Abstract
AbstractMorethan25%of Greek¢shfarmsand20%of Greekhatcheries of gilthead sea bream (Sparus aurata)andsea bass (Dicentrarchus labrax) are located along theWestern Hellenic coast. The part of sea bream pro-duction is about 60% of thetotalproductionof thesespecies. During the last decade, a spectacular in-creaseinboththenumberoffarmsandtheirproduc-tion, accompanied by a substantial price decreaseand modi¢cation of their structure and functioning,has been recorded. These changes resulted in themaintenanceincagesoflargeindividuals(morethan500g) of gilthead sea bream which are potentialspawners. The study, based on both the maturitystage and the decrease in individual mean weightsduring the reproductive period of the species, con-¢rmed reproduction in cages. In parallel, during thelast5yearsaremarkableincrease(about80%)inseabream landings from the ¢sh trap ¢sheries of theMessolonghi-Etoliko lagoon, which is a typical nur-sery for the species, was recorded.The increase wasaccompanied by a decrease both in price and meansize of the 0-group individuals. The possible in£u-ence of the rearingactivities inthearea, thedensity-dependent mechanisms and the negative impacts ofthis unintentional enhancement of the traditionallagoon¢sheriesof theareaarediscussed.Keywords: aquaculture, gilthead sea bream, eco-logical impact, carrying capacity, density depen-dence, Messolonghi-EtolikolagoonIntroductionThe rapid expansion of aquaculture is accompaniedbyan increasedawareness concerning the impact of¢sh rearingonthe environment.These environmen-taleiectsareexpressedatalargevarietyof¢eldsandspatiotemporal scales (Machias, Karakassis, Gian-noulaki, Papadopoulou, Smith & Somarakis 2005).However,therecentspectacularevolutionof theHel-lenicaquacultureindustry,basedmainlyongiltheadseabream(Sparusaurata)andseabass(Dicentrarchuslabrax), masks the potential environmental conse-quences on the coastal zone. In particular, duringthe last 20 years both the number of ¢sh farms andtheir production have increased greatly from12 and100t in 1985, to 269 and 85000t in 2004 respec-tively (source: Mariculture Federation of Greece),with the relative contribution of the two species re-maining rather stable during this period (60% of seabream). In Hellenic waters, the impacts of ¢sh farmsonthemarineecosystemhavebeenwidelyinvesti-gated,includingeiectsonthewaterqualityininten-sive rearing areas (Western Hellenic coast: Belias,Bikas, Dassenakis & Scoullos 2003), on the sea bedand the watercolumn (Aegean and Ionian Sea: Kar-akassis,Tsapakis, Hatziyanni, Papadopoulou & Plaiti2000) and on possible changes of ¢sh assemblagestructureanddiversityclosetotheseafarms(AegeanSea: Machias, Karakassis, Labropoulou, Somarakis,Papadopoulou& Papaconstantinou2004).Worldwide, the interactions between wild andfarmed populations are frequently focused on the
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