Bottom-up control regulates fisheries production at the scale of eco-regions in European seas

We used primary productivity data derived from remote sensing images and catch data for the period 1998 to 2004 to characterize the productivity of eco-regions in the northeast Atlantic, Mediterranean, Black and Baltic Seas, and then analyzed the strength of the trophic linkage between primary productivity and marine fisheries production in European seas. Mean annual primary production (PP) derived from an ocean-color based model was highly contrasted among eco-regions, exceeding 500 g C m(-2) yr(-1) in the Marmara and North Seas but being less than 150 g C m(-2) yr(-1) in the Faroes, Adriatic-Ionian and Aegean-Levantine Seas. Fisheries production expressed in mean annual yield and primary production required to support catches (PPR) varied greatly among eco-regions, from 0.02 t km(-2) and 0.7 g C m(-2) yr(-1) for the oceanic northeast Atlantic eco-region to 6 t km(-2) and 130 g C m(-2) yr(-1) in the Marmara Sea respectively. Linear regression models showed significant positive relationships between PP and yield as well as between PP and PPR, suggesting a strong linkage between marine productivity and fisheries production in European seas. Moreover, this bottom-up control appeared consistent over time: recent mean annual yield for the period 1998 to 2004 reflected the long-term yield averaged over the last 3 decades. We argue that such large-scale coupling is due to energy transfer along the food web (from phytoplankton to predators) through predation processes, primary productivity driving the production of living marine resources and their exploitation at the scale of eco-regions. Our findings have an important bearing for ecosystem approaches to fisheries, particularly for the estimation of the capacity of eco-regions with regard to sustainable exploitation. This is further relevant in a context of climate change, because variations in PP linked to global warming could strongly modify fisheries production in the future.