Environmental Influences on the Survival of North Sea Cod

Abstract

In general, year-class size of cod shows a positive relationship with temp at the poleward limits of its range and a negative relationship at its equatorward limit. The recent cooling tendency of the North Sea, where cod is near the southward limits of its range, has been associated with an increase in year- class size. Critical statistical analyses of multiyear sea temp data for the Hull-Hanstolm and Leith-Bremen sampling routes, which cover some of the most important cod spawning grounds of the central North Sea, and indices of cod recruitment show significantly high negative correlations between year -class size and the sea surface temps from Jan to May, the period of spawning and larval drift. The relationship is most consistently high in Jan and April, and to a lesser extent in May. The mechanisms by which low temps could increase high survival are discussed and it is suggested that they operate by maximizing the proportion of eggs which hatch by enhancing the chance or a match between hatching and production and by optimizing the metabolic range of the sp