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E[?IDANGERED FISHES OF CATARACT CANYON by R.A. Valdez and R.G. Williams BIO/WEST, Inc. 1063 W. 1400 N. Logan, UT 84321 Bureau of Reclamation 125 South State Street Salt Lake City, UT 84147 ABSTRACT A 3-year investigation of the fishes of Cataract Canyon has just been completed. The Final Report on this project will be submitted in early 1989. Cataract Canyon is a 16-mile whitewater region of the Colorado River below the confluence of the Green River and above the inlet to Lake Powell. It is characterized by a steep gradient with a predominantly boulder and cobble substrate and talus shorelines. Law summer flows are about 5,000 cfs, runoff flows are about 70,000 cfs, with a record flow of 120,000 cfs. A total of 28 species of fish, representing 10 families, were found in Cataract Canyon. This includes 20 non-native and 8 native species. The most common species are red shiners (Notropis lutrensis), channel catfish (Ictalurus punctatus), common carp ( rinus carpio), sand shiners (Notropis stramineus), and fathead minnows (Pimephales promelas). These five non-native species make up over 85% of the catch. The native species, according to abundance, include the Colorado squawfish (Ptychocheilus lucius), speckled dace (Rhinichthyes osculus), flannelmouth sucker (Catostomus latipinnis), bluehead sucker (Catostomus discobolus), roundtail chub (Gila robusta), humpback chub (Gila cypha), bonytail chub (Gila elegans), and razorback sucker (Xyrauchen texanus). This investigation has contributed information to the Rare and Endangered Colorado River Fishes Sensitive Areas document. It confirms the presence of adult Colorado squawfish in Cataract Canyon, but fails to document any evidence of spawning adults, although deep pools and cobble/riffle habitat are present, and larval fish less than 25 mm were found. The investigation also upgrades the lower 50 miles of the Green River to a high density nursery area, and extends the YOY nursery area through Cataract Canyon to upper Lake Powell. A concentration of humpback chub is confirmed in Cataract Canyon with the capture of five or more adults in one year. It also can be designated a suspected spawning area because of the presence of larvae, young-of-year, and tubercled adults. However, spawning activity was not confirmed because of a failure to capture ripe females with strippable eggs. This has been shown to be a formible task in Cataract because of high flows during spawning. The Cataract Canyon Study also revealed a possible enclave of bonytail. Several adults and juveniles, as well as one suspected YOY were captured, but the definitive taxonomic status of this enclave remains undetermined. Specimens from Cataract possess many bonytail characters but lack the extreme features associated with the species. We urge inclusion of these specimens in a proposed taxonomic investigation of the Colorado River Gila. If this enclave is confirmed, it can provide a source of genetic material from the upper basin. 25