Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
Pacific bluefin tunaTreasure box for scientific studies
or Pandra’s Box ?
Ziro Suzuki
(National Research Institute of Far Seas Fisheries)Shimizu, Japan
PFRP Research Priorities WS(Nov. 16-18, 2005)
Contents of presentation
There are many important unknowns or uncertainties for this stock which need to be investigated urgently: e.g.,
• Early life history • Difference in age at spawning by area and its implication
to stock structure• Migration patterns• Farming and complete aquaculture, its impact to fisheries• Most of the fisheries exploit juvenile
Studies on early life historyLargest fluctuation of recruitment strength in
tunas( relatively restricted spawning time/area, where is “critical period(s)” and how survival is determined)
* Abundance index for age 0 fish is available
Initiative to investigate source of the fluctuation has been taken under the CLIOTOP WG1, here some preliminary findings of Japanese works are introduced: those indicate many difficulties to overcome
• Establishment of sampling method, then identify major factors both biotic and abiotic ones
• Mortality• GrowthNeed for more field studies compared with experiments in
restricted artificial condition
Shimizu
Tokyo
Research area (Nansei islands)
From 10 May to 10 June 2004
Outline of the tracking buoy
Second patch
0100200300400500
St. 87
St. 89
St. 91
St. 93
St. 95
St. 97
St. 99
St. 101
St. 103
St. 105
St. 107Density (indiv./1000m3 )
7.5 mile
Trend
Horizontal distribution of bluefin tuna larva observed with transect of 20 times 5-min surface tows
Back-calculated SL of PBT larvae in three developmental phase at catch
日齢
Preflexion
Flexion
Postflexion
3
4
5
6
7
8
9
5 6 7 8 9 10 11 12 13 14
n.s.a
aa
aa
a
bb b
b b
bb
c
bb
a
Kruskal-Wallis testp<0.01
SL
(mm
)
Hatching3.7 mm TL
7 DAH4.6 mm TL
14 DAH7.2 mm TL
17 DAH8.7 mm TL
24 DAH27 mm TL
Morphological changes in process of growing in tank (photographed in 2004)
Survival rates of artificially raising bluefin larvae in tank
01020
3040506070
8090
100
0 10 20 30 40
Days after hatching
Surv
ival
rate
(%)
:1999:2003:2004-1:2004-2
Mouth opening
Cannibalism and attacking behavior
Hatching larvae of fish (Snapper)
Artemia nauplii
Rotifer
Fish meat (young sardine)
Sequence of foods in tank
Difference in age at spawning by area and its implication to stock structure
The observed difference could have important implication to stock structure and management for Pacific and Atlantic stocks
• Age at spawning differs significantly by area: how to estimate spawning potential by size ?
• There seems to be a general rule as for timing and area for spawning: spawning begins earliest in the south with large sized fish and late in the north areas with small fish
● Implication to stock structure: Pacific and Atlantic
● Need for genetic/micro-constituent element studies andphysiological/histological studies on spawning size
-125
-150
-175
-200
-225
-250
-125
-150
-175
-200
-225
-250
-125
-150
-175
-200
-225
-250
-125
-150
-175
-200
-225
-250
-125
-150
-175
-200
-225
-250
-150
-175
-200
-225
-250
-125
-150
-175
-200
-225
-250125 cm
175
225
PS
PS
1-3
9-12
5-7
3-5
8-12
3-4
Schematic migratory pattern of adult ABFT
Migration pattern
There are strikingly high similarity between Pacific and Atlantic stocks
• Three major patterns ?• Why seemingly same members of a group show
different migratory pattern: instinct vsopportunity
● Need for more electronic tagging and IBM type of approach as well as environments
Yamadainagake
多様な回遊経路
20 N
30 N
40 N
50 N120 E 140 160 180 160 140 120 W
B
120 E 140 E130
40 N
30 N
20 N
30 N
40 N
50 N120 E 140 160 180 160 W
C
Major patterns: juveniles
-10N
0N
10N
20N
30N
40N
50N120E 130E 140E 150E 160E 170E
Adults
Farming and complete aquaculture, its impact to fisheries and management
Farming poses a number of issues but could potentially revolutionize the tuna fisheries and market if it match with other emerging factors
• Trend in farming activity• Other emerging factors: Complete aquaculture
and increase of sashimi market other than Japan; especially China
• Need for economic analyses for tuna farming with fisheries
蓄養クロマグロ・ミナミマグロの生産:2004年Production of farmed Northern and Southern bluefin tunas in 2004
Mediterranean20,000mt
Australia9、000mt(ミナミマグ
ロ)
Japan3、000mt
Mexico6、000
mt
Bluefin tuna farming in the Mediterranean
0
5000
10000
15000
20000
25000
30000
35000
1997 1998 1999 2000 2001 2002 2003 2004
Est
imat
ed F
arm
ed tu
na (r
ound
MT) Australia
Mexico
Cyprus
Tunisia
Libya
Turkey
Italy
Malta
Croatia
Spain
Estimated farmed tuna production in round MT by country
Average ex-vessel price of Japanese catch (frozen) by species
0
500
1000
1500
2000
2500
3000
3500
1995 1996 1997 1998 1999 2000 2001 2002
Pric
e (Y
en/K
g)
Bluefin BigeyeYellowfin Albacore
Some of management issues
The stock status appears relatively healthy compared with other heavily exploited species but not without issues, of course:
● Massive catch of juvenile fishMore than 95 % of catch in number is juvenile less than 3 years old.
Trade-off between increase in Y/R by taking larger fish and puttingburden to change the fisheries
Importance of keeping the recommendation from the ISC to cap thefishing effort at current level
● Uncertanties Recruitment fluctuation, M vector, Longevity