Status and conservation of Upper Colorado River Basin fishes

Authors: Kevin Bestgen, Koreen Zelasko

Year: 2024

Abstract

The fish community of the Upper Colorado River Basin is depauperate, consisting of only 13 taxa. These include two salmonids, five cyprinids, four catostomids, and two cottids. Native taxa can be grouped into two assemblages, a warmwater group that occupies lower elevation warm water streams and large rivers, and another that occupies smaller and cool to cold streams at higher elevations. The large river assemblage of eight taxa are mainly large-bodied and most are declining, with five listed under the Endangered Species Act: Colorado pikeminnow Ptychocheilus lucius; bonytail Gila elegans; humpback chub G. cypha; razorback sucker Xyrauchen texanus; and Kendall Warm Springs dace, a speckled dace subspecies Rhinichthys osculus thermalis. Three others, flannelmouth sucker Catostomus latipinnis, bluehead sucker Pantosteus discobolus, and roundtail chub Gila robusta, are listed by basin states as needing conservation; small-bodied speckled dace is widespread and abundant. Distribution and status of most fishes in upstream cool water reaches, where less sampling has occurred, is less well understood. Those species include speckled dace, mountain sucker Pantosteus platyrhynchus, mountain whitefish Prosopium williamsoni, mottled sculpin Cottus bairdi, and Paiute sculpin C. beldingii. Status of cold-water Colorado River cutthroat trout Salmo clarki pleuriticus, is well known and consists of several distinct genetic and morphological lineages arrayed across the upper Green, upper Colorado, and San Juan River basins; all are rare. Declining status of most basin taxa is from anthropomorphic affronts including habitat modification, especially in rivers where connectivity is disrupted by dams (large river fishes), introduction of diverse predaceous or competitive nonnatives (all taxa), and hybridization (suckers, trout), with additional overarching negative effects of climate change, ongoing drought, and attendant water consumption issues. Ongoing conservation programs of various non-governmental, state, and federal organizations are bolstering the status of many of these species.