Recruitment of Atlantic cod stocks in relation to temperature and advection of copepod populations

The recruitment of Altlantic cod stocks shows different responses to temperature changes. Cod stacks inhabiting the lower temperature range show generally an increase in recruitment with increasing temperature, while cod stocks inhabiting the uppermost part of the temperature range show a decrease in recruitment with increasing temperature. In the present paper possible functional relationships between temperature and cod recruitment mechanisms are analysed. Temperature influences the recruitment processes in a large number of ways; partly directly on vital rates in cod, and partly indirectly through trophic transfer. The copepod Calanus finmarchicus is the dominant prey species for the early stages of cod. It proposed that the recruitment-temperature relation of Atlantic cad is a proxy for the food abundance during the early stages, and that advection of C. finmarchicus from the core production regions in the central parts of the North Atlantic Subpolar Gyre to the fringes where the cod stocks have their habitats explains the particular recruitment response to temperature.