Variation in the Distribution of Fish Stocks on the Northeast Continental Shelf in Relation to their Environment, 1980-1989

Time-series observations of fish distributions and environmental conditions are used to investigate environmentally induced variation in the fish stocks on the northeast continental shelf of the USA. Standardized bottom-trawl surveys, which have been conducted each autumn since 1963 and each spring since 1968, allow the conditions within the decade of the 1980s to be compared with those of the two previous decades. Significant temperature changes occurred in the spring during the period of these observations, with the 1980s being intermediate between the colder 1960s and warmer 1970s. Interannual variations of ± 2-4°C were observed in all shelf regions. Large decreases in the abundance of many stocks caused by heavy fishing pressure confound analyses of the effects of environmental influence on stock abundance. Changes in the distribution of selected stocks, however, can be identified and attributed to changes in temperature. The distributional change may appear either as a north-south shift or as a change in water depth. The range of observed temperature change is comparable to that anticipated in the Northwest Atlantic under a CO2 scenario. These results may be used as an indicator of potential response of the fish stocks to climate change