Estimating the Impacts of TMDL Regulations on Chesapeake Bay Fisheries

We estimated the benefits of the Chesapeake Bay TMDL to commercial fish harvesters using output from the Chesapeake Bay Eutrophication Model, two different ecosystem models, and a multi-stage inverse demand system. To estimate the water quality influences, we developed habitat volume models based on water quality (salinity, temperature, and dissolved oxygen) parameter estimates and species tolerances for these parameters. Estimates from the habitat volume were used to force two different fisheries models, a simple fisheries ecosystem model based first order species interactions and the Chesapeake Bay Fisheries Ecosystem Model (CBFEM, an ecotrophic fisheries model developed using the Ecopath with Ecosim software).  Two fisheries ecosystem models were used to account for the structural uncertainty of the models.  In these ecosystem models, time varying-water quality conditions were used to drive changes in the habitat volumes of the fished species.  To assess the impacts of TMDL regulation on the fisheries, these models were run using habitat volumes calculated from the Eutrophication model based on watershed scenarios with and without the watershed implementation plans and assuming constant fishing rates.  The changes in biomasses under these scenarios were applied to the multi-stage inverse demand models to estimate the benefits of water quality improvements to fishermen.