Winter Feeding and Changes in Somatic Energy Content of Age‐0 Pacific Herring in Prince William Sound, Alaska

During the winter of 1996–1997, somatic energy content and diets of age‐0 Pacific herring Clupea pallasi from Prince William Sound, Alaska, were examined. From October to March, the standard length of age‐0 recruits continued to increase, indicating either growth or mortality of smaller fish. The whole‐body energy content averaged 4.4 kJ/g wet weight for fish captured in October and increased to 5.0 kJ/g wet weight in November. Thereafter, somatic energy continually declined, reaching 3.9 kJ/g wet weight in March. The December–March decline in nutritional status of the recruits verified that the energy derived from feeding was not enough to meet metabolic needs. The energy density of taxa found in the diets remained steady through the winter and increased in March. Total zooplankton biomass, however, decreased as the mean water temperature decreased. Estimated assimilation rates were lower for smaller fish than larger fish and decreased as winter progressed. We concluded that juvenile herring rely on energy stores to overwinter and that smaller fish are more likely to be affected by starvation. Also, the duration of overwinter starvation may be related more to photoperiod than to mean water temperature.