8249 - Laserfiche WebLink

Home Browse Search

(1991) noted wintering pikeminnow were often associated with an instream cover element (e.g. sand shoals, sand ridges, cobble jetties, or ice jams). They reported that Colorado pikeminnow preferred areas of low velocity (0.0-0.15 m/sec) and moderate depths (0.6-1.1 m). ISMP data indicates that number of Colorado pikeminnow CPUE sampled in the Yampa River by electrofishing over the last nine years has been fairly consistent, ranging from 17 to 23 fish from three sites totaling 25 miles (MeAda 1997). The percent composition of Colorado pikeminnow, for all fish over 15 em, was estimated to be 0.3% downstream of Sunbeam (RM 60-64) and 1.8% 50 miles upstream near Duffy Tunnel (Anderson, in press). Humpback Chub. The humpback chub is a specialized morph of the Gila robusta complex (Minckley et al. 1989, Dowling and DeMarias 1993) that exists almost entirely in high gradient canyon reaches of large rivers in the Colorado River Basin (USFWS 1990b). Because of the difficulty in sampling these remote locations large gaps exist in our knowledge of the ecology of this species. Currently only six, isolated reproducing populations of humpback chub exist in the Colorado River Basin (Gorman and Stone in press). Much of the information that is known of this species relates to spawning chronology and habitat use and movements of adult fishes. In the Little Colorado River (Gorman and Stone in press) and Yampa River (Tyus and Karp 1989, Karp and Tyus 1990) humpback chub spawned on the descending limb of the hydrograph. In the current study, both roundtail chub and humpback chub were observed in spawning coloration (reddish orange ventral surface) during the descending limb of the hydrograph. Movement of spawning humpback chub into the Little Colorado River from the Grand Canyon was coincidental with declines in peak flows (Valdez and Ryel 1995). Karp and Tyus (1990) recaptured several individuals at the same location during the spawning season suggesting fidelity to spawning sites. Little is known of the habitat needs of early life stages (larval, age-O, and juvenile) humpback chub other than they occupy the same reaches of the river as adults and probably utilize large substrate (Valdez et al. 1990). The Little Colorado River is the only location in which young humpback chub are readily collected, and juveniles appear to stay in this tributary for more than a year before they recruit to the Colorado River in the Grand Canyon (Valdez and RyeI1995). Despite having a narrow caudal peduncle and forked caudal fin characteristic offast moving swimmers (Moyle and Cech 1988), adult and subadult humpback chub occupy slow velocity, deep-water habitats (Valdez et al. 1990, Valdez and Rye11995, Gorman 1994). In the Grand Canyon of the Colorado River adult humpback chub were abundant in large 31