Fish can partition themselves in different habitats, depending on the other species present. Therefore, examining how preferred habitat varies with the presence of other species gives a clearer answer as to how fish distribution is shaped under a variety of conditions. Fossil Creek is a tributary of the Verde River and supports five species of native fishes.
Here we compared abundance patterns and developed resource selection models for imperiled native southwestern (U.S.A.) fishes in the presence and absence of Bass Micropterus spp. to evaluate how fishes alter their selection for habitats when sympatric with a nonnative piscivore. We collected data using snorkel surveys and in-stream habitat sampling in Fossil Creek (AZ), upstream (native fish) and downstream (Bass present) of a fish barrier and developed models in a use v. availability framework. The abundance of all Roundtail Chub Gila robusta, small (vulnerable to predation) Sonora Sucker Catostomus insignis, and Speckled Dace Rhinichthys osculus was significantly reduced, but the abundance of Desert Sucker Catostomus clarkii was similar in sampling reaches with Bass. Small native fishes altered habitat selection most. When sympatric with Bass, small Roundtail Chub increased their selection for riffles by 2.57x and small Desert Sucker reduce their selection for pools by 6.90x, while also selecting for increased flow velocity and smaller substrate in riffles and runs. Large (invulnerable to predation) native fishes altered selection least, notwithstanding an increased selection for canopy cover in sampling reaches with Bass. Observed shifts in resource selection are consistent with predator avoidance strategies. Our study stresses the importance of maintaining lotic mesohabitats as potential refugia for vulnerable native fishes. This information will allow for improved habitat management, provide information to aid in protection of in-stream flows, and contribute to recovery of endangered and sensitive native fish species. To date we have conducted fieldwork in Fossil Creek, analyzed data and submitted a publication.