Fraser River sockeye salmon: data synthesis and cumulative impacts

did not correlate well with differences in productivity among different Fraser Basin stocks. Forexample, the two Fraser sockeye stocks that have done well over the last two decades (Harrisonand Late Shuswap) have shown, respectively, moderate and high relative indices of cumulativehabitat stress on spawning and rearing habitats (Table 18 in Nelitz et al. 2011). Furthermore,Nelitz et al. (unpub. analyses) found that indices of the intensity of habitat stressors and habitatvulnerability were not consistent with estimates of the current status of conservation units basedon Pestel and Cass (2009), that is, stock status did not decline with increasing indices of habitatstress and vulnerability.Looking across time, Neltiz et al. found that trends in overall sockeye productivity 9 across 17sockeye stocks were not correlated with either the intensity of habitat stressors on nursery lakesor their core measures of habitat vulnerability. 10 The only variable correlated with trends insockeye productivity was migration distance (i.e., stocks with longer migration distances showedgreater rates of decline), which may reflect other correlated factors (e.g., watershed position,nursery lake elevation) rather than being a direct causative factor. Juvenile productivity (i.e.,juveniles/spawner) was unrelated to indices of forest harvesting and mountain pine beetledisturbance, but showed some indications of negative associations with spring air temperatures atnursery lakes (i.e. juvenile productivity decreases as spring temperatures increase). Finally, thestability over time in juvenile productivity despite declines in overall life cycle productivitysuggests that freshwater habitat factors are not a primary driving factor in the observedproductivity declines, though it is possible that some non-lethal effects during spawning andrearing affect later life history stages. These results are similar to those found in the PSC report(Peterman et al. 2010; Section 4.6).Johannes et al. (2011; Table 2) found that there was either no risk or low risk of impacts tospawning and rearing habitats in the Lower Fraser from population growth, industrial andinfrastructure projects, liquid and solid wastes, ships and vessels, dredging and diking,contaminated materials and exotic species. They assigned a moderate risk level to agriculture andforestry activities in Lower Fraser watersheds where there is a longer duration and greatermagnitude of potential interactions.9 trends in annual residuals in returns/spawner, relative to the expected life cycle productivity based on the numbersof spawners in the brood year, indicator #2 in section 4.1; data from Peterman et al. (2010)10 Predictor variables included those relating to habitat vulnerability (migration distance, ratio of lakeinfluenced:total spawning extent, area of all nursery lakes) and habitat stress (total water license allocations,municipal area, forest harvested area within the last 15 years, road density, water licence restrictions, agriculturalarea, and area disturbed by Mountain Pine Beetle). Source: Table 16 in Nelitz et al. (2011).44