Laserfiche WebLink
in small instars unavailable to fish. Nevertheless, most fish maintain at least a low level of feeding <br />activity during winter, and sometimes switch to alternative, more available food sources. Schmidt et <br />aL (1987) found anadromous and freshwater fishes feeding predominantly on amphipods, the most <br />abundant crustacean in one of two river deltas surveyed. They also found reduced survival by fish <br />with low condition, i.e., lighter fish of a given length failed to attained sufficient energy reserves <br />during the preceding summer to survive winter. <br />Thompson (1989) found that lipid content ofage-0 Colorado squawfish (Ptychocheilus Lucius) <br />was inversely related to winter duration of fish 30 to 44 mm long, held in simulated water <br />temperature aquaria. Percent survival was significantly lower in starved than in fed fish, suggesting <br />that the size at which this species shifts to a piscivorous diet is critical to obtaining an energetically <br />profitable prey and to overwinter survival. Aclosely-related species, northern squawfish, was <br />observed feeding in winter on juvenile salmonids in the tailrace below a Columbia River hydroelectric <br />dam (Fraley et al. 1988). <br />39 <br />