Issues with the Bigeye Tuna Recruitment Trend and

Issues with the Bigeye Tuna Recruitment Trend and MSY-Based Stock Status Determination John Hampton & Shelton Harley SPC Oceanic Fisheries Programme

2010 Base Case Recruitment Estimates

Equilibrium Recruitment

Impact on Stock Status • Equilibrium recruitment is lower than recent average, higher than historical • MSY is << recent catches or the catches that would result at FMSY • SB remains near to or above SBMSY even though F >> FMSY for more than 10 years

Issues • Is the estimated recruitment pattern real, e. g. caused by an environmental regime shift? • If yes, the issue is: – Which regime do we use to characterize equilibrium recruitment for MSY-based stock status determination – early, late or average? • If no, and we accept that the trend results from an estimation bias, the issue is: – How do we eliminate that bias, and its resulting impacts on MSY-based stock status determination

1. Accept the Estimated Recruitment Pattern

1. Accept the Estimated Recruitment Pattern Issue: What to use to characterize equilibrium recruitment for stock status determination?

SRR 1952 -2008 (base case)

SRR 1989 -2008

Stock Status – SB vs SBMSY SRR 1952 -2008

Stock Status – SB vs SBMSY SRR 1989 -2008

“Kobe” Plots

Management Quantities Quantity SRR 1952 -2008 SRR 1989 -2008 0. 98 0. 87 155, 500 t 315, 600 t SB 2008/SBMSY 1. 167 0. 496 F 2008/FMSY 1. 554 1. 827 MSY 73, 440 t 129, 040 t Recent catch 134, 200 t Steepness SBMSY

2. Recruitment Pattern is Due to Estimation Bias • Causes of the estimated recruitment pattern • Steps necessary to remove the trend • Impact on MSY stock status determination

Recruitment and PS Catch

Longline CPUE and PS Catch

Recruitment Trend • Primary cause is relatively flat longline CPUE during and after the period when juvenile PS catch increased • The model’s only possible response is to increase recruitment to explain both the increase in juvenile catch while maintaining a flat LL CPUE • Noting that LL catchability is assumed to be constant over time and M(age) is fixed

Pre-1990 LL Effort R 3, R 4 Removed

Management Quantities Quantity 2010 Base No LL effort R 3, R 4 0. 98 0. 88 155, 500 t 299, 000 t SB 2009/SBMSY 1. 167 0. 87 F 2009/FMSY 1. 554 1. 37 MSY 73, 440 t 105, 000 t Recent catch 134, 200 t Steepness SBMSY

Conclusions • If we accept the estimated base case recruitment pattern, should compute MSYbased stock status based on recent phase • Restricting SRR estimation window to recent 20 years results in steepness estimate approaching the prior mode, higher equilibrium recruitment, higher SBMSY, lower recent SB/SBMSY and higher MSY • Probably a better estimate of current stock status!

Conclusions • If we do not accept the estimated base case recruitment pattern, removing pre-1990 LL effort in R 3 and R 4 eliminates the 2 -phase pattern • This also results in steepness estimate approaching the prior mode, higher equilibrium recruitment, higher SBMSY, lower recent SB/SBMSY and higher MSY

Suggestion • Provide SC 7 with both the standard base case and the run removing LL effort in R 3 and R 4 as a key sensitivity analysis • For the base case, and assuming that the 2 phase recruitment pattern persists in the 2011 assessment, provide management quantities based on SRRs computed for (a) the whole time series and (b) post-1990