Estimating Species Interactions Among Georges Bank Fish Species

An important component of an ecosystem approach to fisheries is the consideration of species interactions and estimation of biomass losses due to predation in addition to fishing.  Georges Bank, a historically important fishing ground within the Northeast U.S. Continental Shelf ecosystem, has undergone extensive changes in community dynamics and ecosystem structure over the last half century, providing an example of an area which could benefit from an ecosystem approach to management.  We estimated the interactions among nine fish species within the Georges Bank ecosystem using a multispecies statistical catch-at-age model and a multispecies production model.  Both approaches incorporate time series of aggregate commercial catch and relative abundance to estimate species-specific biomass and the interactions among species.  Additionally, the statistical catch-at-age model incorporates age-specific fishery, survey, and food habits data to quantify annual recruitment and age-specific predation mortality.  Species-specific biomass estimates are compared between multispecies models and to single species assessment models.  Furthermore, biomass losses due to predation are compared between models and to commercial catches.  A comparison of multispecies modeling approaches is an essential step in developing a robust ecosystem approach to fisheries and moving multispecies models from proof of concept to tools that can be used for tactical management.