Spatially Explicit Bioenergetic Analysis of Habitat Quality for Age-0 Atlantic Salmon

Spatial and temporal variation in growth conditions for young juveniles may determine the ultimate success of salmonid populations. To assess this aspect of habitat quality, we developed a spatially explicit bioenergetics model to predict age-0 Atlantic salmon Salmo salar growth rate potential (GRP) in rearing streams of the Connecticut River, from the time of stocking in the spring, to the end of the summer. During the first month after stocking, there appears to be a paucity of suitable habitat. Most available habitat is predicted to result in low foraging success of small fish and to be energetically stressful because of the combination of high spring discharge and low water temperature. Although less than 14% of available habitat was predicted to support positive growth in the spring, 47% of the fish we observed occupied microhabitats predicted to yield positive growth, indicating the importance of habitat selection. In contrast, from mid-June to August, 67% of available habitat was predicted to yield positive growth, and 92% of all fish occupied positive growth microhabitats. Consistent with these results, sites with higher salmon GRP in the early season, but not in the mid- or late season, had higher final salmon densities by the end of August. Hydroclimatic regimes characteristic of more southerly rearing streams in the Connecticut River basin were predicted from our model to cause a potential shift from early-season to late-season habitat-related growth constraints along this environmental gradient. This work demonstrates the value of applying a bioenergetics approach to issues related to conservation of Atlantic salmon and provides a framework for future research on early life history energetic determinants of habitat quality.