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

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 ), 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 seacages, 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 10 000 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.

Oncorhynchus mykiss escaped from commercial freshwater aquaculture pens in Lake Huron, Canada

“…Naylor et al 2005, Rikardsen et al 2008, Roberge et al 2008, Jensen et al 2010). Yet, in Canada intensive open-pen aquaculture of rainbow trout Oncorhynchus mykiss has been occurring in freshwaters for the past 30 yr, with most production based in the North Channel and Georgian Bay of Lake Huron (Moccia & Bevan 2007, DFO 2009.…”

“…Commercial open-pen farming of salmonid fishes (salmon, trout, charr) has seen unprecedented growth in the past half century, and, although husbandry practices and cage design strive to minimize losses, the escape of farmed fish to the wild remains a serious ecological concern associated with the aquaculture industry (Naylor et al 2005, Weir & Fleming 2006, Jensen et al 2010. Selection for high growth rate coupled with constant food availability and absence of predators, standard in aquaculture hatcheries, have resulted in farmed fish being maladapted to the wild environment (Gross 1998).…”

The German Case Study: Pioneer Projects of Aquaculture-Wind Farm Multi-Uses

“…As G. morhua is a physoclist species, necessary pauses need to be included during vertical movements of the cage (Korsøen 2011). One major problem for cod aquaculture is their ability to bite through the mesh or other materials, which makes them the fish species with the highest escapee rate (Jensen et al 2010), which could have a negative impact on wild population by cross-breeding (Davies et al 2008). The extreme temperature tolerance range from −1 to 23°C and an optimum temperature range from 8 to 12°C (Jobling 1988) make this species a candidate for aquaculture in the German Bight.…”

The influence of fish on the mooring loads of a floating net cage

“…Structural failure of the net cage is a main reason for fish escape in Norway (Jensen et al, 2010) [1]. Since an increase in marine fish farming in more exposed areas is expected, fish farm structures will be subjected to more intensive sea conditions.…”

“…In our considered Reynolds numbers, the boundary layer flow is laminar while the wake is turbulent. Assuming the wake is fully developed behind a smooth and streamlined body, the axisymmetric longitudinal mean turbulent wake flow velocity u can be calcu-55 lated according to Blevins (1984) [8] by equation (1).…”