Barbara Sullivan , J. Williams, D. Van Keuren, R. G. Lough and J. Manning,Planktonic hydroids, primarily Clytia gracilis, are previously unrecognized competitors and predators of larval fish on Georges Bank. Horizontal and vertical distribution of these normally benthic predators appears to be strongly controlled by physical processes of turbulence and advection which result in their accumulation on the Bank's southern flank near patches of larval cod and haddock. Impacts of these predators on larval fish will be strongly dependent on hydroid abundance and degree of overlap between their distribution and that of larval fish. Counts from closely spaced (5 mi) bongo grid surveys and vertically stratified MOCNESS tows indicate highly overlapping distributions of hydroids and fish larvae during spring of both 1994 and 1995. Densities of hydroids were 1-6 hydranths l-1 in the cold, well-mixed water mass inshore of the 60 m isobath where the shelf-slope front intersected the bottom. We are using correlation between abundance of hydroids and hydrographic features to infer physical mechanisms controlling their distribution and abundance. Impacts of hydroids on larval fish will be estimated from field abundance together with information on feeding and growth rates of hydroids in enclosure experiments.