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I I I I I I I I I I I I I I I I I I I 0;;.., ti;- f,-( ! " ~::' <;- ~:,. 15 During the non-reproductive season adult razorbacks may be found widely dispersed in the lakes and riverine sections. Although many individuals show relatively small home ranges, individuals may move upwards of 100 kilometers over the course of one or several years (Minckley et al. 1991). Adults are generally found in slower waters. In the Gila River and from early studies in the Green and Colorado rivers adults apparently preferred quiet eddies and deep pools with sand and silt bottoms where currents were less than 10 cmls (Tyus 1987; Marsh and Minckley 1991). In contrast Tyus (1987) tracked six adults that tended to occupy nearshore runs in spring, mid- channel sandbars during summer where currents average about 50 cm/s, and avoided whitewater canyons. In Lake Mohave razorbacks can be found usually in less than 10m of water over a variety of substrates (Minckley 1983). During the reproductive season fish move inshore to wave-swept gravel beaches in Lake Mohave (Minckley 1983). In riverine sections they migrate and congregate over gravel bars, along flooded alluvial plains and other areas with a clean sand bottom (Tyus 1987; Minckley et al. 1991). Spawning in Lake Mohave begins as early as January and extends into April (Minckley 1983). In the upper basin spawning occurs later in the season, extending from May through June (Tyus et al. 1982), although occasionally, ripe fish are collected much earlier (Minckley et al. 1991). Spawning in the upper basin corresponds to times of peak runoff from winter snowmelt, when substantial amounts of detritus is being transported and the availability of off-channel sites is greatly increased. Although not documented for razorback sucker, recruitment success in squawfish and several other native Colorado River fishes is positively correlated to flow rate ~.... Ji;,