Distribution, Growth, Selective Feeding, and Energy Transformations of Young-of-the-Year Blueback Herring, Alosa aestivalis (Mitchill), in the James River, Virginia

Abstract

A direct relationship existed between standing crops of zooplankton and distribution, growth, and feeding of young-of-the-year blueback herring, Alosa aestivalis, in the James River, Virginia. Zooplankton densities were highest upstream where food consumption and growth rates were correspondingly highest. A progressive downstream decrease and upstream increase in fish abundance occurred during the study. Condition (K) decreased after flooding from Hurricane Camille. Blueback herring fed primarily on copepods (Eurytemora affinis, Cyclops vernalis, and Canthocamptus robertcokeri), but cladocerans (Bosmina sp. and Diaphanosoma brachyurum) were also important. Selection (electivity) was strongest for adult copepods and weakest for copepod nauplii. Selection for copepodites and Bosmina sp. was moderate to weak. Feeding occurred only during daylight. Predation on copepods and copepodites by blueback herring resulted in population dominance by the smaller Bosmina sp. Respiration experiments were carried out in the laboratory. The regression of oxygen consumption on temperature (routine metabolism) was expressed as Log O = -1.4451 + 0.0548 T, where O = oxygen consumption (mg O 2/g wet weight per hr), and T = temperature (C). Energy transformations were computed from growth and respiration values converted to their calorific equivalents. Mean maintenance requirement (% of food assimilated) was 88.3%, compared to 11.7% for growth (% of food assimilated).