Long-term changes in the trophic level of western Mediterranean fishery and aquaculture landings 1 J.K. Pinnegar, N.V.C. Polunin, and F. Badalamenti 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. Résumé : 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 bival- ves 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 débar- quements de poissons et les débarquements totaux soient devenus plus diversifiés. L’inspection des débarquements de pe- tits 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] Pinnegar et al. 235 Introduction Human exploitation of inshore marine resources dates back thousands of years in the Mediterranean, and most commer- cial fish stocks are considered to be greatly overexploited (Farrugio et al. 1993). The intensive exploitation of fish communities often leads to substantial reductions in the abundance of target species and changes in species composi- tion overall. Large or slow-growing species with late matu- rity decline in abundance more rapidly than their smaller, faster-growing counterparts, and because large species gen- erally feed at higher trophic levels, fishing is expected to reduce the mean trophic level of exploited communities (Pauly et al. 1998a). Changes in the composition of landings often reflect changes in the structure of underlying fish communities (Pinnegar et al. 2002). Because landing data are collected for fisheries throughout the world, these data have been used to assess the large-scale and long-term effects of fishing on commu- nity trophic structure. Pauly et al. (1998a) used aggregated landing statistics from the United Nations Food and Agricul- ture Organisation (FAO), together with estimates of trophic Can. J. Fish. Aquat. Sci. 60: 222–235 (2003) doi: 10.1139/F03-016 © 2003 NRC Canada 222 Received 8 May 2002. Accepted 29 January 2003. Published on the NRC Research Press Web site at http://cjfas.nrc.ca on 31 March 2003. J16887 J.K. Pinnegar. 2 Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, U.K. N.V.C. Polunin. School of Marine Science and Technology, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, U.K. F. Badalamenti. Laboratory of Marine Biology IRMA-CNR, Via G. Da Verrazzano 17, 91014 Castellammare del Golfo (TP), Italy. 1 ©British Crown Copyright 2003. 2 Corresponding author (e-mail: j.k.pinnegar@cefas.co.uk).