Evidence for substock dynamics within whiting (Merlangius merlangus) management regions

Whiting in the North Sea and Eastern Channel is currently assessed as a single management unit. However, several studies suggest that this stock may be comprised of more than one sub-population within a larger metapopulation. A key characteristic of metapopulations is asynchrony in the dynamics of component sub-populations. Consequently, in this study, indices of recruitment and spawning-stock biomass were developed to test for asynchrony across putative sub-populations in the North Sea and to the west of Scotland. Differences in SSB and recruitment trends were detected consistent with expectations from metapopulation dynamics. At least 3 different sub-population components; southern and northern North Sea and west of Scotland, were indicated on the basis of differing trends. Analysis of spatial distribution suggested that the boundary between northern and southern North Sea sub-populations was associated with the change in bathymetry that extended from the coast of Norfolk in England to the southern tip of Norway. Consequently, the current management unit in the North Sea seems inappropriate and the assessment of the stocks should benefit from a north – south split along the boundary detected.JRC.G.4-Maritime affair