Potential Effects of Contaminants on Fraser River Sockeye Salmon

Chapter 2 Geographic and Temporal Scope <strong>of</strong> the Investigation2.0 IntroductionThis investigation was conducted to evaluate the potential effects <strong>of</strong> contaminants onsockeye salmon utilizing habitats within the Fraser River Basin (Figure 2.1). Evaluation <strong>of</strong>the effects <strong>of</strong> contaminants requires an understanding <strong>of</strong> the life history <strong>of</strong> the sockeyesalmon that utilize habitats within the Fraser River basin for key elements <strong>of</strong> their lifecycles. Such information is needed to identify where and when sockeye salmon could beexposed to environmental contaminants. This chapter provides a brief overview <strong>of</strong> the lifehistory <strong>of</strong> Fraser River sockeye salmon and conservation units that have been identified formanaging these salmon stocks. In turn, this information was used to identify thegeographic and temporal scope <strong>of</strong> the investigation.2.1 Life History <strong>of</strong> Fraser River Sockeye SalmonSockeye salmon utilizing habitats in the Fraser River Basin (Figure 2.2) exhibit a diversearray <strong>of</strong> life history patterns. The life cycle <strong>of</strong> sockeye salmon begins when the femalesreturn to their natal streams to spawn. The timing <strong>of</strong> arrival at the mouth <strong>of</strong> the FraserRiver varies considerably among sockeye salmon stocks, generally ranging from early Juneto early September (Burgner 1991; Lapointe 2010). Upon arrival, sockeye salmon canmill at the river mouth for a period <strong>of</strong> up to six weeks prior to initiating their ascent up theriver (Johannessen and Ross 2002). Once in the river, sockeye salmon cover distances <strong>of</strong>up to 1000 km over a period <strong>of</strong> up to 24 days (averaging 35 to 50 km/day; Burgner 1991).Hence, migrating sockeye salmon can be in the Fraser River between about the middle <strong>of</strong>June and the middle <strong>of</strong> September each year.Spawning generally occurs in the late summer and early fall (i.e., about mid-August tomid-October), with northern stocks typically spawning earliest and lower Fraser Rivertributary stocks spawning latest (McPhail 2007). These differences in spawning timing aredirectly related to the temperature regime <strong>of</strong> the spawning site and appear to be anadaptation to synchronize emergence timing in the spring (Brannon 1987). Spawningtypically takes place in tributaries to lakes, within lakes, or in outlet streams from lakes inhabitats dominated by gravel and cobbles. After digging a nest (or redd), female sockeyesalmon typically deposit about 2000 to 4000 eggs into the stream-bed or lake-bedsubstrate, which are simultaneously fertilized by one or more males (Burgner 1991).Adult sockeye salmon die after spawning.6