José Maria Bellido

• Biodiversity Journal, 3 (1): 069-078

  Maria Grazia Pennino & José Maria Bellido
  Can a simple Pelagic-Demersal ratio explain ecosystem functioning?

  ABSTRACT
  In quantity terms, the proportion of the total marine fish landings which is accounted for by pelagic fish has increased continuously, with large oscillations reflecting natural variations of resources productivity and fishing strategies. The aim of the present work is to assess this trend in different Mediterranean fishing areas from 1970 to 2005 using the Pelagic/Demersal ratio (P/D). The P/D ratio is a simple ecosystem indicator based on commercial landings and provides a measure of the status of the fish community also in data-poor fisheries situations. Simple statistical techniques were used to study fishery ecosystem through the collection and comparison of geographical parameters as chlorophyll-a (Chl-a) pigmentation intensity and rainfall. In all the Mediterranean the P/D ratio appears to be correlated with the mean Chl-a value and increased with time, this may depend both on a better availability of nutrients in the water column and the overexploitation of resources. The areas where there is a greater presence of zones of upwelling and nutrient inputs are the ones with the highest values of the index. Additionally, comparison with the analysis of the multispecies landings shows that the trend of the index is influenced by the landings of Clupeidae and Engraulidae, a fact showing that fisheries in these areas are increasingly relying on the smaller, short-lived fishes from the lower part of marine food webs.

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