A moveable feast: Striped bass predation on alosines during vernal spawning migrations

Spawning aggregations are localized concentrations of a species at a predictable time of year.  Predators often evolve migratory patterns and feeding strategies that take advantage of these aggregations.  During these relatively small spatio-temporal windows, predators may be highly efficient and thus make an outsized impact on prey populations.  Targeted study of these predator-prey interactions can reveal trophic dynamics that are not readily apparent from studies focusing on other habitats and seasons.  Here we describe predator-prey interactions between striped bass (Morone saxatilis) and anadromous alosines (blueback herring Alosa aestivalis and American shad A. sapidissima) during springtime spawning migrations.  In samples of marine striped bass collected from the Connecticut River in May-June, diet composition varied with striped bass size.  The diet of smaller striped bass reflected a generalist feeding strategy; diet became increasing specialized for alosine prey among larger (> 60 cm TL) individuals.  Approximately 21% of the striped bass population fed heavily on alosines.  Striped bass daily ration estimates (% body weight/day) ranged from 0.1-1.6 % for blueback herring and 0.8-7.0% for shad.  Future analyses will incorporate striped bass predation into quantitative modeling exercises to test the hypothesis that striped bass predation on spawning alosines caused recent declines in alosine populations.