As part of a management strategy evaluation for the Bering Sea, AFSC scientists Drs. Aydin, Holsman, and Ianelli recently investigated the relationship between climate (i.e., water column temperature) and productivity (i.e., spring and fall zooplankton biomass) on spawning stock and recruitment relationships for three species of groundfish: walleye pollock, Pacific cod, and arrowtooth founder. For this approach, recruitment estimates were first derived from a multi-species stock assessment models (MSM) fit to historical survey and fishery data.
Figure 1. Recruitment estimates from the multi-species stock assessment model (black lines) and stock-recruitment regression model estimates for recruitment functions without zooplankton covariates (gray) and with zooplankton covariates (red). Click to enlarge.
The model was run in multi-species mode, where each species is linked through a predation sub-model, as well as in single-species mode, where no predation interactions occur. This produced a time-series of spawning stock biomass and recruitment from the multi-species and single-species models. Total spring and fall zooplankton biomasses (sprZ and fallZ, respectively) predicted from the ROMS/NPZ model for the Bering Sea were then used as covariates on a Ricker recruits (R) per spawner (S) curve and fit through maximum likelihood estimation to recruitment from the multi-species model (Fig. 1). Model estimates were compared via AIC and top models for each species were selected for use in projections of the multi-species model under future climate scenarios from ROMS/NPZ projections based on down-scaled IPCC climate model scenarios (Fig. 2).
By Kirstin Holsman
Figure 2. Projected spawning stock biomass for walleye pollock predicted from single (a) and multi-species (b) modes of MSM under various recruitment relationships and no harvest (“SSB unfished”; dashed line) or harvest that yields 40% of SSB on average during the last 5 years (2045-50) of the projection (B40%; solid line). Click to enlarge.
