1. ASSESSMENT OF BIGEYE TUNA (THUNNUS OBESUS) IN THE EASTERN PACIFIC OCEAN January 1975 – December 2005

2. Overview of assessment Age-structured, statistical, catch-at-length model (A-SCALA). Quarterly time step from 1975 to the start of 2005. No net movement of fish between the eastern and western Pacific.

3. Major changes No major model changes except new and updated catch, effort, and length-frequency data.

4. Sensitivity analyses Spawner-recruitment relationship (steepness = 0.75) Assumed value for the asymptotic length parameter of the Richards growth curve Inclusion of the Chinese Taipei longline length-frequcy data Relationship between recruitment an the el Nino index

5. Bigeye fishery definitions Recent FLT (2-5) Discards (10-13) N Longline (8) S Longline (9) Early FLT (1) Early & Recent UNA (6, 7) 1, 6-7 8 9 2, 10 3, 11 5, 13 4, 12

6. Catch Early FLT N Offshore FLT Equatorial FLTCoastal FLTS Offshore FLT Early UNARecent UNAN LL S LL

7. Effort Early FLT N Offshore FLT Equatorial FLT Coastal FLT S Offshore FLT Early UNA Recent UNA N LL S LL

8. CPUE Early FLT N Offshore FLT Equatorial FLTCoastal FLTS Offshore FLT Early UNARecent UNAN LL S LL

9. Length frequency data Early FLT N Offshore FLT Equatorial FLT Coastal FLT S Offshore FLT Early UNA Recent UNAN LLS LL

10. Discards Southern FLT Equatorial FLT Northern FLT Inshore FLT

11. Results Fit to the length frequency Growth Fishing mortality Selectivity Recruitment Biomass Catchability

12. Average fit to the length frequency data Early FLT N Offshore FLT Equatorial FLT Coastal FLT S Offshore FLT Early UNA Recent UNAN LLS LL

13. Fit to recent length frequency data

15. Growth

16. Fishing mortality 1-4 5-8 9-12 25-28 33-36 37-40 29-32 21-24 17-20 13-16

17. Age-specific fishing mortality

18. Selectivity Early FLT N Offshore FLT Equatorial FLT Coastal FLT S Offshore FLT Early UNA Recent UNAN LL S LL

19. Catchability Early FLT N Offshore FLT Equatorial FLT Coastal FLT S Offshore FLT

20. Catchability Early UNA Recent UNA S LL N LL

21. Catchability Southern FLT Equatorial FLT Northern FLT Inshore FLT

22. Recruitment

23. Biomass

24. Spawning biomass

25. No-fishing plot

26. Average weight Early FLTN Offshore FLT Galapagos FLT Coastal FLT S Offshore FLT Early UNA Recent UNAN LL S LL Combined Surface Combined LL

27. Biomass

28. Recruitment

29. Comparisons to reference points Spawning biomass depletion Yield curve

30. Spawning biomass ratio

31. SBR comparison with last year

32. Time varying indicators

33. Yield curve

34. AMSY-quantities Base case AMSY (mt) 106,722 BAMSY (mt) 326,329 SAMSY 541 BAMSY/B0 0.30 SAMSY/S0 0.22 Crecent/AMSY 1.00 Brecent/BAMSY 1.10 Srecent/SAMSY 0.88 F multiplier 0.68

35. AMSY-quantities -- assumed F F’s 2003 & 2004 – Base case F’s 2002 & 2003 F’s 2004 & 2005 AMSY (mt) 106,722107,71098,665 BAMSY (mt) 326,329326,197314,958 SAMSY 541538531 BAMSY/B0 0.30 0.29 SAMSY/S0 0.22 Crecent/AMSY 1.000.991.08 Brecent/BAMSY 1.10 1.14 Srecent/SAMSY 0.88 0.89 F multiplier 0.680.590.86

36. AMSY-quantities – by fishery All gears Purse- seine only Longline only Purse- seine scaled Longline scaled AMSY 106,72262,116159,174145,593104,371 B AMSY 326,329247,230335,377495,020171,896 S AMSY 541436415852177 B AMSY /B 0 0.300.230.310.460.16 S AMSY /S 0 0.220.180.170.350.07 F multiplier 0.681.532.200.001.86

37. Forward simulations Spawning biomass depletion Biomass Surface fishery catch Longline catch

38. Spawning biomass ratio

39. Biomass

40. Predicted catches

41. Stock-recruitment relationship (h = 0.75)

42. Biomass

43. Recruitment

44. Spawning biomass ratio

45. Spawner-recruitment curve

46. Yield curve

47. Assumed value for the asymptotic length parameter of the Richards growth curve

48. Growth curves

49. Maximum length

50. Likelihoods Linf = 171.5Ling = 201.5 Total11.32-14.03 Length-frequency-13.190.34 Growth27.33-25.37 Selectivity0.50-0.75 Catch-0.210.14 Effort-0.104.43 Recruitment-7.169.41

51. LF fit

53. Biomass

54. SBR

55. Inclusion of the Chinese Taipei longline length-frequcy dat

56. SBR

57. LF fit

58. Selectivity

59. Fishery impact

60. Relationship between recruitment an the el Nino index

61. El Nino relationship

63. Base case Steepness = 0.75 Linf = 171.5 Linf = 201.5 Taiwan AMSY—RMSP 106,722102,263140,329107,812107,973 B AMSY —B RMSP 326,329503,221458,837320,374352,783 S AMSY —S RMSP 541956905480593 B AMSY /B 0 —B RMSP /B 0 0.300.360.280.32 S AMSY /S 0 —S RMSP /S 0 0.220.310.210.250.24 C recent /AMSY— C recent /RMSP 1.001.060.770.991.00 B recent /B AMSY — B recent /B RMSP 1.100.781.740.781.09 S recent /S AMSY — S recent /S RMSP 0.880.611.680.530.87 F multiplier— Multiplicador de F 0.680.511.440.410.65

64. Summary: Main results Biomass trends are similar to those estimated (and predicted) in previous assessments Both total and spawning biomass is estimated to have substantially declined since 2000, but there has been a slight increase recently Current biomass level is low compared to average unexploited conditions The current effort restrictions are not enough to maintain the population a level that will support AMSY

65. What is robust Fishing mortality levels are greater than that necessary to achieve the maximum sustainable yield.

66. Plausible Sensitivities and Uncertainties Results are more pessimistic with the inclusion of a stock-recruitment relationship Biomass trends are strongly related to longline CPUE

67. 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.