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2007 iccat scrs executive summay for atlantic bigeye tuna
2007 ICCAT SCRS Executive Summay for Atlantic Bigeye Tuna


BiologyDistribution : 50N-45S, not in MediterraneanSwimming Behavior : extensive vertical movement, deeper during daytime, shallower at night.Spawning : tropical-subtropical, mature at age 3Nursery : Gulf of GuineaPrey : fish, mollusk, crustaceanGrowth (relatively fast) : Age 3 (105 cm), Age 5 (140cm), Age 7 (163cm)Schooling behavior : Juveniles are mixed with yellowfin and skipjackNatural mortality : estimated by tagging dataStock structure : Atlantic wide


BETCatch

Fisheries : LL(45-50kg), North BB(20-30kg), PS+Trop BB(3-4kg)

LL : Japan, Chinese Taipei, China, Philippines

PS : EC-Spain+France, Ghana, Venezuela (in association with FADs)

Figure 1.

Species composition

data is important

& improved for Ghana

2006 catch

is 65,000 t


BETCatchDistribution

Figure 2.

Geographic distribution of bigeye catches for most recent years (2002-2005) by major tuna fishery.


BET Catch

Unreported catches estimated from trade statistics.

Figure 3.


Bet abundance indices
BET abundance Indices

Figure 4-1.


Bet abundance indices1
BETabundance Indices

Figure 4-2.

New

CPUE


Bet abundance indices2
BET Abundance Indices


Bet assessment models

BET Assessment Models

Consistent with previous assessments, the results from nonequilibrium production models are used to provide our best characterization of the status of the resource. The current MSY estimated using two types of production models was about 90,000 t and 93,000 t, although uncertainty in the estimates would broaden the range. In addition, these estimates reflect the current relative mixture of fisheries that capture small or large bigeye; MSY can change considerably with changes in the relative fishing effort exerted by surface and longline fisheries.

Several types of assessment models including production models, VPA and a statistical integrated model (Multifan-CL) were applied to the available data. There was a range of stock status evaluations from the various model formulations applied, not all of which were judged to be equally likely.


Bet model results estimated msy 90 000 93 000 t
BETModel Results Estimated MSY : 90,000 – 93,000 t

Figure 5.

Trajectories of B-ratio and F-ratio obtained from ASPIC base case run.


Bet model results
BETModel Results

MFCL run results. Selectivity curve for each decade (left). MSY estimates.

1960s

1970s

MSY estimates

1980s

1990s

2000s


Bet model results1
BET Model Results

Figure 6.

Estimated range of stock status results (B/BMSY and F/FMSY) in 2005

which characterizes our uncertainty in stock status (right panel). Time

series of B/BMSY and F/FMSY from 1950 to 2005 (left panel).


Bet outlook
BET Outlook

85K

Figure 7.

Stock projections by ASPIC model assuming a catch of 71,000 t in

2006 and varying levels of the constant catch thereafter.


Bet effects of current regulations
BET Effects of current regulations

  • Multi-year Conservation and Management Program Rec[04-01] sets :

  • TAC for Major Countries at 90,000 t.

  • A specific limit for the number of vessel for several country/entity.

  • Closure for surface fisheries in the area 0˚-5˚N, 10˚ W-20˚W during November (in the Gulf of Guinea).

    The closure is much smaller in time and space compared to the previous one. Need to expand it if we want to be more effective.


Bet trend in catches of small bet
BET Trend in catches of small BET

Figure 8.


Bet management recommendation
BETManagement Recommendation

  • Projection indicates that catches of 85,000 t or less will permit the stock to rebuild in the future.

  • However, if the entire catch limit set under 04-01 were to take and others stayed at recent level, the total catch could exceed 100,000 t.

  • Considering above, the Committee recomends that the total catch not exceed 85,000 t.


ATLANTIC BIGEYE TUNA SUMMARY

Maximum Sustainable Yield 90,000 t-93,000 t 1 (68,000- 99,000) 2

Current (2006) Yield 65,000 t

Replacement Yield 2006 Slightly below MSY1

Relative Biomass (B2006/BMSY) 0.921 (0.85-1.07)2

Relative Fishing Mortality FMSY 0.201 (0.07-0.33) 2

F2005/FMSY 0.871 (0.70-1.24) 2

Conservation & management measures in effect:

[Rec. 04-01] replaced [Rec. 79-01 and Rec. 99-01]

after June, 2005.

− Total allowable catch for 2005 is set at 81,400 t for major country and entity

− Limits on numbers of fishing vessels less than theaverage of 1991 and 1992.

− Specific limits of number of longline boats; China(45), Chinese Taipei (98), Philippines (8).

− Specific limits of number of purse seine boats for Panama (3).

− No purse seine and baitboat fishing during November in the area encompassed by 0º-5ºN and 10º W-20º W.

1 Base Case production model (Logistic) results based on catch data 1950-2005.

280% confidence limits


BET-Table 1. Estimated catches (t) of bigeye tuna (Thunnus obesus) by major area, gear and flag.


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