7984 - Laserfiche WebLink

Home Browse Search

squawfish in the Green and Yampa Rivers (Tyus 1985; Wick et al. 1986; Tyus 1990). Some authors suggest that repeated use of the same spawning areas may reflect a limited availability of spawning habitats (O'Brien 1984; Archer et al. 1985). However, Tyus (1990) reported that migrating Colorado squawfish pass through many miles of potential spawning habitat to reach specific spawning areas in Yampa Canyon. Colorado squawfish may not spawn annually, and a lack of long-distance migratory behavior has been associated with less than annual spawning and sexual immaturity (Wick et al. 1983; Tyus 1990). One dramatic example of movement was provided by a fish radio-tagged in Gypsum Canyon of upper Lake Powell on April 5, 1982. On July 9, 1982, the fish was in lower Cataract Canyon. The next contact was made above the Black Rocks area of the Colorado River some 160 miles upstream. This was 41 days later and believed related to spawning. At the end of September, the fish was in the Colorado River near Clifton, Colorado, approximately 200 miles from its initial downstream location. Not all radio-tagged fish display such dramatic migratory behavior. Radiotelemetry studies conducted in the Grand Valley region of the Colorado River found that movement during April to October was generally limited to 25-30 miles ( Archer et al. 1985; Osmundson and Kaeding 1989; McAda and Kaeding 1991). Young Colorado squawfish also undertake movements, and Tyus (1991b) documented diel movements of age 0 and age 1 fish. The young fish moved in response to changing water temperature and water levels. HUMPBACK CHUB (Gila cypha, Miller 1946) The humpback chub is endemic to the Colorado River Basin and is part of a native fish fauna traced to the Miocene epoch in fossil records (Miller 1955; Minckley et al. 1986). Hump- back chub remains have been dated to about 4000 B.C., but the fish was not described as a species until recent times (Miller 1946). This recent discovery has been attributed to its restricted distribution in remote, white water canyons (USFWS 1990b), and its earlier abundance and distribution is not well known. HISTORIC DISTRIBUTION AND ABUNDANCE Historic distribution of the humpback chub includes portions of the mainstem Colorado River and four of its tributaries: the Green, Yampa, White, and Little Colorado rivers (Figure 4). However, its original distribution throughout the Basin is not known with certainty. Considerable manmade alteration occurred in the Colorado River before the 1940's, especially in the Lower Basin (Miller 1961), and humpback chub may have disappeared from some river reaches before their existence was documented. For example, Miller (1955) reported remains of this species from an Indian site near Hoover (Boulder) Dam. Thus, the population in this area may have been eliminated when Hoover Dam was built in the 1930's. 24