ABSTRACT
Patterns of Energy Flow and Utilization on Georges Bank
D.J. Gifford (URI), James J. Bisagni (UMassD), J.S. Collie (URI),
E. G. Durbin (URI), Michael Fogarty (NMFS), Jason
Link (NMFS), Lawrence P. Madin (WHOI), David Mountain (NMFS),
Debbie Palka (NMFS), Michael F. Sieracki (BLOS),
John Steele (WHOI),
and B.K. Sullivan (URI)
The overall objective of the research is to provide
a broad ecosystem context
for interpretation of the population dynamics of the Georges Bank GLOBEC
target species. The proposed research will synthesize 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 are to examine several alternate model outcomes of
GLOBEC and GLOBEC-related studies that will help to address a number of
outstanding issues and to reexamine patterns of energy flow on Georges Bank.
The proposed research will enhance and expand 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 will permit a more detailed understanding of production processes on
the Bank. The first four elements will help provide the broader ecosystem
context, while the last provides the link to one of the US-GLOBEC program's
principal themes, climate change. The latter will be 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 cannot be attained without
consideration of changes in other ecosystem components. Individual model
networks will be formulated initially to represent each of the above periods.
Subsequently, dynamic modeling will be developed to describe the
transformations or shifts between these regimes.