DENSITY-DEPENDENT HABITAT SELECTION BY JUVENILE HADDOCK (MELANOGRAMMUS-AEGLEFINUS) ON THE SOUTHWESTERN SCOTIAN SHELF

Positive correlations between total abundance and indices representing distributional area have been reported for several marine fish stocks. Different indices can produce different results for the same stock and many indices scale positively with total abundance. We describe an alternative approach to modelling the distributional response to variation in total abundance using data for juvenile haddock (Melanogrammus aeglefinus) from the southwestern Scotian Shelf. Annual bottom trawl surveys having a stratified random design were used to estimate the local density of haddock age 1 and 2 in each strata. Estimates of total abundance-at-age were obtained from sequential population analysis. The relationship between local density and total abundance-at-age was described for each strata using an exponential model with a Poisson error structure. Systematic variation among strata in the model parameters was indicative of density-dependent habitat selection and supported a previous study showing a positive correlation between distributional area and total abundance. Density-dependent habitat selection by juvenile haddock did not generate correlations between mean length-at-age and total abundance-at-age because the proportional abundance of haddock in areas of differing growth rates remained approximately constant as total abundance-at-age increased.