Further Statistical Catch-at-Age Assessment Results together with Biological Reference Point estimates for Gulf of Maine cod, October 2012
The Statistical Catch-at-Age assessments of the Gulf of Maine cod stock by Butterworth and Rademeyer (2012) are extended, with a particular focus on the estimation of Biological Reference Points (BRPs). The analysis supports starting these assessments from an early year to provide precise estimates of these BRPs, and the estimation n of the Ricker form of the stock–recruitment relationship within the assessment is found to be preferred. Across a wide range of sensitivity tests the 2011 spawning biomass is robustly estimated at about 14 thousand tons with specific estimates ranging from about 12.5 to 16 thousand tons. When starting the assessments in the 1960s or earlier with a Ricker stock-recruitment function, most estimates of the spawning biomass which provides MSY are around 25 thousand tons for the M = 0.2 scenario, and around 13 thousand tons for the M increasing scenario; the corresponding estimates of MSY itself are about 13 and 6 thousand tons respectively. The AIC selection criterion and a reduced retrospective pattern suggest that greater weight should be accorded to results for the M increasing compared to the M = 0.2 scenario.