Fishery and environmental factors affecting trends and fluctuations in the Georges Bank and Gulf of Maine Atlantic cod stocks: an overview
The Georges Bank and Gulf of Maine Atlantic cod stocks have been commercially exploited for centuries, and continue today to support important commercial and recreational fisheries in both the United States and Canada. Prior to 1960, the two stocks were fished exclusively by the United States. During the 1960s, marked increases in exploitation occurred due to the development of Canadian and distant?water fisheries on Georges Bank. Total landings from the two stocks increased from 14 4001 in 1960 to 57 5001 in 1966, but subsequently declined to 30 0001 in 1976. Under extended fisheries jurisdiction - enacted in 1977 by both the USA and Canada - landings and stock sizes initially increased and a record-high catch (71 000 t) was attained in 1982. However, during the late 1980s and early 1990s, fishing effort and fishing mortality also increased to record-high levels, resulting in marked reductions in spawning-stock size. Research vessel indices, commercial c.p.u.e. indices, and VPA results all indicate that biomass levels in both stocks are now at record-lows. Although it is clear that fishery-induced perturbations have had a major impact on the Georges Bank and Gulf of Maine stocks, environmental and biotic influences may also have affected the stocks. These influences are not easily discernible, given the magnitude of the fishery-induced changes. Biophysical processes appear to be extremely important during the first year of life of cod and affect growth, mortality, and year-class strength. These processes are reviewed and discussed in relation to their impacts on various life history stages of cod. Current and future research studies aimed at differentiating environmental from fishery-related factors affecting recruitment and abundance of cod in the Georges Bank-Gulf of Maine region are discussed.