Longitudinal variation and habitat associations of small fishes in the Bighorn River, Wyoming: influences of river regulation and introduced fishes

Abstract

We assessed variation in longitudinal distributions of native and introduced fishes and their occurrences in different habitat types downstream from Boysen Dam in the Bighorn River, Wyoming. The closure of Boysen Dam in 1952 and construction of three downstream water diversion dams have led to channel changes in the Bighorn River causing reductions in the numbers and areas of side channels, backwaters, and riffles. Eleven native and five introduced fish species were collected by seining during 2005. Fish samples were dominated by sand shiner (Notropis stramineus), flathead chub (Platygobio gracilis), and longnose sucker (Catostomus catostomus). Introduced fish species included common carp (Cyprinus carpio), emerald shiner (Notropis atherinoides), plains killifish (Fundulus flavis), yellow perch (Perca flavescens), and sand shiner. Differences in relative abundances of fishes among habitat types were observed. Fathead minnow (Pimephales promelas), longnose sucker, white sucker (Catostomus commersoni), plains killifish, and sauger (Sander canadensis) were found almost exclusively in backwaters, and channel catfish (Ictalurus punctatus) was collected almost exclusively in side channels. Changes from the pre-European fish community are occurring in association with invasions of introduced fish species and losses of side channels, backwaters, and riffles.