Fraser River sockeye salmon: data synthesis and cumulative impacts

4.2.6 ConclusionsTable 4.2-1 follows the logic of the flow chart in Figure 3.3-1, showing our conclusionsregarding the effects of each stressor on life history stage 1 (including eggs, alevins, fry, andparr). Our conclusions relate to the overall trends in sockeye productivity over the last twodecades.Table 4.2-1. Evaluation of the relative likelihood that potential stressors encountered by Fraser River sockeyesalmon during life history stage 1 (including eggs, alevins, fry, and parr), have contributed to overalldeclines in productivity in recent decades. Some factors may have had effects on some stocks in some years(e.g., density dependence affecting Quesnel sockeye), but are unlikely to have been responsible for theoverall pattern across all Fraser sockeye stocks. See section 4.7 for further discussions of correlations.Factor Mechanism Exposure Correlation/Consistency Other LikelihoodEvidenceForestry b Yes Yes No No a UnlikelyMining Yes Low Not done No a UnlikelyLarge hydro Yes Yes No Against UnlikelySmall hydro Yes Low 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 PossibleChangeevidencea 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.With the exception of climate change, which we consider to be a possible factor, and pathogens(for which no conclusion is possible due to data gaps), it is unlikely that the above 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 theprimary drivers behind long term declines in sockeye productivity across the Fraser Basin. We48