WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 31 (CONTINUED ON PAGE 32) trophic resources. • Interference competition: escaped seabass and seabream may compete directly with conspecifics or other species and interfere with foraging, survival and reproduction by preventing their physical establishment in natural habitats. • Predation impact: escaped seabass and seabream affect wild conspecifics or other marine species directly through predation on them. • Competition over mating opportunities may exist when wild seabass and seabream are outcompeted by escaped fish or the occurrence of escaped fish disrupts the natural spawning pattern of wild fish. • Escaped fish could spread diseases to conspecifics or other species. Based on the available information regarding these impacts, the environmental risk assessment of seabass and seabream escapes can be characterized as having low intensity, low probability and high uncertainty. Regarding the transfer of disease, there is no clear evidence of pathogen transmission, except for some examples. Diamant (2007) described bacterial infection by Mycobacterium marinum and Streptococus iniae, typical of cultured stocks, causing morbidity and mortality in wild fish, indicating that intensive sea cage farming acted as pathogen “amplifiers,” with diseases transmitted in both directions between wild and cultured fish populations, with the specificity (or lack of it) of each pathogen for a host playing an essential role. Predation on conspecifics or other fish species is more probable for seabass. Young seabass form schools, but adults appear to be less gregarious; seabass feed chiefly on shrimps and molluscs, also on fishes. Juveniles feed on invertebrates, taking increasingly more fish with age and adults are obligate piscivores, Kuwait (APROMAR 2011). World production of seabass in 2011 was 126,240 t, a reduction of 5.8 percent from 2010. Main producers are Turkey with 43,200 t (34.2 percent), Greece (34.1 percent) and Spain (11.4 percent). This species is produced in nineteen countries, including Italy, France, Croatia, Portugal, Cyprus, Tunisia, Egypt, Unit Arab Emirates, Libya, Israel, Malta, Montenegro, Bosnia, Morocco, Slovenia, United Kingdom and Algeria. In addition, Egypt produces more than 200,000 t per year of mullet, mainly Mugil cephalus in landbased facilities. As an emerging species, meagre production in Europe was 3,770 t in 2011, 4.2 percent less compared to 2010. Main producers of meagre are Spain (76.4 percent), France and Italy (APROMAR 2011). Potential Impacts of Seabream and Seabass Escapes Despite the potential magnitude of impacts of escapes from Mediterranean fish farming, specific knowledge concerning ecological and genetic impacts of escaped fish on the Mediterranean ecosystem remains sparse. It is impossible to evaluate the evolving historical changes on wild fish populations specifically caused by escaped fish. For new species such as meagre the information is non-existent. However, drawing on experiences with Atlantic salmon, it is appropriate to assess the potential risk of escapes from cage aquaculture for improved environmental management and develop mitigating and contingent actions. Other than genetic effects, the environmental effects of escaped fish on wild populations may be divided into five general categories: • Exploitation competition: the possibility that escaped seabass and seabream affect wild conspecifics or other marine species indirectly through consumption (predation) of shared TOP, FIGURE 2A. Net holding seabream in a typical Mediterranean floating cage, with wild fish swimming around (Photo: P. Sanchez-Jerez). BOTTOM, FIGURE 2B. Holes favor the small scale escapes but also can produce bigger escapes if it is broken during a storm (Photo: P. Sanchez-Jerez).
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