9305 - Laserfiche WebLink

Home Browse Search

11 Flow fluctuations in the winter may affect fish use of preferred winter habitats. Movement patterns of radio-tagged fish suggested that such fluctuations result in greater movement of Colorado squawfish than in more stable conditions (Valdez and Masslich 1989; Wick and Hawkins 1989). Valdez and Masslich (1989) believed that a rapid change in river-stage altered locations of squawfish preferred microhabitats resulting in greater fish movement. Increased movement was hypothesized as resulting in increased energy expenditure and decreased body condition. Decrease`s in body condition during winter may affect ova development, number, and size. In spring and early summer, adult Colorado squawfish are most often located in seasonally inundated shoreline habitats, including backwaters or bottomlands (Tyus 1990). Radio-tracking data indicated use of shoreline backwater habitat in the 1981 low-flow year and use of flooded bottomlands during the 1983 high- flow year (Tyus and Karp 1989). During the 2 high-flow years, 1983 and 1984, adult Colorado squawfish also used flooded shorelines (Tyus et al. 1987). From late April to May in 1985 and 1981, at flows of 8,000-10,000 cfs, they used the inundated portions of Old Charley Wash. Wick et al. (1983) noted that in 1982 (an average-flow year) that adult Colorado squawfish used backwater and eddy habitats as runoff flows increased from early may through mid-June. In May, backwater habitat use occurred in backed-up tributary mouths and diked-off side channels. Adult squawfish moved to main channel habitats as the river level dropped. Adult Colorado squawfish occupy a variety of habitats in mid-to-late summer but are most common in eddies, pools, runs, and shoreline backwaters over sand and silt substrates {Tyus et al. 1984 and 1987). Visual observations of fish in shallow water suggests that adults use sheltered microhabitats behind boulders, flooded vegetation, or other cover. During the sunnier, radio-tagged fish were most often located in deeper shoreline habitats where movements suggested heavy use of the eddy-run interface (Tyus et al. 1987). Capture of introduced northern pike, Esox Lucius, and channel catfish, Ictalurus punctatus, in habitats shared by adult Colorado squawfish (Wick et al. 1985; Tyus and Beard 1990) suggests a potential for competition and/or predation during times of resource limitation. Although Pimentel et al. (1985) found that Colorado squawfish did not prefer channel catfish as prey, observations of channel catfish lodged in throats of adult Colorado squawfish (McAda 1983; Pimentel et al. 1985; Wick et al. 1985) indicate that these introduced fish are eaten by Colorado squawfish, and some may cause mortality. However, little is known concerning conditions that either favor or impede nonnative fish. McAda and Kaeding (1989) found that during years of low annual runoff, numbers of nonnative fish increased; yet in years of moderately high runoff, their relative abundance decreased. Predacious fish of concern include channel catfish, northern pike, and walleye, Stizostedion vitreum.