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

Collie, J. S., Gifford, D. J., and Steele, J. H. 2009. End-to-end foodweb control of fish production on Georges Bank. – ICES Journal of Marine Science, 66: 2223–2232. The ecosystem approach to management requires the productivity of individual fish stocks to be considered in the context of the entire ecosystem. We derive an annual end-to-end budget for the Georges Bank ecosystem, based on data from the GLOBEC programme and fisheries surveys for the years 1993–2002. Scenarios based on this budget describe the consequences of various alterations in the Georges Bank trophic web: reduced nutrient input, increased benthic production, removal of carnivorous plankton, and changes in species dominance within fish guilds. Potential yields of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) are compared with historical 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 early 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 foodweb.