Fine-scale study of microhabitat use by brook trout in NE Ohio streams

Brook trout (Salvelinus fontinalis) are threatened in Ohio. A Habitat Suitability Index (HSI) was previously used to identify streams suitable for trout reintroductions within the historic range, resulting in mixed success at establishing self-sustaining populations.  Preliminary observations suggest that one unsuccessful stream may possess insufficient pools to sustain brook trout, although the HSI found no deficiency in pools. To test the hypothesis that brook trout occupy pools more than riffles or runs, a fine-scale examination of microhabitat use was performed in three successful streams. A 60 m section of each stream was surveyed at 2 m intervals for depth, width, flow velocity, and substrate type and embeddedness. Visual characterization of microhabitat types were confirmed statistically with velocity/depth ratios and Froude coefficients. Microhabitat use was assessed through visual observations and electrofishing. In all three streams brook trout occupied pools significantly more than riffles or runs. Substrate profiles were consistent across the three streams, and trout had no preference for any particular substrate. Future research will compare pool depth, width, and prevalence between successful and unsuccessful streams. Modification of the existing brook trout HSI to incorporate fine-scale measures of microhabitat may improve future model performance for predicting successful reintroductions.