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

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-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