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

Abstract

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 (<3 km). The bulk of meagre recaptures were during the first two days after release (>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.