The recent history of the Northwest Atlantic fish community has been well documented. The effects of overfishing, primarily on key gadids and flatfish, have been and continue to be examined, but the effects on the internal dynamics within this fish community, namely species interactions, are less obvious. What impact predation, competition, and similar interactions have on community structure and dynamics is not well known, especially relative to fishing mortality.
The ecosystem approach to fisheries management is a holistic view distinct from classical population models standard to fisheries analyses. Ecosystem management, multi-species modeling, food web analysis, and similar concepts provide insights into fish communities where classical methods are unable to do so.
The NEFSC has long taken a progressive approach to studying the fish
community in this region from an ecosystem perspective. The NEFSC Bottom
Trawl Survey Program includes components designed to collect data on food
habits in a multi-species survey. This historical perspective, coupled
with specific studies, has provided basic food habits information for more
than three decades.
The FWDP evaluates species interactions, predation mortality, and the
structure and function of the fish community in the Northwest Atlantic
ecosystem primarily through stomach analysis. Numerous analyses and derivative
parameters are ascertained from the relatively simple observations of these
diet data.
An important component of understanding the dynamics of key fish stocks
is a knowledge of fish diet and prey fields. For example, the abundance
and quality of prey items in estuaries can affect larval fish mortality,
and hence impact stock productivity and future yields. Management scenarios
such as reliably predicting the recovery of a stock or closing geographic
areas to fishing depend upon a knowledge of food availability to a given
stock.
Recent History of the Northwest Atlantic Fish Community
During the 1960's, 70's, 80's and to the present, significant changes
in the northwest Atlantic continental shelf fish community structure (primarily
on Georges Bank) occurred, from one dominated by high value groundfish
and flounders (e.g.
Atlantic cod, Gadus morhua, haddock,
Melanogrammus aeglefinus, and yellowtail flounder,
Limanda ferruginea)
to a system comprised by lower valued elasmobranchs (e.g. spiny
dogfish, Squalus acanthias, and skates) and pelagics (e.g.
Atlantic herring, Clupea harrengus, and Atlantic mackerel, Scomber
scombrus) (see Figure). For more information, see the NEFSC
Status of the Stocks. These changes were caused primarily by the arrival
of distant water fleets and great increase in fishing pressure exerted
on the fishery beginning in the early 1960's. As a result of the dramatic
increase in landings (and presumably high discards), the estimated total
biomass in the region declined by at least 50%. Even with the foreign fleets
displaced from the U.S. EEZ in the late 1970's, effective effort on the
fish stocks has remained high, and for many species, stock biomass dropped
to historically low levels in the 1990's due to the increased capacity
and efficiency of the domestic fleet (Fogarty and Murawski 1998, NEFSC
1998). The effect on the trophic dynamics of the ecosystem due to this
dramatic change in the community structure must be examined in order to
develop an ecosystem approach to the management of the region.
