RELATIONSHIPS BETWEEN GEOGRAPHIC-DISTRIBUTION AND ABUNDANCE OF AMERICAN PLAICE (HIPPOGLOSSOIDES-PLATESSOIDES) IN THE SOUTHERN GULF OF ST-LAWRENCE

Optimal foraging theory predicts the expansion of population range int o marginal habitat as abundance increases; percent changes in local de nsity should be greater in marginal than in optimal habitat as populat ion size changes. Using data from annual bottom trawl surveys (1971-19 92), we found that the abundance of American plaice (Hippoglossoides p latessoides) in the southern Gulf of St. Lawrence varied fivefold duri ng this period, but its geographic range (area containing 95% of the p opulation) showed no tendency to expand as population size increased. The area of highest density (area containing 50% of the population) di d show a slight tendency to expand with population size, but contrary to predictions, there was no tendency for changes in density to be pro portionally greater in marginal areas where plaice were uncommon. Slig ht but significant (P < 0.05) differences in geographic distribution o ccurred between periods of low and high abundance but accounted for on ly a small proportion of the total variation in catch rates. Average c atch rates were highest in the same areas in both abundance periods, a nd no large shifts in distribution occurred between the two periods. T hese results contrast with published results for Atlantic cod in the s outhern Gulf of St. Lawrence.