Science Briefing

ACAR has produced a Summary of Scientific Papers on Impacts of Open Net Pen Farming on Wild Populations and the Natural Environment, which can be downloaded here and will be updated as new and relevant science becomes available.

This review is not meant to be an exhaustive review of the literature, however it is intended to cover the most recent and pertinent research on the impacts of open net pen salmon aquaculture.

A summary of portions of the document is produced below.

Pollution

• With such a high concentrations of fish, large amounts of waste will inevitably accumulate on the bottom under a sea cage. Current speed and depth of cage siting are key variables in determining the extent of impact to the benthic environment (Borja et al., 2009).

Sea Lice and Wild Salmon

• Sea lice are copepod crustaceans which live on the outside of salmon and feed on their mucous, skin and blood. Though most ocean-going adult salmon carry sea lice, juveniles in coastal waters do not (Chapter 5, Royal Society of Canada 2012).
• Migrating juvenile pink (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) were sampled as they passed a salmon farm on their migration to the open ocean. Infection pressure for sea lice was up 73 times greater near the farm than ambient levels; likelihood of infection was found to be above ambient levels up to 30 km surrounding the salmon farm. Additionally, sea lice already infecting the wild juveniles were able to reproduce during their migration and re-infect the juveniles which increases the range of the farm’s effect on infection to 75 km Krkošek et al. (2005).

Disease

• Because sea lice reduce the fitness of salmon, it leaves them vulnerable to other parasites and disease. The most problematic disease in Atlantic-based salmon aquaculture is the infectious salmon anemia virus (ISA). As the name suggests this causes severe anemia in the fish caused by a binding of the virus to red blood cells. Though the ISA virus is endemic to the Atlantic, transmission and prevalence of this disease is greatly increased on salmon farms due to the high density at which the fish are kept. This poses a huge threat to wild salmon stocks which are already struggling, particularly when the farm is located near an estuary frequented by a wild population.

Pesticides

• In Nova Scotia, the main concern surrounding the use of SLICE® is its potential impacts on the American Lobster (Homarus americanus) which is an incredibly important to the area as a commercial species. Waddy et al. (2002) found that 44% of female lobsters exposed to small doses of emamectin benzoate moulted prematurely, and those which were carrying eggs aborted their brood. This would seriously affect the reproductive ability of wild lobsters near salmon farms and could have a profound effect on Nova Scotia’s lobster fishery.
• Salmosan® (active ingredient azamethiphos) is currently approved for emergency use in New Brunswick, Nova Scotia, and Newfoundland and Labrador. Burridge et al. (2008) shows that repeated short term exposure to azamethiphos can have lethal and sublethal effects on American lobsters.
• In 2009 and 2010 there were a number of incidents of dead and dying lobsters found in traps pens and pounds in southwestern New Brunswick. Cypermenthin, a pesticide used in salmon aquaculture but not approved for use in Canada, was detected on these lobsters. A New Brunswick based salmon aquaculture company and three of its executives are facing significant charges under the Fisheries Act in relation to these lobster kills.

Escapes & Gene Transfer

• Open net pen fin fish farming can lead to frequent escapes which can occur as a result of storms or equipment malfunctions. Escapes can have severe impacts on wild populations of salmon. Morris et al. (2008) compiled a series of studies and found that
escaped farmed salmon had been found in 87% of the rivers studies within a 300 km radius of aquaculture sites in eastern North America. This included 11 rivers that were home to endangered populations.
• Fleming et al. (2000) found that farmed Atlantic salmon (Salmo salar) were competitively and reproductively inferior to their wild counterparts, with less than onethird the reproductive success. Despite their decreased ability to compete, the farm
fishes still were able to compete with the native population, as its productivity decreased by more than 30%.

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