Comparing Ecosystem Models As Fisheries Management Tools: A Case Study in the California Current

Ecosystem modeling is becoming a more integral part of fisheries management, and there is a need to quantify differences between various models currently being employed for scientific and management purposes. Using two models, Ecosim and a size- and –trait based model, we simulate ecological consequences of fishing to identify commonalities and differences in model predictions for the California Current fish community. We predict the maximum sustainable yield of each fish species and the fishing mortality required to reach it. Secondly, we investigate the fish community response to small perturbations, to find the most important components as well as bottom-up and top-down changes due to fishing. We find that the most important differences between models are 1) The fishing mortality needed to reach MSY differs systematically between models 2) competition in the trait-based model causes increased abundance of larger species when forage fish are removed, whereas bottom up consequences are more unpredictable in Ecosim, 3) diet matrices in Ecosim change the responses of individual species compared to a size based food selection approach. We conclude that the choice of ecosystem model critically influences the outcome of a given fishing scenario and conclusions from a single model should be drawn carefully.