Spatial and temporal variability in the diet of juvenile Pacific herring (Clupea pallasi) in Prince William Sound, Alaska

The diet of juvenile Pacific herring, Clupea pallasi, from four bays in Prince William Sound, Alaska, varied spatially and seasonally. In Zaikof Bay, which was sampled in each season, stomach fullness of this herring was highest in May and declined significantly through the winter. Diversity of prey taxa in the diet was highest in June, after the spring phytoplankton bloom. In October, Oikopleura species were dominant in the fish diets of all bays. In March, fish eggs, Cirripedia nauplii, small Calanoida, and large Calanoida were the dominant prey in Eaglek, Simpson, Whale, and Zaikof bays, respectively. Energy density of stomach contents was highest in May, highlighting the importance of high lipid copepod taxa in Zaikof Bay. Estimated assimilation rates suggest that the diets of smaller age-0 herring provide close to maintenance levels of energy prior to winter. Therefore, variability in diet composition and diet energy density could account for relative differences in nutritional conditions of age-0 herring in Prince William Sound.