AGE-DEPENDENT AND DENSITY-DEPENDENT BATHYMETRIC PATTERN OF ATLANTIC COD (GADUS-MORHUA) IN THE SOUTHERN GULF OF ST-LAWRENCE

I examined the bathymetric pattern of Alantic cod (Gadus morhua) in Se ptember in the southern Gulf of St. Lawrence for age groups 3-8+ over the period 1971-91 using data from annual bottom trawl surveys. Mean a ge of cod tended to increase with depth in all years. The age-specific bathymetric patterns underlying this relationship differed markedly b etween periods of low and high abundance. When abundance was high, cod densities tended to be highest at intermediate depths, and the positi ve correlation between age and depth reflected a tendency for density to be highest in progressively deeper water for older fish. When abund ance was low, density was either unrelated to depth or highest in shal low water, and the positive correlation between age and depth reflecte d a tendency for older cod to be more widely distributed than younger cod (i.e., density decreased less sharply with depth for older cod). I suggest explanations for this density dependence of cod bathymetric p attern and discuss these results in relation to the factors underlying habitat selection and bathymetric segregation by age in this populati on.