Potential Effects of Contaminants on Fraser River Sockeye Salmon

• Sufficiency - For a cause and effect relationship to exist, the intensity orfrequency <strong>of</strong> a cause must be adequate to produce the observed magnitude <strong>of</strong>effect. Insufficient data are available to quantify exposures <strong>of</strong> Fraser Riversockeye salmon to endocrine disrupting compounds or contaminants <strong>of</strong>emerging concern. However, exposure to certain endocrine disruptingcompounds, such as PBDEs and PBBs, has likely increased exponentially overthe past two decades (Johannessen and Ross 2002). Such increases inexposure is illustrated by levels <strong>of</strong> PBDEs in osprey eggs collected nearCastlegar, British Columbia in 1991 and 1997 (BCMOE 2007). These datasuggest that PBDE levels in freshwater fish (the principal component <strong>of</strong> ospreydiets) have increased by nearly a factor <strong>of</strong> 30 (i.e., bird egg concentrationsincreased from 7.8 µg/kg WW in 1991 to 195 µg/kg in 1997; BCMOE 2007).Exposure to other contaminants that cause endocrine disruption (e.g., APEOs)has likely also increased over the past two decades. While evidence <strong>of</strong>increasing exposure to endocrine disrupting compounds and othercontaminants <strong>of</strong> emerging concern provides some <strong>of</strong> the information needed todemonstrate sufficiency, actual exposure data and toxicity data are needed todetermine if the concentrations <strong>of</strong> these contaminants in the Fraser River Basinare sufficient to cause the decline <strong>of</strong> Fraser River sockeye salmon over the pasttwo decades.No data are available to demonstrate that endocrine disrupting compoundconcentrations in the study areas in 2007 were sufficient to cause the lowreturns <strong>of</strong> sockeye salmon to the river in 2009. Therefore, it is not possible toevaluate the sufficiency <strong>of</strong> the exposure to elicit the observed effects.• Temporality - For a cause and effect relationship to exist, a cause must precedeits effect. For endocrine disrupting compounds and contaminants <strong>of</strong> emergingconcern, exposure occurs primarily within migration corridors within the upperFraser River mainstem, the Thompson River mainstem, and the lower FraserRiver. The results <strong>of</strong> several studies indicate that juvenile chinook salmon areexposed to endocrine disrupting compounds or other chemicals <strong>of</strong> potentialconcern during residence in contaminated estuaries. Mortality <strong>of</strong> these juvenilesalmon occurs during transition to the marine environment, frequently inconjunction with infection by one or more disease agents (Varanasi et al.1993). Therefore, the cause (i.e., exposure to endocrine disrupting compoundsand contaminants <strong>of</strong> emerging concern with immunosuppressive effects)precedes the effect (i.e., mortality <strong>of</strong> salmon following entry into the marine116