Interactions between bluefish Pomatomus saltatrix (L.) and coastal sea-cage farms in the Mediterranean Sea

Coastal sea-cage farms aggregate large concentrations of pelagic and demersal fish. The large numbers of cultured fish and aggregated wild fish often attract a range of marine mammal predators which may break into cages and attack the cultured fish. To date, predation by a finfish species within sea-cages has not been documented. In the Mediterranean Sea, the bluefish Pomatomus saltatrix (L.) aggregates around sea-cage farms and enters into cages to predate on the cultured fish. We obtained information about the effects of bluefish predation on aquaculture production through a questionnaire that was completed by fish farmers in Spain, Italy, Malta, Turkey, Greece and Cyprus. In addition, we identified the abundance, size and stomach contents of bluefish aggregated around three fish farms on the coast of Spain through visual counts, and from captured bluefish both inside and outside of the sea-cages. Bluefish occurred around fish farms in Spain, Italy, Malta and Turkey. Farmers in SE Spain reported its presence only inside seabream (Sparus aurata) cages, while in Turkey bluefish were reported from inside seabass (Dicentrarchus labrax) and seabream cages. Greatest aggregated biomass of bluefish reached 1049 and 3191 kg at the Altea and Guardamar farms, respectively, with abundance peaking at 4500 individuals at both farms. Size structures differed markedly between farms, with smaller individuals aggregating at Altea. Stomach content analysis revealed that bluefish on the outside of sea-cages consumed pelagic species such as Sardinella aurita and Trachurus mediterraneus, while they predated on seabream once they incurred into cages, often consuming only the tails of many fish. The interaction of bluefish with sea-cage aquaculture is, at present, a problem of local concern restricted to some areas of the Mediterranean Sea, but its widespread distribution suggests this piscivore may be a problematic predator in other regions

Recovery of disturbed deep Posidonia oceanica meadows after protection by antitrawling reefs

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Response of Rocky Reef Top Predators (Serranidae: Epinephelinae) in and Around Marine Protected Areas in the Western Mediterranean Sea

International audienceGroupers species are extremely vulnerable to overfishing and many species are threatened worldwide. In recent decades, Mediterranean groupers experienced dramatic population declines. Marine protected areas (MPAs) can protect populations inside their boundaries and provide individuals to adjacent fishing areas through the process of spillover and larval export. This study aims to evaluate the effectiveness of six marine reserves in the Western Mediterranean Sea to protect the populations of three species of grouper, Epinephelus marginatus, Epinephelus costae and Mycteroperca rubra, and to understand in which circumstances MPAs are able to export biomass to neighbouring areas. All the studied MPAs, except one where no grouper was observed, were able to maintain high abundance, biomass and mean weight of groupers. Size classes were more evenly distributed inside than outside MPAs. In two reserves, biomass gradients could be detected through the boundaries of the reserve as an indication of spillover. In some cases, habitat structure appeared to exert a great influence on grouper abundance, biomass and mean individual weight, influencing the gradient shape. Because groupers are generally sedentary animals with a small home range, we suggest that biomass gradients could only occur where groupers attain sufficient abundance inside MPA limits, indicating a strongly density-dependent process

Recapturing fish escapes from coastal farms in the western Mediterranean Sea: Insights for potential contingency plans

Escape incidents of farmed fish involve economic losses to fish farms, interactions with local fisheries and environmental impacts to coastal ecosystems. More attention should clearly be paid to preventive measures. It is also essential to develop and establish contingency plans in case of escapes, to mitigate potentially negative socioeconomic and environmental impacts. Three mark-and-recapture experiments simulating escape incidents of sea bass (N = 1000 ind.), sea bream (N = 1000 ind.) and meagre (N = 1000 ind.) were carried out at three coastal fish farms located along the Mediterranean Coast of Spain. First, targeted experimental fishing trials in collaboration with artisanal netters were attempted at each location as potential fast-response contingency plans for recapturing escapees. Targeted fishing was successful on meagre (N = 38 ind., CPUE: 2.2 ind 10 m−2 h−1) and sea bream (N = 8 ind., CPUE: 1.3 ind 10 m−2 h−1), while no sea bass were recaptured. Secondly, recaptures reported from local fishermen (professional and recreational) during the study period were also considered. Altogether, total recapture rates were similar among the three species (sea bass: 5.4%; sea bream: 7.1%; meagre: 8.7%), although the spatial and temporal observations of recaptures varied among species. Recreational fishermen were the only contributors, recapturing 54 tagged sea bass (angling: 85%; spear-fishing: 15%) in mainly shallow coastal waters and about three km distance from the fish-farm during the weeks after release. A total of 71 escaped sea bream were recaptured by both recreational and artisanal fishermen, contributing similarly (recapture rates: 47.9% and 40.8% of total, respectively). Most sea bream recaptures were during the first nine days after release (86% of total recaptures), mainly near the farm facilities (95%), mainly by experimental and artisanal netting (38 and 47 individuals respectively) again near the facility. In parallel, an underwater visual census was carried out at coastal locations and Natura 2000 sites in each study area, to assess the presence of escapees in marine habitats of special interest. Neither escaped sea bass nor escaped meagre were observed during underwater surveys, and only three tagged sea bream were found together at artificial reefs. Given that recaptures of tagged fish differed among fish species and fishing techniques following simulated escape incidents at W-Mediterranean coastal facilities, diverse potential contingency plans are here discussed.This research was part of ESCAFEP project, cofunded by the European Fisheries Fund (EFF) and the Biodiversity Foundation, in collaboration with the Spanish Ministry of Agriculture, Food and the Environment