Potential Effects of Contaminants on Fraser River Sockeye Salmon

analysis do not provide convincing evidence that the measured levels <strong>of</strong> contaminants <strong>of</strong>concern in surface water have played a major role in the recent declines in sockeye salmonabundance in the Fraser River Basin (Figure 5.3). While surface-water contaminant <strong>of</strong>concern concentrations in spawning and incubation habitats explained about eight percent<strong>of</strong> the variability in the freshwater productivity data, the relationship was not statisticallysignificant (Figure 5.3). For fry rearing habitats, smolt outmigration corridors, and adultupstream migration corridors, significant relationships between productivity and waterquality index scores were not observed or productivity declined with increasing waterquality index scores (i.e., improving water quality conditions; Figure 5.3).To further evaluate relationships between contaminant <strong>of</strong> concern exposure and sockeyesalmon productivity, the available data were compiled for the pre-1990 and post-1990period and the relationships between contaminant <strong>of</strong> concern concentrations and sockeyesalmon life-cycle productivity were determined. The results <strong>of</strong> these analyses show thatexposure to contaminants <strong>of</strong> concern in any <strong>of</strong> the four habitat types did not explain morethan seven percent <strong>of</strong> the variability in the productivity data for Fraser River sockeyesalmon for either the pre-1990 period or the post-1990 period (Figure 5.4). Therefore, itis likely that exposure to the contaminants <strong>of</strong> concern represented in the water qualityindex is not the most important factor influencing the abundance <strong>of</strong> sockeye salmon in thestudy area. Examination <strong>of</strong> the available productivity and contaminant exposure data on aconservation unit-specific basis (Figures 5.5 to 5.23) revealed a number <strong>of</strong> relationshipsthat are consistent with the expected pattern (e.g., Weaver outmigration for both periods,Birkenhead outmigration for both periods, Gates outmigration for post-1990, Portageoutmigration for both periods, Raft outmigration for pre-1990, Seymour outmigration forpre-1990, late Shuswap rearing for post-1990, Scotch rearing for pre-1990, Chilkooutmigration for both periods, late Stuart outmigration for post-1990, Stellako spawningfor pre-1990 and outmigration for post-1990, Nadina outmigration for post-1990, andBowron outmigration for post-1990). However, most <strong>of</strong> these relationships are notstatistically significant, do not explain much <strong>of</strong> the variability in the productivity data,and/or have limited range <strong>of</strong> the exposure variable (water quality index).In summary, the results <strong>of</strong> analyses <strong>of</strong> the available data do not implicate water qualityconditions as a major factor influencing trends in sockeye salmon abundance in the FraserRiver Basin. However, these results should be kept in perspective considering thelimitations on the available data. These data gaps and limitations are listed in Section 7.4<strong>of</strong> this document. Furthermore, as shown in Figure 4.20, all <strong>of</strong> the sockeye salmon stocksthat rear for protracted periods (at least one year) in freshwater habitats have exhibiteddeclining productivity over the past 20 years. The Harrison River stock, which spends the67