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EXECUTIVE SUMMARY

The escape of fish from sea-cage aquaculture is perceived as a threat to natural biodiversity in Europe's marine waters. Escaped fish may cause undesirable genetic effects in native populations through interbreeding, and ecological effects through predation, competition and the transfer of diseases to wild fish. Technical and operational failures of fish farming technology cause escapes. Cages break down in storms, wear and tear of the netting causes holes, and operational accidents lead to spills of fish. The Prevent Escape project conducted and integrated biological and technological research on a pan-European scale to improve recommendations and guidelines for aquaculture technologies and operational strategies that reduce escape events.

Through research focused on sea-cages and their immediate surrounds, the Prevent Escape project determined that escape events are widespread throughout European sea-cage aquaculture. From 2007-2009, we documented 255 escape events across 6 countries involving Atlantic salmon, Atlantic cod, rainbow trout, seabream, seabass and meagre production. 9.2 million fish escaped from these 255 events, which mostly occurred due to structural failures during storms and the appearance of holes in nets. Seabream accounted for the highest number of escapes (74%) followed by Atlantic salmon (11.8%). On a pan-European scale, we estimate that this directly cost the industry !47.5 million per year. Costs to the reputation of the industry were not able to be assessed, but were likely substantial. In addition to juvenile and adult fish escaping, both seabream and Atlantic cod mature and spawn in sea-cages. They produce viable eggs which flow out from fish farms and enter wild populations.

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A detailed analysis of escapes in Europe’s largest industry, Atlantic salmon production in Norway, revealed that after the Norwegian technical standard (NS 9415) for the design, dimensioning and operation of sea-cage farms was implemented in 2006, the total number of escaped Atlantic salmon declined from >600 000 yr–1 (2001 to 2006) to <300 000 fish yr–1 (2007 to 2011), despite the total number of salmon held in sea-cages increasing by >50% during this period. Based on the success of this measure, to prevent escapes of juvenile and adult fish as sea-cage aquaculture industries develop, the Prevent Escape project recommends that policy-makers introduce a technical standard for sea-cage aquaculture equipment, coupled with independent mechanisms to enforce the standard.

Determining the behaviours of fish which may pre-dispose them to escape is a key step in designing farming strategies to reduce escape risks. Experiments identified that both seabream and Atlantic cod exhibit a range of behaviours that may pre-dispose them to high rates of escape through holes as they swim close to net walls and bite the netting. Manipulative experiments of the cage culture environment determined that cage management strategies could be effective in reducing escape risk. These strategies include maintaining well-fed fish, using environmental enrichment to distract fish from engaging in escape-related behaviours and maintaining clean nets.

Fast, accurate and cost-effective tools for identifying escapees are central for assessments of the extent and consequences of fish escapes. The project tested a range of techniques to distinguish escaped fish within wild populations. Ultimately, the selection of suitable indicators depends on the final stakeholder. Farmers and consumers could use external appearance and morphometry for rapid assessment, however, trace elements in scales and fatty acid profiles are more useful for fisheries and environmental management applications. Where individuals need

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to be discriminated with a high degree of accuracy to farmed or wild origin, we recommend genetic methods, scale features and trace elements of scales as suitable methods. To identify the specific farm where an escape event occurred, only genetic methods are currently capable.

Re-capturing escapees is a possible method to mitigate escapes. Tracking of escaped cod, salmon, seabream, meagre, and seabass, indicated that unless recapture efforts are initiated within 24 hours after an escape incident, the potential for successful recapture of escapees is limited. Further, by-catch of wild marine fish was high during recapture efforts, implying that large-scale recapture efforts must be weighed against the possibility of affecting wild fish populations negatively. Wild fish that aggregated around fish farms where fish escapes were highly effective in predating escapees, thus maintaining healthy populations of predators around sea-cage facilities could assist in mitigating escapes.

Sea-cage equipment is marketed and used across Europe, thus knowledge relevant to the culture of numerous species in diverse environments is required to produce robust equipment and implement risk-adverse operations. Prevent escape has delivered new knowledge on the materials and properties of sea-cage components and innovated new system designs to reduce the risks of specific escape events from occurring. Information from this component of the project will assist in benchmarking the performance of equipment during farming, improve operations and equipment production, and advance national and international standards for the design, construction and use of aquaculture equipment.

These key pieces of information, when added to existing knowledge, have allowed a series of practical, implementable measures to prevent escapes and mitigate the effects of escapees. Ultimately, if prevention and mitigation are more successful, genetic and ecological impacts of escaped cultured fish on wild fish populations should diminish.

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