DEVELOPMENT AND EVALUATION OF ALTERNATIVE HABITAT SUITABILITY CRITERIA FOR BROOK TROUT

We developed habitat suitability criteria (HSC) for mean column veloci ty and depth from a foraging model (foraging-model HSC) that incorpora ted the energetic costs and benefits of a foraging location for drift- feeding brook trout Salvelinus fontinalis in Hunt Creek, Michigan. We compared these criteria to HSC developed from frequency-of-use data (u se HSC) collected in Hunt Creek. Foraging-model HSC predicted that a s ingle mean column velocity was optimal and depended on fish size, wher eas a range of optimal mean column velocities was predicted from frequ ency-of-use data. The optimal velocities predicted from foraging-model HSC for yearling and older brook trout (range 32-49 cm . s(-1)) were greater than the highest optimal velocity (27 cm . s(-1)) predicted by use HSC. The optimal-velocity values predicted from foraging-model HS C for age-0 fish (23 and 29 cm . s(-1) for 5- and 7.5-cm fish, respect ively) were within the range of optimal velocities (6-30 cm . s(-1)) p redicted from use HSC. The predicted range of usable velocities was na rrower for foraging-model HSC than for use HSC, regardless of fish siz e. Foraging-model HSC values for depth were a function of current velo city and fish size and were similar to use HSC. Use HSC suitability sc ores for an independent set of habitat use observations in Hunt Creek were significantly higher than foraging-model HSC for age-0 fish but n ot for yearling and older fish. This may indicate that use HSC are too general and do not represent the actual suitability of foraging micro habitats in Hunt Creek. Yearling and older brook trout used microhabit ats with higher mean column velocities and greater depths than age-0 f ish.