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hybrid) forms captured during our four year study suggested that <br />hybridization in DNM chubs, if occurring, was not widespread. <br />Food habits of humpback chubs are largely unknown because of federal <br />restrictions regarding their sacrifice, but they have been reported <br />feeding on dipterans in the Little Colorado River (Kaeding and Zimmerman <br />1983; Minckley 1981). Capture of humpback chubs at the surface and at <br />various levels within the water column with baits, and presence of Mormon <br />crickets and hymenopterans in stomachs and feces of some fish, indicated <br />that this fish used a wide range of habitat for feeding. Capture of some <br />fish in the interface between the shoreline eddy and adjacent run during <br />the day may indicate that humpback chubs use such areas for feeding on <br />drifting foods. Surface feeding by chubs for terrestrial insects has also <br />been observed by others (Vanicek and Kramer 1969; Tyus and Minckley 1988; <br />C.O. Minckley, Northern Arizona University, personal communication). The <br />influx of vast numbers of Mormon crickets into the river in some years <br />constituted a significant portion of the natural food base of humpback <br />chub in DNM, as noted earlier by Tyus and Minckley (1988). Both the <br />roundtail chub and bonytail are known to feed on shoreline vegetation <br />(e.g., Equisetum species), perhaps incidentally, and terrestrial and <br />aquatic insects (Banks 1964; Vanicek and Kramer 1969; Tyus and Minckley <br />1988; Griffith and Tiersch 1989). <br />The high number of channel catfish in eddies and pools used by <br />humpback chub during spring runoff and late summer low flows, and the <br />gross overlap in foods consumed and in feeding habits, including surface <br />feeding (Banks 1964; Holden and Stalnaker 1975a; Tyus and Minckley 1988; <br />Tyus and Nikirk, in press), suggests that negative interactions between <br />15