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28 GREAT BASIN NATURALIST Vol. 48, No, 1 upstream of the confluence (13-km reach), and none of 25 individuals of the same three species collected there had consumed crick- ets, DISCUSSION Mormon Crickets and Stream Ecology The movements of large bands of Mormon crickets into the Green and Yampa rivers in DNM in 1986 and 1987 provided a substantial and high-quality organic input to this system. This must have been the case in other years of major outbreaks, such as from 1980 to 1987 in DNM (Capinera and MacVean 1987, National Park Service 1986). Mormon cricket availabil- ity may be important to the ecology of both native and nonnative fishes, This is especially true in DNM, which contains the only known spawning site for the endangered humpback chub in the Green River Basin, and one of the two confirmed spawning sites for the endan- gered Colorado squawfish (Tyus et al. 1987). Various investigators have studied Green River fishes (Holden and Stalnaker 1975, Miller 1964, Miller et al. 1982, Vanicek and Kramer 1969) with emphasis on rare, native species listed or considered for listing as threatened or endangered (U.S. Department of the Interior 1985). The fauna also includes numerous nonnative fishes introduced for sport, forage, food, or by accident (Tyus et al. 1982), Food habits of native fishes are gener- ally known (Vanicek and Kramer 1969, Jacobi and Jacobi 1982), but their seasonal use of terrestrial animals is not, Foods of nonnative species are described for other rivers (e.g" Carlander 1977), but few data exist in DNM, Mormon cricket movements into rivers in DNM in spring provide food for stream fishes. This is a time when flooding, scouring, and annual insect emergence reduce food availability, High-water turbidity presumably reduces visual feeding efficiency of predatory fishes, yet large numbers of crickets at or near the water surface are vulnerable to aquatic predators, Cricket availability coincides with prereproductive periods for some native spe- cies, including round tail and humpback chubs, flannelmouth sucker, and Colorado squawfish, As reported by Defoliart et al. (1982), adult Mormon crickets have a mean crude protein content of 58% and a fat content of 16,5%, Such abundant and high-quality food might enhance fish reproductive success, postreproductive recovery, or both, We do not advocate that native fishes time reproductive behavior to cricket input. How- ever, a demonstrable relationship between nutrition and reproductive success in these fishes would be of interest, and long-lived fishes could incorporate such unpredictable major outbreaks to advantage in life-history strategies (Smith 1981, Tyus 1986), Longevi- ties of endemic Colorado River fishes studied to date indicate long life is an exceptional attribute of this fauna, Bony tail chub (Gila elegans) older than 40 years have been re- ported, razorback sucker (Xyrauchen tex- anus) commonly reach 30 to 40 years, and Colorado squawfish that formerly achieved L 8 m in length must have lived even longer (McCarthy and Minckley 1987, Rinne et al. 1986). Periodic outbreaks of Mormon crickets could contribute significantly to nutrition, di- rectly or indirectly, for a number of consecu- tive or disjunct years during such a long pe- riod oflife, High flows and seasonal flooding in the mainstream Green River are now reduced by dams (Joseph et al. 1977). This alters or pre- cludes floodplain inundation and removes particulate organics through reservoir entrap- ment (e, g., Minckley and Rinne 1986), Flooded lowlands were formerly expansive during sustained high flows, which often ex- ceeded mean discharge (181 m3/second, based on an 86-year record at Jensen, Utah) by more than an order of magnitude during snowmelt (Remilliard et al. 1986), Floodplain communi- ties were thus made available to predation by riverine fishes, as observed elsewhere (Welcomme 1979). In the Green River, Colo- rado squawfish and razorback sucker have been radio tracked to flooded lowlands, where they presumably feed (Tyus 1987, Tyus et al. 1987), Flood reduction and loss of al- lochthonous inputs may make seasonal inputs of terrestrial animals, including Mormon crickets, more important now than histori- cally. Mormon Cricket Control In their natural grassland or sagebrush- dominated habitats, Mormon crickets prefer to feed on succulent, herbaceous vegetation, Damage to range grasses is considered so slight that they are not generally considered a . \ ...