Attraction of wild fish to sea-cage fish farms in the south-western Mediterranean Sea: spatial and short-term temporal variability

Abstract

Aggregations of wild fish were counted around 9 floating sea-cage fish farms along a 300 km stretch of the Spanish coastline in the southwestern Mediterranean Sea. Each fish farm cultivated Sparus aurata and Dicentrarchus labrax in 6 to 16 floating sea cages between 10 m and 7.4 km from the coast. During September and October 2001, assemblages of fish were counted on 3 separate days at each of 9 farms. Six 5 min rapid visual counts using SCUBA and covering 11 250 m 3 were performed within each farm complex and at open water control sites 200 m distant from farms. Abundance (52 to 2837×), biomass (2.8 to 1126 ×) and number of species (1.6 to 14 ×) were greater in fish farm counts than control counts at all locations. Twenty-seven species were recorded at fish farms, with 2 families, Sparidae (12 species) and Carangidae (4 species), being particularly abundant. Over 85% of farm-associated fish were of adult size. Assemblages of wild fish differed greatly between farms separated by 10s to 100s of km, although there was some evidence to suggest that similar assemblages occur at farms separated by 100s of m to several km. Abundance, biomass and number of species differed among fish farms, with all 3 variables negatively correlated with distance of farms from shore and positively correlated with size of farms. Limited variability of wild fish assemblages and abundance of the dominant taxa at each farm among times sampled indicated some degree of temporal stability on a scale of several weeks. Due to the strong aggregative effect of fish farms, possible residence of fishes for periods of weeks to months and the prohibition of fishing within farm leasehold areas, we suggest that coastal sea-cage fish farms may act as small (up to 160 000 m 2), pelagic marine protected areas (MPAs). Furthermore, at farms where wild fish are abundant, ecological interactions that may influence both wild fish stocks and the impact of farms must be considered.

Ecological Features of Large Neotropical Reservoirs and Its Relation to Health of Cage Reared Fish

“…Attractiveness is directly related to availability of food resources, especially remains of feed. These are similar to the findings for marine aquaculture in coastal ecosystems, which also found the effect of attractiveness of these systems (Boyra et al, 2004;Dempster et al, 2002;Håkanson, 2005). The results presented allow the conclusion that remains of feed are used by omnivorous species with large feeding plasticity, which certainly justifies its dominance in sites used for cage aquaculture.…”

“…These feed losses can cause problems related to eutrophication (Beveridge, 1984) and/or be used as a food resource by local biota (Beveridge, 2004;Håkanson, 2005;Ramos et al, 2008;Vita et al, 2004), resulting in ecological changes around these systems (Beveridge, 2004;Håkanson, 2005;Ramos et al, 2008). Besides these impacts, several authors as Agostinho et al (2007); Beveridge (1984Beveridge ( , 1996Beveridge ( e 2004; Dempster et al (2002) Zanatta et al (2010) discuss the problems of this activity in coastal and inland waters. These authors cite impacts upon water quality and sediment which have implications on the structure of benthic communities, plankton and fish, and furthermore, the inherent scapes of caged fish.…”

First occurrence of Caprella scaura Templeton, 1836 (Crustacea: Amphipoda) on off-coast fish farm cages in the Mediterranean Sea

“…Moreover, fish farms attract large aggregations of wild fish in their surroundings (Dempster et al 2002). This concentration of fish increases the fishing pressure around the farms, with commercial and recreational fishing vessels moving around different fish farms along the same coastal area (Arechavala-Lopez et al 2011).…”

Aggregations of wild Atlantic Bluefin Tuna (Thunnus thynnus L.) at Mediterranean offshore fish farm sites: Environmental and management considerations

“…Akyol and Ertosluk (2010) recorded ABT at Turkish sea bream and sea bass fish farms. Dempster et al (2002) and Fernandez-Jover et al (2008) observed ABT at two sea bream and sea bass cages sited off the Spanish coast. Moreover, fish farmers and fishermen from various sites around the Mediterranean have reported an increase in the number and frequency of occurrence of aggregated ABT in the vicinity of tuna farms.…”