Potential Effects of Contaminants on Fraser River Sockeye Salmon

Exposure to endocrine disrupting chemicals and/or contaminants <strong>of</strong> emergingconcern caused or substantially contributed to declines in the abundance <strong>of</strong>Fraser River sockeye salmon over the past two decades and/or to low returns <strong>of</strong>Fraser River sockeye salmon in 2009.A total <strong>of</strong> five characteristics <strong>of</strong> causal associations (as identified by Suter et al. 2007)were used to consider the available evidence for a cause and effect relationship betweenexposure <strong>of</strong> sockeye salmon to endocrine disrupting compounds and/or contaminants <strong>of</strong>emerging concern and declines in sockeye salmon abundance in the Fraser River,including:• Co-occurrence - For a cause and effect relationship to exist, an effect mustoccur where and when its cause occurs and cannot occur in the absence <strong>of</strong> itscause. For endocrine disrupting compounds and, potentially, certaincontaminants <strong>of</strong> emerging concern, it is hypothesized that increased mortalityoccurs when sockeye salmon that have been exposed to such contaminantsduring smolt outmigration transition to the marine environment. All stocks <strong>of</strong>sockeye salmon are exposed to these contaminants in the lower Fraser River,with the magnitude <strong>of</strong> exposure likely increasing over the past two decades.The evidence suggests that sockeye salmon exhibit high mortality after leavingthe Fraser River. The observed effect is consistent with observations thatjuvenile chinook salmon exhibit high mortality during transition to saltwaterafter exposure to endocrine disrupting compounds (such as PCBs and PAHs)in contaminated estuaries (Varanasi et al. 1993; Arkoosh et al. 1998). Asexposure <strong>of</strong> sockeye salmon to such endocrine disrupting compounds has likelyincreased over the past two decades and returns <strong>of</strong> sockeye salmon to theFraser River have declined over the same time period, it is likely that there is aco-occurrence between the cause and the effect. This co-occurrence betweenthe cause and the effect would be demonstrated if toxicity thresholds <strong>of</strong> one ormore endocrine disrupting compounds were exceeded on an increasinglyfrequent during the post-1990 period, but not or only infrequently before thattime. However, the data needed to determine if critical levels <strong>of</strong> endocrinedisrupting compounds were exceeded starting in the early 1990's are notavailable.The status <strong>of</strong> the Harrison River stock potentially provides evidence againstco-occurrence between the cause (endocrine disrupting compound exposure)and effect (reduced sockeye salmon abundance). Based on the available113