DENSITY-DEPENDENT GEOGRAPHIC-DISTRIBUTION OF ATLANTIC COD (GADUS-MORHUA) IN THE SOUTHERN GULF OF ST-LAWRENCE

We tested effects of population size on the geographic distribution of Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence for age groups 3-8 + over the period 1971-90. Distribution was density dep endent for all six age groups. Geographic range or stock area increase d with abundance for each age group. Variation in abundance explained 63-94% of the variation in stock area. During periods of low abundance , the highest cod densities occurred in western regions of the souther n Gulf for all age groups. Geographic distribution during these period s was more restricted for younger cod than for older cod. Density of a ge-3 cod was relatively high in only one of three western regions wher eas densities of older cod were relatively high in two or all of these regions. As abundance increased, density increased slowly in the regi ons where cod were concentrated at low population sizes and more rapid ly in surrounding regions. The greatest densities were found in the sa me area at low and high levels of abundance for younger cod but in dif ferent areas at these two abundance levels for older cod. We discuss t his variation in geographic distribution in terms of density-dependent habitat selection and note its implications for stock assessment.