Foraging and growth in relation to habitat use of young-of-the-year Atlantic salmon (Salmo salar)

Using snorkeling observations, I examined the habitat use and preference of 216 individually tagged young-of-the-year Atlantic salmon in their first summer of life, using both a univariate and a multivariate approach. Habitat preference was determined by comparing the habitat used by fish to that available in the stream. The univariate analyses showed that salmon preferentially used a wide range of current velocity (6–48 cm·s−1) and water depth (20–39 cm) and a narrower range of cover (complete cover from aerial predators) and substrate (pebbles). However, a multivariate logistic regression approach showed that only water depth and current velocity were key variables in habitat selection. Indeed, habitat preference of salmon increased with current velocity and water depth and then decreased at water depths above 30 cm. Drift rate within the stream was surveyed in order to predict food abundance for each fish in the study site. Correlates of fitness (i.e. foraging rate and growth rate) were also measured to relate individual fitness of each fish to their habitat choice. The results showed that y-o-y Atlantic salmon did not grow at a faster rate in the preferred habitats, despite the increase in food abundance and a higher foraging rate. I suggest that young-of-the-year salmon can grow reasonably well in a variety of habitat types and that the ideal free distribution may be a better description of their habitat use than the ideal despotic distribution.