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 marin e statistical areas around Europe, GIS techniques were used to estimate som e simple geographical parameters in both these areas and their surrounding catchments. Indices included the ratio of catchment area to sea area, chlor ophyll-a (Chl-a) pigmentation intensity from remote sensing imagery and a s imple index of the degree of geographical enclosure. These indices were com pared 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 impac t of nutrients on pelagic and benthic system, in that benthic/demersal comp onents are negatively affected by hypoxia resulting from excess primary pro duction, which has less negative effects, (or may even be positive), for pe lagic 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 an d 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 w ith the mean Chl-a value. (C) 2000 International Council for the Exploratio n of the Sea.