importance of life stage to population connectivity in whiting (Merlangius merlangus) from the northern European shelf

Juvenile movements are rarely considered in studies of connectivity. This study investigates movements in juvenile and adult life stages of an ecologically important temperate piscivore, the whiting (Merlangius merlangus). Adult movement was assessed from tag-recapture data collected between 1958 and 1980 around the coast of Scotland. Displacement distances ranged from 53 to 123 km. Adults rarely dispersed offshore in the North Sea, and exchange with the west of Scotland was negligible. Connectivity between nursery and spawning grounds was investigated using otolith microchemistry. Five juvenile nursery areas were discriminated with an accuracy of 75-85%. Comparing isotopic signatures of adults and juveniles indicated that several nursery areas contributed to each spawning aggregation. The lack of evidence for return migrations suggested an opportunistic and non-philopatric recruitment strategy within a single population unit. Differences in the proportion contribution of juveniles to adult aggregations also indicated that the “value” of nursery areas differed and the Scottish west coast could be viewed as a net source of recruits to the North Sea. Given the extent of juvenile dispersal, this study highlights the fact that all stages of the life cycle should be considered in studies of connectivity.