COMPARATIVE FEEDING-HABITS OF JUVENILE CHINOOK SALMON, STEELHEAD, ANDSACRAMENTO SQUAWFISH IN THE LOWER AMERICAN RIVER, CALIFORNIA

We compared diets of juvenile chinook salmon, Oncorhynchus tshawytscha , steelhead, O. mykiss, and Sacramento squawfish, Ptychocheilus grandi s, in the lower American River from February through July 1992 and 199 3. Chinook salmon and steelhead fed primarily on chironomids (all stag es), baetids (adults and nymphs), and hydropsychids (larvae and pupae) ; their diets overlapped significantly in May and June. Squawfish diet consisted mainly of corixid adults and chironomid larvae and did not overlap significantly with either chinook salmon or steelhead diets. F ood habits changed somewhat as the season progressed and the fish incr eased in size. In 1993, chinook salmon and steelhead fed less than in the previous year and relied more on chironomids. We attribute these d ifferences in diet to the major fluctuations in discharge and lower wa ter temperatures that occurred in the lower American River that year.