Atlantic salmon (Salmo salar) in the Pacific Northwest:: assessing the risk of impact on wild Pacific salmon

Atlantic salmon (Salmo salar) are commercially reared in marine net-pens in Washington State. The industry produces over 10 million pounds of salmon each year with a total annual economic, value which exceeds $40 million. The salmon net-pen industry in British Columbia (BC), Canada, is ten times larger than that of Washington. One aspect of fish farming which concerns fishery managers is the escape of farmed fish and the impact that escaped fish might have on native salmon stocks. This is of particular interest because of the recent listing of many salmon stocks in Washington as endangered or threatened under the Endangered Species Act. The number of salmon which escape from pens in BC annually is estimated to be approximately 60,000 fish. Annual escapes in Washington before 1996 were not recorded. However, in 1996, 1997, 1998 and 1999, catastrophic events resulted in the escape of 107,000, 369,000, 23,000 and 115,000 Atlantic salmon, respectively. The scientific evidence available before the summer of 1998 suggested that escaped Atlantic salmon were not colonising local watersheds and did not significantly affect native fish. However, in 1998 and 1999, naturally produced Atlantic salmon were discovered in streams on Vancouver Island, BC. This evidence indicated that escaped Atlantic salmon are capable of successfully producing offspring in the wild and compete, to some degree, with juvenile wild salmon. No naturally produced Atlantic salmon juveniles have been observed in Washington State. To date, there is no evidence of a naturally produced Atlantic salmon surviving in the wild to maturity and spawning in Washington or BC. Other risk factors which were identified (e.g. hybridisation, predation and pathogen transfer) were not found to be significant. Current risk management would become more effective with the following measures: co-operation among Washington State and fish management agencies in BC and the aquaculture industry to ensure the implementation and enforcement of consistent aquaculture regulations. the implementation of an Atlantic salmon breeding programme which requires the use in production of either monosex or triploid fish (i.e. fish which are unable to reproduce in the wild) the institution of a comprehensible code of practice for commercial salmon aquaculture administered by the Washington Department of Fish and Wildlife to ensure environmentally sound fish culture.