7/24/2019 Upstream Summer Migration of Eels
1/13
This article was downloaded by: [118.92.18.216]On: 30 January 2015, At: 18:29Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office: Mortimer House, 37-41 Mortimer Street,London W1T 3JH, UK
New Zealand Journal of
Marine and Freshwater
ResearchPublication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/tnzm20
Summer upstream
migration of juvenile
freshwater eels in New
ZealandD. J. Jellyman abaMarine Laboratory, Department of Zoology ,
Victoria University of Wellington , Private
Bag, Wellington, New ZealandbFisheries Research Division , Ministry of
Agriculture and Fisheries , P.O. Box 19062,
Wellington, New Zealand
Published online: 30 Mar 2010.
To cite this article:D. J. Jellyman (1977) Summer upstream migration of
juvenile freshwater eels in New Zealand, New Zealand Journal of Marine and
Freshwater Research, 11:1, 61-71, DOI: 10.1080/00288330.1977.9515661
To link to this article: http://dx.doi.org/10.1080/00288330.1977.9515661
PLEASE SCROLL DOWN FOR ARTICLE
http://dx.doi.org/10.1080/00288330.1977.9515661http://www.tandfonline.com/action/showCitFormats?doi=10.1080/00288330.1977.9515661http://www.tandfonline.com/loi/tnzm207/24/2019 Upstream Summer Migration of Eels
2/13
Taylor & Francis makes every effort to ensure the accuracy of allthe information (the Content) contained in the publications on ourplatform. However, Taylor & Francis, our agents, and our licensorsmake no representations or warranties whatsoever as to the accuracy,completeness, or suitability for any purpose of the Content. Anyopinions and views expressed in this publication are the opinions and
views of the authors, and are not the views of or endorsed by Taylor& Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information.Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilitieswhatsoever or howsoever caused arising directly or indirectly inconnection with, in relation to or arising out of the use of the Content.
This article may be used for research, teaching, and private study
purposes. Any substantial or systematic reproduction, redistribution,reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of accessand use can be found at http://www.tandfonline.com/page/terms-and-conditions
Downloadedby[118.9
2.18
.216]at18:2930January2015
http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions7/24/2019 Upstream Summer Migration of Eels
3/13
N.Z. Journalof Marine andFreshwater Research11 1) :6 1 - 7 1 . March1977
SUMMER UPSTREAM MIGRATION OF JUVENILE
FRESHWATER EELS
IN NEW
ZEA LA N D
D. J.
JELLYMAN*
Marine Laboratory, Department of Zoology, Victoria University of
Wellington, Private Bag, Wellington, New Zealand
ABSTRACT
During summer, upstream migrations
of
juvenile freshwater eels (elvers)
of
both species (Anguflla australis schm idtii Phillipps,
the
short-finned
eel, and
A. dieffenbachii
Gray,
the
long-finned
eel) are
observed
at
hydro-electric dams
and waterfalls. The migration was sampled at Karapiro Dam on the Waikato
River,
1970, 1971, and 1974, and
samples from
a
further
11
areas throughout
the country were analysed.
Elvers, active
at
night
or
during overcast
and
damp days, surmount steep
obstacles
by
climbing; they adhere
to
damp surfaces
by
friction
and
surface
tension, obtaining maximum resistance
by
undulating their bodies
and
keeping
them closely adpressed
to the
substrate.
The
maximum size
for
vertical climbing
is
12
cm .
As
elvers were sampled
at
sites where their migration
was
interrupted,
no distinct schools were observed,
but the
elvers were strongly social
and
thigmotactic.
Migrations are made up of elvers of similar size of one or both species.In
large river systems, elvers apparently migrate successively further upstream each
year for several, years. North Island samples contained elvers up to 3 y of age,
but
in the
South Island elvers
up to 7 y old
were recorded; aging
was by
burnt
otoliths. Migration
is
perhaps initiated
by
increases
in
water temperature,
day
length, and sociability; increased water flow may also coincide w ith 'runs '.
Electric fishing of streams shows that the two species hav e different ha bita t
preferences,
and
these
are
reflected
in the
proportion
of
elvers caught
at
different
sites: longfins prefer swift stony rivers, shortfins silty backwaters and lakes,but
both
are
often found together. Longfin elvers have thick dermal skin layers,
and experiments in air of constant temperature and hum idity showed that they
cannot survive prolonged exposure requiring cutaneous respiration
as
well
as
shortfins; longfins
may
also have h igher oxygen requirem ents.
INTRODUCTION
With the onset of summer each year, mass upstream migrations of
juvenile freshwater eels of both Anguilla australis schmidtii Phillips,
the short-finned eel, and A. dieffenbachii Gray, the long-finned eel, take
place in rivers throughout the country. Such eels are referred to as
elvers , as distinct from glass-eels , which is the stage at which eels
arrive in fresh water.
Present address:
Fisheries Research Division, Ministry
of
Agriculture
and
Fisheries,
P.O. Box
19-062, Wellington,
New
Zealand.
Received8July1975;revision received21July1976.
Fisheries Research Division Publication
262
Downlo
adedby[118.9
2.1
8.2
16]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
4/13
62 N.Z.
J O U R N A L
OF
M A R I N E
&
F R E S H W A T E R R E S E A R C H [ M A R C H
TABLE 1Species
proportions
(%) and
mean lengths L,
cm) of
migratory
elvers
(Anguilla
spp.) sampled 1970, 1971, 1974.
ARE A
Te Kauwhata
Karapi ro
DAT E
Jan.
1971
J a n - Fe b
1970,
1971, 1974
Matahina
Mokau River
Shannon
Makara si te
a
Makara si te
b
D obs on
Lake Coleridge
Aviemore
Waitaki
Roxburgh
Jan
1974
Jan
1971
Feb.
1971
Feb.
1972
Jan. -Feb.
1972
Jan.
1971
Jan.
1971
Feb.
1971
Feb.
1971
Jan-Feb.
1971
n
7 4 3
3646
1 6 8
2 3 2
2 3 3
169
4 4
2 1 6
8 0
2 6
6 5
2 0 7
%
100
6 2
7 9
18
18
9 6
6 1
12
0
0
9
1
A. austral.
L
8. 1
9.0
9.0
9.4
10.2
7.5
7.9
10.1
13'.
5
12 . 0
(1
S.D.)
(0.87)
(0.98)
(0.88)
(0.81)
(0 .66)
(0.75)
(1.22)
(0.88)
( L 8 6 )
(0.30)
is
Range
5 . 9 - 1 1 . 4
6 . 6 - 1 2 . 9
7 . 2 - 1 1 . 5
7 . 6 - 1 1 . 1
8 . 3 - 1 1 . 6
6 . 2 - 1 1 . 3
6 . 3 - 1 1 . 6
8 . 1 - 1 1 .
8
10 8 16 1
11.7-12.3
%
0
38
2 1
8 2
8 2
4
39
88
1 00
1 00
9 1
9 9
A. di effenbac hli
L(l S.D.)
9'.
9 .
1 0 .
11.
8 .
8 .
1 1 .
1 6 .
1 6 .
1 6 .
1 4 .
9 (L36)
2 (0.86)
2 (0.99)
1 (0.80)
1 (0.91)
4 (0.92)
9 (1.30)
2 (1.81)
9 (2.79)
7 (2.41)
9 (4.00)
Range
6 .
8 .
8 .
9 .
7 .
7 .
9 .
1 2 .
1 1 .
1 2 .
1 0 .
8-15.1
1-12.5
3-13.0
4-13.6
4-10.2
2-10.4
7-15.8
9-21.9
6-23.7
6-22-3
8-31.5
As glass-eels
are
generally sedentary during their first year
in
fresh
water, elvers which have been resident
in
streams
and
rivers
for a
year
or more comprise most
of the
m igration. B ecause man y eels spend their
first year
in
fresh water
in the
upper estuarine
or
tidal area,
the
greatest
concentrations
of
elvers
are
recorded from
the
lower reaches
of
water-
ways.As
elvers make their
way
steadily upstream , their num bers become
reduced
by
mortality
and by
diversion into tributaries
or
other suitable
habitat.
The
most easily observed
and
well-known migrations
are
those
whose progress
is
interrupted
by
hydro-electric dams.
Karapiro
Dam, 130 km
upstream
on the
Waikato River,
is the
first
of several power stations
on
this river.
The
ann ual elver m igration the re
is sometimes great enough
to
clog
the
chambers
of
turbines shut down
for maintenance. Smaller migrations
are
known
at
other hydro stations
and waterfalls. Normally elvers
can
surmount such obstacles
by
leaving
the water
and
climbing along splash zones
of
waterfalls
or
discharge
chutes. Some falls
can act as an
effective barrier
to the
passage
of
elvers, particularly
if
there
is a
swift current rushing over bare smooth
rock: Huka Falls
on the
upp er W aika to R iver prevent eels from enter-
ing Lake Taupo (Cairns 1941).
MA T E R I A L S
AND
ME T H O D S
The elver migrations were sampled
by the
author
at
Karapiro
Dam
(February
1.970,
January
1971,
Feb ruary 1974),
Te
Kauwhata
on the
Waikato River (January 1971),
and at two
sites
in the
M akara Stream,
Wellington, during January
and
February
1972. The
downstream site
at
the Makara Stream (Site
a in
Table
1) was 1.2 km
from
the
mouth ,
while Site
b was 2.5 km
from
the
m outh . Elvers from seven ad ditional
localities were obtained during January
and
February
1971
with
the
co-operation
of
hydro station staff
(Fig. 1). The
specimens from
the
Mokau River were collected
by Mr J.
Josephs
of New
Plymouth
in
January
1971.
Downloadedby[118.9
2.1
8.2
16
]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
5/13
1977]
J E L L Y M A N M I G R A T I N G E L V E R S
63
FIG. 1Locationsmen-
tioned
in the
text
at
which elvers
(Anguilla
spp.) were sampled,
1970-74.
170 E
Lake Cofetidge
Aviemore*
W a i t a k i *
Roxburgh*
Hydro station
Further elvers from theW aikato R iver w ere collectedby the author
at the E l b o w , 16 kmfrom theriver m ou th, w hile fishingfor glass-eels
during August andSeptember 1970.Theseareincluded here,but, com-
pared with the summer migration, thenumbersof elvers moving during
the winter
are
small.
The elversat the dams were densely concentrated, and samples could
be scooped out with a hand-net or large container. At the E lbow ,
Makara St ream, and M oka u Rive rs, set-nets were use d. Elvers were
preserved with 7% formalin, or frozen, or sent to thelab orato ry alive
in plastic bags containingalittle waterandinflated with oxyg en.
MIGRATORY BEHAVIOUR
PERIODICITY
Most samples were collected during January andFeb ruary (Table1).
Discussions with hydro station staff indicated
a
consistency
in
arrival
times of elvers from year to year; C airns (1 941) recorded the first
appearance
of
elvers
at the
lowest hy dro station
on the
W aikato River,
then slightly above Karapiro, between 18 and 22Jan ua ry during four
consecutive years, 1936-39. My data are similarly consistent: in 1970
Downlo
adedby[118.9
2.1
8.2
16]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
6/13
64 N.Z. JOURNAL OF M AR INE & FRESHWATER RESEARCH [MARCH
the run com men ced in m id -J an ua ry (precise date of first arrivals un-
known), in 1971 on 18 January, in 1973 on 17 January, and in 1974 on
15 Jan uary (no data are available for 1 972 ).
Some elvers move upstream in the company of glass-eels during
winter and. spring months. During August 1970 a sample of 206 elvers
was caught am ong several thousan d glass-eels at the E lb ow . These
were all shortfins (m ean length 8.6 cm, rang e 6.9-1 3.2 cm ). In ad dition ,
during Septem ber-D ecem ber 1971, 94 elvers were caught at the mo uth
of the Makara Stream among a total catch of 773 glass-eels: 93 were
shortfins (m ean length 13.9 cm, range 8.2-27.4 c m ) , and some stom achs
contained marine invertebrates. Probably, these elvers had been resident
in the lower estuary or the adjacent sea.
C L I M B I N G
During visits to Ka rap iro Da m in 1970 and 197 1, little daytime activity
of elvers was observed. However, power station operators report that
during the peak of the season, elvers actively ascend the spillway and.
face of the dam during daylight if rain is falling or the weather overcast.
Large numbers of elvers were present at night. Larger eels of both
species were also present. These would immediately move out of a
strong torch beam, but elvers were less disturbed but would eventually
leave an area of strong illumination.
Concentrations of elvers were greatest where running water entered
the main pool, and here the concrete was covered for a width of up
to 3 m by a mass of elve rs. Progress against the spillway cu rre nt w as
either in a series of vigorous darts forward or by crawling along the
damp margin at the edge of the main flow.
The method of vertical climbing consisted of a series of jerky move-
ments, comm encing with the body forming a com pacted W shape.
While the tail remained stationary, the head was extended forward and
swung to one side. The hind part of the body was then pulled upward.
The head alternately swung to the right and left, and so the body
formed a W or an M shape. A fuller acco unt of similar vertical
climbing by South African elvers is given by Skead (1959). Climbing
elvers appeared to cling by both friction and surface tension, as elvers
climbing vertically could not pass over any object which caused a
substantial break in contact between themselves and the substrate.
The lengths of elvers found, climbing a vertical wall were as follows
with the figures in brackets being measurements of a random sample
collected from the base of the spillway:
Shortfins: m ean length 8.8 cm (9. 5), range 7.4-11.8 (7 .4- 1 2.9 ),
n = 174 (227)
Longfins: m ean length 9.6 cm (10 .8), range 7.9-12.0 (7 .7 -1 4.8 ),
n = 50 (257)
T he p ercen tage of eels less tha n 10 cm long in the clim bing sam ples
was 9 1 % and 7 2 % for shortfins an d longfins respectively; equivalent
Downloadedby[118.9
2.1
8.2
16
]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
7/13
1977] JE L L Y M A N M I G RA T I N G E L V E RS 65
figures for the general sample were shortfins 73% and longfins 28%.
Small size is an advantage in climbing, as the surface area to weight
ratio decreases with increasing size. The maximum length for vertical
climbing is prob ably 12 cm, which corresp ond s to a w eight of 2.5 g.
Elvers also showed distinct .thigmotaxis and crammed together in all
crevices and pools on the spillway and elsewhere. These aggregations
were partly enforced by the limited cover and resting areas available,
but laboratory observations confirmed this social behaviour. When
placed in an aquarium containing several sections of pipe as cover, the
elvers did not disperse but congregated under one pipe. Thigmotaxis
was also demonstrated in escape reactions. If the leading members of a
column of climbing elvers were disturbed, their vigorous attempts to
escape were transmitted through the whole column, and most elvers
would rapidly re-enter deeper water.
H A B I T A T PRE FE RE N C E S
A comparison between glass-eel and elver catches for the Waikato
River shows gross differences in the species composition for the two
stages. Th us, the gran d me an for the E lb o w glass-eel samples (N =
3004) recorded to early 1974 is 98% shortfin in contrast to 62% short-
fin, elvers at K arap iro
(N
= 36 46 ). Elvers attempting to enter La ke
Waikare (Te Kauwhata) were all shortfins (Table 1), and local fisher-
men confirmed that this lake is inhabited by shortfins only.
During electric fishing in Wellington streams and rivers, small eels of
both species were frequently observed to show definite habitat prefer-
ences.
F or exam ple, the catch of eels less than 26 cm long o n coarse
gravel and rock su bstrate in, the W aika nae River (Fig. 1) was 94 %
longfin and 6% shortfin (n = 41 2), but samples from the W aimeha
Stream , 2.5 km north, w here the b ottom is sil ty mu d, contained 9 7 %
shortfins a nd 3 % longfins (n = 1016) .
T o exam ine hab itat preferences am on g eels 26 cm and less long, a
scries of five stations, chosen for consistency of bottom type was electric-
fished in the Makara Stream. Although shortfins were predominant in
all areas, longfins preferred stony areas with swift flows to sillier areas
with slower flows. Thus, in two stations where the bottom type was silt
an d the flow rates 0.12-0.18 m .s-
1
, 99% of all eels
(N =
136) were
shortfins, whereas in two upstream stations where bottom types were
line-coarse rubble and. flow rates were 0.41-0.48 m.s~\ only 76% of all
eels
(N
178) we re shortfins. In bot h species (bu t mo re obviously in
shortfins), the smaller size groups predominated in downstream areas;
this observation supports the concept of successive summer migrations
penetrating further up stream.
Sig
Downlo
adedby[118.9
2.1
8.2
16]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
8/13
66 N.Z .
JOURNAL
OF
MARINE
&
FRESHWATER RESEARCH [MARCH
TABLE 2Species proportions (%) and mean lengths (L, cm) of samples of migratory
elvers
(Anguilla
spp.) from base of spillway of K ara pi ro Dam (samples arranged
by mon ths over the migration season; * = data from W oods (1964); - = not given;
.. = not calculated)
DATE
19 January 1971
26 January 1971
28 January 1971
28 January 1971
5 February 1970
12 February 1970
19 February 1974
*27 February 1962
*5 March 1963
Total
n
276
484
657
333
376
647
254
35 7
314
3698
86
47
63
65
62
48
74
74
76
63
L
8 .4
9 . 5
9 .3
9 .3
8 .9
8 .9
8 .9
9 .3
9 . 7
9 . 1
A.au stralis
(1 S.D.)
(0.83)
(1.03)
(0.97)
(1.15)
(0.73)
(0.81)
(2.34)
(2.22)
Range
6 .7-10.6
7 .4-12.9
7 .1-12.5
6 .9-12.4
7 .1-11 .1
6 .6 -11 .6
6 .8-11 .1
-
-
%
14
53
37
35
38
52
26
26
24
37
A.
L
9 . 0
10.8
10.3
10.3
9 . 3
9 . 4
10.2
9 . 8
10.4
10.0
dieffenbachii
(1 S.D.)
(0.97)
(1.29)
(1.26)
(1.13)
(1.42)
(1.14)
(1.24)
(2.24)
-
Range
7 .3-12.2
7 .7-14.8
7 .8-15.1
7 .3-13.3
7 .0-14.4
6 .8-13.9
7 .7-15.3
_
COMPOSITION
OF
SAMPLES
SPECIES PROPORTIONS
T ab le 1 gives the percentag es of each species for th e various sam ples.
M ost specimens (8 9% ) came from the N orth Island. H ere, 6 5 % of the
catch were shortfins, whereas in the South Island shortfins comprised
only 6%. However, these figures are not representative of the country
as a whole, as habitat has a marked influence on species composition.
The fluctuations which occur in the proportions of both species
arriving at Karapiro Dam are shown in Table 2. No trend is obvious,
but the overall predominance of shortfins is apparent.
LENGTH
T h e m ean lengths given in Table 1 indica te the variable size of
migrating elvers at different localities. In all elver samples containing
both species, the mean length of longfins exceeds that of the shortfins,
as it does in glass-eels (Jellyman, in press). As expected, elvers recorded
at upstream sites are larger than those from down stream on the same
river. This is seen in both the Makara Stream and the Waikato River,
but not from the Waitaki River (Waitaki and Aviemore samples),
where numbers are small and cover a large size range (12cm). General-
ly, the length-frequencies of elvers eorrespond well to a normal distribu-
tion pattern; Fig. 2 shows four typical samples.
In a large river system, several separate migrations may take place
concurrently during summer, with waves of eels, grouped approximately
by size, penetrating further upstream each year; migrations apparently
cease at an app rox im ate length of 30 cm, wh en a m ore sedentary mo de
of life is adopted. Table 2 gives the mean lengths of elver samples
collected from the base of the spillway at Karapiro Dam. During 1971,
Downloadedby[118.9
2.1
8.2
16
]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
9/13
1977]
JELLYMANMIGRATING ELVERS
67
A austral is
A dieffenbachi i
Karapiro
Dam
28-1-71
n=415
Dobson
8-1-11
n=27
Roxburgh
25-1-71
6 8 10 12 14 16 18 20
n = 147
10
12 14 16 18 20
l e n g t h
(cm)
L e n g t h
(cm)
2Length-frequency distributions
of
samples
of
elvers
(Anguilla spp.)
from four
localities.
Downloadedby[118.9
2.1
8.2
16
]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
10/13
68
N.Z.
JOURNAL
OF
M A R I N E
&
FRESHWA TER RESEARCH [MARCH
TABLE
3Age
distributions and length ranges (cm) of elvers in Waikato and Mokau
River samples (SF=short-finned eel
Anguilla australis,
LF=long-finned eel
A. dieffenbachii;
=number aged; - = nil)
AREA
Waikato
'Elbow'
DATE
August
1970
Waikato January
Te Kauwhata 1971
Waikato
Karapiro
D am
Mokau
January
1971
January
1971
SPECIES
SF n
Range
%
SF
n
Range
%
SF n
Range
m
LF n
Range
/o
SFn
Range
/
0
11
6.9-8.4
57
7
6.5-7.3
21
8
6.6-7.7
8
1
7.8
6
1
7.6
2
8
7 .
7
8,
8 .
A G E
1
15
.2-10.7
39
6
5-9.6
76
10
.9-9.8
77
15
.2-10.4
63
4
.5-9.3
55
GROUPS
2
4
11.0-12.9
4
2
10.4-11.0
3
7
10.2-12.3
15
10
9.9-12.4
31
4
9.8-11..1
43
3
-
_
-
-
-
_
L F
n
Range
8.5-10.1 10.6-11.3 12.2-13.0
57 30 13
seasonal variations in length of 1.1 cm and 1.8 cm occurred for short-
fins and longfins respectively. Also, an increase or decrease in mean
length
for one
species
is
paralleled
by an
equal change
in the
other
species: the two samples collectedon 28 Jan u ary 1971 (Table 2) were
takenan hour apart,and gave almost identical analyses.
A G E G R O U P S
Age groups could not be distinguished from examination of the
length-frequency data,and age determinations were m ade by examina-
tion of burnt otoliths. If an overlap in body length occurred between
successive
age
groups
the
mid-point
of the
overlap
was
taken
as the
limit between groups. Similarly, if successive ranges did not meet, the
mid-point of the difference wasdefinedas thegro up limit. Resu lts from
Waikato and M okau Rivers are presented in Table 3. Unfortunately,
South Island specimens were all preserved in strong formalin, and the
otoliths were generally unreadable. Roxburgh and Aviemore samples
were examined, and both contained eels from age groups 3-7, but
deteriorationof otoliths prevented reliable reading.
Downloadedby[118.9
2.1
8.2
16
]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
11/13
1977] JELLYM AN MIGR ATING ELVER S 69
MORTALITY
Numerous dead elvers and others in very poor condition were found
at Karapiro Dam, and predation by larger longfins and catfish Ictalurus
nebulosus
(Le Sueur) was observed. Other predators include brown
trout Salmo trutta L., shags (cormorants), ducks, kingfishers, and
wa ter rats.
In live samples, the proportion of longfins that died in transit far
exceeded that of shortfins. A trial was run to compare survival rates
of elvers of both species exposed to humid air in a constant temperature
cabinet: three trays containing ten elvers of each species were used,
and the deaths recorded over a week. At 15c, 70% of the longfins
died, but no shortfins; at 20c, 90% of the longfins and 40% of the
shortfins died; and at 25c, 100% of both species died, but the longfins
died before the shortfins. Thus, longfins are less able to survive pro-
longed periods of exposure which require cutaneous respiration,
especially under the additional stresses of high temperature and crowd-
ing.
D I SC U SSI O N
Summer migration of juvenile freshwater eels is not confined to New
'Zealand.
Skead (1959) reviewed several years' observations on the
migration of elvers of
A. mosscimbicci
Peters in the B uffalo Rive r, So uth
Africa. Summer migrations of Australian elvers are recorded by Kershaw
(1911) and Whitley (1929). A similar phenomenon was witnessed in
New Guinea by Herre (1930), and summer migrations of juvenile
European eels have long been known.
In New Zealand and apparently elsewhere, the stimuli which initiate
migration are unknown. Although low temperatures (less than 10c)
could inhibit mass movements of elvers, the fact that summer migrations
occur within a few weeks of each other throughout the whole country
indicates that it is not the reaching of any specific temperature which
triggers migration. Temperatures recorded in the Makara Stream over
the migratory period ranged from 14.2-21.5c, bu t the two ru n s
recorded at the downstream site did not correspond with any common
value or fluctuation. The lunar cycle appears to have no direct effect, as
seen by the consistency of arrival times each year at Karapiro Dam.
A small migration was recorded at M aka ra during a fresh in the
stream, but larger movements took place when the stream level was
normal. Hardy (1950) observed that increased water flow did not
induce a larger number of elvers to climb the margins of a small water-
fall in a North Canterbury stream.
Migration may be initiated by the summation of several factors. A
temperature greater than a threshold value, the increased day-length of
summer, and a rapidly increasing tendency to school shown initially by
Downlo
adedby[118.9
2.1
8.2
16]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
12/13
70 N.Z. JOURNAL OF M AR INE & FRESHWATER RESEARCH [MARCH
a few elvers, may all contribute to the onset of migration. Increased
water flow producing a strong rheotactic reaction among elvers may
also be a contributing agent, but is not the causative one.
The annual migration enables small eels to populate upstream areas.
If suitable habitat is encountered, many eels probably choose to remain
rather than progress further upstream. In this way, eels are able to
disperse and occupy the available habitats along the complete river
system, including territories vacated by migrant eels.
The differences noted between species proportions of glass-eels from
the E lbo w and elvers from K arap iro Dam , and also the age group
distributions from the E lbo w samp le (see T ab le 3) , indicate that a
considerable proportion of shortfins choose to spend at least the first
2 y of freshw ater life in th e up pe r estua rine a rea s. Age class 0 w hich
dom inates the Au gust E lb ow samples, is pro m ote d to age class 1
in the January Te Kauwhata and Karapiro Dam samples, where i t is
again dominant. In both these latter samples, age class 0 represents the
previous year's glass-eels and is understandably more prevalent in the
downstream (Te Kauwhata) sample than in the Karapiro Dam sample.
Longfins, which are absent from the E lb o w and Te K auw hata
samples, are also most strongly represented at Karapiro Dam by age
class 1. Although longfins prefer swift and stony waters typical of
upstrea m areas, substantial num bers of age gro ups 0 and 1 live down-
stream of Karapiro Dam. Therefore, although a large percentage of
shortfin glass-eels remain resident in the lower reaches of rivers, those
that do migrate upstream do so more rapidly than longfins.
Specific habitat preferences reduce intraspecific interaction and imply
different feeding habits. Unfortunately, few data are available to com-
pare the feeding habits of small eels of each species. It is not certain
whether selective feeding occurs in areas where both species coexist:
Cairns (1942) combined both species for the smallest size group he
examined, and Hopkins (1970) assumed diets of both species were
similar. Burnet (1952) showed that apparent feeding preferences in
longfins largely reflected the abundance of organisms in the fauna.
Thus, the suitability of the habitat rather than the availability of
specific food types may be the primary requirement in habitat prefer-
ence.
Relative mortalities of asphixiated glass-eels and elvers suggest that
longfins have higher oxygen demands than shortfins, but this has not
been tested experimentally. If correct, the habitat preferences of both
species would be plausibly explained. Also, the thicker dermal layer of
longfins may result in less efficient cutaneous respiration than in short-
fins. Under critical conditions, this and their possibly higher respiratory
demands would lead to the increased mortality of longfins relative to
shortfins.
Downloadedby[118.9
2.1
8.2
16]at18:2930January2
015
7/24/2019 Upstream Summer Migration of Eels
13/13
1977] JELLYMANMIGRATING ELVERS 71
ACKNOWLEDGMENTS
I wish to thank the various personnel of the NewZealand Electricity Depart-
ment
and Mr J.
Josephs
of New
Plymouth
for
providing elver samples.
I
also
wish to thank Mr A. M. R. Burnet and Dr R. M. McDowall for adviceand
criticism
of the
manuscript.
LITERATURE CITED
BURNET,
A. M. R. 1952:
Studies
on the
ecology
of the New
Ze ala nd long-finned
eel, Anguilla dieffenbachii Gray. Australian Journal of Marineand
Freshwater Research
3
(
1
)
: 32-63.
CAIRNS,
D. 1941 :
Life-history
of the two
species
of New
Ze alan d freshwater
eel. Par t 1 -Taxonom y,
age and
growth, migration,
and
distribution.
N.Z. Journal of Scienceand Technology, SeriesB, 23
(
2
) :
53-72.
1942: Life historyof the twospeciesof freshwater eel in NewZealand.
II. Food,
and
inter-relationships with trout. N.Z.
Journal
of
Science
and Technology, Series
B, 23
(
4
)
:
132-48.
HARDY, C. J. 1950: Summary of a report on eel trapping and observations at
Lakes Taylor
and
Shcppard.
North Canterbury Acclimatisation
Society, Eighty-Sixth Annual Report:24-6.
HERRE,
A. W. 1930: A New
Cuinea eel-fair.
Science (
New
York
) 71
: 16.
HOPKINS,
C. L. 1970:
Some aspects
of the
bionomics
of
fish
in a
brown trout
nursery stream.
N.Z.
Marine Department Fisheries Research Bulletin
4.38 pp.
JELLYMAN,
D. J. (in
p re ss ): Freshwater invasion
of a New
Zealand stream
by
glass-eels
of two Anguilla spp.
N.Z.
Journal
of
Marine
and
Fresh-
water Research.
KERSHAW, J. A. 1911: Migration of eels in Victoria. Victorian Naturalist 27:
196-201.
SKEAD,
C. J. 1959: The
climbing
of
juvenile eels.
Piscator
13
(
46
)
:74-86.
WHITLEY,
G. P. 1929: An
eel-fare
at
Parramatta.
Australian Museum Magazine
3
(
10
)
:
348.
WOODS,
C. S. 1964:
Fisheries aspects
of the
Tongariro power development
project. N.Z. Marine Department Fisheries Technical Report 10.
214
pp.
Downloadedby[118.9
2.1
8.2
16]at18:2930January2
015