Long-term changes in the trophic level of western Mediterranean fishery and aquaculture landings

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Abstract:

We explored changes in western Mediterranean fishery and aquaculture landings using trophic level (TL) estimates derived from nitrogen stable isotope analysis combined with geographically detailed fishery data collated by the General Fisheries Council for the Mediterranean (GFCM). Our analyses confirmed earlier suggestions that there has been a significant decline in the mean trophic level of Mediterranean landings (by ~0.15 TL over 26 years). However, this decline is suggested to be almost entirely a result of increased landings of bivalve molluscs from mariculture and not due to changes in landings from capture fisheries. The mean trophic level of finfish landings has not changed significantly since 1973, although both fish and total landings have become significantly more diverse. Inspection of small pelagic fish landings revealed a marked decrease in the contribution played by anchovy and replacement of this species by sardine. Since 1981, cage culture of high trophic level species such as sea bass (Dicentrarchus labrax) and seabream (Sparus aurata) has become increasingly important, such that when clupeoid landings were excluded from the analyses, the mean trophic level of finfish landings was actually demonstrated to have increased over the past 26 years.

L'estimation des niveaux trophiques (TL) par des analyses des ions stables d'azote combinée à des données sur les pêches commerciales comportant des informations géographiques détaillées et compilées par la Commission générale des pêches pour la Méditerranée (GFCM) nous a permis d'étudier les changements dans les débarquements des pêches commerciales et de l'aquaculture en Méditerranée occidentale. Nos analyses confirment les suggestions antérieures qui veulent qu'il y ait eu un déclin significatif du niveau trophique moyen des débarquements en Méditerranée (de ~0,15 TL en 26 ans). Cependant, ce déclin est dû, croyons-nous, presque entièrement à l'augmentation des débarquements de bivalves provenant de l'aquaculture et non à des changements dans les débarquements de poissons provenant de la pêche. Le niveau trophique moyen des débarquements de poissons n'a pas changé significativement depuis 1973, bien que les débarquements de poissons et les débarquements totaux soient devenus plus diversifiés. L'inspection des débarquements de petits poissons pélagiques révèle un déclin marqué de la contribution des anchois et leur remplacement par les sardines. Depuis 1981, la culture en cages d'espèces de haut niveau trophique, telles que le bar (Dicentrarchus labrax) et la dorade (Sparus aurata), est devenue de plus en plus importante, si bien que, si l'on exclut les débarquements de clupéidés des analyses, il apparaît, en effet, que le niveau tropique moyen des débarquements de poissons a augmenté au cours des 26 dernières années.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 1, 2003

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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