A sustainability criterion for the exploitation of North Sea cod

The spawning stock biomass of cod, Gadus morhua, in the North Sea has been in decline for many years. There is evidence that at low stock sizes recrui tment is reduced. Using non-parametric methods, equilibrium spawning stock biomass and yield curves are constructed, which are consistent with annual observations that show the continuous decline in the spawning stock can be explained by high fishing mortality rates. A new reference point, G(loss), is defined, which corresponds to the stock replacement line at the lowest o bserved spawning stock size. Recent fishing mortality rates yield replaceme nt lines with a high probability of exceeding G(loss) and therefore indicat e there is a high probability of further stock decline and a possibility of collapse. The replacement line is very sensitive to fishing mortality rate which makes managing the stock at high rates of exploitation risky. A redu ction in fishing mortality rate by approximately 30-40% is required to ensu re the probability of collapse is small. (C) 1998 International Council for the Exploration of the Sea.