FISHES, MACROINVERTEBRATES, AND AQUATIC HABITATS OF THE PURGATOIRE RIVER IN PINON CANYON, COLORADO

We describe physical habitat and aquatic biota of a relatively undisturbed canyon reach of the Purgatoire River and its tributaries in southeastern Colorado. Flow regimes are highly variable due to unpredictable, brief, intense summer floods. River habitat consists of long, deep, silty pools with few large boulders separated by short cobble riffles, whereas tributaries contain isolated pools maintained by groundwater. Water chemistry and temperatures were within ranges tolerable by plains stream fishes at all sites. Benthic macroinvertebrate assemblages included representatives of four regional faunas. At lotic sites, a few taxa of two detritus-collecting functional groups predominated. The fish fauna is depauperate, consisting of only 11 native species which we divided into river, perennial stream, and generalist faunal associations. However, most fishes have generalized habitat, trophic, and reproductive requirements, which seem to adapt them to survive the harsh environmental conditions in this plains stream. Although the four species that made up 95% of individuals generally persisted at river sites over the 5- to 7-year period sampled, the abundance of red shiners declined markedly from 1983 to 1987 despite favorable flow regimes.