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

1. ASSESSMENT OF BIGEYE TUNA (THUNNUS OBESUS) IN THE EASTERN PACIFIC OCEAN January 1975 – December 2006

2. Outline • Stock assessment • Overview of assessment model • Fishery data • Assumptions • Results of base case model • Projections • Sensitivity analyses • Summary and conclusions • Discussion

3. 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

4. 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

5. 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

6. Data - discards Northern FLT Inshore FLT Equatorial FLT Southern FLT

7. 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

8. 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

9. Data - Length frequency data Quarter 1997 2005 2000

10. 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

11. Assumptions (base case) - growth • Von Bertalanffy – fixed parameters

12. Assumptions (base case) – M

13. Assumptions (base case) - cont. • Age-specific maturity and fecundity indices • No S-R relationship (steepness = 1)

14. Results (base case) • Fit to the length frequency • Fishing mortality • Selectivity • Recruitment • Biomass

15. Fit to LF data – Pearson residuals

16. Fit to CPUE data – Floating object

17. Fit to CPUE data – Longline

18. 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

19. Age-specific fishing mortality 1993-2006 1975-1992

20. Size selectivity S Offshore FLT Early FLT Equatorial FLT N Offshore FLT Coastal FLT Early UNA S LL N LL Recent UNA

21. Recruitment

22. Biomass Biomass of fish 0.75 + years old

23. Spawning biomass Population fecundity

24. No-fishing plot

25. Average weight

26. Retrospective analysis - biomass

27. Retrospective analysis - recruitment

28. Comparisons with A-SCALA

29. Comparisons with A-SCALA assessments

30. Comparisons with A-SCALA assessments

31. Comparisons to reference points • Spawning biomass depletion (SBR)

32. Spawning biomass ratio

33. SBR comparison with A-SCALA

34. Time varying indicators

35. AMSY-quantities

36. AMSY-quantities – by fishery

38. Forward simulations • Biomass • Spawning biomass depletion • Surface fishery catch • Longline catch

39. Spawning biomass ratio

40. Predicted catches – purse-seine

41. Predicted catches – longline

42. 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

43. Stock-recruitment relationship (h = 0.75)

44. Biomass

45. Recruitment

46. Spawning biomass ratio

47. Spawner-recruitment curve

48. Use of CPUE time series for southern longline fishery only

49. Spawning biomass ratio

50. Model fit to CPUE data