Influence of environment and fleet dynamics on catch rates of eastern Scotian Shelf cod through the early 1980s

An analysis of the Atlantic cod (Gadus morhua) fishery on the eastern Scotian Shelf indicates that environmentally induced fluctuations in fish abundance or availability can influence catch rates beyond the immediate area of their impact through fleet dynamics. Each autumn, cod leave the Gulf of St. Lawrence and move on to the northeastern portion of the Scotian Shelf(Laurentian Slope). These movements. and the associated increases in catch rates. have been attributed to frontal concentrations of cod associated with the marginal ice zone. However, variation in catch rates on the eastern edge of the Scotian Shelf was correlated with variation on the central Scotian Shelf, beyond the extent of the marginal ice zone and the seasonal migration of fish from the Gulf. Changes in the distribution of fishing effort suggest that both fleet dynamics and the local availability of fish are important in determining realized catch rates. In light of fleer dynamics, differences in catch rates between the two regions of the Scotian Shelf suggest that the Laurentian Slope is a more costly region for fishing activities. Under these circumstances, trends in cpue will provide a poor indication of the distribution of fish between the two regions unless vessel distributions are also considered.