Use of Habitat Guilds of Fishes to Determine Instream Flow Requirements

We grouped eight warmwater fishes, each represented by one to four life stages, into habitat-use guilds (i.e., groups of species) to select target species for instream flow studies. Cluster analysis of depth, velocity, substrate, and cover use identified four primary habitat-use guilds, which were distinguished largely on the basis of water velocity. Habitat-suitability criteria were developed for each species and life-stage combination, and these criteria were used in physical habitat simulations to determine relations between weighted usable area (WUA) and discharge for three streams in the upper James River basin, Virginia. Weighted usable areas for species within each habitat-use guild generally exhibited similar responses to discharge except those for some stream-margin inhabitants and for strongly cover-oriented species. Four types of habitat-discharge relations, which were consistent among streams, were identified. Curves of WUA versus discharge for habitat generalists and some specialists indicated relatively stable WUA over a wide range of flows. Target species and life stages should be selected from appropriate habitat-use guilds to ensure that flow recommendations represent the best compromise between the needs of fast-water and slack-water inhabitants