Density-dependent growth of young-of-the-year Atlantic salmon (Salmo salar) revisited

The length of individual young-of-the-year (YOY) Atlantic salmon (Salmo salar) in Catamaran Brook decreases with increasing population density following a negative power curve. Because most of this decrease in growth rate occurs at low densities (< 1 fish center dot m-2), (Imre et al. 2005; Journal of Animal Ecology, 74: 508-516) suggested that exploitation competition for drifting prey rather than space limitation might be responsible for this pattern. Recently, (Ward et al. 2007; Journal of Animal Ecology, 76: 135-138) showed that the negative power curve of growth rate versus density can be caused by other mechanisms and suggested that Imre et al.'s evidence for density-dependent growth would have been stronger if we had analysed final size versus initial density rather than final density. We examined (i) whether the negative power curve of size versus density was also apparent in an analysis of final size versus initial density and tested two predictions that emerge from Ward et al.'s model, (ii) the variance in body size increases with population density, and (iii) the maximum fish size at a site is density-independent. The final size of YOY salmon decreased with increasing initial density following a negative power curve. Our data did not provide strong support for the above predictions emerging from Ward et al.'s model. Our analyses of different years, sites and seasons were consistent with the hypothesis of density-dependent growth of YOY salmon.