Assessment of bigeye tuna thunnus obesus in the eastern pacific ocean
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ASSESSMENT OF BIGEYE TUNA ( THUNNUS OBESUS ) IN THE EASTERN PACIFIC OCEAN PowerPoint PPT Presentation


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ASSESSMENT OF BIGEYE TUNA ( THUNNUS OBESUS ) IN THE EASTERN PACIFIC OCEAN. January 1975 – December 2006. Outline. Stock assessment Overview of assessment model Fishery data Assumptions Results of base case model Projections Sensitivity analyses Summary and conclusions Discussion.

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ASSESSMENT OF BIGEYE TUNA ( THUNNUS OBESUS ) IN THE EASTERN PACIFIC OCEAN

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Assessment of bigeye tuna thunnus obesus in the eastern pacific ocean

ASSESSMENT OF BIGEYE TUNA (THUNNUS OBESUS) IN THE EASTERN PACIFIC OCEAN

January 1975 – December 2006


Outline

Outline

  • Stock assessment

    • Overview of assessment model

    • Fishery data

    • Assumptions

    • Results of base case model

    • Projections

  • Sensitivity analyses

  • Summary and conclusions

  • Discussion


Overview of assessment

Overview of assessment

  • Age-structured, statistical, catch-at-length model (Stock Synthesis II).

  • Same type of model as A-SCALA or MULTIFAN-CL

  • Differences between SS2 and A-SCALA


Bigeye fishery definitions

8

5, 13

9

3, 11

4, 12

1, 6-7

2, 10

Bigeye fishery definitions

Recent FLT (2-5)

Discards (10-13)

N Longline (8)

S Longline (9)

Early FLT (1)

Early & Recent UNA (6, 7)

FLT – Floating objects; UNA - Unassociated


Data catch

Data - catch

Disc -N FLT

S LL

Disc – coastal FLT

Disc – Eq FLT

Disc - S FLT

N Offshore FLT

Early UNA

Recent UNA

N LL

S Offshore FLT

Equatorial FLT

Coastal FLT

Early FLT


Data discards

Data - discards

Northern FLT

Inshore FLT

Equatorial FLT

Southern FLT


Data effort

Data - effort

Disc -N FLT

Disc – coastal FLT

Disc – Eq FLT

Disc - S FLT

S LL

Recent UNA

N LL

N Offshore FLT

Early UNA

Equatorial FLT

Coastal FLT

Early FLT

S Offshore FLT


Data cpue

Data - CPUE

Disc -N FLT

Disc – Eq FLT

Disc - S FLT

S LL

Disc – coastal FLT

N Offshore FLT

Early UNA

Recent UNA

N LL

Early FLT

S Offshore FLT

Equatorial FLT

Coastal FLT


Data length frequency data

Data - Length frequency data

Quarter

1997

2005

2000


Assumptions base case movement

DATA

  • Tagging records indicate little exchange of bigeye between E and W Pacific

  • Results from conventional and archival tagging indicate regional fidelity for bigeye in EPO

  • Different CPUE trends between EPO and WCP

ASSUMPTIONS

  • Single stock of bigeye in EPO

  • No net movement of fish between the eastern and western Pacific

  • SA for EPO and Pacific wide are consistent

Assumptions (base case) - movement


Assumptions base case growth

Assumptions (base case) - growth

  • Von Bertalanffy – fixed parameters


Assumptions base case m

Assumptions (base case) – M


Assumptions base case cont

Assumptions (base case) - cont.

  • Age-specific maturity and fecundity indices

  • No S-R relationship (steepness = 1)


Results base case

Results (base case)

  • Fit to the length frequency

  • Fishing mortality

  • Selectivity

  • Recruitment

  • Biomass


Fit to lf data pearson residuals

Fit to LF data – Pearson residuals


Fit to cpue data floating object

Fit to CPUE data – Floating object


Fit to cpue data longline

Fit to CPUE data – Longline


Fishing mortality

Fishing mortality

Ages 5-8

Ages 1-4

Ages 9-12

Ages 13-16

Ages 17-20

Ages 21-24

Ages 25-28

Ages 29-32

Ages 33-36

Ages 37-40


Age specific fishing mortality

Age-specific fishing mortality

1993-2006

1975-1992


Size selectivity

Size selectivity

S Offshore FLT

Early FLT

Equatorial FLT

N Offshore FLT

Coastal FLT

Early UNA

S LL

N LL

Recent UNA


Recruitment

Recruitment


Biomass

Biomass

Biomass of fish 0.75 + years old


Spawning biomass

Spawning biomass

Population fecundity


No fishing plot

No-fishing plot


Average weight

Average weight


Retrospective analysis biomass

Retrospective analysis - biomass


Retrospective analysis recruitment

Retrospective analysis - recruitment


Comparisons with a scala

Comparisons with A-SCALA


Comparisons with a scala assessments

Comparisons with A-SCALA assessments


Comparisons with a scala assessments1

Comparisons with A-SCALA assessments


Comparisons to reference points

Comparisons to reference points

  • Spawning biomass depletion (SBR)


Spawning biomass ratio

Spawning biomass ratio


Sbr comparison with a scala

SBR comparison with A-SCALA


Time varying indicators

Time varying indicators


Amsy quantities

AMSY-quantities


Amsy quantities by fishery

AMSY-quantities – by fishery


Forward simulations

Forward simulations

  • Biomass

  • Spawning biomass depletion

  • Surface fishery catch

  • Longline catch


Spawning biomass ratio1

Spawning biomass ratio


Predicted catches purse seine

Predicted catches – purse-seine


Predicted catches longline

Predicted catches – longline


Sensitivity analyses

Sensitivity analyses

  • Spawner-recruitment relationship (steepness = 0.75)

  • Growth

    • Growth estimated

    • Linf fixed (171.5 and 201.5)

  • Fitting to the initial equilibrium catch

  • Use of iterative reweighting of data

  • Time blocking of selectivity and catchability for southern longline fishery

  • Inclusion of new Japanese longline data


Stock recruitment relationship h 0 75

Stock-recruitment relationship (h = 0.75)


Biomass1

Biomass


Recruitment1

Recruitment


Spawning biomass ratio2

Spawning biomass ratio


Spawner recruitment curve

Spawner-recruitment curve


Use of cpue time series for southern longline fishery only

Use of CPUE time series for southern longline fishery only


Spawning biomass ratio3

Spawning biomass ratio


Model fit to cpue data

Model fit to CPUE data


Assumed value for the asymptotic length parameter of the vb growth curve

Assumed value for the asymptotic length parameter of the VB growth curve


Growth curves

Growth curves


Assessment of bigeye tuna thunnus obesus in the eastern pacific ocean

SBR


Fit to initial equilibrium catch

Fit to initial equilibrium catch


Spawning biomass ratio4

Spawning biomass ratio


Use of iterative reweighting

Use of iterative reweighting


Iterative reweighting

Iterative reweighting


Spawning biomass ratio5

Spawning biomass ratio


Fit to cpue data

Fit to CPUE data


Residual plot

Residual plot


Use two time blocks for selectivity and catchability of the southern longline fishery

Use two time blocks for selectivity and catchability of the southern longline fishery


Fit to lf data base case

Fit to LF data – base case


Spawning biomass ratio6

Spawning biomass ratio


Fit to cpue data1

Fit to CPUE data

Without iterative reweighting

With iterative reweighting


Residual plot1

Residual plot


Inclusion of the new japanese longline data

Inclusion of the new Japanese longline data


Biomass2

Biomass


Recruitment2

Recruitment


Assessment of bigeye tuna thunnus obesus in the eastern pacific ocean

SBR


Comparisons between models

Comparisons between models


Summary main results

Summary: Main results

  • Both total and spawning biomass is estimated to have substantially declined since 2000

  • Current biomass level is low compared to average unexploited conditions

  • The current effort levels are too high to maintain the population at level that will support AMSY

  • Yileds could be increased if more of the catch was taken in the longline fisheries


What is robust

What is robust

  • Fishing mortality levels are greater than that necessary to achieve the maximum sustainable yield

  • Two exceptions: Lmax fixed and time blocks


Plausible sensitivities and uncertainties

Plausible Sensitivities and Uncertainties

  • Results are more pessimistic with the inclusion of a stock-recruitment relationship

  • Biomass trends are sensitive to the weighting of different datasets

  • Recent estimates are uncertain and subject to retrospective bias


Conclusions

Conclusions

  • Current spawning biomass is unlikely to remain at or above the level required to produce AMSY.

  • In the most recent years the fishing mortality is greater than that required to produce AMSY.

  • Under average recruitment, the stock is predicted to be below the level that would support AMSY unless fishing mortality levels are reduced further than the current restrictions.


Comparisons between models1

Comparisons between models


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