Optimum temperature and food-limited growth of larval Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on Georges Bank

We estimated recent growth of Atlantic cod (Gadus morhua) and haddock (Metahogrammus aeglefinus) larvae collected on the southern flank of Georges Bank in May 1992-94 from the ratio of RNA to DNA (RID) and water temperature. Growth of both species increased with water temperature to about 7degreesC and then decreased. The highest growth rates were observed in May 1993 at water temperatures around 7degreesC. These data confirm an earlier observation of comparable temperature optima for growth of Atlantic cod and haddock larvae in the north-West Atlantic. Comparisons of field growth rates and temperature optima with data for larvae cultured at high temperatures and prey densities in the laboratory suggest that growth may have been food-limited at higher temperatures on Georges Bank. Given that 7degreesC is the long-term mean water temperature on the southern flank in May and that climate models predict a possible 2-4degreesC rise in water temperatures for the western North Atlantic, our findings point to a possible adverse effect of global warming on Atlantic cod and haddock.