ABSTRACT
Two south-west Mediterranean fish farms were monitored over a period of 22 months to test if sea-cage fish farms act as settlement habitats for juvenile fish. Twenty juvenile fish species were found to settle at farms throughout the year. Fish assemblage composition varied markedly over time and was dependent on the spawning period for each species. The most abundant species were Obladamelanura, Atherina sp., Diplodussargus, Boopsboops and Lizaaurata. Up to 3783+/-1730 individuals/cage were found closely associated with the cages. Highest densities were observed during the warmer summer and autumn months. Zooplankton sampling and stomach content analyses of the most abundant species were done to assess prey availability, selectivity and diet overlap among species. Copepods were the main prey item for all juvenile fish species, irrespective of fish size. Ivlev's Index indicated that food was not a limiting factor for juvenile fish at farms. Furthermore, food pellets from the farm affected the food chain by modifying the fatty acid profiles of farm-associated zooplankton and juveniles of L. aurata and O. melanura. These results show that aquaculture can directly influence the body composition of juvenile fish that recruit to sea-cage fish farms.
Subject(s)
Aquaculture , Fishes/growth & development , Animals , Censuses , Diet , Ecosystem , Environmental Monitoring , Fatty Acids/analysis , Fishes/metabolism , Food Chain , Gastrointestinal Contents/chemistry , Gastrointestinal Contents/microbiology , Housing, Animal , Lipids/analysis , Population , Zooplankton/isolation & purification , Zooplankton/metabolismABSTRACT
Marine protected areas (MPAs) could be useful as fisheries management tools for the exportation of pelagic eggs, larvae and adult fish. A decreasing gradient of fish biomass across MPAs boundary may indicate export. We determine whether gradients of decreasing biomass of fish assemblage occurred in Tabarca Marine Reserve over two habitats with different continuity across the boundaries, to test if the patchy nature of the marine environment might act as a barrier for the fish export. In general, significant decreasing gradients in total fish biomass and biomass of some species were observed on P. oceanica and rocky substrates, independently of their different continuity through the reserve boundaries. Changes in the multivariate structure of the fish assemblage were correlated with the distance from integral reserve. All of these results support the hypothesis that the exportation of adult fish from Tabarca Marine Reserve occurs, and this process may influence the surrounding fished areas.
