An assessment of the transferability of habitat suitability criteria for smallmouth bass, Micropterus dolomieu

The purpose of this study was to determine if habitat suitability criteria developed in the summer months for sma11mouth bass were transferable among streams representing different eco regions.

Habitat suitability criteria were developed for depth, mean column velocity, cover and substrate for two size classes of sma1lmouth bass, 100-199mm and >200mm, in the North Anna River and Craig Creek, Virginia.

Criteria that accurately describe habitat selection by a species or guild in a system different from where the criteria were developed are said to be transferable to that system. The transferability of suitability criteria between the North Anna River and Craig Creek, as well as depth and velocity criteria from Minnesota, the Huron River, Michigan and the Upper James River, Virginia, to the North Anna River and Craig Creek were tested using a 2x2 contingency table analysis.

Depth criteria for the smaller sizes of sma1lmouth bass did not transfer well between regions; 4 of the 8 transferability tests (50%) failed. Depth criteria for larger sma1lmouth bass transferred to the North Anna River and Craig Creek in all cases.

Velocity criteria developed for the smaller size classes did not transfer well among regions; only 3 of the 8 transferability tests were positive. Likewise, velocity criteria for larger sizes of smallmouth bass did not transfer well; only 1 of 8 tests were positive.

General criteria were developed for depth and mean column velocity by averaging the suitability values reported from this and 3 other studies. General depth and velocity criteria transferred well to the North Anna River and Craig Creek for both the larger and smaller size classes of smallmouth bass; all depth tests were positive and 3 of 4 velocity tests were positive. The improved success of transferability warrants investigation of developing general criteria for smallmouth bass.

Cover criteria for both size classes of smallmouth bass were transferable from the North Anna River to Craig Creek but not vice versa. Substrate heterogeneity criteria were not transferable between the North Anna River and Craig Creek for either size class of smallmouth bass. Criteria developed for the percentage of substrate particles >15cm (smallmouth bass >200mm only) were transferable from Craig Creek to the North Anna River but not vice versa.

The transferability of habitat suitability criteria among regions was inconsistent and it is recommended that site-specific criteria be developed for each stream to which habitat assessments are applied. Additionally, nose velocities used were more consistent between the North Anna River and Craig Creek than were mean column velocities used. Hence, it is recommended that information on nose (focal point) velocities be incorporated into habitat studies to more accurately describe smallmouth bass velocity requirements.