Potential Effects of Contaminants on Fraser River Sockeye Salmon

Collectively, the results <strong>of</strong> studies on immunosuppression indicate that exposure toendocrine disrupting compounds has the potential to adversely affect salmon during theirtransition to the marine environment. If the concentrations <strong>of</strong> endocrine disruptingcompounds were sufficient to elicit these types <strong>of</strong> effects in the Fraser River, the resultantmortality <strong>of</strong> smolts during transition to the marine environment could have contributed tolong-term declines in sockeye salmon abundance.Exposure to endocrine disrupting compounds may be an even greater concern for sockeyesalmon returning to the Fraser River for several reasons. Sockeye salmon are exposed topersistent endocrine disrupting compounds, such as PCBs, PCDDs, and PCDFs, duringoutmigration and during their residence in the marine environment (Krummel et al. 2003).During upstream migration, adult sockeye salmon utilize lipid and protein stores tosupport gonadal development (females) and morphological alterations (males). Therigours <strong>of</strong> upstream migration and associated physiological changes can result in 50 - 90%depletion <strong>of</strong> somatic energy reserves (Hendry and Berg 1999). As a result, theconcentrations <strong>of</strong> these contaminants in somatic or gonadal tissues can increasedramatically between the time fish enter the mouth <strong>of</strong> the Fraser River and arrive at theirnatal streams. DeBruyn et al. (2004) estimated that the concentrations <strong>of</strong> PCBs, PCDDs,and PCDFs in muscle tissue could increase by 4.8 to 10.4 times for various Fraser Riversockeye salmon stocks, with the highest magnification rates predicted for the fish thatcomplete the longest migration. Predicted contaminant magnification rates weresomewhat lower (i.e., 3.9 to 7.9) for gonads. Such contaminant magnification waspredicted to result in concentrations in eggs that exceeded the toxicity threshold forsalmonid fishes <strong>of</strong> 3 ng/kg lipid, which is associated with 30% mortality <strong>of</strong> eggs (DeBruynet al. 2004). Although little information is available with which to make inferences, it ispossible that exposure <strong>of</strong> adult sockeye salmon to endocrine disrupting compounds insurface water during upstream migration could also compromise immunocompetence. Ifso, such exposures could make sockeye salmon more susceptible to infection by diseaseagents, particularly during migration periods characterized by elevated watertemperatures. Such effects could translate into increases in en-route mortality and/or prespawningmortality.6.2 <strong>Potential</strong> <strong>Effects</strong> <strong>of</strong> <strong>Contaminants</strong> <strong>of</strong> Emerging Concern on SockeyeSalmonThe term “contaminants <strong>of</strong> emerging concern” is used to describe a broad group <strong>of</strong>chemicals that were previously unknown or were not previously recognized as being <strong>of</strong>105