Three options for rebuilding the cod stock in the eastern Baltic Sea

摘要

The cod Gadus morhua stock in the eastern Baltic Sea has seen a recent miraculous recovery, mainly due to a drastic decrease in fishing mortality (F). Here we explore 3 options for rebuilding the stock to the size (biomass that can produce the maximum sustainable yield, or B_(msy)) that is required by international law and that can support high long-term yields. The first option implements a fishing mortality of F = 0.3, as is aimed for under the current European Commission management plan. The second option implements in addition the current constraint of a maximum annual increase of 15% in total allowable catches until a catch corresponding to F= 0.3 is reached. The third option freezes the 2010 catch for 2 yr before allowing a linear increase with spawning stock biomass towards 90 % of the maximum sustainable yield. We show that the first option provides the highest catches for the first 3 yr, but fails to rebuild the biomass to the level of B_(msy). The second option rebuilds the biomass above B_(msy) only temporarily and results in the lowest catches over a 10 yr period. The third option rebuilds the biomass above B_(msy) and provides high catches and the highest profit within 10 yr. Within a decade, all 3 options provide several-fold higher biomasses, catches, and profits compared to the current situation, underlining the benefits that can be obtained from proper fisheries management. In comparison, the so-called precautionary management approach (F = 0.6) implemented until 2006 would perform worse in every respect.