Feeding ecology and energy density of juvenile chum salmon, Oncorhynchus keta, from Kuskokwim Bay, western Alaska

Abstract

Juvenile chum salmon from Kuskokwim Bay were sampled for patterns in diet and energy density in 2003 and 2004. Comparisons were made interannually, seasonally, between juvenile size classes, and between sailinity ranges. Sampling was conducted using a modified Kvichak Trawl. Bomb calorimetry was used to obtain energy density values. Feeding success and feeding intensity increased with fish size and season, and was highest in waters with moderate salinity. Feeding success and intensity were lowest for smaller juvenile chum salmon collected early in the season in water with low salinity. Prey composition was similar in both years, but varied with fish size, salinity ranges, and sampling weeks. Calanoid copepods and insects combined made up>50% of all prey items consumed and>80% of the overall prey biomass for all size classes, salinity ranges, and weeks. Feeding by juvenile chum salmon in Kuskokwim Bay appeared to be opportunistic. In 2003, no significant differences in energy density were found. In 2004, energy density decreased significantly from mid-May to mid-June and with increasing fish size. Decreasing energy density with season and size suggests that juvenile chum salmon were allocating the majority of their energy towards growth and smoltification, rather than lipid storage. Results from this study indicate that Kuskokwim bay may provide a suboptimal estuarine rearing habitat for juvenile chum salmon. If seasonally increasing energy demands are not balanced by an increasing food supply, the severe implications potentially include declines in growth rates and possibly overall survival probability of chum salmon juveniles in Kuskokwim Bay.