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temperature-dependent (Raney and Webster 1942; Oence 1948) and/or stream ~ di scharge-dependent (Walton 1980). Sudden temperature drops may dimi ni sh or .))) stop mi grat ion (Raney and Webster 1942; Oence 1948). White suckers usually migrate from lentic systems or stream pools to spawning riffles; therefore, it is assumed that distance to spawning habitat may be a factor in determining opt imum habi tat. Raney and Webster (1942) observed whi te suckers mi grat i ng from only a few hundred meters to as much as 6.4 km upstream where obstructions blocked further passage. Oence (1948) reported that a rock 1 edge 2.5 feet (76.2 cm), with a moderately fast current, stopped the migration of most dwarf suckers, Catostomus commersoni utawana (closely related to the white sucker): Suckers depend to some degree on local landmarks and primarily on olfaction during the spawning run (Oence 1948; Werner 1979); therefore, it is assumed that impacts which could change the spawning stream integrity may affect spawning run success. White sucker spawning habitat is generally considered to be areas in inlets, outlets, small creeks, and rivers with relatively swift shallow waters running over a gravel bottom (Forbes and Richardson 1920; Dence 1948; Nelson 1968; Carl ander 1969; Schneberger 1977). Rei ghard (1913) suggested that the essential breeding habitat requirement is suitable substrate, not running water, but Curry (1979) indicated that spawning site selection is influenced primarily by water velocity and depth of substrate type. Nelson (1968) reported that spawning over gravel was usually at water depths less than 30 cm. Fuiman (1978) stated that egg collections in his study typically took place in shallow (15 to 20 cm deep) gravel riffles. Curry (1979) reported spawning site depths of 20 to 25 cm. A clean bottom of coarse sand (Minckley 1963) or gravel is an essential quality of the spawning habitat for white suckers (Oence 1948). Curry (1979) reported that, after white suckers cleaned out a spawning site, the remaining gravel was larger and more free of silt and sand than when the site was selected. Curry (1979) reported that white suckers spawned over medium-sized gravel (2 to 16 mm). Nelson (1968) reported that white suckers apparently seldom spawn in deep waters with a sand bottom, although Raney (1943) observed spawning in a relatively deep, quiet pool with a gravel substrate. Pflieger (1975) reported spawning in gravelly areas near the lower end of pools, in quiet water or where the current begins to quicken. Gravel appears to be the preferred substrate. If access to streams with suitabl e spawni ng habi tat is limited, lacustrine populations may spawn on sand or gravel shoals subject to wave action (Reighard 1913; Hayes 1956; Olson 1963; Krieger 1980). t Nelson (1968) reported that the velocity in rivers where white suckers congregated for spawning varied from a low of 14 cm/sec to a high of 90 cm/sec. White suckers also were observed in streams with mean spring velocities of 60 to 90 cm/sec (Minckley 1963; Curry 1979). Although white suckers have been observed at velocities> 60 cm/sec, Symons (1976) reported that white suckers in an artificial stream with fast velocity were most often located at modal velocities of 30 to 49 cm/sec. Curry (1979) reported spawning site velocities for white suckers of 50 to 59 cm/sec. Although Oence (1948) never observed suckers in the act of spawning in deep pools where the current was very slow, 2 t