Spatial and temporal depletion of haddock and pollack during the last century in the Kattegat-Skagerrak

By reconstructing a centennial time-series of stock spatiotemporal dynamics and commercial landings, the long-term erosion is shown of the spatial structure of haddock and pollack in the Skagerrak and Kattegat that resulted in their regional depletion in the area. The erosion occurred in parallel with the development of the industrial fisheries and the peak in landings was followed by a decline in adult biomass and individual size. Also found was that pollack adult biomass was significantly lower for elevated water temperatures, while the response for haddock was less clear. However the main decline of both stocks and the disappearance of their adult aggregations occurred several decades before the unprecedented warming trend, which started in the Skagerrak and Kattegat only in the mid-1980s. These findings also suggest that haddock in the study area is not responding to the scale on which the management of the neighbouring North Sea haddock stock is currently performed. These results illustrate the hazardous consequences of prolonged overfishing on the population structure of commercially exploited stocks and the lack of knowledge which ultimately leads to spurious assumptions on the recovery potential of many fish stocks. Also argued is that the continuation of commercial fishery at sustainable levels adjusted to the present stock productivity might hinder the recovery of these depleted stocks for a long period of time.