Modelling recruitment and abundance of Atlantic cod, Gadus morhua, in the eastern Skagerrak-Kattegat (North Sea): evidence of severe depletion due to a prolonged period of high fishing pressure

摘要

In exploited fish populations, most of the variance in stock size is attributed to highly variable recruitment. Understanding the recruitment process and how it relates to stock size (i.e. the often sought for stock-recruitment functions) and to environmental stochasticity is of central importance to fisheries science and management. However, in many, if not most, exploited marine fish populations, fishing mortality is the other major force affecting stock size. Here we explored the effects of several biotic and abiotic variables on Atlantic cod (Gadus morhua) recruitment and abundance in the eastern Skagerrak-Kattegat area by deploying a GAM (general additive model) type of modelling. It was recognised that fishing pressure and not variable environment via recruitment was the pivotal variable explaining the dynamic of the cod stocks. Due to a prolonged period of high fishing intensity, local cod stocks in the study area, such as the one in the Kattegat may be considered as severely depleted, or possibly, on the verge of total extinction. It was further observed that population biomass and recruitment were substantially uncoupled, which may be regarded as an effect of continued transportation of recruits from spawning aggregations in adjacent areas such as the North Sea.