Interactions of Atlantic salmon in the Pacific Northwest: VI. A synopsis of the risk and uncertainty

Abstract

The paper collates conclusions of the five literature reviews of the possible interactions of Atlantic salmon in the environment of the Pacific Northwest, and prioritizes the issues in order of magnitude of risk to the aquatic ecosystem of Puget Sound. Two issues appear to carry the most risk for the region. These are the impact on the sediments beneath net-pen farms from bio-deposits, and the accumulation of heavy metals (zinc and copper), both of which can remediate within 1–2 years with fallowing. Eight issues appear to carry a low risk, the majority of which concern the effects on other biota in the immediate vicinity of net-pen farms. These include physiological effect of low dissolved oxygen levels in the water column; the toxic effect of hydrogen sulfide and ammonia emanating from the bio-deposits; the toxic effect of algal blooms which might be enhanced by the dissolved inorganic wastes; changes in the epifaunal community caused by the accumulation of organic wastes; the proliferation of human pathogens, and fish and shellfish pathogens in the environment; the increased incidences of disease among wild fish; and the displacement of wild salmon in the marketplace by farmed salmonids. Finally, three issues, and their sub-sets, carry very little or no risk. Two are specific to the environment, namely the escape of a non-native species and possible hybridization with other salmonids, colonization of salmonid habitat, competition with native species for forage, predation on indigenous species, and as vectors for the introduction of exotic pathogens; and the impact of antibiotic-resistant bacteria on native salmonids. The third concerns human health and safety regarding possible heavy metal contamination of farm products, rendered animal products in animal feeds, genetically modified (GM) ingredients in fish feeds, ingredients and additives in animal feeds, residual medicines and drugs in farmed products, biological hazards in farm products, transgenic farm fish, workers’ safety, public safety and navigational hazards, and impacts on nearby property values. The paper ends with discussion on the management of risk and uncertainty in the context of impacts on the environment, human health and safety, and the escape of farm animals.