34 DECEMBER 2013 • WORLD AQUACULTURE • WWW.WAS.ORG global finfish production is carried out with the use of aquafeeds with very little or no fishmeal because of the low trophic level of freshwater species such as carp, catfish and tilapia. Some effort has been made to improve knowledge on basic physiological functions and feed technology on species diversification in this way. As an example, rabbitfish (Siganus spp.) are extensively produced in tropical countries such as Tanzania, Indonesia and Australia (Soto 2009). In the Mediterranean, aquaculture of Siganus rivulatus has started to develop. This species can be an alternative to high trophic level species such as seabream and seabass, reducing the environmental costs and dependence on small pelagic fish products for feeding. Research has been done on basic culture requirements, dietary needs and health (Saoud and Anastasiades 2012). However, rabbitfish is a non-native, introduced species. The genus Siganus is widely distributed in the Indo-West Pacific Region but Siganus rivulatus migrated to the eastern Mediterranean through the Suez Canal and has since established large populations in its new environment. The species has spread from Egypt to Libya and Greece and has also been recorded around Malta. Voluntary and or accidental introduction of exotic aquatic species (alien species) can negatively impact native ecosystems. The ICES Code of Practices on the Introductions and Transfers of Marine Organisms (2005) and the considerations and suggestions of the report on Alien Species in Aquaculture by IUCN (2006) should be considered before developing aquaculture of any non-native species. If rabbitfish aquaculture is developed in the open ocean using cages, the most suitable system for a low-price species, escapes may have deleterious effects on natural habitats. For example, escapes of tens of thousands of rabbitfish can increase the herbivorous pressure on algae beds or affect fragile habitats, such as meadows of the seagrass Posidonia oceanica, which is also an important part of its diet. Recommendations Environmental risk, understood as the exposure to circumstances that cause potential ecosystem damage arising from an event, such as fish escapes, that is not managed appropriately, must be evaluated before making an investment. It is important to develop mitigating strategies and contingent actions because risk management needs to address both sides of the risk: what lies behind it (the source) and what lies in front of it (the consequences) (Husdal 2009). Risk impacts are addressed by using mitigating strategies aimed at eliminating the source or driver. Improved physical containment at marine fish farming sites, through research and development of fishfarming technology, has been a central recommendation of many international workshops and forums on the environmental impacts of escapees. For example, the FP-6 EU Coordinating Action on the genetic impact of aquaculture activities on native populations (GENIMPACT) has concluded that efforts should be made to prevent escapes. “Instead of trying to protect wild populations from escapees, the best logical solution would be to try to prevent escapes. This will rely on technical improvements from the industry …” (Triantafyllidis 2007). Therefore, for well-established species, the most important management issue at present is the need to reduce the numbers of escaped fish. Contingent strategies are aimed at eliminating impacts, such as programs to recapture escapes. Recapture may be a practical option for reducing the impact of escape events. This is included in several regulations regarding the environmental management of escapes (Washington, WAC 220-76-120; Chile RAMA 2001, Article. 5 and 6; Canada, ZZA fishing licence) but have many practical difficulties. In addition to specific recapture measures, professional and recreational fisheries often record high recapture rates after escape events. A major proportion of escaped fish can be recaptured if the catch effort in an area within several kilometres of the farm is implemented early after the escape event and lasts for several weeks to minimize the survival of escaped fish. Most critical would be the use of introduced species in marine aquaculture. The Berne Convention in 1979 provides that “each contracting party undertakes … to strictly control the introduction of non-native species,” which is very difficult with floating cages. The EC Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora requires member states to “ensure that the deliberate introduction into the wild of any species which is not native to their territory is regulated so as not to prejudice natural habitats within their natural range or the wild native fauna and flora and, if they consider necessary, prohibit such introduction” (article 22(b)). More specifically, EU directives legislate to protect the ecosystem against adverse effects of aquaculture-related introduced organisms (Directive on the deliberate release into the environment of Genetically Modified Organisms; 90/220/ FIGURE 5. Tagged seabream ready for release during an experiment about escapes recapture.
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