Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

Effective fishery management necessitates a general understanding of resource partitioning by fishes that inhabit complex systems composed of biotic and abiotic features. Evaluations of nonnative species introductions have continually demonstrated adverse effects associated with abundance and distribution of native fishes. As such, garnering an understanding of resource selection and interactions between native and nonnative species is important for recovery efforts involving native fishes. We evaluated habitat use by two native (Largescale Sucker Catostomus machrocheilus and Mountain Whitefish Prosospium williamsoni) and one nonnative (Pumpkinseed Lepomis gibbosus) fish species of the Kootenai River, Idaho, in a laboratory stream system. Trials were conducted in allopatry and in sympatry with and without the presence of wood to describe and evaluate competitive interactions in the context of on-going habitat rehabilitation efforts. Competitive interactions were evident between native Largescale Sucker and nonnative Pumpkinseed concerning use of a woody structure and current velocity. Mountain Whitefish used low-velocity habitats and selected locations that were further from wood when in sympatry with Pumpkinseed. Logistic regression models containing all habitat variables provided the most support to explain the effect of interspecific competition for all species, indicating that competition is a complex process composed of multiple interactions that occur simultaneously.