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gurgitated prey were classified as "consumed." In all experiments, 36 (11.4%) of the 315 consumed live prey were regurgitated. Only 3 (0.7%) of 441 consumed dead fish were regurgitated. Discussion Northern squaw fish consumed a significantly higher proportion of dead juvenile chinook salm- on than expected, whether the ratio of dead to live prey was I: I or I :4. Dead prey are not commonly reported to be eaten by fishes; moreover, for many fishes prey movement appears to be an important feeding cue (Ware 1973; Howick and O'Brien 1983; Irvine and Northcote 1983; Luczkovich 1988). Irvine and Northcote (1983) found that un- deryearling rainbow trout Oncorhynchus mykiss preferred live over dead prey and suggested that predators select moving prey to avoid ingesting nonnutritious inorganic or dead material. Con- versely, dead prey are more easily captured than live prey, and the nutritional value of newly killed and live prey may be similar. Optimal foraging theory suggests that predators should maximize their rate of energy intake by preferentially se- lecting non evasive prey if the energy contents of alternative prey are equal (Ivlev 1961; Stephens and Krebs 1986). In a location with substantial numbers of newly killed prey, selection of dead individuals might be advantageous. Northern squawfish consumed a much higher percentage of dead juvenile chinook salmon in bright light (88%) than in darkness (31 %). Light levels may affect predation by influencing both predator activity and prey behavior (Cerri 1983). During darkness, live prey are more at risk to pre- dation because schooling behavior and reaction distance are reduced (Whitney 1969; Emery 1973; Vinyard and O'Brien 1976: Cerri 1983), whereas dead prey may not be as easily detected due to their lack of movement. In bright light, the ability oflive juvenile chinook salmon to avoid northern squawfish might have resulted in preferential con- sumption of dead individuals. A better under- standing of how northern squawfish use vision, smell, or other senses to detect prey would greatly aid in interpreting our results. Peak feeding by northern squawfish has been reported to occur during the day in John Day Reservoir, but during the night and early morning just below McNary Dam (Vigg et al. 1991). Feeding patterns at dams may be strongly influenced by timing of prey availability, however; juvenile salmonids often pass dams during darkness (Long 1968; Vigg et a!. 1991). NOTES 683 Northern squawfish captured but regurgitated II % of all live chinook salmon consumed. If re- gurgitation occurs in the field, estimates of pre- dation mortality based on analysis of stomach contents would be biased. The direction of pha- ryngeal tooth marks on regurgitated chinook salmon indicated that prey were being held tail- first. Prey orientation at capture is unknown, but northern squawfish may prefer to swallow prey headfirst, as has been noted for European perch Perca j/uviatilis (Hoogland et a1. 1956), or their prey may be able to escape more easily when held tailfirst. Regurgitation could also be related to prey size. Larger prey may be more difficult to manip- ulate and take longer to handle, resulting in prey escape or release (Beyerle and Williams 1968; Al- lan and Hecker 1988). The proportion of dead juvenile salmonids con- sumed by northern squawfish in the field is un~ known, but is dependent not only on absolute pro- portions of prey types available, but also on en- counter rates between northern squawfish and live and dead salmonids. Encounter rates are largely determined by fish movements and distribution patterns. In the laboratory, dead juvenile chinook salmon sank to the tank bottom and slowly moved with water movements, whereas live prey fre- quently schooled. Northern squawfish were often motionless near the tank bottom unless disturbed or feeding. In the field, turbulence below dams probably keeps dead juvenile salmonids suspend- ed and mixed with live salmonids for a period of time. Live salmonids would eventually move downriver, whereas dead fish would settle in areas with low water velocities, such as back eddies. Areas of calm water are also preferred locations for northern squawfish (Faler et al. 1988). Newly killed juvenile salmonids in the Colum- bia River are more abundant immediately below dams than in other parts of the river-reservoir system. Rieman et al. (1991) estimated a com- bined spillway, turbine, and turbine bypass mor- tality of 4-10% at McNary Dam among juveniles passing downriver into John Day Reservoir. The rate of consumption of juvenile salmonids by northern squawfish is also greatest at these sites. In John Day Reservoir during 1983-1986, ap- proximately 26% of the 2.1 million juvenile salm- on and steelhead Oncorhynchus mykiss lost sea- sonally to northern squawfish were consumed near McNary Dam (Rieman et a1. 1991). Predation and dam passage mortality estimates may not be in- dependent, however. Because, as we have shown, northern squawfish feed on dead prey, it is pos- J