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Humpback chub, possible bony tail discovered in Cataract Canyon By Richard A. Valdez Senior Fishery Biologist BIOiWEST, Inc. Logan, Utah Researchers have discovered a small, reproducing population of humpback chub and six adult fish that are suspected to be bony tail chub, the rarest of the fish in the Upper Colorado River Basin. The four-year study was completed in 1988 in Cataract Canyon -- a 16-miIe reach of white water that runs from the confluence of the Green and Colorado rivers through Canyonlands National Park to upper Lake Powell -- and in 50-mile stretches of the Green and Colorado rivers upstream from Cataract Canyon. According to the Humpback Chub Recovery Plan, only two self-sustaining populations currently are recognized: the Little Colorado River in the Lower Basin and the Black Rocks/Westwater Canyon area of the Colorado River in the Upper Basin. Other areas where humpback chub exist include the Yampaand Green rivers in Dinosaur National Monument, Gray Canyon in the Green River and now Cataract Canyon in the Colorado River. The largest population of humpback chub is the one in the Little Colorado River. Individual chub have occasionally been reported from several other areas in the lower and upper Colorado River basins. Humpback chub (Gila c\1lha) prefer deep, swift regions with rocky shorelines like the habitat found in Cataract Canyon. Tagging studies have shown that many humpback chub spend their entire lives in small reaches of these canyon regions. Continued research will help detennine the number of fish in the Cataract Canyon area. The six fish thought to be bony tail chub CD.i!.i! eIee:ans) were all returned to the river alive. Their presence could be a significant contribution to retaining the gene pool of this species in the Upper Basin. This species once was believed to be widespread in the Colorado River System. Recently, wild bony tail have been found only in Lake Mohave in the Lower Basin. Only one other bonytail chub has been reported in the Upper Basin in the last 10 years. That was in the B lack Rocks area in Colorado. The U.S. Fish and Wildlife Service plans to examine specimens from the Cataract Canyon area in 1990 and 1991 to determine the genetic purity of the bonytail chub and evaluate possible hybridization with humpback or roundtail chub (Gila robusta). (See article on "Chub identification... ") BIO/WEST, Inc., a private environmental consulting finn in Logan, Utah, conducted the study in cooperation with the National Park Service, Utah Division of Wildlife Resources and U.S Fish and Wildlife Service. The Bureau of Reclamation contracted with BIO/WEST to determine the imponance of this region to the endangered fish of the Colorado River. During the study, researchers also found relatively large numbers of young-of-the-year Colorado squawfish (Ptvchocheilus lucius) in nursery backwaters in the lower 50 miles of the Green River just above Cataract Canyon. This indicates that Colorado squawfish are successfully reproducing in the lower reaches of the Green River, probably in "alluvial cobble areas," rocky regions formed by tributaries to the river. In Cataract Canyon itself, researchers found few young-of-the-year squawfish and linle evidence of spawning. The survival rate of young squawfish is unknown. More fish were found in backwaters in the fall, shortly after hatching, than in the spring, when the fish were 7 or 8 months old. The drop in numbers may be from over. winter mortality, movement to other habitats or transport from the area by river currents. Further investigations may determine the causes for the decline. Small numbers of young Colorado squawfish and humpback chub were found where the Colorado River flows into Lake Powell. However, nursery backwaters in this 10-miIe region are only marginally suitable for the young endangered fish. Fluctuating lake levels, variable river flows and silting shorelines often cause the backwaters to dry out. Only one razorback sucker (Xvrauchen texanus) was captured during this study. This adult was caught in an area where several fish had been found in previous years. This is further evidence of the species' steady decline. A limited supply of copies of the fmal report, "The Endangered Fish of Cataract Canyon," is available. For a copy, write: Biological Support Branch, Bureau of Reclamation, P.O. Box 11568, Salt Lake City, Utah 84147, or BIO/WEST, 1063 W. 1400 North, Logan, Utah 84321. 11