End-to-end foodweb control of fish production on Georges Bank

Abstract

The ecosystem approach to management requires the productivity of individual fish stocks to be considered in the context of the entire ecosystem. In this paper, we derive an annual end-to-end budget for the Georges Bank ecosystem, based on data from the GLOBEC program and fisheries surveys for the years 1993-2002. We use this budget as the basis to construct scenarios that describe the consequences of various alterations in the Georges Bank trophic web: reduced nutrient input, increased benthic production, removal of carnivorous plankton such as jellyfish, and changes in species dominance within fish guilds. We calculate potential yields of cod and haddock for the different scenarios, and compare the results with historic catches and estimates of maximum sustainable yield (MSY) from recent stock assessments. The MSYs of cod and haddock can be met if the fish community is restructured to make them the dominant species in their respective diet-defined guilds. A return to the balance of fish species present in the first half of the 20th century would depend on an increase in the fraction of primary production going to the benthos rather than to plankton. Estimates of energy flux through the Georges Bank trophic web indicate that rebuilding the principal groundfish species to their MSY levels requires restructuring of the fish community and repartitioning of energy within the food web.