HATCHING, ESTUARINE TRANSPORT, AND DISTRIBUTION OF LARVAL AND EARLY JUVENILE ATLANTIC TOMCOD, MICROGADUS TOMCOD, IN THE HUDSON RIVER

Atlantic tomcod larvae, hatching in late February and early March 1975 and 1976 into a regime of accelerating river flows, were moved rapidl y downriver from milepoint 42-54 (MP 0 is the estuary mouth) to the mo st seaward reaches of the estuary. This resulted in a spatiotemporal d istribution markedly different from that of other Hudson River fish sp ecies. Peak tomcod density on posthatch sampling dates was observed mo st frequently at the George Washington Bridge station (MP 11). Correla tion between movements of the 1.0 parts per thousand salt front and mo vements of the age-0 tomcod population was high (r = 0.82); and may ha ve been enhanced by high freshwater flows. The population epicenter wa s always seaward of the 1.0 parts per thousand salt front and mean dis tance between the two was 16-17 km. Moved by tidal and freshwater flow s, the tomcod population oscillated between MP 0 and MP 43 during Marc h-May 1973-1976. Location of the population epicenter after mid March was predicted (r(2) = 0.76) to be seaward of the Tappan Zee Bridge (MP 30) when freshwater flows were greater than 450 m(3) s(-1). During fl ow regimes greater than 1,290 m(3) s(-1), the epicenter was predicted to be seaward of the George Washington Bridge (MP 11). An optimum-allo cation sampling design for age-0 tomcod showed that 58% of the total e ffort from mid March to early June should be directed to the river reg ion between MP 0 and MP 24, a region largely ignored in previous studi es.