This project synthesizes key aspects of production and energy flow, based on US-GLOBEC studies in the Northwest Atlantic, and augment the US-GLOBEC data with information from other sources on production processes at the lower and upper levels of the food web. The primary objectives examine several alternate model outcomes of GLOBEC and GLOBEC-related studies that help address a number of outstanding issues and re-examine patterns of energy flow on Georges Bank. This research enhances and expands the findings of previous investigations, with explicit consideration of factors not addressed in earlier models of this system including: (1) the microbial food web, (2) consideration of new and recycled primary production, (3) spatial heterogeneity of primary and secondary production on Georges Bank, (4) changes in biomass and production at higher trophic levels, and (5) the effects of environmental forcing on production processes. Incorporation of these elements into the modeling effort permits a more detailed understanding of production processes on the Bank. The first four elements provides the broader ecosystem context, while the last provides the link to one of the US-GLOBEC program.s principal themes, climate change. The latter is being addressed by comparing several different decadal-scale time periods that reflect differing environmental and fish community regimes: (1) the cold 1960s characterized by abundant groundfish stocks fished by distant water fleets; (2) the 1970s, characterized by "average" water temperatures, increased domestic fishing effort, and depletion of groundfish stocks; (3) the 1980s, characterized by "average" water temperatures, overfishing of groundfish stocks, and increases in elasmobranchs; and (4) the "average" temperature, lower salinity 1990s, characterized by reduced fishing mortality, rebuilding of groundfish stocks, and increases in elasmobranchs and pelagic fish. Because of large-scale changes in the fish community structure as a result of over-exploitation, a full understanding of the population dynamics of the target species will not be attained without consideration of changes in other ecosystem components. Individual model networks are being formulated to represent each of the above periods. Subsequently, dynamic modeling will be developed to describe the transformations or shifts between these regimes.
