Parental migration, climate and thermal exposure of larvae: spawning in southern regions gives Northeast Arctic cod a warm start

Temporal variability in environmental conditions met by early life stages is considered a key driver of fluctuations in recruitment and abundance of fish stocks. Variability in spawning grounds selected by the parental population can change the environmental conditions encountered by the offspring, with consequences for recruitment. We compared how changes in spawning ground distribution and interannual climatic variation influenced the temperature exposure of eggs and larvae of Northeast Arctic cod Gadus morhua along the Norwegian coast. By using a general circulation model and 20 yr of forcing data, we tracked eggs and larvae from various spawning grounds and mapped temperature exposure, potential growth rate and theoretical survival probabilities in space and time. We found that the temperature history integrated over the early larval stages decreased by almost 4°C from southern to northern spawning grounds. Thus, variations in spawning ground usage have the potential to outweigh the interannual environmental variability, and consequently, shifts in spawning grounds may be more important than climatic variability in determining recruitment success. The long-term northbound shift and truncation of spawning grounds of the Northeast Arctic cod is thought to be caused by a size-selective trawl fishery in the Barents Sea, which promotes smaller and early maturing individuals to spawn farther north. This selection could increase offspring vulnerability to climatic changes, thereby strengthening the link between climate and recruitment.