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

Abstractde Castro, C., Wright, P. J., Millar, C. P., and Holmes, S. J. 2013. Evidence for substock dynamics within whiting (Merlangius merlangus) management regions. – ICES Journal of Marine Science, 70: 1118–1127. 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 subpopulation within a larger metapopulation. A key characteristic of metapopulations is asynchrony in the dynamics of component subpopulations. In this study, indices of recruitment and spawning–stock biomass (SSB) were developed to test for asynchrony across putative subpopulations in the North Sea and west of Scotland. Differences in SSB and recruitment trends were detected, consistent with expectations from metapopulation dynamics. At least three different subpopulation 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 the northern and southern North Sea subpopulations was associated with the change in bathymetry that extended from the coast of Norfolk in England to the southern tip of Norway. The current management system for whiting in the North Sea assumes a unit stock, which is contrary to current sources of biological evidence and seems inappropriate. Consideration of a north–south split along the boundary detected should be beneficial for both assessment and management of the resource.

Quota allocation in mixed fisheries: a bioeconomic modelling approach applied to the Channel flatfish fisheries

Marchal, P., Little, L. R., and Thébaud, O. 2011. Quota allocation in mixed fisheries: a bioeconomic modelling approach applied to the Channel flatfish fisheries. – ICES Journal of Marine Science, 68: 1580–1591. A simulation modelling approach is used to assess the respective performances of different regimes of quota allocation (fixed or transferable), quota ownership (owned or not by fishers), and taxation for catching fish above quota. The simulations account for a variety of fleet behaviours (ranging from fixed by tradition to dynamic economics-driven). The modelling framework is applied to the Channel flatfish mixed fisheries. Transferable quota allocation regimes would particularly benefit small netters and beam trawlers, which would achieve a profit of €50–150 million without compromising the conservation of eastern Channel sole, but it could impair the sustainability of other stocks. If quota is owned by fishers, the least fishing-efficient fleet stops fishing, but makes substantial profit from leasing quotas to beam trawlers and to small and large netters, which remain actively fishing. The highest economic return for quota owners (€200–300 million) is achieved when effort allocation is fixed by tradition. The profit achieved by small netters is greatest when fleets are almost entirely economics-driven. Increasing overquota landing taxes generally leads to conservation benefits for all stocks, but at the expense of lower profitability for the fishery overall.