Predation risk on larval gadids by pelagic fish in the Georges Bank ecosystem. I. Spatial overlap associated with hydrographic features

We investigated the relationship between hydrographic variables on Georges Bank and the spatial distribution of larval Atlantic cod (Gadus morhua), la rval haddock (Melanogrammus aeglefinus), and two planktivorous fish, Atlant ic herring (Clupea harengus) and Atlantic mackerel (Scomber scombrus). We c onducted cruises during April-May of 1990, 1994, and 1995 to document spati al distributions and employed logistic regression and a spatial-overlap ind ex to assess relationships between hydrographic variables, spatial distribu tions and spatial overlap between gadid larvae and planktivorous fish. Cod larvae were more abundant in shallow well-mixed areas, while both haddock l arvae and herring were more abundant in stratified areas. Atlantic mackerel occurred in deeper water and had little spatial overlap with the other spe cies. In 1995, the presence of Scotian Shelf water and an intrusion of cont inental slope water altered temperature and salinity distributions and incr eased spatial overlap between cod larvae and herring. The stratified areas offer a higher concentration of prey for larval haddock, however there is i ncreased exposure to planktivorous fish predators, creating a potential tra de-off between predation and starvation. Due to the high abundance of plank tivorous fish and high spatial and temporal overlap, predation is likely an important factor influencing survival of gadid larvae on Georges Bank.