DEVELOPMENT AND EVALUATION OF BIOENERGETIC-BASED HABITAT SUITABILITY CRITERIA FOR TROUT

We constructed energetic models of habitat use for 82-322 g rainbow tr out (Oncorhynchus mykiss) in a large regulated river, and 8-28 g Color ado River cutthroat trout (O. clarki pleuriticus) in a small headwater stream, to determine if observed summer habitat use by these species could be attributed to net energy acquisition, and to develop habitat suitability criteria based on net energy gain. Metabolic models of ene rgy expenditure were derived from literature sources, but measurements of energy availability were site-specific. From the energy models, we assigned a suitability value of 1.0 to the entire range of velocities where positive net energy gains were predicted, and a suitability val ue of zero to velocities where negative net energy gains were predicte d. Predicted net energy gain velocities were compared with observed ve locities used by each species. For rainbow trout, the energetic model predicted energetically profitable velocities ranging from 5 to 45 cm s(-1). Predicted velocities were similar to velocities used by rainbow trout. This indicated that rainbow trout, as a group, were using ener getically profitable stream locations, but some rainbow trout used non -profitable velocities. For Colorado River cutthroat trout, the energe tic model predicted energetically profitable velocities ranging from 5 to 45 cm s(-1). however, Colorado River cutthroat trout used signific antly lower velocities than predicted. The dissimilarity between veloc ities predicted and used by Colorado River cutthroat trout may be attr ibuted to their inability to utilize energetically profitable velociti es available in the stream because of depth restrictions. The results suggest that the predictive abilities of energetic models vary between streams because of differences in depth and velocity availability. (C ) 1997 by John Wiley & Sons, Ltd.