Potential Effects of Contaminants on Fraser River Sockeye Salmon

productivity data, it is apparent that the Harrison River stock has higherproductivity than other sockeye salmon stocks in the Fraser River. For the cooccurrencebetween cause and effect to exist for the Harrison River stock,either its exposure to endocrine disrupting compounds and other contaminantswould need to be lower than that for other sockeye salmon stocks or a factorthat triggers mortality in sockeye salmon exposed to these contaminants wouldneed to be absent for this stock. Although little is known about exposure <strong>of</strong>Harrison River sockeye salmon during freshwater residence, it could bepostulated that this stock receives increased exposure to endocrine disruptingcompounds and/or other contaminants <strong>of</strong> emerging concern while rearing infreshwater sloughs and backwaters within the Lower Fraser River Area <strong>of</strong>Interest (i.e., assuming that such areas are more contaminated by endocrinedisrupting compounds than the lakes utilized by other sockeye salmon stocks).If this is true, then co-occurrence can only exist if Harrison River fish are notexposed to a supplemental factor (e.g., disease agent) that triggers mortality inother sockeye salmon stocks or their prolonged residence in the estuaryprovides some protection against acute infection by a disease agent.Alternatively, co-occurrence can exist for Harrison River fish if the freshwatersloughs in which they rear are actually less contaminated than other areaswithin the lower Fraser River and the fish have low exposure to endocrinedisrupting compounds in the lower Fraser River due to their short migration tosaltwater.Data on the productivity <strong>of</strong> sockeye salmon stocks utilizing spawning andrearing habitats in other river systems may provide evidence against exposureto endocrine disrupting compounds and other contaminants <strong>of</strong> emergingconcern as a causative factor in the decline <strong>of</strong> sockeye salmon in the FraserRiver Basin. For example, Columbia River sockeye salmon generallydemonstrated a trend toward increasing abundance during the period 1995 to2008 (NOAA Fisheries 2009). The Pacific Salmon Commission (Gallaugherand Woods 2010) indicated that such improving productivity occurred despiteconsiderable contamination in the Columbia River Basin. However, sockeyesalmon in the Columbia River (i.e., Osoyoos /Skaha Lakes and LakeWenatchee stock) are not directly exposed to contaminants originating in theWillamette River (i.e., Portland Harbor Superfund Site) and contamination <strong>of</strong>surface waters within the Hanford Reach is uncertain. Therefore, it isuncertain if the supposition <strong>of</strong> exposure to considerable contamination isdirectly relevant to upper Columbia River sockeye salmon stocks.114