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Aquaculture Environment Interactions

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AEI 1:71-83 (2010)  -  DOI:

Escapes of fishes from Norwegian sea-cage aquaculture: causes, consequences and prevention

Ø. Jensen1, T. Dempster1,2,*, E. B. Thorstad3, I. Uglem3, A. Fredheim

1Centre for Research-based Innovation in Aquaculture Technology (CREATE), SINTEF Fisheries and Aquaculture, 7465 Trondheim, Norway
2Department of Zoology, University of Melbourne, Victoria 3010, Australia
3Norwegian Institute for Nature Research, 7485 Trondheim, Norway
*Corresponding author. Email:

ABSTRACT: The escape of fish from aquaculture is perceived as a threat to wild fish populations. The escapes problem is largely caused by technical and operational failures of fish farming equipment. In Norway, 3.93 million Atlantic salmon Salmo salar, 0.98 million rainbow trout Oncorhynchus mykiss and 1.05 million Atlantic cod Gadus morhua escaped from 2001 to 2009. Salmonids primarily escape after structural failures of containment equipment, while a far greater proportion of cod than salmon escape through holes in the nets. Correlative evidence suggests that after the Norwegian technical standard (NS 9415) for sea-cage farms took effect in 2004, the total number of escaped Atlantic salmon declined from >600000 (2001 to 2006) to <200000 fish yr–1 (2007 to 2009), despite the total number of salmon held in sea-cages increasing by 44% during this period. No similar decrease in escaped cod has occurred, suggesting that other measures, such as improved netting materials for sea-cages, are required. In addition to escaping as juveniles or adults, cod may reproduce in sea-cages, and thus fertilised eggs escape to the environment. The ecological effects of ‘escape through spawning’ are unclear, and methods to inhibit escape by this mechanism are being explored. To prevent escapes of juvenile and adult fish as sea-cage aquaculture industries develop, we recommend that policy-makers implement a 5 component strategy: (1) establish mandatory reporting of all escape incidents; (2) establish a mechanism to analyse and learn from the mandatory reporting; (3) conduct mandatory, rapid, technical assessments to determine the causes of escape incidents involving more than 10000 fish; (4) introduce a technical standard for sea-cage aquaculture equipment coupled with an independent mechanism to enforce the standard; and (5) conduct mandatory training of fish farm staff in escape-critical operations and techniques.

KEY WORDS: Salmonids · Cod · Technology · Regulation · Standard · Competition · Disease ·Interbreeding · Fish farming

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Cite this article as: Jensen Ø, Dempster T, Thorstad EB, Uglem I, Fredheim A (2010) Escapes of fishes from Norwegian sea-cage aquaculture: causes, consequences and prevention. Aquacult Environ Interact 1:71-83.

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