & Shimizu, 1955; 1959), 4. Hokusogaura; 5. Murasakiseto; 6. Kamoise; 7. Ashigaura; 8. Ikatsukiura. and the east coast of Tsushima in

Nagasaki Prefecture (Matsumura,

Senta & Taniguchi, 1959).

- 31 -

(2) Swarming phenomena at Akashima and Ashigaura near Kamoise-cho on

the east coast of Tsushima in Nagasaki Prefecture

The occurrence records of swarming phenomena in the vicinity of Kamoise-cho

are given below.

Occurrence date Number picked up Swarming site

December, 1942 200,000 Fukaura

December 22, 1957 8,000 Hokusogaura

December 23, 1957 80 , 000 Hokusogaura

January 12, 1959 21,000 Hokusogaura

December, 1959 13,000 Fukaura

December, 1960 1,000 Fukaura

December, 1960 several hundred Shichikamaura

January, 1961 several hundred Shichikamaura several thousand - tens of

December, 1961 thousands several times Akashimaura

December, 1961 5,000 Pukaura

December, 1961 300 Shichikamaura

December 28, 1961 130 Hokusogaura

December, 1962 several thousand several times Akashimaura

December, 1962 500 Shichikamaura

January, 1963 several hundred several times Akashimaura

January 10, 1963 300 Hokusogaura

In addition to the above, swarming phenomena has occurred everywhere at

Shirakiura, Mioteura, Inoshishiura, Odairaura, Ashigaura, and Ikatsukiura, and

particularly at Mloteura, Ashigaura and Ikatsukiura, from olden times there have

frequently been massive swarmings in the tens of thousands, but ever since the

stationary nets were strung across the fish-way at the entrance of the bay, drastic

reductions are said to have taken place in every case.

(3) Swarming phenomena in the Oki Islands in Shimane Prefecture

Subsequent to the actual cases reported previously by the authors (Hamabe

& Shimizu, 1955; 1959) 9 the following new swarmings have taken place.

Occurrence date

Dec. 1, 1959

Dec. 7, 1959

Dec. 8, 1959 Dec. 11, 1959

Dec. 12, 1959

Dec. 18, 1959

Jan , 10, 1960

Jan , 15, 1960

Feb. 7, 1960

Number Time picked up

23h 10,000

19-22h 540

23h 1,000

22h 200

23h 200

18h 200

23h 200

23h30m 2,600

23h 600

tl

I t

I ,

I t

It

tl

- 32 -

Swarming Water Environmental conditions site temp.°C

Clear, SW breeze, warm Yuranohama 17.8

Cloudy, NU 4, cold

Clear, no wind, warm, moonlight

Clear, warm, starlight

Cloudy, NE 3, cold

Cloudy, NU breeze

Clear, no wind, warm, moonlight

Cloudy, NU 4, warm

Clear, SW 4, warm, moonlight

Nov. 28, 1960 unknown 300

Dec. 4, 1960 unknown 60

Jan , 27, 1961 20-21h 295 Cloudy, NE 4

Feb. 24, 1961 19h3Ôm 700 Very clear, no wind, warm, moonlight"

(4) Recapitulation and discussion

Within the Tsushima warm current system, while other swarming sites are

surmised to exist in addition to those locations in the Oki Islands reported thus

far, it is well nigh impossible to obtain accurate swarming records for every one

of them. Consequently, the swarming phenomena in the Oki Islands for which the (28)

authors were able to collect records over a long period by examining the facts in

the past (Hamabe & Shimizu, 1955; 1959) were combined with the records of swarming

phenomena at Tsushima newly investigated on this occasion and with the recent addi-

tional data on swarming phenomena in the Oki Islands, to make up representative

data of the swarming phenomena in the southwestern waters of the Sea of Japan, on

the basis of which a discussion has been presented with particular reliance on the

thoroughly complete Oki Islands data.

Putting the months during which swarming occurred in the Oki Islands in

proper sequential order, it occurred in September once, in October once, in November

15 times, in December 39 times, in January 7 times, in February 4 times, and in

March twice, with December having the highest number of occurrences.

16.6

16.5

17.2

17.4

16.0

14.2

13.2

12.7

17.0

16.7

11.0

10.9

- 33 -

The monthly maximums of the number picked up in a single swarming were 800

in September, 1,000 in October, 9,000 in November, 20,000 in December, 2,600 in

January, 800 in February, and 6,000 in March, with December indicating the largest

A On the 144° E meridian south of Kushiro

B Eastern offing of Ozaki, Kamaishi harbour, Iwate Prefecture

C Northern offing of Ramada harbour, Shimane Prefecture

D Tsushima Kibihara lki - Ikizukishima • Kibihara Genkaishima

Fig , 5. Contraction of the warm current as seen in the vertical distribution of water temperature at various Japanese coastal points (Central Meteorological Observatory, 1954-1955).

A Aug. 4-11 Observation by 4th District Headquarters of the Maritime Safety Agency

Dec. 5-6 Hakodate Oceanic Weather Observatory

B Aug. 17 Dec. 17-18 Iwate Pref , Fish. Exp. Station Jan. 14

C Aug. 2-3 tt Tottori Pref , Fish. Exp. Station Oct. 11-16 Shimane II Dec. 6-7 Tottori ti

D Aug. 6-7 Fukuoka Dec. 11 tt Saga Jan , 12-14 Fukuoka

II '

-34-.

mass swarming throughout the year.

As for the relationship between water temperature and swarming,

of the 38 cases measured, swarming occurred once in the 10°C block, 3 times in the

11°C block, once in the 12°C block, twice in the 13°C block, 3 times in the 14°C

block, 8 times in the 15°C block, 9 times in the 16°C block, 8 times in the 17°C

block, twice in the 18°C block, and once in the 23°C block, indicating that most

of the occiirrences were in the 15-17°C water temperature range. In addition,

looking at the relationship with the age of the moon, there were 8 occurrences in

the dark phase with the age of the moon being 24-6 days old, while there were

56 occurrences during the moonlight phase with the age of the moon being 7-23

days. The 56 occurrences during the moonlight phase were further divisible into

almost two equal parts on either side of ages 14 and 15, there being 29 occurrences

on the first quarter side and 27 occurrences on the last quarter side, thus inscrib-

ing an arch-like figure with the full moon at the center and the first and last

ouarters at the ends of the bow.

As for the time of occurrence of the swarms, looking at the 58 occurrences

on which records are available, it seems to range from 16 hours until 9 hours . the

following morning, with most of the occurrences being between 22 hours and 24 hours,

as many as 22 occurrences being noted at 23 hours.

Looking at the relationship with the weather and meteorological conditions

from the records of 62 occurrences, there were 37 occurrences under clear skies,

21 under cloudy skies and 1 on a dark night, and judging from the number of clear-

sky days in winter in the Oki area, it becomes cuite apparent that swarming occurs

selectively on clear moonlit nights. This is one aspect of the relationship between (29)

the age of the moon and the swarming phenomena, and suggests that the massing activ-

ities of the squids are intensified by moonlight. In addition, looking at the

effect of wind and other meteorological conditions, there were 28 occurrences in

. -35 -

no wind, 26 occurrences in warm weather (by experience), 14 occurrences in strong

wind, 8 occurrences in cold weather (by experience), 2 occurrences in snowfall, and

1 occurrence in rainfall. In the foregoing, the conditions of no wind and warm

weather suggest a southerly wind direction along with its associated meteorological

conditions, while the conditions of strong wind and cold weather suggest a northerly

wind direction with its associated meteorological conditions, and this seems to

correspond to the fact that the coastal reflux zone active on the southeastern coast

of the Oki Islands moves shoreward under southerly winds and leaves the coast under

northerly winds.

When the flow conditions of the Tsushima warm current at the times swarmings

occur are looked at on the basis of the vertical water temperature distribution ob-

served at various coastal points on the Sea of Japan, the Tsushima warm current is

in the process of rapidly contracting and moving towards the coastal region, and

the warm water mass is brought into contact by this process with the topographical

indentation and protrusion areas of the coastal region as well as with isolated

islands. It thus clashes and creates a vortex motion with the cold water mass that

drives in behind it from the offing, with the result that a coastal reflux zone is

formed, and it is here in the final link of a chain of warm water vortex motions

that the common squid group first of all takes shelter.

Examining the actual characteristics of a swarming site, in the southern

Kuriles there is Shiretoko Peninsula on the west and Kunashir Island on the east,

while the northern side opens onto the Sea of Okhotsk and the southern side is an

extensive shallow of less than 10 m deep Nozuke Channel. Since the shallow of

Nozuke Channel is a topographical barrier that obstructs the movement of both the

water mass and the common souids, the isolated warm water mass that is cut off from

the Soya warm current by the east Sakhalin cold current is blockaded and intensified

on the coast of Kunashir Island. Looking at the tides in Nozuke Channel, the falling

- - 36

tide flow southward while the rising tide flows northward, but when a westerly dry

wind blows, the water temperature in the offing 2,000 m out becomes 2°C from the

surface to the bottom layer, while the coast similarly becomes 0°C at falling tide

and 1.00C at rising tide, clearly forming a super-cooled environment for the squids.

The coastal reflux enveloped in such an environment, despite its inherent Warm water

characteristics, rapidly contracts toward the shore by virtue of weakening as a

result of being cut off from any replenishment of warm water, and the fairly dense

common squid group contained within it is also deemed to be blown shoreward by the

strong westerly dry winds (Hokkaido Fish. Exp. Station, 1928c; 1929b; 1929c) (Mete-

orological Agency, 1959-1960; Aratani & Kawasaki, 1962).

In the Oki Islands in Shimane Prefecture, there is a cold water mass developed

in a northeasterly-southeasterly direction at the 100 m line of the bottom layer at

the time of swarming, and around the islands on the inner side of the cold water mass

there is relatively warm water of 15-16°C, while at the 75 m layer there is an

optimum warm water mass for the mating group of 18-19°C only in the vicinity of

the Oki Islands (Hamabe, 1961a). Since the warm water mass containing the common

squids is driven and intensified by the cold water mass from a northeasterly direc-

tion towards the southeastern coast of the Oki Islands, it is here that a sheltering

ground for the common squids is formed (Hamabe & Shimizu, 1955; 1959). In this way, (30)

when the coastal reflux zone forms on the southeastern coast of the Oki Islands,

since the sweeping wind that drives this reflux zone to the southern coast is an

easterly-southerly wind, it is at the time of southerly winds that swarming seems

to frequently occur.

On the east coast of Tsushima in Nagasaki Prefecture, a warm water reflux

zone influenced by the Tsushima warm current is formed at the 50 m layer of the coast

in December, and likewise in January a similar warm water mass of 15.5 - 16.0°C water

temperature forms a tidal boundary near the east coast of Tsushima and moves north-

II

ward. This comes into contact with a southbound cold water mass of less than 13.5°C

water temperature to form a vortex zone (Mon i & Nishimoto, 1957), and it is when

this is driven to the east coast of Tsushima by easterly winds that swarmings are

deemed to occur (Mon, 1959).

Judging from the 3 foregoing cases, as far as the localities where swarmings

occur within the Tsushima warm current region are concerned, they lie in a position

where powerful warm water coastal refluxes are topographically formed, and where juts

of rapid cold water currents or strong winds become one of the motive forces that

drive the reflux zone onto the shore.

The biological characteristic of the common souids at the time the swarmings

occur is that they are of the mating group (Hamabe & Shimizu, 1959) as shown in

Table 2 ,

Table 2. Composition of the sex ratio and maturity stage of common squids at the time and place of swarming within the Tsushima warm current system.

Females Males Occurrence Occurrence I Original

No. Maturity stage Mat- No. Maturity stage 1 area period 8xam- Imma- Ma- Fulbn ing exam- Imma- Ma- records

ined ture turefflFe Spent rate ined ture ture Spent

Kunashir Is., Dec 1928- % % % % % /

/0 % % Hokk.Fish. S. Kuriles Jan 1929 7 100 - _ - 8 50 50 - Exp.

(1928c, 1929b, c)

Okhotsk coast Aratani & of Hokkaido: Dec 1961 202 99.5 0.5 - - 1 229 97 3 Kawasaki Monbetsu-Raushi (1962)

Hakodate, Dec 1929 100 - - 28 ? 41 59 Hokk.Fish, Hokkaido Exp.(1929a)

Hachinohe, Nov 1953 26 100* _ _ 34 70 30* - Tohoku Reg. Sanriku coast Fish.Res.

Lab.(1956)

Oki Islands Dec1954-60 710 75 24 1 - 100 819 - 100 -

Oki Islands Jan1954-60 351 53 46 1 - 100 485 - 100

Tsushima Dec 1962 45 63 33 4 - ? 36 57 43 _ Tanaka & Iizuka (1956)

Tsushima Jan1961-63 187 75 25 - - 100 216 1 - 100 -

* Those with ovary weight of less than 2.5 g, or testis weight of less than 5 g, were deemed to be immature.

- 38 -

The common squids of the swarming season are the 2nd southward migratory

group which moves southward in the Sea of Japan in December-January, and this group

transits all the way from Hokkaido to Tsushima largely as a mating group. In addi-

tion, the characteristics of the swarming squids themselves are those of the so-called

2nd southward migratory group, and the peculiarity of their ecology is that empty

spermatophore sheaths and sperm sacs are discernible in the stomachs of the females

as proof of mating (Hamabe ec Shimizu, 1959), clearly suggesting that they swarm

ashore in conjunction with the activity of the mating group. Furthermore, since

there appeared to be a cyclic fluctuation among the three factors consisting of

swarming, the age of the moon, and volume of catch, the relationship between the

fluctuation in the volume of catch by stationary squid nets and single line, and

the fluctuation in the illumination of the moon (age of the moon) was examined along

with the traces of mating (Hamabe & Shimizu, 1959), whereupon the movement of the

common squid group was found to be active on moonlit nights, with vigorous mating

activity taking place within the group, and even among the moonlit nights, the move-

ment and mating were found to be particularly vigorous at the time of first quarter

and last quarter (Hamabe, 1964). From this fact, in the mating group of December,

some sort of abnormal condition associated with group mating on moonlit nights was

deemed to be responsible for driving them towards the shore.

(5) Summary

1. The swarming phenomena of common squids were noted to occur around December-

January at such localities within the Tsushima warm current region as Kunashir

Island in the southern Kuriles, Hakodate in Hokkaido, Ofunato Bay in Iwate Prefec-

ture, the Oki Islands in Shimane Prefecture, and Tsushima in Nagasaki Prefecture.

The remote environmental cause for the occurrence of swarming includes the shore-

ward contraction of the Tsushima warm current and the resultant intensification in

the coastal region of the common squid group contained in the warm water mass. In

- 39 -

addition, the direct cause for the occurrence of swarming lies in the fact that the

warm water coastal reflux zone of dense common squids is driven by the force of

rapid tides and wind-blown currents to isolated islands and topographical indenta-

tions.

2. The common squid group in which swarming occurs is the 2nd southward migratory

group, and this group is a mating group. The movement and mating activities of the

common squid mating group take place on moonlit nights, being particularly vigorous

at the time of first quarter and last quarter while quietening down on dark nights,

and consequently the squids vigorously engaged in movement and mating on moonlit

nights are thought to undergo swarming as an abnormal activity associated with mating.

V. SEXUAL MATURATION PROCESS - MATING SEASON AND SPAWNING SEASON -

With regard to the common squid groups that undertake long-range migration,

because a number of genealogical groups are seen to overlap and intermingle both

seasonally and geographically, in order to separate them and trace a specific group,

it is necessary to make an accurate analysis of the sexual maturation process. Look-

ing at the case of the Oki Island waters, the common squid group born at the same

time and place and forming a uniform group and developing in the same environment,

attains a biologically minimum size at a mantle length of around 20 cm (Hamabe

Shimizu, 1959), after which it enters into the reproductive stage. At this point,

the male species of the common squid attain maturity of the gonads earlier than the

females, and a sort of male prematurity phenomenon can be detected. From this pecu-

liarity in gonad maturity, the reproductive stage of the adult group can be divided

into the mating period centering around the males and the spawning period in which

the females predominate. While there are mutual overlaps at the mid-point of the (31)

two periods, the peak mating period and the peak spawning period are seemed to occur

separately near the middle of the mating period and spawning period respectively.

• •,‘

While the separateness of the mating group and spawning group of the common squids

produced in the Oki Island waters has already been examined by Sasaki (1921), wi th

the acquisition of additional information concerning their development at this time,

this bas been re-examined.

1. Principal mating season of the nocturnal surface layer squid group of the

coastal region seen in the case of the Oki Islands

From the developmental state of the hectocotylus and the corresponding

testis, Sasaki (1921) reported that the gonads of the males mature in December in

Hokkaido (mantle length becomes 19 cm or more), and year-round in the Oki Islands

(refers to the period when squids measuring 17.6 cm or more in mantle length are

present, but there are not many males in the spring and early summer), and regarding

the coital implantation of the sperm-sac in the outer labia of the oral bulb of the

female as the index of mating commencement, he surmised the principal mating season

to be early winter in Hokkaido and from summer to winter in the Oki Islands.

Judging from the observations of the author in mating experiments (Hamabe,

1961a), the mating pattern of a. specific day or period during the mating season can

be objectively learned by the quantitative degree of mating traces that can be seen

within the stomachs of female squids in the group, and thus there can be no objection

to considering the period when such occurrences are maximal to be the principal

mating season. According to the results of a continuous survey on the mating traces

of common squids produced in the Oki Island waters, the months showing the maximum

traces of mating are December-February, and the larger the size of the females, the

more mated females there are (Hamabe & Shimizu, 1959: Tables 3 - 5). On the other

hand, the monthly variation in the number of spermatophores possessed by the males in

the same period is as shown in Table 3, with October-:March being the highest, and

especially November showing the maximum. Judging from these indications, the

principal mating season of the coastally-produced common squids in the southwestern

waters of the Sea of Japan as typified by the Oki Island samples is deemed to be

December-February, with December and January in particular being the peak season.

Table 3. Monthly variation in the number of spermatophores possessed by the male common squids produced in Oki Island waters.

Number Proportion (%) of the total number examined <59 pods 60-109 pods 110-159 pods 160-209 pods 210 pods<

April, 1 57 1 100 - - - -

May 24 63 37 _ - _

June 8 63 12 12 12 -

July 22 59 27 9 5 -

August 25 60 28 8 - 4 September 3 100 - - - -

October 88 16 52 23 6 3

November 69 17 39 38 3 3

December 82 37 45 11 5 2

January, '58 109 20 57 13 9 1

February 73 40 45 12 3 -

March 27 41 44 15

Month & year

ege

2. Principal spawning season of the nocturnal surface layer squid group of the

coastal region seen in the case of the Oki Islands

Concerning the maturity of the reproductive organs of female squids, Sasaki

(1921) attached importance to the mutual relationship between the mantle length and

nidamental gland length, and as a result of considering both the whitening conditions

of the seminal receptacle and the emergence pattern of the juveniles together, he

reported that the spauning season in Hokkaido is Decamber, and in the Oki Island

waters from summer through winter, terminating in April. The egg glands of the

female squids were reportedly discernible from a mantle length of about 15 am, being

approximately 2 cm in immature squids with a mantle length of 20 cm, while for

mantle lengths of 20 cm or more they were said to measure about 12 an in normal

6

■•••

•••••

7

1

0.01

QOM

Month & year Number examined

April, t57

May,

June,

July,

August,

September,

October,

November,

December,

January, 1 58

February,

March,

1

14

81

75

23

3

81

131

125

90

107

73

- 1 100 _ 1

- i 7 - 21 7 7

1 4 15 19 7

3 1 875

- 4 17 26 17 13

_ 33 66

- - 2 4 11 14 6 -

- 4 15 27 19 15 8 5 5

- 9 28 26 17 11 5 1 3

- 20 34 21 16 8 1 -

1 6 34 29 22 6 3 - -

- 1 1L1. 12 37 18 15 1 1 1

0 62 1

I•M ••■•

••■•

.I••■ ••••• 11•••

- 7 1 141 - 29 -

1 37 5 4 -

- 6)4 9 - -

- - L. - L 9

•

- 42 -

mature state squids in which mature eggs could be detected within the oviduct, and

as much as 18 cm in fully mature squids measuring 28 cm in mantle length. As a result

of year-round measurements, the months of September-October, in which normal mature

state squids were most numerous, were reported to be the principal spawning season.

On the other hand, Hamabe & Shimizu (1956) deemed the spawning season in

these waters to be April-June, while Soeda, Aratani, Otsuki & Machinaka (1958) have

regarded November-March as being the principal spawning season, so that depending (32)

on the researchers, there are the 3 theories of September-October, November-March,

and April-June. Accordingly, a basis for proper determination, in short the charac-

teristic features of the spawning group, must first of all be clarified, and the

grounds for the 3 theories must each be examined.

From the results of physical measurement surveys conducted by the authors,

the monthly variation in the nidamental gland length of common squids produced in the

Oki Island waters appears as shown in Table 4.

Table 4, Monthly variation in the egg gland length of common squids produced in Oki Island waters.

Freq. (%) of appearance of diff. classes of egg gland length <1 1 1 2 1 3 1 4 5 6

( (

7 8 9 10 11 12 13 cm

— 43

Table 5. Monthly variation in the maturity state of the female common squids produced in Oki Island waters (1957-1959).

According to . this table,

the common squids produced in

No.of No.of (Both oviducts+ovary wt:Y the Oki Island waters are most times squid Month & year exam- exam-.

ined ined <4 5-9% 10%< numerous in the 5-6 cm aass of _

Apr. 1957-59 5 6 1 2 3 nidamental gland length in December-

May t! 24 46 5 7 34 March, while in April-November June 11 34 132 7 35 90

July n 8 26 2 15 9 there appear to be 2 groups

Aug. 11 6 26 6 18 2 divided between the 1-3 cm class Sept. n 1 2 0 2 0

and the 9-10 cm class. At this

Nov. 1i 6 97 82 12 3 point, looking at the summarized

Dec. n 4 200 191 9 0 Jan. 1958-61 8 167 157 10 0 relationship between nidamental

Feb. n 5 256 232 24 0 gland length and spawning from the

Mar. ti 4 169 J 138 29 2 results of spawning experiments

(Hamabe, 1961b; 1962b), spawning

occurred with fully mature squids having a mode of 9 cm (range 7-14 cm) in nidamental

gland length, while spawning did not occur with normal mature squids having amode of

7 cm (range 6-9 cm) nor with immature squids having a mode of 6 cm (range 2-8 cm), and

therefore the entire group of December-March and the 1-3 cm nidamental gland length

class group of April-November are not deemed to have spawned, leaving only the 9-10

cm nidamental gland length class group of April-November to be deemed the virtually

certain spawning group.

From the same experimental results, those whose incubatory organ (ovary and

left and right oviducts) weight exceeds 1C% of the body weight can be regarded as

being in spawning, and in the common squid group produced in the Oki Island waters,

those that have this characteristic feature are none other than the summer squids

of April-August and the autumn squids of October-November (Table 5, Fig. 6). While

a few squids having similar characteristics can also be seen in March, the principal

Body weight

Oct. . 9 r 33 9 19 5

Total 6 F 1 20 F 13M 1M

Successive months

Year

1954-'55 1955-'56

1956- 1 57

1957-'58 1958-'59 1959-'60

Number of reproductively exhausted squids collected

IV

^

F

3F 5 F

13F - 6 F

4F - -

V: VI VII VIII

5M 3 F

-

LX

1F

X I XII 1 I II III

1 M 5 F

5m. 3 F

1 M 13M

month

Fig, 6. Appearance pattern of spawning common squids in Oki Island waters (1957-59).

o

r-L H

j Pti

o P 0

0 -P 0

-44-

body of spawning squids is deemed to be

the spawning group of the 3rd northward

migratory grcup of May-June, and this

group has a higher degree of maturity

than the spawning group of the let south-

ward migratory group of October-November.

In addition, the yearly occur-

rence pattern of gonad exhausted squids

(Hamabe, 1963a) in the Oki Island waters

was tabulated, using the number collected

monthly during 1954-1960 as sample data as shown in Table 6. Owing to the small

number of squids examined, no conclusive opinion can be rendered on this basis, but

it would seem that spent male squids are most numerous in March and September while

spent female squids are most prominent during April-September and particularly in

June. Moreover, when the occurrence pattern of juveniles under 3 cm in mantle

length is also included in the consideration, the spawning season in the Oki Island

waters becomes April-November, with April-June in particular being properly thraught

to be the principal spawning season of the year in these waters.

Table 6. Monthly number of reproductively exhausted squids collected in the Oki Island waters (1954-1960).

In the common squid group produced in the Oki Island waters, the squid

group containing many females whose incubatory organ weight exceeds 10% of the

- 45 -

body weight is the spawning group of the 3rd northward migratory group. In addition,

the spawning group of October-November is the spawning group of the 1st southward

migratory group, and the common squid spawning season in the Oki Island waters is

thus deemed to be characterized by 2 squid groups that differ in genealogy and

migratory direction.

When the determinative basis for the common squid spawning group produted in

the Oki Island waters is applied to the squid group of the Tamma coast and Tsushima

(Tanaka & Iizuka, 1956), a more or less common tendency is indicated (Appended Figs.

1 and 2). Consequently, it is felt that the principal spawning season of nocturnal

surface layer squids of the coastal region in the southwestern waters of the Sea of

Japan can properly be regarded as being April-June.

3. Principal mating season and principal spawning season of the nocturnal surface

layer squid group in the southwestern offing region of the Sea of Japan

Soeda, Aratani, Otsuki & Machinaka (1958) surmised that, as the gonads of

the common squids mature, a change in their ecology takes place and they move to a

particular environment. On the basis of this viewpoint, even assuming that the

squids in the coastal region are strictly of the mating group, it can be thought

that only the spawning groun forms a separate group in the polar frontal zone of the

off ing or in environments isolated from normal fishing grounds such as the sea-bed.

The specimens obtained by the author, which were caught by single line at night by

employees of a dredging-net fishing vessel in the surface layer of the offing region

some 80 nautical miles north of the Oki Islands, are believed to be examples of this

separate group, but according to the results of measurements, these specimens turned

out to be of the mating group having the same maturity stage of gonads as the 2nd (3)4)

southward migratory group which is the principal group in the coastal region during

this period. Looking at the dredging-net catch results in the offing region during

this period, from all indications there are hardly any common squids present near

- L6 - •

the sea-bed, and so those distributed over the offing region in the southwestern

waters of the Sea of Japan in winter are the 2nd southward migratory group-type

mating group similar to the one in the coastal region, and the pattern where the

spawningggroup is specially distributed could not be seen. However, since the spawn-

ing group of the genealogically different 1st southward migratory group can be seen

to enter into the offing region in the fall, in this limited context spawning can

be considered in the offing region, but judging from their spawning habits whereby

the demersal adhesive egg masses are surmised to be implanted on the sea-bed or on

objects near the sea-bed (Hamabe, 1961b; 1962b; 1963b), it is rather doubtful

whether spawning takes place in the cold water region of the offing by submerging to

even colder layers below. While the nocturnal surface layer squids in the south-

western offing region of the Sea of Japan are seen to enter their prinCipal mating

season around December-February which is the stationary period of the 2nd southward

migratory group, whether spawning takes place in the offing region or not is at the

moment not clear.

L. Principal mating season and principal spawning season of the diurnal bottom

layer squid group in the dredging-net fishing grounds of the southwestern

waters of the Sea of Japan

Looking at the results (Appended Fig. 3) of measurements summarized by month

involving common squids caught by dredging-nets in the diurnal bottom layer in 1961-

1963, the diurnal bottom layer squids exhibit the same gonad maturity stage as the

nocturnal surface layer squids caught in the saine waters at the saine time, and there

is almost no ecological difference between the two. In other words, the principal

mating season of the diurnal bottom layer squid group is deemed to be Decamber-

February, and its principal spawning season to be April-June.

5. Discussion

It is necessary to examine whether it is correct to regard the 2nd southward

migratory group in the southwestern waters of the Sea of Japan as a spawning group,

-47-

and whether December-March is the principal spawning season.

According to the report of Soeda, Aratani, Otsuki & Machinaka (1958), the

monthly volume of catch of common squids in the western sector of the Sea of JaPan

is as shown in Fig. 7.

Tens of thousand kan (1 kan - 8.28 lbs.)

Fig. 7. Monthly volume of catch of common squids in the western sector of the Sea of Japan. (from Soeda, et al., 1958)

Assuming that the volume of catch of common squids is, to a certain degree,

proportional to the squid resource volume of that area at that time, this diagran

shows that in the southwestern waters of the Sea of Japan, the mixed group consist-

ing of the spawning group and the new-born group of summer-autumn is larger than the

mating group of winter. Even assuming that both are equal and that the sex ratio

is 1, the proportion of fully mature females in each respective case would be 15-25%

in the former when 30-50% are adults (females almost fully mature), and in the lat-

ter case 11% of the total, or 22% of the female half of the population (Soeda, Ara-

tani, Otsuki & Machinaka, 1958). Consequently, the spawning group, and by inference

also the spawning quantity, are deemed to be maximal throughout the year in the

summer-autumn group.

In addition, the number of squids used in the spawning experiments conducted

in the Oki Islands between April 1958 - June 1959, amounted to 165 in 45 trials in

- 48 -

Mar ch, 5 in 2 trials in April, 40 in 18 trials in May, 43 in 23 trials in June and

114 in 31 trinls in December, among which spawning actun]ly occurred in 16 cases (35)

in May, 13 cases in June and 1 case in December (Hamabe, 1961b). The fact that

there was a spawning case in December in the Oki Islands is contradictory to the

mating theory discussed by the author hitherto, and so upon making a detailed exam-

ination of the measurement values for this squid, it was found to be a large-size

common squid with a mantle length of 30.7 cm and an incubatory organ weight of 35.0

g, which should clearly be deemed by its characteristics to be a remnant of the

spawning group belonging to the 1st southward migratory group and not as a spawning

case of the 2nd southward migratory group of December.

Also, it is necessary to examine the gonad maturity state of the 2nd south-

ward migratory group in the northwestern waters of Kyushu. According to the results

of measurements of 7,981 squids obtained by single line on the east coast of Tsushima

during September-February of 1954-1957, and of squids obtained from stationary nets

at Arikawa on Goto Island during October-February of 1954-1957 (Fujikawa, et al.,

1958), the mean measured values for 250 memales of December 1956 at Tsushima are

recorded as being 25.16 cm in mantle length and 0.61 g in oviduct weight, with al-

most all of the females having completed emission, that is having completed their

spawning. In addition, according to Matsumura, Senta & Taniguchi (1959), the meas-

ured values for the Tsushima squids of winter were similar to those reported by

Fujikawa, et al., and by detecting ecologically mature eggs only in the ovary and

noting the emptiness of the oviducts as proff of spawning, they acre apparently

deemed to be post-spawning squids. Looking at it in this manner, both of the fore-

going reports would appear to suggest that the 2nd southward migratory group in the

southwestern waters of the Sea of Japan as a whole completely becomes a spawning

group around December-January in Tsushima waters, but judging from the standards

adopted by the author, their degree of gonad maturity corresponds to the immature -

normal mature state, and even upon comparison with the observational results for

- 49 -

gonad exhausted squids (Hamabe, 1963c), it is difficult to consider them as being

post-spawning squids. The gonad maturity state of the 2nd southward migratory group

at Tsushima in December measured by the author himself is as shown in Appended Fig. 1,

and this differs very little from what was reported by Tanaka & Iizuka (1956). Judg-

ing from this, it is felt correct to deem that the 2nd southward migratory group

becomes a spawning group only after crossing Tsushima Channel and entering the East

China Sea waters including Tsushima - Goto Island.

VI , SPAT.TNING GROUNDS

1. Distribution of the spawning group

(1) Collection results in the nocturnal surface layer

When the pattern in which the spawning group was caught by such fishing

implements as single line, stationary nets and purse-nets were examined from existing

reports, the records included catches in July at Utsuryo Island in Korea and in

November at Pusan (Yamamoto, 1946), June-October at Tsushima (Tanaka & Iizuka, 1956),

April-November in the Oki Islands (Hamabe & Shimizu, 1955; 1957a; 1959), May-October

on the Tama coast (Nasumi & Yoshioka, 1958), November at Oki Bank (Kyoto Pi-cf. Fish.

Exp. Station, 1962), July-September at Ryotsu in Sado (Niwa, Yoshida & Sato, 1957),

and March-November at Ebgami Bank (Sugano, 1958), and since female squids are caught

during July-October in Hokkaido, the spawning groups are found to appear everywhere

on the entire Sea of Japan coast except in winter, making it clear that they divide

into 2 series of spawning groups consisting of the spring-summer spawning group and

the autumn spawning group.

Relationship between the summer offing group and the autumn spawning group:

While it has been reported that there is a large number of common squids in the summer

time in the central part of the Sea of Japan (Ishii, 1924; Fisheries Agency Investi-

gative Research Section, 1962; Japan Sea Reg. Fish. Res. Lab., 1964), their gon.

- 50 -

maturity state has not been really clarified. Examining the composition of the

nidamental gland lengths of squids caught by line near Yamato Bank during May-

September 1962 as an example of such offing squids of the summer, a mode of 3 cm in

July-August and 5 cm in September were indicated, and while a tendency for advance-

ment in maturity was noted with the passage of the months, it was confined through-

out to the immature stage (Fisheries Agency Investigative Research Section, 1962).

Judging from this fact, the offing group of summer is deemed to be a mating group

differing in the degree of gonad maturity from the spawning group of the coastal

region. Into this mating group in the offing region, a large-size spawning group of

the 1st southward migratory group suddenly makes its entrance around August-November

(Kyoto Pref. Fish. Exp. Station, 1962). However, the movement of this large-size

spawning group is rapid, and it is thought to cross the distribution zone of the

mating group in the offing to become the first to advance into the coastal region.

The coastal spawning group of summer: By taking the case of the Tamma coast

and looking at the distribution pattern of the common squid group that arrives near

the homeland coast from the west in summer, it would seem that 3 distribution zones (36)

are formed within an offshore band of 60 nautical miles, consisting of the distri-

bution zone of the new-born group in the offing, an intermediate zone where the new-

born group and spawning group intermingle, and the coastal zone in which only the

spawning group is distributed. Now, upon comparing the spawning groups in the inter-

mediate zone and the coastal zone, the former consists of small-size squids and is

believed to be an offshoot of the 3rd northward migratory group, that is a genealog-

ically different group moving northward from the westernmost warm water region (two

squids bearing Korean tags and surmised to be of south Korean coastal origin were

recently recovered on the Tamma coast), but this could not be clarified. The latter

is seen to be a spawning group of the 2nd southward migratory group and the 3rd north-

ward migratory group, having the same features as the "Harami (pregnant) squid" in

the Oki Islands (Hamabe er. Shimizu, 1955) and commonly referred to as "Tokkuri (sake

-1 5 - ,

bottle) squid". Looking at the results of surveys conducted at Takenohama in Hyogo

Prefecture during May-June of 1962-1963, the fishing grounds were found to be formed

centering around reefs near the 70 m water depth 1,000-2,000 m off the coast, clearly

indicating it to be a reef spawning group (Appended Fig. 2).

Putting all these facts together, as far as the southwestern waters of the

Sea of Japan are concerned, apart from the distribution of a small transitory spawn-

ing group heading for the coastal region from the offing region in autumn being

detected, the distribution of the spawning group as a whole cannot be seen in winter,

while in the spring-summer season, the spawning groups are deemed to group collect-

ively at places less than 200 m deep in the coastal region. The shoreward limit of

the spawning group in its natural environment is in the neighbourhood of the 70 m

water depth, and the reef formations located in this vicinity are most likely used

as the spawning bed.

(2) Collection results in the diurnal bottom layer

In the case of the previously mentioned nocturnal collections, the spawning

group caught by purse-nets using illumination tended to be predominantly male, while

the spawning group caught by stationary nets without illumination tended to be pre-

dominantly female, and when the two are combined the females constantly outnumber

the males. Looking at the collection results of diurnal bottom layer squids using

dreding-nets, very few of the mating group of winter are caught, while the spawning

group of spring is caught in bunches at specific areas, and from these facts, it would

seom that the spawning females become weak in light tolerance and their living pattern

shifts to that of a demersal life form.

Consequently, the dredging-net fishing grounds extending over most of the

area 100-500 m deep in the southwestern waters of the Sea of Japan have a good pos-

sibility of containing a considerable portion of the spawning grounds of common squids

within them. The primary fishing port for dredging-net fisheries in this area is

Kasumi harbour, and there are 32 medium-size dredging-net fishing vessels in the

-52-

40-ton class operating out of this port, with each trip consisting of 7-10 days of

continuous operation, and the area of operation extending from north of the Oki Is-

lands to the Mishima offing in Yamaguchi Prefecture. In addition, there are 2 small-

size dredging-net fishing boats in the 15-ton class, which operate in the offing of

Hyogo Prefecture on 2-3 day schedules. As a result, the common squids mixed in their

fishing catch are deemed to reflect to a certain extent the actual pattern of distri-

bution of the spawning group over the entire bottom layer of this area.

Accordingly, a sampling survey was undertaken of the squids caught by all

the dredging boats entering port every day . from September 1962 to June 1963, along

with a verbal survey of the catch pattern of common squids by dredging, the fishing

ground, and the fishing conditions. In Table 7 is presented a composition of the

sizes of dredged common squids landed at Kasumi harbour.

According to this table, even though the common squids of winter are caught

by line in substantial numbers in the nocturnal surface layer, very few enter the

Table 7. Composition of sizes seen in a sampling of dredged common squids landed at Kasumi harbour.

Examination Range of mantle lengths of different sizes Month e: year No. of No. of Small Medium Large Total

times vessels <1-9 cm 10-19 cm 20 cm < box box box box*

September t62 2 3 _ _ 2.0 2.0

October 4 13 6.8 7.0 18.8 36.6

11 68 2.2 7.5 16.6 26.3 November (32.5) (32.5)**

22 107 3.3 1.3 7.6 12.2 December

(2.477) ( 2 .477)

11.0 11.0 January 1 63 10 48 - - (11.0) (11.0)

February 2 6 - - 6. 0 6.0

March 21 124 _ 56.0 1.2 57.2

April 22 172 - 161.2 10.0 171.2

May 23 116 0.5 47.1 105.0 152.1

* 23 kg in a box. **Figures in parentheses denote squids caught by single line by dredging boat crew members.

(37)

Fig. 8. Fishing sites and volume of catch for single line squid fishing in the dredging grounds for Dec. 1962 and Jan. 1963.

a...region north of Oki b...region north of Tsushima c...Ishimi-Chomon region d...Izumo region e...Imban region f...Tamma region

White dots denote 5 boxes of reported catch, and black dots denote 10 boxes (23 kg in a box).

-53-

dredging-nets in the same fishing ground by

day or night, but in the spring-summer sea-

son the spawning group and new-born group

enter the dredging-nets in considerable

numbers during the day, indicating the

largest volume of catch throughout the year.

In addition, the volume of catch of the

common squid spawning group correlates

positively with that of Sillago japonica,

while correlating inversely with that of the

sand-fish, and the favourable fishing ground

sites summarized by month are surmised to be

as shown in Figs. 8 - 11.'

Looking now at the ecology of

Sillago japonica, this fish generally groups

in a warm water mass of 10 - 20 ° C water

temperature and more than 19.00% chlorinity, favouring the sea-bed vicinity contain-

ing reefs at depths around 150 m, and favourable fishing grounds are seen to be

located on the warm water side of the boundary between the cold water mass and the

warm water mass. Judging from this fact, the common squid spawning group contained

in the dredging grounds of the southwestern waters of the Sea of Japan would appear

to be concentrated in the reef formations continuing extensively along the sea-bed

at depths around 150 m, and amidst a complex collection of demersal fish groups, it

is said to indicate a distribution pattern related very closely to such warm water

demersal fish groups as Sillago japonica which permanently inhabit depths of 200 m

or less.

- 54

2. Distribution of squid weakened by spawning and squid dead from spawning

(1) Collection results in the nocturnal surface layer

In looking at the results of past surveys conducted by the author on spent

specimens in the squid groups of the northern offing area of the Oki Islands and

the Oki Island waters, Tsushima and Goto Island waters, and the Tamma coast, they

have appeared during November-January in the northern offing area of the Oki Islands,

January-November in the Oki Island waters, and June-November on the Tamma coast, and

while none were detected in the Tsushima and Goto Island waters, they are also sur-

mised to exist here in the spring-summer season. In addition j looking at the month-

ly occurrence pattern of spent squids in the Oki Island waters (1954-1963), males

predominate in January-March and in September, with females predominating in April-

August and September, while on the Tamma coast (1962-1963), males appear in June-

September and October-November, with females appearing in May-July and October,

indicating that they are most numerous in the spring-summer season and in the fall,

but this cannot be stated for certain because of the small number of collected

samples.

(2) Collection results in the diurnal bottom layer

Among the common squids caught in the dredging-nets, males with exhausted

gonads have appeared in October-November while females in similar conditions have

also appeared in November. The collection site for such spent squids are located

on the sea-bed at depths of 150 m in Agriculture and Forestry Ministry . Fishing Zones

No. 162, 109, 193, 199., 218, and 247.

(3) Name of the so-called udead common squidsn collected in the diurnal

bottom layer

In the dredging-nets of the Sea of Japan, the dead corpses of common squids

are said to be netted extensively and in large numbers (Hokkaido Fish. Exp. Station,

1928b; Kato, 1951; Nasumi, 1958; Kawana, 1953), and so it is necessary to examine

- 55 -

(38)

Fig. 9. Diagram showing the correlation between the fishing sites for the common squid spawning group using dredging-nets and. the favourable Sillago japonica fishing grounds for the period of December 1962 -March 1963.

(The horizontal distribution pattern of water tempe rature at the 150 m layer is from Sea of Japan Sea State Reports

No. 139 and 140.)

Dotted lines denote the favourable Sillago japonica fishing grounds (mean volume of catch of over 50 kg per dredging-net). 22,ach black dot denotes 1 box (23 kg) of common squids caught at the reported fishing site.

White dotes denote the fishing sites of unmixed catch.

- 56 -

(39)

1

1

1

1

Fig. 10. Diagram showing the correlation between the fishing sites for the common squid spawning group using dredging- nets and the favourable Sillago japonica fishing grounds for the period of April-May, 1963. (The water temperatures at the 150 m layer are from Sea of Japan Sea State Reports No. 1)41 and 142.) Symbols are identical to those in Fig. 9.

whether these are in fact the spent species of common squids or not. Summarizing

the contents of past reports, they can be divided into two varieties consisting of

the type which is sevtrely water-bloated with reddish skin being slipperily stripped

off and decaying fluid containing red pigments dripping out, and the type in which

the skin of a flatly sunken mantle is peeled all over in spots. The former was found

to be caught frequently and in large numbers at the "Zuwai" crab and red halibut

- 57 -

fishing grounds, and it was this that was discovered to be the so-called "dead

corinnon squid" referred to by fishermen.

Upon obtaining a red, water-bloated "dead common squid" netted by a dredging-

net at the 330 m water depth line in Agriculture and Forestry Ministry Fishing Zone

No. 152 north of the Oki Islands on December 4, 1962, this was examined in accord-

ance with Sasaki (1929b), whereupon it turned out to be a Gonatus magister Berry

said to be produced in large numbers in cold northern waters.

3. Distribution of younglings

(1) Collection results in the nocturnal surface layer

According to surveys by the author in 1957, the period of occurrence of

juveniles in the Oki Island waters is divided into the two periods of October-January

and March-June, with the largest number throughout the year appearing in March-June.

In addition, on the Tama coast, apart from the fact that the period of occurrence

(40 )

Fig. 11. Diagram showing the correlation between the fishing sites for the common squid spawning group using dredging-nets and the parallel row of reef formations between Yamaguchi, Shimane, Mishima and Oki Islands in June 1963. A. Parallel row of islands and reefs (according to Watanabe,

Ito, et al., 1960). a-h Reef formation between Mishima and the Oki Islands.

Each black dot denotes 1 box (23 kg) of catch at the fishing sites for spawning common squids using dredging-nets.

- 58 -

continues until around August, it is largely the same as in the case of the Oki Is-

lands. Comparing this with the reports of Sasaki (1921) and Ishii (1924), no differ-

ence whatever can be discerned in the distribution pattern of juveniles. In other

words, on the Sea of Japan coast, as can be seen in the case of the southwestern

waters of the Sea of Japan, the maximum occurrence of juveniles throughout the year

is generally in the spring-summer season, and in the fall only a trace of the

juvenile group can be seen.

(2) Collection results in the diurnal bottom layer

In the surveys of 1961-1963 on bottom layer squids, the period when

juveniles of approximately 3 cm in mantle length uere collected was March-May. Since

it is cmmuon for the period of occurrence of juveniles in the bottom layer to be 1 - 3

months earlier than the appearance of the spawning group in the same bottom aayer,

the juvenile group is deemed to be transported to the southwestern waters of the

Sea of Japan by ocean currents after being produced in other waters, and it mingles

with the new-born group in the process of being produced in these waters, an

increasing mixture rate of small-size juveniles being noted progressively later.

4. Spawning environment

Judging from the results of spawning experiments conducted using the natural

environment of Urago Bay in the Oki Islands, the optimum spawning environment seems

to be located in the sea-bed vicinity of a coastal warm water mass of 15 - 20 ° C

water temperature, 19.04 - 19.08% chlorinity, 8 m transparency, and around L. in

water colour. Combining this with the information on the fishing ground environment

of the summer spawning group obtained by single line, and also the information on

the fishing ground environment of the spawning group obtained by dredging-nets, the

spawning grounds of common squids in the southwestern waters of the Sea of Japan

are seen to be established in the sea-bed vicinity of depths less than 150 m, con-

centrating on areas abundant in reefs, and located within coastal warm water masses of

- 59 -

10 - 20 0 C water temperature and more than 19.00% chlorinity under the influence of

warm currents. 'While this spawning environment gradually moves eastward as the

coastal tributary of the Tsushima warm current expands in power during the spring-

summer season, in the southwestern waters of the Sea of Japan the most favourable

spawning environment throughout the year is thought to be formed around May-June.

5. Discussion (41)

Examining the spawning grounds on the basis of the spawning group, spent

squids, juveniles, and spawning environment, and summarizing the relationship be-

tween the spawning grounds and genealogical groups, the southward migratory period

of the large-size corunon squid spawning group (1st southward migratory group) that

reaches the southwestern waters of the Sea of Japan from the central part around

October-November (even in the Tsushima and Goto Island waters, October is the peak

period in which dense groups appear, and so the southwestern waters of the Sea of

Japan can sooner be thought of as corresponding to the fringe of the arrival area),

coincides with the period in which the optimum spawning environment of autumn forms

in the southwestern waters of the Sea of Japan, and for this reason, they are believed

to spawn here and then move further southward from Tsushima Channel to the west coast

of Kyushu while continuing to spawn on the way. Judging from the fact that fully

mature spawning squids are caught in bunches in the dredging-nets operating in the

waters midway between Tsushima and. Goto Island. around November-December, the end of

spawning is surmised to be after December on the East China Sea coast.

The 2nd southward migratory group that moves southward from the northern part

of the Sea of Japan around December-March is thought to pass right through the south-

western waters of the Sea of Japan as a mating group and continue moving further

southward until reaching the northeastern - central sections of the East China Sea

from the Tsushima and Goto Island waters, where it groups and spawns in reef forma-

tions at depths less than 150 m in coastal warm water masses influenced by the warm

-6o-

current. Under normal conditions, the main group which leads in both the speed and

period of southward movement, is surmised to have already finished spawning and is

engaged in mass dying by the time the

trailing group presents itself in the

southwestern waters of the Sea of Japan

around February-Earch.

The 3rd northward migratory

group that arrives from the coastal

frontal zone around the end of the

winter fishing season remains as it

is in the southwestern waters of the

Sea of Japan, and spawns here when the

Water temp. Chlorinity in °C at the in % at the 50 m layer 50 m layer

Fig. 12. Horizontal distribution pattern of water temperature and chlorinity in the western waters of Kyushu during Nov. 1955 - Mar. 1956. (According to Nagasaki Pref. Fish. Exp. Station, 1956.)

Fig. 13. Pattern of the sea system in the western waters of Kyushu. (According to Nagasaki Pref. Fish. Exp. Station Data No. 114, 1957.)

1. Approximate range of flow of the Tsushima warm current northbound in the western waters of Kyushu.

2. Pattern showing the mixture of the eastward moving cold continental water of the Yellow Sea with the coastal water of the west coast of Goto Island and Genkai whilst heading for Tsushima - Iki.

3. Pattern showing the entry of part of the warm current to the bottom layer water rising as a result of the topography of the sea-bed from near Koshiki Island towards the Danjo Islands, and the resultant inflow to Goto Sea.

4. Coastal water mass located,north of the central part of Goto Sea and having comparatively little connection with the warm current system.

5. Outflow of the water from within Ariake Bay.

6. Genkai coastal sea zone. 7. Intermediate sea zone.

Tidal ridge. a Upner Kakino Shoal. b Western Kakino Shoal. c Eastern Kakino Shoal. d Ikikaki. e Socotra Rock.

- 61 -

's•

spawning environment forms in the spring-summer season. While the fact that the (42 )

eastern Sanin coast west of Noto Peninsula becomes the spawning ground in spring

for the Sea of Japan is as explained above, judging from the fact that Toyama Bay is

the hibernating ground for the 2nd southward migratory group, and the resting ground

for the 3rd northward migratory group, looking at the Sea of Japan as a whole in

the spring-summer season, it is presumable that traditional spawning grounds are

formed in the Toyama Bay - Sado area.

What is important in thinking

about the spawning grounds of common squids

produced in the Sea of Japan is the fact

that the 2nd southward migratory group

does not spawn in the Sea of Japan but is

surmised to cross Tsushima Channel and

move southward to the East China Sea be-

fore spawning in the northeastern-central

sections of the East China Sea including

Tsushima Channel.

Surmising from the spawning envi-

ronment of the southwestern waters of the

Sea of Japan, the spawning environments

formed in the East China Sea are deemed

to include those areas shown in Figs. 12

and 13 as the Goto Sea coast (3, 4, 5 of

Fig. 13), Genkai Sea coast (6 of Fig. 13),

and the intermediate sea zone in the

northern part of the East China Sea (7 of

Fig. 13), all of which are coastal water

masses influenced by the warm current.

Fig. 14. Collection sites for squid juveniles and common squid juveniles in the eastern part of the East China Sea, and fishing sites for the common squid juvenile group on the coast.

N Northern-central survey line in the East China Sea of the Nagasaki Pref. Fish. Exp. Station.

K Western survey line in the East China Sea of the Kagoshima Pref. Fish. Exp. Station.

• 1 common squid juvenile collected. o 1 squid juvenile collected. * Kakino Shoal formation. Arabic numerals indicate the month of catch of the juvenile group.

62

In addition, the spawning season is deemed to be December-March.

Looking at the results of a survey based on existing reports (Yamamoto, 1946,

Yamaguchi Pref. Fish. Exp. Station, 1957-1959; Kagoshima Pref. Fish. Exp. Station,

1957; Kanamori, et al., 1957; Nagasaki Pref. Fish. Exp. Station, 1956-1959; Kumamoto

Pref. Fish. Expé Station, 1959) on the collection of comnon squid juveniles in the

East China Sea and its adjacent waters, the months with the highest occurrence of

juveniles are February-March, and Fig. 14 shows the region in which the common squid

juvenile group is caught in collective bunches. It is noted that this region over-

laps Goto Sea, Genkai Sea and the intermediate sea zone in the northern part of the

East China Sea shown in Fig. 13, and these areas are surmised to be highly important

waters even as spawning grounds themselves.

VII. FEEDING HABITS

1. Past observations

Included among the studies of feeding habits based on the variety and weight

of the stomach contents are the reports of Soeda (1956), Yasui & Ishibe (1955), Ito

(1957), Aratani & Nakamichi (1962), Okutani (1962), and Okiyama (1965), among others.

Since these reports generally involve examinations of the specimens caught in the

nocturnal surface layer, emphasis has been placed on describing the food chain rela-

tionship involving mainly the sardine species and horse-mackerel species of the

surface layer fishes. On the other hand, there is none that discusses the actual

life of the common squids in the diurnal bottom layer which occupies half their

life-time, and particularly the presence or absence of any feeding activity during

that time, as well as its degree, if any. In order to clarify the habits of the

common squids in the diurnal bottom layer, the authors made a comparative examination

of the variety, composition and weight of the stomach contents of squids caught float-

ing in the nocturnal surface layer and of squids caught demersally in the diurnal

(43)

Fig. 15. Diagram showing that the stomach content composition of common squids inhabiting the nocturnal surface layer in Oki Island waters, varies according to mantle length and season.

A: 773 specimens (479 females:294 males) of April-November 1957.

B: 739 specimens (427 females:312 males) of Dec. 1957-14ar. 1958. Uk unknown, E...Euphausiacea, Amphipoda, plankton other than E and T,

along with shrimp and crab younglings, squids, Fs...surface fish,

Fb damersal fish, Fm transitory fish between the

two layers (Saurida argyro-phanes),

V vacant spaces.

5

■ -cr

- 63 -

bottom layer at the same fishing grounds

in the southwestern waters of the Sea of

Japan.

2. Stomach content composition and stomach

weight of nocturnal surface layer

squids of different mantle lengths

The principal ingredients of the

stomach contents of common squids are

generally known to be surface fishes

prominent at common squid fishing grounds

in squid fishing seasons, other squids,

and plankton. With regard to the stomach

contents of common squids caught in the

nocturnal surface layer in Oki Island

waters using all the various fishing

implements and methods employed in catch-

ing nocturnally active squids including

single line, purse-nets, stationary nets,

and picking up swarming squids, the eaten

fish examined by the authors included the

sardine, round-herring, "Katakuchin sardine

saurel horse-mackerel, saury, flying-fish, HSoda" bonito, yellow-tail, sea-bream,

"Nembutsun sea-bream, silvery anchovy, goat-fish, gurnard, and "Nezuppon, while the

cephalopods detected were the "Bud& squid,Watasenia scintillans (Berry), calamary

and Todarodes pacificus Steenstrup, and the plankton were of the Copepoda, Amphipoda,

Euphausia superba, Euphausiacea, and Phyllopoda varieties, on which the juveniles

of shrimps and crabs were seen. In the case of the specimens from the stationary

nets, such demersal fish as the gurnard and "Nezuppon were included, but since a fair

6)4

number of demersal fin enter the stationary nets, it is thought that the demersal •

fish were preyed upon within the net, on the basis of which their frequency of

occurrence was slight in comparison to surface fish in genera1.

Aiming these food organisms, those detected frequently were put together and

classified into 9 groups consisting of Amphipoda (T), Euphausiacea (E), plankton

other than the foregoing two, along with shrimp and crab juveniles (C), squid (S),

surface fish and shore fish (Fs), transitory fish (Saurida argyrophanes) between the

surface layer and bottom layer (Fm), demersal fish (Fb), empty stomachs (V), and

unknown (Uk), and by arranging the 773 specimens (479 females :294 males) of April-

November 1957 as well as the 739 specimens (427 females :312 males) of December 1957-

March 1958, according to their different ranges of mantle lengths, Fig. 15 was pro-

duced. What requires a note of caution here is the fact that, when more than one

food organism was detected in the stomach of the same specimen, thè detected organ-

isms were added separately to the applicable groups above, with the result that the

number of occurrences has exceeded the number of specimens involved. In addition,

the detected items as a whole and the percentage of frequency with which each item

was detected have been shown for the different ranges of mantle lengths.

While it is problematical whether the fragments or residual bones of organ-

isms detected as stomach contents do in fact properly reflect the entire form of the

organisms eaten, and also whether the tabulation by different ranges of mantle lengths

is in fact a proper procedure for tracing the dietary change in different develop-

mental stages, the differences in the compositional variety of the stomach contents

according to Fig. 15 were decided to be taken as being one reflection of the change

in so-called feeding habits.

What can be surmised from Fig. 15 is that, among the common squids that in-

habit the surface layer, in the case of juveniles measuring 15 cm or less in mantle

length, many feed principally on Amphipoda along with some Euphausiacea, fish, and

- 65 -

other squids, while in the case of immature - mature squids measuring 16 cm or more (44)

in mantle length, the plankton feeding habits disappear, and fish and other squids

appear in the main, fish being favoured in the spring-summer period and other squids

being favoured in winter, with progressively larger size squids appearing with more

empty stomachs in the spring-summer season.

Fig. 16. Diagram showing the decreasing pattern of stomach weights from around a mantle length of 20 cm in common squids (female) inhabiting the nocturnal surface layer in Oki Island waters.

Fig. 17. Diagram showing the decreasing pattern of stomach weights from around a mantle length of 20 cm in common squids (male) inhabiting the nocturnal surface layer in Oki Island waters.

With each of the specimens used in the compositional study of the stomach

contents, the ratio of the stomach weight to the body weight was found and plotted

as shown in Figs. 16 - 17. Summarizing the indications of these diagrams, the common

squids inhabiting the nocturnal surface layer suddenly decrease in stomach weight

II '

- 66 -

II upon attaining a mantle length of approximately 20 cm or more, and at the same time

an increasing trend in the number of empty stomachs can be discerned.

3. Stomach content composition and stomach weight of diurnal bottom

layer squids of different mantle lengths

For purposes of contrast with Fig. 15, the corresponding data on diurnal

bottom layer squids of April 1957 - Maxch 1958 should be used, but unfortunately the

survey on diurnal bottom layer squids was conducted after the examination of the

nocturnal surface layer squids in the Oki Islands was completed, and so no data for

the same period has been obtained, with the result that there was no alternative but

to use the data of April 1962 - March 1963. This fact is clearly one of the weak

points of this comparison.

At the dredging-net fishing grounds in the southwestern waters of the Sea of

Japan, an examination was conducted of 3,096 common squids caught during the afore-

mentioned period by the dredging-nets of medium-size motor vessels operating out

of Kasumi harbour in Hyogo Prefecture. Upon examining the stomach contents of these

squids inhabiting the vicinity of the diurnal bottom layer, the content variety was

highly diversified, with such fish being detected as the "Hatsume", red Scombrops

boops, Sillago japonica, "Sohachi", "Mushi" halibut, "Hireguro", and Saurida argyro-

phanes, while among the cephalopods there were the •atasenia scintillans (Berry) and

Todarodes pacificus Steenstrun, as well as shrimp and crab juveniles. The important

ones among these were the Sillago japonica and the "Sohachi" and "Mushi" halibut

belonging to the warm water halibut family.

As done in the case of the nocturnal surface layer squids, the stomach con-

tents were divided into 9 variety groups, and the percentage of frequency with which

each was detected was found for the different ranges of mantle lengths as shown in

Fig. 18. In addition, using the same specimens, the ratio of the stomach weight to

body weight was determined and plotted as shown in Figs. 19 - 20.

(45) Considering the living habits, and

-67-

Fig. 18. Diagram showing that the stomach content composition of common squids inhabiting the diurnal bottom layer in the southwestern waters of the Sea of Japan, does not differ with mantle length or season,

A: 1,339 specimens (728 females: 601 males) of April-Nov. 1962.

B: 1,757 specimens (9)41 females: 816 males) of December 1962- March 1963.

Symbols used are the same as in Fig . 15.

especially the feeding pattern, of common

squids inhabiting the diurnal bottom layer

by mens of these diagrams, in general the

following observations can be made.

While the common squid juveniles

inhabiting the bottom layer are prominent

plankton eaters, with Copepoda, shrimp and

crab juveniles, and Amphipoda being among

the variety of organisms eaten, those

measuring 11 cm or more in mantle length

appear to have adult feeding habits

favouring other squids and fish. Never-

theless, a plankton diet, albeit small,

can also continue to be detected.

Additionally, in the adult bottom layer

squids there is no conspicuous decreas-

ing trend in the stomach weight as seen in

the adult surface layer squids, and those with empty stomachs also appear inversely

to the case of surface squids, with the number decreasing among progressively larger

size squids. This fact is deemed to indicate that the squids inhabiting the diurnal

bottom layer almost certainly engage in highly vigorous feeding activity.

4. Discussion

In order to ascertain the different feeding habits by day and night of the

common squids inhabiting the nocturnal surface layer and common squids inhabiting

the diurnal bottom layer, a comparative examination was made of the composition of

their stomach contents and their stomach weights. However, since the data dealt

with thus far differ geogranhically, in that the former was confined to the Cki

68

(46)

Islands vicinity while the latter involved the entire dredging-net fishing grounds in

the southwestern waters of the Sea of Japan, as well as there being a difference in the

year of collection between the two, and also because no oceanographic surveys were

undertaken simultaneously to determine the effects of varying environment on the

quality and quantity of the various food organisms involved, the significance of the

study is somewhat limited to the extent that there was no alternative but to proceed

with the study by disregarding the yearly variation in the natural environment of

the sea and the resultant qualitative and quantitative changes that occur among the

food organisms concerned.

Fig. 19. Diagram showing that the stomach weight of common squids (female) inhabiting the diurnal bottom layer in the southwestern waters of the Sea of Japan, does not vary greatly with the different ranges of mantle lengths.

'Fig. 20. Diagram showing that the stomach weight of common squids (male) inhabiting the diurnal bottom layer in the southwestern waters of the Sea of Japan, does not vary greatly with the different ranges of mantle lengths.

69

Bearing the foregoing points in mind, our discussions thus far have been

confined only to the stomach contents of 'the specimens of 1,512 nocturnal surface

layer squids obtained in the Oki Island waters between April 1957 and March 1958,

and 3,096 diurnal bottom layer squids obtained in the southwestern waters of the

Sea of Japan from April 1962 to March 1963. However, taking a somewhat rough but

broadminded standpoint, with the premise that the wider the fishing grounds and the

larger the number of specimens the better, if the effect of environmental variations

is going to be disregarded, 16,422 specimens from January 1954 up to June 1963 were

used to represent the nocturnal surface layer squids in the southwestern waters of

the Sea of Japan, and 9,014 specimens from November 1960 up to June 1963 were used

to represent the diurnal bottom layer squids in the same waters, and the percentage

of each of the 9 groups in the stomach con-

tent composition for the different ranges

of mantle lengths was determined to see

whether or not a stable stomach content

composition was present, by means of which

the change in feeding habits with the growth

stage could be discerned. According to

Fig. 21, plankton eaters are prominent up

to a mantle length of around 14 cm, with

Amphipoda being in the main for the nocturnal Fig. 21. Comparison of the stomach

content composition of common surface layer, and Copepoda followed by squids inhabiting the nocturnal surface layer (A) and of common Euphausiacea being in the main for the diurnal squids inhabiting the diurnal bottom layer (B) in the south- bottom layer, while at mantle lengths of 15 western waters of the Sea of Japan. cm or more in both cases, there is a transi-

A. Those caught by a variety of tion toward a fish and squid diet, with fishing implements during January 1954-June 1963. increasing occurrences of eating their own

B. Those caught by dredging-nets during Nov. 1960-June 1963. kind and of empty stomachs in progressively

-70-

larger size squids in the nocturnal surface layer, whereas in the diurnal bottom

layer on the other hand, the plankton diet of the juvenile stage continues some-

what longer than in the case of the nocturnal surface layer, and the occurrence of

demersal fish becomes increasingly greater than other squids while the frequency of

empty stomachs decreases. This is largely identical to what was surmised from

Figs. 15 - 20, and is deemed to indicate that adult common squids engage in feeding

activity more vigorously in the diurnal bottom layer than in the nocturnal surface

layer.

In the compositional variety of the stomach contents of common squids

inhabiting the diurnal bottom layer, the frequency of occurrences of Sillago

japonica is extremely high while the sand-fish almost nover appears. Since the

difference in the occurrence rate between the two species of fish is due to a com-

bination of the upper limit of the vertical distribution zone of each of the two ( )47)

fish and the lower distribution limit of common squid, it would seem to suggest that

the lower vertical distribution limit of the common squid is in the vicinity of the

150 m depth which happens to be the permanent habitation zone of the much eaten

Sillage japonica. Among the fish that are eaten, the one most peculiar is Saurida

argyrophanes which migrates vertically by day and night (Fm in Fig. 21), this fish

being preyed upon by common squid indiscriminately as to the nocturnal surface layer

or the diurnal bottom layer.

Generally speaking, in the nocturnal surface layer the feeding activity is

deemed to be sluggish, while in the diurnal bottom layer the feeding activity is

deemed to be engaged in rather vigorously, somewhat resembling the juvenile stage,

and this fact is seen to reflect the ecological two-sidedness associated with repro-

duction which becomes prominent in the adult stage. In other words, it is surmised

that in the peak mating period, the feeding activity in the nocturnal surface layer

becomes sluggish and the group mating phenomena (Hamabe, 196)4) intensify, whereas

71

in the diurnal bottom layer the feeding activity is brisk while the reproductive

activity becomes sluggish.

VIII. SUMURY

1. To provide a basis for an ecological discussion of the common squids in the

southwestern waters of the Sea of Japan, a detailed physical dimension survey was

conducted involving a total of 26,339 squids caught while inhabiting the nocturnal

surface layer or diurnal bottom layer in the Oki Islands in Shimane Prefecture,

Tsushima and Goto Island, the Tamma coast in Hyogo Prefecture, and the dredging-net

fishing grounds in the southwestern waters of the Sea of Japan during the period of

1954-1963.

As the authors were interested in the maturity state of the gonads at dif-

ferent stages, this was emphasized throughout the study. The determinative basis

for the degree of maturity of the gonads was that, in the female squids, those whose

total weight of the incubatory organs (ovary and left and right oviducts) was 10%

or more of the body weight were taken to be fully mature, those between 9 - 2% with

a few mature eggs in the oviduct but deemed to be still too early to spawn were

considered mature, and those 2% or less with no mature eggs whatever were taken to

be immature. For the male squids, the distinction between mature and immature squids

was based on the presence or absence of the formation of spermatophores within

Needham's sac. In addition, in both the males and females, those whose skin was

stripped, and mantle was sunken, and whose liver and reproductive organs were

noticeably reduced in capacity and weight, were taken to be spent squids.

2. The detailed physical dimension data were classified and arranged according to

year, month, sex and mantle length, and a comparative examination was made of such

ecologicarcharacteristics as the correlation between mantle length and gonad maturity

stage as well as the variation in sex ratio.

I 1

- 72

Now, disregarding the fact that a number of other morphological and ecological

aspects which should naturally be considered have not been touched upon, along with

the fact that there are all too many unknown points in discussing genealogy, and

confining our view to these results alone, while there are instances of mutual ove r-

lap and intermixture in the fringe areas, the principal groups consisting of the

autumn squid, winter squid and summer squid as distinguished by their respective

arrival period in the southwestern waters of the Sea of Japan, are deemed to correspond

respectively to the following 3 genealogical groups.

(1) 1st southward migratory group: This is a large-size common squid group with

mature mantle lengths of 27 - 33 cm, and surmised to have a life-span of over one

year. This group inhabits the 3rd tributary of the Tsushima warm current or the

central part of the Sea of Japan influenced by the east Korean warm current, and its

area of distribution is surmised to extend as far as the cold continental waters

beyond the polar frontal zone and even to the continental coastal zone. The arrival

period of this group in the southwestern waters of the Sea of Japan is September-

November, and there are many females in the coastal visitation group, with the gonads

of the females being either mature or fully mature, while those of the males are all

in the mature stage corresponding to the spawning group. This group is surmised to

cross Tsushima Channel and leave the Sea of Japan by December.

(2) 2nd southward migratory group: This standard size common squid group has a

mature mantle length of 24 - 27 cm, and is said to have an estimated life-span of

approximately one year. Inhabiting the 2nd tributary region of the Tsushima warm

current, this group makes the entire Hokkaido coast including the Sea of Okhotsk and

the Sanriku coast as its area of distribution. This northerly group enters the Sea

of Japan around October-Nzvember, moves into mass southward migration around December,

and leaves the Sea of Japan from Tsushima Channel around March. The sex ratio of

the group when it arrives in the southwestern waters of the Sea of Japan reveals a

tendency for male dominance in the early stages, but gradually the males and females

-73-

1

become equal in number. In addition, while the males of this group are all mature,

the majority of the females is generally immature and belongs to the mating group.

(3) 3rd northward migratory group: This is a small-size common squid group with

a mature mantle length of 15 - 23 cm, and is said to have an estimated life-span of

approximately one year. The habitation area of this group extends from the west (48 )

coast of Noto Peninsula through Tsushima Channel to the East China Sea. Making the

southwestern waters of the Sea of Japan as its main area of distribution, its center

of distribution is the 1st coastal tributary region of the Tsushima warm current.

The sex ratio of this group features the same number of males and females/ with a

mixture of mature and immature squids among the males, while almost all of the

females are immature and hence belong to the unmated pre-mating group.

As a species, the common squids have a life-span of approximately one year,

and assuming the growth rate of the mantle to be 3 - 4 cm per month until they reach

their biologically minimum size (mantle length of 20 cm) and 1 cm per month after

that, a hypothetical depiction of the growth of the 3 genealogical groups was pro-

sente d.

3. By means of tagging experiments, the migratory activities of the common squids

that come and go in the southwestern waters of the Sea of Japan were traced. In

normal years, the forerunners of the 3rd northward migratory group arrive in the

Oki Islands around March, while the main portion of the group migrates northward to

the eastern Sanin -Walcasa Bay coast and becomes the summer spawning group tradition-

ally caught around June. Looking at the results of accurate physical measurements

taken simultaneously with the tagged releases, it was found that 3 months were

required for this mating group to become a spawning group.

In accordance with the biological circulation of the seas, the common squids

assemble and become intensified in the coastal region together with the shoreward

movement of the warm water mass in the autumn and winter months, but in the course

of being transported by the vortex chain of the warm water mass, that is the Tsuchima

warm current, the squids themselves are surmised to take the first step of migration

by transferring reflexively to other vortices that come in contact with the vortex

containing them. In this way, ultimately those that continually transfer to water

masses suited to their ecological requirements (ecological changes favpuring narrower

bands of warm temperature seem to occur with maturity of the gonads) would be the

ones that migrate to progressively warmer areas.

4. The swarming of common squids occurs within the Tsushima warm current system at

Kunashir Island in the southern Kuriles, Hakodate in Hokkaido, Ofunato Bay in Iwate

Prefecture, the Oki Islands in Shimane Prefecture, and on the east coast of Tsushima

in Nagasaki Prefecture.

Looking at the topographical characteristics comon to these 5 areas, there

are isolated islands and topographical indentations on the coast, and coastal warm

water reflux zones are formed under the influence of the warm water mass that moves

shoreward in these localities. Since these reflux zones constitute the final link

in the chain of warm water vortices, the common squids intensified in the coastal

region are induced by the vortex chain to transfer and end up here, and are then

presumably driven towards the beach by the force of rapid tides and wind-blown

currents.

In addition, the period in which swarming occurs at all 5 localities is

centered around December, and the squids at that time are all of the 2nd southward

migratory group. The ecological characteristic of the 2nd southward migratory group

is that it is a peak mating group most vigorous in both migratory activity and mating

activity, and there is an intensification of abnormal activity associated with mating

in this group. The swurming phenomena occur presumably as a result of a mutual

interaction of the concentrative function of the environment and the behavioral

intensification of the animals themselves.

5. The reproductive stage of the adult group is divided between the mating period

centering around the males and the spawning period predominated by the famales.

-75-.

while there is a mutual overlap in the middle of the two periods, the peak mating

period and the peak spawning period are each deemed to cccur separately near the

middle of the mating period and the spawning period respectively.

In order to confirm the principal mating season and principal spawning sea-

son in the southwestern waters of the Sea of Japan, representative specimens of the

3 squid groups consisting of the nocturnal surface layer squids in the coastal

region, nocturnal surface layer squids in the offing region, and diurnal bottom

layer squids of the entire dredging -net fishing grounds were taken, and a study was

made as to what stage of development their gonads were in and when, in each of the

respective regions.

6. Using such vidence as the empty spermatophore sheaths detected in the stomachs

of mated female squids to be one of the traces of mating, and considering the time

of overlap between the period with the maximum occurrence rate of mating females

among female squids and the period with the highest number of spermatophores

possessed by male squids to be the principal mating season, the variation in the

mating rate and spermatophore number was observed over a lengthy interval of time.

The result was that, for the nocturnal surface layer squids in the coastal region,

the mating period was found to be December-February, with December-January in

particular being deemed as the peak mating season. Homever, since it is also

December-February for the nocturnal surface layer squids in the offing region, and

likewise December-February for the diurnal bottom layer squids in the dredging-net

fishing ground's, there should be no argument with the conclusion that December-

February is the principal mating season of common squids in the southwestern waters

of the Sea of Japan.

7. Because the range of nidamental gland lengths of spawned female squids is 7 - 14

cm, with the mode being 9 cm, the period in which squids with such nidamental gland

lengths and having incubatory organs weighing lC% or more of their body weight (49)

are present, and at the same time, in which squids with exhausted gonads and juveniles

measuring 3 cm or less in mantle length appear, was considered to be the principal

1

,

-76-

•

>spawning season, and the occurrence of these conditions was gin lengthy observation. II

With the nocturnal surface layer squids in the coastal region > this divides into the

primary season of April-June and the secondary season of September-November. While

it is ùnknown for the nocturnal surface layer squids in the offing, since it is also

April-June with the diurnal bottom layer squids in the dredging-net fishing grounds >

the principal spawning season of common squids in the south•estern waters of the Sea

of Japan can therefore be considered primarily to be April-June and secondarily to be

Septamber-November.

8. The spawning grounds of the common squids can be ascertained by the presence of

four necessary conditions consisting of the spawning group, spawn-exhausted squids

and spawn-spent corpses, minimum size juveniles, and spawning environment. While

the 2nd southward migratory group becomes a spawning gruup only after entering the

East China Sea, the 3rd northward migratory group is the main spawning group in

summer in the southwestern waters of the Sea of Japan, while the 1st southward migra-

tory group is a spawning group that remains briefly in autumn and is seen to spawn

only slightly. Consequently, from the fishing ground environment of the spring-

summer season and the fall in which the 3rd northward migratory group and the 1st

southward migratory group are seen, it should be possible to analogize the spawning

environment of the 2nd southward migratory group in the East China Sea.

The spawning environment established in the suuthwestern waters of the Sea

of Japan is deemed to be the sea-bed at depths of 20 - 150 m within coastal warm

water masses influenced by- warm currents of 10 - 20 ° C in water temperature and 19.00%

or more in chlorinity, with reef zones in this locality being favoured. Surmising

from this, the principal spawning grounds of the 2nd southward migratory group are

in the northeastern part of the East China Sea including Tsushima Channel, and are

presumed to be mainly the Goto Sea coastal zone, the Genkai coastal sea zone, and

the intermediate sea zone near Kakino Shoal in the East China Sea. It is hoped to

study this further in the future.

1 - 77 - I

9. Using the examination results of the stomach contents of 16,422 surface layer

squids caught at night and 9,014 bottom layer squids caught by dredging-nets in the

daytime in the southwestern waters of the Sea of Japan, an attempt was made to surmise

the change in feeding habits according to the stage of development and the zone of

habitation.

While plankton eaters are prominent up to a mantle length of around 14 cm,

the diet changes to other squids and fish for mantle lengths of 15 cm or more. With

adult squids, a difference appears between the zone of' habitation, with the occur-

rence of preying on their own kind and of empty stomachs increasing in the nocturnal

surface layer, while demersal fish occur increasingly and empty stomachs decrease in

the diurnal bottom layer. This suggests the fact that, among the adults, feeding

activity is more vigorous in the diurnal bottom layer than in the nocturnal surface

layer, and is believed to reflect an ecological two-sidedness associated with

reproduction which becomes prominent in the adult stage.

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(1931a). A comprehensive view of the species of common squids. Periodic Bull. Hokkaido Fish. Exp. Station, (1 )48).

(1931b). Common squid surveys of the Tankai-maru. Periodic Bull. Hokkaido Fish. Exp. Station, (1)49).

Ito, Kachiyo (1952). Surveying observations of the common squids in Ryotsu Bay at Sado. Collection of articles commemorating the 3rd anniversary of the establishment of the Japan Sea Reg. Fish. Res. Lab.

Ishii, Shiro (192)4 . Basic research report on the secondary squid fishing industry in the Oki waters. Bull. Shimane Prof, Fish. Exp. Station.

Ishikawa, Chiyomatsu (1930). On hibernating sweet-fish. Scientific Knowledge, (10).

Ito, Yukata (1957). Number of sardines eaten and destroyed by squids. Annual Bull. Japan Sea Reg. Fish. Res. Lab., (3).

, Muneo Okiyama, Shogo Kasahara (1965). Some information on the common squids in the offing of the Sea of Japan. Bull. Japan Sea Reg. Fish. Res. Lab., (15).

Kato, Genji (1951). Mass deaths of squids. Japan Sea Reg. Fish. Res. Lab. & Fish. Exp. Station Intercommunication News, (11).

(1959). Tracing the genealogical groups of common squids from an ecological aspect - I. Annual Bull. Japan Sea Reg. Fish.Res. Lab., (5).

-so-

t Kato, Genji (1960). Tracing the genealogical groups of connon squids from an eco-logical aspect - II. Annual Bull. Japan Sea Reg , Fish. Res. Lab., (6).

Meteorological Agency (1959-1960). Periodic Bulletin on the National Sea State, (460-513).

Kawana, Takeshi (1953). Some problems concerning the common squids. Fisheries Technique Improvement, (5)

Kyoto Prefectural Fisheries Experimental Station (1962). Data of the 1962 Study Conference on the Development of Common Squid Fishing Grounds.

Kojima, Toshihira (1959). A study of fishing conditions involving common squids in the Oki Islands vicinity - III. Japan Fish. Soc. Journal, 25(4).

Kagoshima Prefectural Fisheries Experimental Station (1957). Report on Tsushima Warm Current Development Research (II et. III). Kagoshima Pref. Fish, Exp. Station Data.

Kanamori, Masaharu, et al.; Tadahiko Imai, et al. (1957). Data on TsushimaWarm Current Development Research (4). Data of Fac. of Fish., Kagoshima Univ.

Machinaka, Shigeru (1957). On the tagging experiments of summer squids and winter squids in the Sea of Japan. Data of the 8th Symposium on Tsushima Warm Current Development Research.

(1959). On the results of common squid tagging experiments in the Sea of Japan. Bull. Japan Sea Reg. Fish. Res. Lab., (7).

Matsumura, Gizen, Tetsushi Senta, Chieko Taniguchi (1959). Surveys in Goto Sea and its vicinity (27). On the "Common squids" in the western waters of Kyushu. Nagasaki Prof. Fish, Exp. Station Data, (130).

Mon, Isamu, & Fukuo Nishimoto (1957). Survey of sea conditions in the Goto and Tsushima vicinity. Nagasaki Pref. Fish. Exp. Station Data, (130).

(1959). Surveys in Goto Sea and its vicinity (33). Survey of sea con- ditions on the east coast of Tsushima. Nagasaki Pref. Fish. Exp. Station Data, (161).

Nagasaki Prefectural Fisheries Experimental Station (1956-1959). Surveys in Goto Sea and its vicinity (19-33). Nagasaki Pref. Fish. Exp. Ptation Data, (91-161).

Niwa, Shoichi, Shokichi Yoshida, Tsutomu Sato (1957). Table of physical measure-ments of common squids. Summary Report on Tsushima Warm Current Develop-ment Research (6). Niigata Pref. Fish. Exp. Station Data, (7).

Nasumi, Tatsuro (1958). Common squids of Tamma. Japan Sea Reg. Fish. Res. Lab. e: Fish. Exp. Station Intercommunication News, (88).

Saburo Yoshioka (1958). Survey of resources on the Sea of Japan coast (common squid survey). Hyogo Pref. Fish. Exp. Station 1958 Operations Report.

- 81 -

e Japan Sea Regional Fisheries Research Laboratory (1964). 1964 Research Data on the Development of Common Squid Fishing Grounds in the Offing of the Sea of Japan, (3).

Okutani, T. (1962). Diet of the Common Squid, Ommastrephes sloani pacificus, landed around Ito Port, Shizuoka Prefecture. Bull. Tokai Reg. Fish. Res. Lab., (32).

Okutani, Takashi (1965). Studies concerning the early life history of the squid species - I. Bull: Tokai Reg. Fish. Res. Lab., (41).

Okiyama, Mimeo (1965a), Feeding habits of the common squid, Todarodes pacificus Steenstrup, in the offing of the Sea of Japan. Bull. Japan Sea Reg. Fish. Res. Lab., ( 14).

(1965b). Some information on the eggs and larvae of the common squid, Todarodes pacificus Steénstrup. Bull, Japan Sea Reg. Fish. Res. Lab., (15).

Sasaki, M. (1921), On the life history of an economic cuttlefish of Japan, Ommastrephes sloani pacificus. Trans, Wagner. Free Inst., 9.

(1929a), Supplementary notes on the life history of an economic cuttlefish, Ommastrephes sloani pacificus, Jap, Jour. Zool. 2 (2).

• .-Ir....••••••••••

(1929b). A monograph of the dibranchiate cephalopods of the Japanese and adjacent waters, Jour. Coll, Agr. Hokkaido Imp. Univ., 20 (Suppl.).

Soeda, Junsuka (1950), On the migration of the common squid, Ommastrephes sloani pacificus(Steenstrup), on the Sea of Japan coast. Bull. Hokkaido Fish. Exp. Station, (4)

(1952). Artificial insemination of common squids and their early cleavage. Bull, Hokkaido Fish, Exp. Station, (5).

. (1954). On the fertilization of common squid eggs and their forms. Bull, Hokkaido Fish. Exp. Station, (11).

(1956), Studies concerning the ecology and propagation of common squids. Bull, Hokkaido Fish, Exp. Station, (14).

, Hisao Aratani, Toshiaki Otsuki, Shigeru Machinaka (1958). Studies concerning the common squids, Report on Tsushimailarm Current Development Research, (4), Fisheries Agency.

Sugano, Yoshihiko (1958). The common squids of Shonaihama, Japan Sea Reg. Fish. Res. Lab. & Fish, Exp. Station Intercommunication News, (88).

Fisheries Agency Investigative Research Section (1962). Summary. Report on the Development Research of New Fishing Grounds in the Cold Northern Waters of the Sea of Japan, (2),

Tanaka, Otohiko, & Shoji Iizuka (1956). On the common squids in the northwestern waters of Kyushu. Bull. Fac, of Fish., Nagasaki Univ., (4).

Tanauchi,Morisaburo (1941) 1 On the stock of common squids. Japan Fish , Soc. Journal, 10 (1.3).

' - 82 -

II Uchihashi, Kiyoshi (1960a). On the stationary natation of fish. Japan Fish. Soc. Journal, 126 (3).

(1960b). The natation of fish and their stationary phenonena. "Teichi", (26-27).

Yamaguchi Prefectural Main Sea Fisheries Experimental Station (1957-1959). Operations report of the Yamaguchi Prefectural Main Sea Fisheries Experimental Station for the period 1956-1958.

Watabe, Taisuke (1965). On the distribution pattern of common squid larvae in the southwestern waters of this country during the winters of 1959-1962. Bull. Tokai Reg. Fish. Res. Lab., (43).

Yasui, Tatsuo (1961). Summary of results of common squid tagging experiments. Dredging Information of the Hachinohe Branch of the Tokai Reg. Fish. Reg.

Lab., (27).

& Yoshio Ishibe (1955). On the growth rate and snawning season of the common squid, Ommastrephes sloani pacificus. Bull. Tokai Reg. Fish. Reg. Lab., (4).

Yamamoto, Koji (19 )46). On the eggs and larvae of common squids obtained from Korean waters. Shell-fish Journal, 14(5-8).

'

S-•

258

.("c7 Stationary net at 252 Noimura, Yataba-gun,

Shimane Prefecture.

-83-

Appended Table 1. Results of tagged release surveys in the Oki Islands during 1950-1960. (52)

Release Recovery

No. of trials Position Month

& year No. of squids Position

No. of squids

Number of elapsed days 0-5 16-10111-15 16-2121-25 daysidaysIdays daysIdays

26 days'

Oki Is., Shimane Pref: Nakanoshima on Dozen.

3 Takatahana. 15-12 mi. Dec 50 1,500 SSW off Chichiisàki, Omori Is. Single line.

Nakanoshima on Dozen, Takatahana, 1-3 mi. S off Chinsaki. Single line.

13 13 0 0 0 0 0

Dozen. Nakanoshima. 1 1-10 mi. SSW off Taka- Mar, 51: 283 . 0

tahana. Single line. 1-10 mi. SSW off Shi- Nishinoshima on Dozen,

5 rasaki Lighthouse on Dec 55 1,400 Urago Bay common 1 0 1 0 • 0 0 0 Dogo. Single line , squid stationary net.

Nishinoshima on Dozen. . Nishinoshima on Dozen. ti t shi kano ma saonary 109 106 4 Nakanoshima common Jan 57 3,200 Na 3 0 0 0 0 net and single line; squid stationary net. Doge single line.

Dozen. Nishinoshima Dozen. Nishinoshima 1 common squid Feb 57 300 common squid 3 3 0 0 0 0 0

stationary net. stationary net.

Dozen. Nishinoshima 6 common squid

stationary net.

Dozen, Nakanoshima 5 common squid

stationary net.

Nishinoshima on Dozen. Nakanoshima stationary a) . net. (a) Kyoto Pref. 1-46 Mar 57 2,000 195 193 0 0 0 0 inhabitant. (b) Single b) line at Etsuzen-cho, 1-75 Fukui Prefecture.

Apr 57 89 0

2 Dogo, 1-10 mi. off Jan 58 Saigo. Single line.

Dogo, 1-10 mi. off 3 Saigo. Single line.

Nishinoshima on Dozen. 6 Chiburi Is. common Mar 58 1,200

squid stationary net.

Dozen, Nishinoshima 1 common squid Jan 59 1,000

stationary net.

Feb58

Nishinoshima on Dozen. Chiburi Island common squid stationary net. Jabbing net.

( 1 0(c)1 0 0 0 0

5 5 0 0 0 0 0

Dozen, Nishinoshima common squid station-ary net & single line. (d) Off Mitsushima-cho, Shimoken-gun, Nagasaki Prefecture.

3 2 0 0 (d) 1 0 0

Dozen, Nishinoshima 6 common squid Mar 59 3,800

stationary net.

Dozen, Nishinoshima, Nakanoshima, Chiburi 122 122 0 0 0 0 0 Is. common squid sta- tionary net. Purse-net.

1 •

1

1

1

1

Dozen, Nishinoshima common squid stationary net.

Dozen, Nishinoshima common squid stationary net.

Dec 59 500

500 Jan 60

16 16 0 0 0 0 0

16 16 0 0 0 0 0

e). 16 15 0 0 0 0 1-28

1 1

Total 17,282

1 1 1

1 1 1 1 1 1

Dozen ., Nishinoshima common squid stationary net.

-84-

Dozen, Chiburi Island common squid stationary net. Dozen, Chiburi Island offing, single line. Dozen, Chiburi Is. Naka-noshima stationary net. TDozen. Nishinoshima Icommon squid stationary

Mar 60 1,000 net & single line. ( a) Rikkango offing, Uome-cho, Goto Island, Nagasaki Prefecture.

49 Total 500 491 5 0 1 0 3

( 53 ) Appended Table 2. Results of tagged release surveys in the Oki Islands and at Tamma during 1962 and 1963.

Release Recovery

No. of Month No. of No. of Number of elapsed days

Position Position d, 0-5 6-10 11-1516-2021-2526 </ trials & year squids „ —I„i-- - days days days days days day*

6-30 mi.N off various harbours on the Tama

Tsuiyama & Shibayama coast in Hyogo Pref., b) on the Tamma coast in single line. (a) 7 mi. a) 1 Hyogo Prefecture. Jun 62 1;950 N off Mikuni harbour, 31 25 0 0 1 0 20 mi. off Takeno Fukui Prof., single 4

harbour, single line line. (b) Etsuzen-cho, Fukui Prefecture, stationary net. '

tc7 Mihoseki, Yataba- Oki Is., Shimane Pref. gun, Shimnne Pref.,

c) d)e) Dozen, Nishinoshima single line. (d) Off

1 Jan 63 2,000 3 1 0 2 0 0 0 common squid Kamoise, (e) off Hi- stationary net. dàkatsu, Tsushima,

Nagasaki Prefecture. Oki Islands, Dozen,

1 Nishinoshima common Mar 63 2,000 0 squid stationary net. 30 mi. NE off Kasumi

1 harbour on the Tama May 63 400 0 coast, single line. 30 mi. NE off Kasumi Ine-cho, Kyosha- f).

3 harbour on the Tamma Jun 63 1,500 gun, Kyoto Prof., 1 0 0 0 0 0 1 coast, single line. stationary net.

10 Total 7,850 Total 35 26 5 2 0 1 1

1

-85-

Appended Fig. 1. Mating pattern of the females and composition of the different gonad maturity stages of the males and also the composition of the different gonad maturity stages of the females (B) of common squids inhabiting the nocturnal surface layer and diurnal bottom layer at Tsushima and Goto Island during 1960-1963.

- 86 - •

Appended Fig., 2. Mating pattern of the females and the composition of the different gonad maturity stages of the males (J1) and also the composition of the different gonad maturity stages of the females (B) of common squids inhabiting the nocturnal surface layer at Tamma during 1962-1963.

1. Summer squid group in the Kasumi offing. 2. Summer squid group at Takenohama.

-87-

(55)

Appended Fig. 3. Composition of the different gonad maturity stages of the female species of common squids inhabiting the bottom layer and caught in the daytime at the dredging-net fishing grounds in the southwestern waters of the Sea of Japan during 1961-1963.

24

•■ OE) .84

yr

, 20

e • ek 16

4 a >74.

W

'

!

q'

1

• -

V / /J , f

32

28

1

I •

• , • „, Peninsula o • ..... _ .

II

cm

Fig. 1. Hypothetical growth curve:of the 5 genealoecal groups of common squids. •

Fie. 2. Assumed mieratory routes of common squids in the southmestern waters of the Sea of Japan.

Explanation of symbols: • .0 -iWinter ÇDecember-January) release point, 0.1Spring \March) release point. • .----Assumed migratory route of above, - 'Assumed migratory route of above. 60 :Release point from which remote recovery occurred, @ ;Remote recovery point.

• ---, Assumed migratory route to remote points: „. Common squid stationary nets in the Dozen area

• of the -Oki Islands, N Yellow-tail stationary nets in ditto. W Hakashima X Urago-cho Y Sakimura Z Saigo-cho ,

• Remote recovery cases Those released in Those released On Oki Island waters the Tamr.la coast

a 3/6 '60-4/3 '60 • b 1/23'59 ----2/11'59

• c 2/6 '58 ----2/15'58 d 3/22'57----5/7 '57 ' e 3/22'57----6/4 '57 1 .

• f 1/2 '63 ----1/4 '63 g 1/2 '63 ----1/14'63 h 1/2 '63 ----1/16'63

i 6/22'62----7/14'62 1 . j 6/27'62----7/6 '62 lc 6/9 '63----7/18'63 •

Those released in Yamato Bank waters . i 8/2 '629/1 '62 • 1 rft 9/17'62-10/11'62 .

Table 1. Monthly volume of catch of common squids in the 11 prefectures adjoining the western Sea of Japan and East

China Sea areas (1955-1956). (unit: ton)

Pr---5-327171"th : xi ,55 i I i I Pi V

X X1 1 111 1 0: X X1 )1 '561 1 I 2 ' Total ,.......,' ., ------ '

.. .

l'ulcui • .: 866 0 41 0 01 5) 443 3601 2331 41 04 16101 94 0 02,239

Kyoto 120 0 01 0 0 33 191 1391 81 4 • 8 - 4 0 0 516 ,

Hyogo ;1,283 53 01 -1 0 191 93 6231 531 38 195 11 71 416 e 0 3,864. Tottori ,« 735 11 01 • 0 0 34 323 281 Ill 150 158 8 251 21 0 0 2,172:

Shimane 1,748 611 150 23 23 98 26 0 38 41 11 769 1,286 188 83 5,1561 Yamaguchi, 0 0— — — 0 001 01 0 G 1 68 . 15 . 0 91 r Polcuoka 23 n — — --.1 .... — — — .--1 7 0 0, 0 0 113 '

Saga - o -- --1 ol 0 71 94 0 0 -- 11 4 30 7 0 217: raga11119.1Ci 5 ,5083,008 765 161 HI 90 15 0 0 278 55 454 2,75 4,55 803 371 15,354 : Kum r-amoto ' 0 0- 4 7 4 41 -n 0 -1 -- 01 0 • « 23 %

I Kagoshima 0 4 41 0, 01 4 01 4 0! 0 0 0 7 11 7 4 ' 46

9,2833,7211 923 184 3414522,0781,54 309 1 5491,058 507 4,024 6,676 1,0201 46 21 32,811 ' Totali

le: I 1 1

!:.p. -imraature group • 'Ilating group - S'-,)etwning group

Migratory direction .

Fig. 3. Hypothetical diagram concerning the migration and distribution of the 3 genealogical groups of common Squid s . in the Sea of . japan.

A: Central erowth area . 1: 1st southward group B:.Northern growth area 2: 2nd southward Froup

.C: Coastal growth area 3: 3rd northward group

• > U. Single line fishing ground

Sea-bed reef zone Stationary squid net

rig. 4. tiagram showing the occurrence sites : of swarming phenomena near Kamoise-cho on the east coast of Tsushima in Nagasaki Prefecture.

• 1: Akashima. 2: Okinoshima. 3: Kuroshima. 1. Fdkaura; 2. Shichikamaura; 3. Mioteura; 4. Hokusogaura; 5. Murasekiseto; 6. Kamoise; 7. Ashigaura; 8. Ikatàukiura. .

! :

I

•

■ •

.1

i

50

100

150

100

200

0 ` 10 i 25

50

75

11 12 1 2 3Y1 • • laon th. . -._ 4 6 6 7

1 • - $s-

b,

• .C.

;

54 • so

e.:52 ee

60 CeO

S .-.ee 20

E-I

6. Appearance pattern of • spawning common squids in •

Oki Island waters (1957-59).

Fig. S. Fishing sites and volume of catch for single line squid fishing in the dredging grounds •for Dec. 1962 and ibn. 1963. •

a...region north of Oki b...reeon north of Tsushima . c...Ishimi-Chomon region d....Izumo region • . e...Imban region •

, f...Tamma region

• White dots denote 5 boxes of reported catch, and black dots

:denote 10 boxes (23 kg in a box).

Iwate Pref. Fish. Exp. Station

Tottori Pref. Fish. Exp. Station Shimane 'Tottori

Fukuoka ,aga Fukuoka

IT

II

Il

it

it

51

It

11

rri

. Tens of,thoUsand ken ' (1 ken = 8.28 lbs.).

• .

•1

I‘

579 '1 3 5 7 91 "1 3 5 7 911 1 3 5 7 911 1 3 5 7 9 I 3 5 7 9 II

. • 1951 1952 1953 1954 1955 1956

rt

so

• •

A on the 144° E meridian south of Kushiro

• _J

110954 12,10/4 4110 1020 36 0 2.0 31 ..>1 41,1

diti.«.11einlailLi . B 'Eastern offinE of Ozaki,

0 • SO

' 100

• .

200

8,1954 r„.c.1 12,1254 L,1 rn 1, 1955 . 10 2. 0 3,9 41 %0 , 1,9 . nc .1.3 5 :1

.0 10 n .9 40 50 „22

14 1 15 -•-•12

1 n 7.5 ....--,..,<\ ? 1n

Kamaishi harbour„Iwate Prefecture

Kibihara - Genkaishima

Fig. 5. Contraction of the warm current 'as seen in the vertical distribution of water temperature at various Japanese coastal points (Central Meteorological Observatory, 1954-1955).

A Aug. 4-11 Observation by 4th District Headauarters of the Maritime-Safety Agency -

5-6 Hakodate Oceanic Weather Observatory

C Northern offing of Hamada harbour Shimane Prefecture 8 4 1954 10,1951- , 12,1954

10 An 40 t 9 -' , 0 40 en an;D. 09 58 . s_.., :191+

7,>--'-■-10 -----0e-■------ ----,."10 ,.----..,4".=

: °'---\s_Y S'--: -.-----7----.. '

D Tsushima Kiblhara Iki - Tkiukishima

8,1951 12,1954 1,1955 trzg.i 1 2 '',i,5'1% Mee te.1.2 )31.:32,',112 1

25

.,.' 16 /

f '

l(1

• ..--:::::19 . 18 • 19

20

Dec.

B Aug. 17 Dec. 17-18 Jan. 14

C Aug. 2-3 Oct. 11-16 Dec. 6-7

D Aug. 6-7 Dec. 11 Jan. 12-14

-

Fig. 7. Monthly volume of catch of common squids in the western sector of the Sea of Japan. (from Soeda, et al., 1958)

1252- 12g Dee 62 500 01

• „ 10

*.• I 10

"«. • A

/ 10. •

r....... , .

15

1963=F--- 1 11 Jan 63

— 28—

• : s . ..... , .., ./...,...

• I : ,,,,.>•,... 1 , ; ..."-.4•\ : ,."

,... .. • ; .. are . ''... ; •., .,....

......., ......„,,. „. ,. .- ...• ..._., ." .. . ... ........... . —,-,•:<7.ei,.....-,r.r.- .:., • ,

Fig. 9. Diagram showing the correlation between the fishing sites for the conmion squid spawning zroup using dredging-

. nets and the favourable Silo japonica fishing grounds

. for the period of December 1962 - March 1963.

(The horizontal distribution pattern of water temperature . at the 150 m layer is from Sea of Japan Sea State Reports

No. 139 and 140.) • Dotted lines denote the favourable Sillaeo japonica fishing

: grounds (mean volume of catch of over 50 kg per dredging-net). nach black dot denotes 1 boX (23 kg) of common squids caugbt at the reported fisbing site. White dots denote : the fishing sites of unmixed catch.

4‘

—39-..

. 1963* 4 A •

Apr (;3

1

- - -

2 00 • • y

•

s oo Ws.

• •

-

1963*5 iay é"?3

I. et; I i

•Water temp. • Chlorinity -in c1C7 at the in';;g at the 50m layer 50 m layer _ .

ippt

Fig. 12. Horizontal distribution pattern of water temperature and chlorinity in the western waters of Kyushu during Nov.. 1955 - Mar. 1956. .

(According to Nagasaki Pref. Pish. Exp. Station, 1956.)

à

Pie. 10. Diagram showing the correlation between the fishing sites for the common . squid spawning group using dredging-nets•and. the favourable Sao japonica fishing grounds for the period of April-May, 1963. .

(The water temperatures at the 150 m layer are from Sea of Japan Sea State Report S No. 141 and 142.)

5 ctc-e Symbolee:,leidentical twig. 9.

Fig. 11. Diagnam showine the correlation between the fishing sites for the common squid spawning group using dredgin-nets and the parallel row of reef formations between Yamaguchi, ShiMane, Mishima and Oki Islands in June 1963.

A Parallel row of islands and reefs (according to Watanabe, Ito, et al., 1960). •

a-h Reef formation between Mishima and the Oki Islands.

Each black dot denotes 1 box (23 kg) of catch at the fishing sites for spawning common squids using dredeing-nets. •

13 135

- 39 - M9 - 1 4G

-I •

-1 209 13 69 5 81 _ 5 3 9 19

15 59

;91

Tl

135

Fig.. 14. Collection sites for squid ›..uttsiltsy;lw4Lings and common squidtrg-},ue, des 14n-ip in the eastern part of the

East China Sea, and fishing sites . for the common squid group on the coast.

• N Northern-central survey line in

the East China Sea of the Nagasaki . . Prof. Fish. Exp. Station. Western survey line in the East China Sea 'of the Kagoshima Prof.

Fish. Exp. Station. ,( • 1 common squidaeeigic3e collected. O 1 squid y- 14ïll'in. collected. * Kakino Shoal formation. Arabic numerals indicate the month of. • catch of the y.-un.71'ng- •group. -

,sp.r.ve'n't re,

à

Table 6. Monthly number of reproductively exhausted squids collected in the Oki Island waters (1954-1960).

Successive months

year 1954 - '55 1955 -- '56 1956 '57 1957 -- '53 1953 -''59

1959 60 •

Total

Number of reproductively exhausted squids collected

‘1 1 IX. X XI I XI I 1 I* 1ln N Y

49

7-1

49

Fig. 13. Pattern of the sea system in the western waters of Kyushu. -

(According to Nagasaki Pref. Fish. Exp. Station Data No. 114, 1957.) .

1. Approximate range of flow of the Tsushima warm current northbound in the western waters of Kyushu.

2. Pattern showing the mixture of the eastward moving cold continental water of the Yellow Sea with the coastal water of the west coast of Goto Island and Genkai whilst headine for Tsushima - Iki.

3. Pattern showing the entry of part of the warm current to the bottom layer water rising as a result of the topography of the sea-bed from near Koshiki Island towards the Danjo Islands, and the resultant inflow to Goto Sea.

4. Coastal water mass located north of the central part of Coto Sea and having comparatively:little connection with the warm current system.

5. Outflow of the water from within Ariake Bay.

6. Genkai coastal sea zone. • 7. Intermediate sea zone. -- Tidal ridge. a Upper Kakino - Shoal. b Western Kakino Shoal. . c Eastern Kakino - Shoal. d Ikikaki. e Socotra Rock.

I 1: 4

I 3.;71 j

1957e4 —11A (N.439) Apr-Nov 57 •

.0: • •

. WY . • •

• n•-••••

I 95712F3 —1958* 3 frjOi.427) Dec 57-Mar 58

30

13

e:■10 " • .( .- 63) " e

1957$ 4 —11F1 cil.294) Api--Nov 57

. . •: .

1957-le I2â —15S$3 J1 (11.312/

Dec 57-Mar 58

•

•,. , • • ,

pz» •fz

o

- Ii

Pq

a . U ZI 334 .m

Mantle ei• e 11 Length

Fig. 16. Diagram showing the decreasing pattern of stomach weights from around a mantle length of 20 cm in common squids (female) inhabiting the nocturnal surface layer in Oki Island waters.

:

' C.)

o -p

Mantle el- ist Length

Fig. 17. Diagram showing the decreasing pattern of stomach weights from around a mantle length of 20 cm in common squids (male) inhabiting the nocturnal surface layer in Oki Island waterà-.

0 cli 0 4,3

A

ML 1 2- 5.. IS

12 6-10

IS 11-15 :1 IL

m-20

111 PL_

433

26-30 .

E.1

1.

•

URCETSFiFxFa 3113.6ETSF.F.7FaV , .

Fig. 15. Diagram showinfr that the stomach content composition of common squids inhabiting the noctùrnal surface layer in Oki Island waters, varies accordinit

. to mantle length and season.

A: 773 snecimens (479 females:294 males) of April-November'1957.

B: 739 specimens (427 females:512 males) of Dec. 1957-Mar. 1958.

13k. ...unknown, E. . .Euphausiacea, T...Amphipoda, C...plankton other than E and T,

along with shrimp and crab younlings,

S...squids, Ps ...surface fish, Pb...demersal fish, Pr ...transitory fish between the

two lavers (Saurida argyro- nhanesj,

V...vacant spaces.

1

1

. 4 ML I- 5.. I. I

III II ro=.,...... 6-10 li

Z1M 217 Il-15

_. In LL IL 124 6 - 20 231

im a 4 23 _21 - 26

L.. _n _J 13 26 - 30 12S

..... 111

0- CET6F>FmFx6 3 e.CET 8 Fahl 6a6

Fig. 18. Diagram showing that the stomach content composition of common squids inhabiting the diurnal bottom layer in the southwestern waters of the Sea of Japan, does not differ with mantle length or season.

A: 1,339 specimena (728 females: 601 males) of April-Nov. 1962.

B: 1,757 specimens (941 females: 816 males) of December 1962-

'• March 1963. •

Symbols used are the same as in Fig.. 15. •

196212/ —1963 3 1,1 (0 .941) Apr-Nov 62 Dec 62-eiar 63

. • . .• •

• ... • • •

œ .• .., . . .

21 33 24 . • I. 14 33 34 a. 32

Mantle e Length • le

1962* 4 —11/J01.128;

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fè 12 .

al

0. 'd

tn •

4-)

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1062.4 —11M (Lam ..itpr—Nov 62.

U62;5-12n —1963 3 A (min)

Dec 62-Mar 63

• . le

Pig. 19. Diagram showindthat the stomach weight of common squids (female) inhabiting the diurnal bottom layer in the.southwestern waters of the Sea of Japan, does not vary greatly with the different ranges of mantle lengths.

Mantle e e Length .

.Fig. 20. Diagram showing that the stomach weight of common squids (male) inhabiting the diurnal bottom layer in the southwestern waters of the Sea of Japan, does not vary greatly with the different ranges of mantle lengths.

1

40

to

I

A

m4m. ML 0— 4.. IL D

F nu . 5— 9 ms

—F- lu: W—M 27m

el _n- 114 15-19 n.

2 rek-,', R ,,, rl 21___ - ing 20 -24 ust

. nn 25— x4°

.16....., H r4:7. U.0 ET S Fla F. V U4 CET S Fs Fb. Fe V

Fig. 21. Comparison of the stomach content composition of common squids inhabiting the nocturnal surface layer (A) and of common squids inhabiting the diurnal • bottom layer (B) in the south-western waters of the Sea of Japan.

•A. Those caught by a variety of fishing implements during • January 1954-June 1963.

B. Those caught by dredging-nets : during Nov. 1960-June 1963.

20

20

25 30 20

e - Mhntle lcngth

20 30

Females Males

rei Immature • Immature

:M!Mature

;Fully mature Mature 0 :Spent Spent

•Eli:Unmated Mated • . . .

o

P .

0.4

0 y . o

à

20

Appended Figure Symbols

1961111 1963V--

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,—,••4"PzFi ,r - 2 F -

r -1, „_4n1„.,19601 I M

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1960 14- rp__ 10f ,eire,Itlill Log. tttttt

20 25 30 20 25

91- e Mantle length

squids

: 40

sauids

40

20

20

40

20

30 Cm

,Appended Fig. 1. Mating pattern , of the females and composition •

of the different gonad maturity stages of the males (A) and also

• the composition of the different gonad maturity stages of the females (B) of common squids

• inhabiting the nocturnal surface layer and diurnal bottom layer at Tsushima and Goto Island during 1960-1963.

D.• 1

Fci ■

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d- P 0

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No. of squids

I 1962* 1 â 19 63ee —,1111 .

2 n _ — _ J1111— , -1

- 3 â _

r1 _ . 4 A '

•9 5 â

.. .

1.•::'17,,,t,e

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I

. q K----- '''-f ----"'»--77,•- -:2:1''''''3:,-..,.1-9,9

1961*

!

411

20

40

20

80

60

40

20

100

80

60

. 40

20

30 20 25 20 25 30 cm

Mantle el- Length

Appended Fig. 3. Composition of the different gonad maturity stages of the female species of common squids inhabiting the bottom layer and caught in the daytime at the dredging-net fishing grounds in the southwestern waters of the Sea of Janan during 1961-1963.

î •

Date Due

FEB-1 j-19.99

BRODART, CO. Cat. No. 23-233 •003 Printed in U.S.A.