Habitat Criteria for Rearing Steelhead: A Comparison of Site-Specific and Standard Curves for Use in the Instream Flow Incremental Methodology

Habitat utilization curves developed for fry and juveniles of steelhead Oncorhynchus mykiss in Big Creek, a small stream of moderate to high gradient in California, were compared with three standard habitat utilization curves. Comparisons were made of the amount of weighted usable area generated by the curves from the instream flow incremental methodology computer program. The narrower range of usable habitat in Big Creek resulted in utilization curves with ranges narrower than those of the standard utilization curves and with much less weighted usable area for fry and juvenile steelhead at all flows above 3.0 ft3/S. Stream width, depth, flow, gradient, substrate particle size, pool : riffle ratio, seasonal hydrography, and other habitat characteristics should be compared before habitat utilization curves from one stream are applied to another.