The Role of Channel Morphology and Hydraulics in Shaping Spatial Patterns of Foraging Habitat for Drift-Feeding Trout in Small Streams

Spatial arrangement of habitat influences a number of ecological process in fish populations. We have examined how distribution of foraging habitat for stream-dwelling salmonids is controlled by channel morphology and flow characteristics. We specifically investigated Coastal Cutthroat Trout (Oncorhynchus clarki clarki) habitat in morphologically distinct reaches of a small stream in British Columbia. To this end, we coupled a hydrodynamic model with a bioenergetic model for drift-feeding trout and parameterized them using field data. Our results point to two major conclusions. First, they indicate the existence of differences in the energetic quality of foraging habitat between the study reaches as well as clear longitudinal and cross-stream trends in net energy intake within each of the reaches. We identify and discuss specific channel features which generate the modeled patterns. Second, the model suggests that these within and between-reach patterns may differ for fish belonging to different body size classes. Overall, these results provide a set of mechanistically-based hypotheses regarding the role that physical controls such as channel morphology and hydraulics may play in generating the commonly observed patterns of space use by stream-dwelling salmonids. The reported findings contribute to better understanding of fish-habitat relationship and are relevant to river restoration.