30 DECEMBER 2013 • WORLD AQUACULTURE • WWW.WAS.ORG Escapes of juveniles and adults from sea cages have been reported for almost all species presently cultured around the world in this culture system and are caused by technical and operational failures, extreme sea conditions or predator activity. Recently fertilized eggs spawned by farmed individuals are also considered as a potential vector for introduction of farmed fish into marine ecosystems. This aspect has forced a redefinition of the term ‘escapes from aquaculture’ to include the escapement of fertilized eggs (Jørstad et al. 2008). The impact of escapes on wild populations or natural habitats has been comprehensively studied for species such as the Atlantic salmon, identifying frequently negative effects on wild salmon. A recent study within the European project “PreventEscape” (Jackson et al. 2013; www.preventescape.eu) reported the causes of escaped fish based on questionnaires of producers in six European countries (Ireland, Scotland, Norway, Spain, Greece and Malta). In the Mediterranean, the main causes of escape incidents for seabream and seabass were caused by biological (51.5 percent; e.g. net biting, predator attack) or structural failures (39.4 percent; e.g. cage break, mooring failure, mechanical net damage), rather than operational failures (6 percent; e.g. harvesting, grading, transport). Although there are no official statistics on the extent of escapes from cages in Mediterranean countries, data available from companies that insure fish farm businesses indicate that escapes were a significant component of economic losses claimed by farmers (EU FP-6 ECASA project; www.ecasa.org. uk). From 2001-2005, 76 claims accounting for 36 percent of the total value of all insurance claims made by fish farmers in Greece were related to stock losses from storms, while damage to farm equipment from storms accounted for 19 percent. Further, 39 registered ‘predator attacks’ resulted in claims of 10.4 percent of the total value of all insurance claims, although the proportion of this that relates to stock loss or cage damage is unknown. The existing evidence suggests that escapes were a relatively frequent occurrence on a pan-European scale, but impact intensity depended on environmental and genetic factors (Thorstad et al. 2008). Fish Escapes from Cage Aquaculture in the Mediterranean Pablo Sanchez-Jerez An Overview of Marine Finfish Aquaculture in the Coastal Mediterranean The long shoreline and the oceanographic and geographic features of the Mediterranean Sea offer numerous possibilities for development of open-sea aquaculture and floating fish farms, comprised of tens of individual cages, widely used because of their adaptability to different sea conditions. Trujillo et al. (2011) analyzed the expansion of fish farms in the Mediterranean Sea, examining 91 percent of the Mediterranean coast, and counted 248 tuna cages (40-m diameter circular cages) and 20,976 other fish cages within 10 km of shore, the majority of which were off Greece (49 percent) and Turkey (31 percent). They estimated 225,736 t of farmed finfish (not including tuna) were produced in the Mediterranean Sea in 2006. Considering only the Mediterranean and Black Sea Statistical Area (FAO Major Fishing Area 37), the aquaculture sector has developed rapidly and production has increased by over 42 percent over the last five years, from 291,838 t in 2004 to 415,036 t in 2008. Over the same period, production increased by 47.5 percent for Mediterranean countries in FAO Statistical Area 01 (North Africa). The main growth in production in the Mediterranean Sea over the last 20 years is associated with marine finfish aquaculture, which has increased from 127,025 t in 1998 to 434,095 t in 2008, for an average annual growth rate of 16 percent. Most Mediterranean countries produce seabream Sparus aurata and seabass Dicentrarchus labrax, often coexisting in the same facility. The meagre Argyrosomus regius is becoming more widespread in the region, also sharing the same facilities. Total seabream production in 2011 was 151,346 t (FEAP), compared to 155,805 t in previous years, indicating a slight decrease. Nineteen countries produce seabream; Greece is responsible for 60,000 t (39.6 percent), followed by Turkey (22.5 percent) and Spain (11.2 percent). Italy, Egypt, France, Cyprus, Portugal, Croatia, Malta, Albania, Libya and Tunisia also produce seabream. Other countries located outside of the natural distributional range of seabream have an incipient industry, such as the Dominican Republic, Unit Arab Emirates, Oman and FIGURE 1. Conceptual model regarding the impact of escapes on marine ecosystem. (modified from Arechavala-Lopez 2013)
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