7771 - Laserfiche WebLink

Home Browse Search

reach) and 21-30 mm TL (lower reach), to proportions of zooplankton consumed. Degree of diet overlap was greatest in comparisons with channel catfish and green sunfish. DISCUSSION Comparisons among food-habits investigations are difficult because of differences in study design, location, and season. However, our observations on diets of native and nonnative fishes in backwaters of the Green River generally agree with results of prior studies in the Upper Colorado River Basin (e.g., Vanicek and Kramer 1969, Jacobi and Jacobi 1982, McAda and Tyus 1984, Grabowski and Hiebert 1989, Osmundson and Kaeding 1989) and reported food habits of the nonnative species within their native ranges (e.g., Carlander 1969, 1977, Cross and Collins 1975, Pflieger 1975, Harlan et al. 1987). Larger YOY or yearling red shiner, sand shiner, speckled dace, flannelmouth sucker, channel catfish, and green sunfish eat mainly immature aquatic insects. Diets of larger YOY or yearling fathead minnow and blue head sucker consist mostly of algae and organic debris. The diet of YOY Colorado squawfish consists primarily of zooplankton and immature insects (especially chironomid larvae) and occasionally includes fish. The reported size at which wild Colorado squawfish shift to a more piscivorous diet varies, but generally, fish become an important food item after Colorado squawfish attain a length of> 40 mm. Osmundson and Kaeding (1989) suggested that slower growth and poorer condition observed for YOY and especially yearling Colorado squawfish in grow-out ponds with lower densities of appropriate-size forage fish might have been due to their higher reliance on insect forage. Identifiable fish reported in digestive tracts of YOY Colorado squawfish here and by McAda and Tyus (1984) and Grabowski and Hiebert (1989) were either red shiner or fathead minnow larvae. These nonnative species are 11