Potential Effects of Contaminants on Fraser River Sockeye Salmon

• Data collected for migration corridors between May 1, 1993 and June 30, 1993were compiled to evaluate exposure <strong>of</strong> smolts to chemicals <strong>of</strong> potentialconcern during outmigration;• Data collected for migration corridors between June 1, 1995 and September30, 1995 were compiled to evaluate exposure <strong>of</strong> adults to chemicals <strong>of</strong>potential concern during upstream migration.This approach to summarizing the available surface-water chemistry data is based onseveral assumptions. First, it assumes that the general life history pattern is the same forall stocks (i.e., one year <strong>of</strong> freshwater rearing followed by two years <strong>of</strong> ocean residence).In addition, it assumes that the timing for each life history stage is the same for all sockeyesalmon stocks. While both <strong>of</strong> these assumptions are not precisely correct, they aresufficiently reasonable to support evaluations that facilitate comparisons <strong>of</strong> exposure overtime and space.Due to limitations on the availability <strong>of</strong> sediment chemistry it was not possible to sort thedata in a way that would support spatial or temporal trend assessment for most <strong>of</strong> theareas <strong>of</strong> interest and most <strong>of</strong> the life history stages. Therefore, the data were grouped intotwo categories for each area <strong>of</strong> interest to determine if the concentrations <strong>of</strong> chemicals <strong>of</strong>potential concern exceeded toxicity screening values during the pre-1990 and post-1990time frames. These two time periods were identified for several reasons. First,examination <strong>of</strong> the general trends in sockeye salmon abundance show marked declinesover the past 20 years (Figure 1.1). Accordingly, the available productivity data (i.e.,mean Ricker residuals were plotted for the pre-1990, and post-1990 time periods (Figure4.20). These results showed that most <strong>of</strong> the Fraser River sockeye salmon stocks hadmean Ricker residuals (i.e., positive values) indicative <strong>of</strong> increasing productivity prior to1990. However, marked declines in productivity (as indicated by negative mean Rickerresiduals) for most stocks was observed after 1990. Hence examination <strong>of</strong> water qualityconditions for these two periods could provide information relevant for explaining declinesin the abundance <strong>of</strong> sockeye salmon in the Fraser River Basin.In this study, exposure <strong>of</strong> sockeye salmon to chemicals <strong>of</strong> potential concern was quantifiedby calculating exposure point concentrations. More specifically, exposure pointconcentrations were estimated for each <strong>of</strong> the habitat types (e.g., spawning and incubationhabitat) contained within each area <strong>of</strong> interest (e.g., Chilko River Area <strong>of</strong> Interest) foreach time period (e.g., August 1, 1991 and May 31, 1992) by determining the maximumconcentration <strong>of</strong> each chemical <strong>of</strong> potential concern. This is consistent with the availableguidance for estimating exposure point concentrations in screening-level ecological risk50