Is the pelagic-demersal ratio from fishery landings a useful proxy for nutrient availability? A preliminary data exploration for the semi-enclosed seas around Europe

In this comparative study of fishery production from 14 semi-enclosed marine statistical areas around Europe, GIS techniques were used to estimate some simple geographical parameters in both these areas and their surrounding catchments. Indices included the ratio of catchment area to sea area, chlorophyll-a (Chl-a) pigmentation intensity from remote sensing imagery and a simple index of the degree of geographical enclosure. These indices were compared with the ratio of pelagic to demersal plus invertebrate landings (the P/D ratio). The P/D ratio appears to be a proxy for the differential impact of nutrients on pelagic and benthic system, in that benthic/demersal components are negatively affected by hypoxia resulting from excess primary production, which has less negative effects, (or may even be positive), for pelagic fish production. P/D ratios shows a wide dynamic range from <1.0 for nutrient-limited or oligotrophic seas (e.g. the Aegean and Ionian) to 10 and more for more eutrophic water bodies such as the Black and Azov Seas. Chi-a appears related to the degree of enclosure, perhaps implying significant nutrient run-off from land, while the P/D ratio appears to be correlated with the mean Chl-a value. (C) 2000 International Council for the Exploration of the Sea.