Do Naked Goby (Gobiosoma bosci) Larvae Exhibit Periodic Vertical Movements in Order to Facilitate Upriver Migration in the Hudson River Estuary?

Estuaries provide high quality nursery habitat for larval fishes due to high productivity, predator protection, and warm temperatures. Previous studies suggest that larval naked gobies (Gobiosoma bosci) are capable of upriver migration and estuarine retention despite net seaward flow. Gobiosoma bosci larvae were collected at a fixed site in the Hudson River estuary in late July of 1998 from 4 discrete depths to provide a time-series of depth-stratified abundance during both a spring and a neap tide. Larvae were concentrated at depth, indicating that depth preference behavior is present and will likely contribute to up-river transport. Harmonic regression analysis revealed that larvae are most abundant in samples at night due to periodic diel vertical migrations in which they move deeper than the sampled region during daytime. Dependent upon hydrography of this site, diel vertical movements may also contribute to up-river transport. Larval depth distribution was not homogenized by spring tide mixing. Large larvae were generally found deeper and moved over a greater vertical range than small larvae. A separate component of the sampling design involved collection of individuals from the length of the river over a series of several weeks. We are using growth rates established from otolith analysis to determine along-river movement rates of larval cohorts in order to allow determination whether the behaviors characterized in this experiment actually facilitate up-river movement