What drives dynamics in the Gulf of Alaska? Integrating hypotheses of species, fishing, and climate relationships using ecosystem modeling

Abstract

We use a dynamic ecosystem model to evaluate the relative effects of fishing history, climate change, and predator–prey interactions in determining biomass trajectories for 12 species groups ranging from marine mammals through commercially exploited fish and invertebrates in the Gulf of Alaska (GOA). Ecosystem model fits under six alternative hypotheses relating fishing, climate, and predation were evaluated. Fishing alone explained few GOA biomass trajectories; it was necessary to both estimate specific predator–prey relationships and provide some mechanism for increased production. No single control hypothesis explained all species dynamics simultaneously, suggesting that in the GOA, there is no single main driver of the ecosystem. Furthermore, the alternative control hypotheses implied contrasting sets of predator–prey relationships (estimated functional response parameters). Therefore, a single set of “best fit” parameters for a given control hypothesis is unlikely to be useful in forecasting. Future modeling efforts supporting ecosystem-based fishery management could retain multiple working models to accommodate complex forcing (fishing, keystone species production, and environmental) differentially affecting components of the ecosystem.