8204 - Laserfiche WebLink

Home Browse Search

Wydoski 1980, Lanigan and Tyus 1989, John Hawkins, Colorado State University, pers. comm., 1995). In the upper Colorado River, most razorback suckers occurred in the Grand Valley (Valdez et al. 1982), but captures of wild fish have declined (Osmundson and Kaeding 1990). Razorback suckers also have been captured in the mainstream Colorado River downstream of the Green River confluence, including Cataract Canyon, and in Lake Powell (Minckley et al. 1991). Individuals of the fish have been captured in the flooded San Juan River arm of Lake Powell, but few specimens have been confirmed in the riverine portion of the San Juan River upstream of Lake Powell (Platania et al. 1991, Minckley et al. 1991). Fifteen adults have been captured and removed from Lake Powell (11 from the San Juan arm of the lake and 4 from the Colorado River arm; unpublished U.S. Fish and Wildlife Service [USFWS] permitting records, Denver, CO), and a few individuals presumably remain there. Larval and juvenile razorback suckers have been captured in different locations of the upper Colorado River basin, and especially in the Green River in the last 20 years (Tyus 1987, Gutermuth et al. 1994, Muth et al. 1998), but identification of razorback sucker larvae has been difficult or impossible when other catostomid larvae were present. Recent advances in taxonomic techniques have made it possible to identify razorback sucker larvae, even in the presence of other catostomid (Muth et al. 1998). Using these new techniques the Larval Fish Laboratory at Colorado State University conducted an intensive survey of the Green River from 1992 to 1996. During this period, 1,735 larval razorback suckers (99% of captures) were taken from the "middle" portion of the Green River, including the Escalante, Jensen, and Ouray reaches, and 440 larvae were identified from samples taken from the Labyrinth and Stillwater canyons, near the confluence of the San Rafael River, Echo Park, and Green River valley (Muth et al. 1998). The exact origin of these larval fishes is unknown due to larval drift, but is presumed to be nearby in upstream areas. Despite the presence of these larvae, no significant recruitment to any population has been documented (Tyus and Karp 1990, Minckley et al. 1991, Modde et al. 1996). Razorback suckers have been reintroduced at several locations in the upper and lower Colorado River basin. More than 12 million young and juvenile razorback suckers were reintroduced into riverine habitats in Arizona and California from 1981 to 1990, but indications are that most of these stocked fish were consumed by nonnative predatory fishes (Marsh and Brooks 1989; Minckley et al. 1991; Mueller 1995). More recent stockings completed or planned in the Salt and Verde rivers, Lake Mojave, Lake Havasu, and the Imperial Division (unpublished USFWS stocking records) have utilized larger fish to reduce predation risks. Some small-scale augmentation stockings also have occurred in the Green, Colorado, Gunnison, and San Juan rivers upper basin (unpublished records). Recapture results indicate that some fish survive, and thus these stockings have been successful in the short term (e.g., Ryden and Pfeifer 1995). 7