Fraser River sockeye salmon: data synthesis and cumulative impacts

Nelitz et al. (2011; Table 18) found that their index of cumulative habitat stress 11 to migratoryhabitats (which included the zone within a 1 km buffer along migratory habitats) was relativelyhigh for all sockeye conservation units with a migration distance greater than 750 km. The stressindex was however also relatively high for some conservation units with short migratorydistances but exposed to more intensively disturbed regions (e.g., Cultus (111 km migration),Chilliwack (156 km), Kakawa (164 km), Nahatlatch (255 km)). Two stocks of particular interestbecause of their relatively healthy trends in productivity, the Shuswap (487 km migration) andHarrison (127 km), had (respectively) relatively high and moderate levels of the migration stressindex.MacDonald et al. (2011) assessed the exposure to water contaminants during downstreammigration by selecting data during May and June for the appropriate migratory routes for eachstock. For sediment contaminants, they grouped sites into pre and post-1990 periods.4.3.3 Correlation/consistency with patterns in Fraser River sockeyeproductivityWe do not know smolt survival rates for most of the Fraser River stocks. There are someestimates of velocities and survival rates of sockeye smolts migrating downstream from variousFraser watersheds, based on acoustic tags (e.g., Melynchuk et al. 2010). However, these data setswere not included in any quantitative analyses conducted for the Cohen Commission, due to timelimitations. Our analyses of migratory stage stressors (and those conducted by other CohenCommission technical reports) used indices of post juvenile or full life cycle productivity as thedependent variable to be explained. These indices do not allow us to clearly separate effects onsurvival in the downstream migration from effects occurring in the ocean, though we do explorewhether stressor indices in different life history stages are better correlated with full life cycleproductivity.Nelitz et al. (2011; Table 16) found that overall life cycle sockeye productivity was negativelyassociated with migration distance (the only factor with a strong association), but they have nodirect explanation for why this occurred. It might relate to differential exposure to a suite ofstressors along the migration route, or could be capturing parallel influences on total productivitythat are unrelated to stresses associated with human activities, since migration distance is11 This index of cumulative habitat stress was developed by first applying cluster analysis to each of the land usestressor indices, scoring each conservation unit as 1 (low), 2 (moderate) or 3 (high) relative levels of stress, with ascore of 0 assigned in cases where a habitat had no spatial overlap with a stressor. The scores across all stressorindices were then summed to give an overall index of cumulative habitat stress for each CU.51