Climate-driven changes in growth and size at maturity of Gulf of Maine lobster stocks: implications for stock assessment models

Crustacean species are socioeconomically and ecologically cru-cial across the world. For crustaceans, as ectotherms, anthropogenic climate change threatens to significantly alter key life history characteristics, such as size at maturity and growth rate. Because crustaceans are difficult to age, length data are used in assessments of crustacean stocks; however, climate-induced changes in maturation and growth can greatly influence the performance of size-structured stock assessment models. We coupled individual-based and size-structured models for American lobster (Homarus americanus) off northeastern North America in the Gulf of Maine— to conduct a novel sensitivity analysis of the effects of maturity and growth-related input parameters on model outputs. For this analysis, we used a bottom-up approach (with parameters shifted independently) and a top-down approach (with parameters shifted jointly as they were predicted to be influenced by climate change). We found that our American lobster stock assessment model is resilient to relatively extreme shifts in biological input parameters. For size-structured modeling in assessments of crustacean stocks, we recommend the expansion of sensitivity analyses to include evaluation of the influence of climate-driven changes on input parameters based on time-varying life history traits.