Seasonal energy dynamics of young-of-the-year Hudson River striped bass

Mortality of young-of-the-year (age-0) temperate fish during the winter has often barn attributed to depletion of energy reserves, which results in st arvation. We examined the seasonal energy cycle in age-0 Hudson River strip ed bass Morone saxatilis with field collections and laboratory experiments to determine if winter mortality could be attributed to starvation. Composi tional analyses of wild fish showed that age-0 striped bass stored energy i n the form of lipids prior to winter and then experienced an energy deficit , losing 7 and 16% of total body energy, respectively, in the two winters e xamined. Compositional analyses were performed on fish from a laboratory ex periment in which age-0 striped bass were exposed to ambient winter conditi ons. Mortality was associated with low energy levels in unfed treatments bu t not when food was provided daily. In neither treatment did starvation app ear to be the ultimate cause of death, as wild fish were captured with ener gy levels lower than those observed among mortalities in either experimenta l treatment. Our results suggest that starvation is not the only cause of w inter mortality that produces the observed size-dependent patterns among ag e-0 striped bass. Other stresses associated with overwintering likely inter act with the energy deficit to determine the size-dependent patterns of win ter mortality that are observed in temperate fishes.