Fraser River sockeye salmon: data synthesis and cumulative impacts

Table 4.3-1. Evaluation of the relative likelihood that potential stressors encountered by Fraser River sockeyesalmon during their smolt migration from rearing habitats to the Fraser Estuary (Stage 2) have contributedto overall declines in productivity in recent decades. See section 4.7 for further statistical analyses relevantto the correlation/consistency column.Factor Mechanism Exposure Correlation/Consistency Other LikelihoodEvidenceForestry b Yes Yes No No a UnlikelyMining Yes No Not done No a UnlikelyLarge hydro Yes Yes No Against UnlikelySmall hydro Yes No No No a UnlikelyUrbanization Yes Yes No No a Unlikelyabove HopeAgriculture b Yes Yes No No a UnlikelyWater Use Yes Yes No Yes UnlikelyContaminants Yes Yes No Yes UnlikelyDensity Yes Some No No UnlikelyDependentMortalitystocksPathogens Yes Few data Not done Yes NoconclusionpossiblePredators Yes Few data No No UnlikelyL. Fraser land Yes Yes for No No Unlikelyusesag/for; Nofor othersClimate Yes Yes Weak evidence Mixed PossibleChangea It is difficult to establish hazard thresholds for the proportion of watershed area above which there are negativeimpacts on sockeye spawning and rearing. Such thresholds are better defined for contaminants and water use.bAgriculture and forestry rows include evidence from both Technical Reports 3 (Nelitz et al. 2011) and 12(Johannes et al. 2011). Forestry includes logging, Mountain Pine Beetle and log storage.As for Stage 1, we conclude that with the exception of climate change, which we consider to be apossible factor, and pathogens (for which no conclusion is possible due to data gaps), it isunlikely that other factors (i.e., forestry, mining, large and small hydro, urbanization, agriculture,water use, contaminants, density dependent mortality, predators, and Lower Fraser land use)taken cumulatively, were the primary drivers behind long term declines in sockeye productivityacross the Fraser Basin. A major reason for this conclusion is the short time period over whichmigrating smolts are exposed to the above stressors. Though not primary drivers of the Frasersockeye situation, each of the factors considered for Stage 2 may still have had some effects onsome Fraser stocks in some years (the data are insufficient to reject that possibility).However, since smolt migration occurs subsequent to enumeration of fry and smolts in rearinglakes, we have no analyses relating survival rates during this life history stage to potential54