Temporal, Intra-population Differences in Energy Allocation and Use by American Shad (Alosa sapidissima) During the Spawning Migration

Abstract

The intra-population tissue weight dynamics and bioenergetics of American shad (Alosa sapidissima) were studied during the freshwater migration in the Connecticut River. Emphasis was on the extent and significance of temporal differences in the magnitude and rate of depletion of stored body reserves. This was accomplished by the comparison of body reserves of shad sampled at various locations and times along the migratory route. Somatic weight loss and associated energy depletion was extreme (45–60%); up to 50 and 70% of available body protein and lipid, respectively, were used to fuel the migration. The extent of reserve depletion was sex- and size-specific. Small individuals and males suffered the greatest tissue depletion. High water temperatures accounted for the reduced energy efficiency of late migrant shad (average of 42 vs. 24 KJ∙kg−1∙km−1 expended by earlier migrants), and resulted in, greater depletion of total body reserves. More extensive depletion may contribute to the higher mortality reported among this component of the population. Gonad development was complete prior to entry into the river. This may spare somatic reserves during the freshwater fast and hence maximize survival. The pattern and extent of energy utilization in other anadromous fish species are discussed with reference to possible influence on demographic parameters, especially the repeat spawning habit.Key words: American shad, Alosa sapidissima; energetics, allocation, weight loss, temporal differences, Connecticut River, migration