Fraser River sockeye salmon: data synthesis and cumulative impacts

dependence is unlikely to have been a primary factor causing productivity declines (discussed insection 4.2 for life stage 1) reflects the net effect across all life history stages.While the timing of en-route mortality coincides generally with the Fraser sockeye situation,the Fraser sockeye productivity indices already account for en-route mortality (i.e., recruits =spawners + harvest + en-route mortality). The only possible effect on productivity indices worthexploring are inter-generational effects, for which the evidence is limited and equivocal. Wetherefore conclude that it is unlikely that en-route mortality or pre-spawn mortality are a primaryfactor in declining indices of Fraser sockeye productivity. However, en-route mortality hasdefinitely had a significant impact on the sockeye fishery and the numbers of adult fish reachingthe spawning ground, particularly for the Early and Late runs. Pre-spawn mortality, habitat,and contaminants are unlikely to be responsible for the overall pattern of declining sockeyeproductivity; no conclusion is possible regarding pathogens due to insufficient data. None of thefactors assessed for this life history stage are likely to have shown significant changes between2009 and 2010.Table 4.6-1. Evaluation of the relative likelihood that potential stressors encountered by Fraser River sockeyesalmon from the time returning adults enter the Fraser Estuary to when they spawn (Stage 5) havecontributed to the overall decline of the population in recent decades. Since various habitat measures areidentical to Table 4.3-1, they have been grouped together. Correlation/consistency column includes 3different sets of measures of impact on the Fraser sockeye fishery: a) life cycle and post-juvenileproductivity indices; b) harvest; and c) escapement.Factor Mechanism Exposure Correlation/Consistency Other LikelihoodEvidenceHabitat d Yes Yes No No UnlikelyContaminants Yes Yes No Yes UnlikelyPathogens Yes Few data Not done Yes NoconclusionpossibleClimatechange,Yes Yes Yes b,cn.a. aYesNoDefinitely b,cUnlikely atemperatures& en-routemortalityPre-spawnmortalityYes Yes No a, b,c (only increased inLate run)Mixed Unlikely b,cUnlikely aa life cycle and post-juvenile productivity indices already incorporate en-route mortality, so correlations are notapplicable. Available (limited) data does not show that en-route stress has intergenerational effects.bharvestc escapementdHabitat row includes evidence from both Technical Report 3, discussing all Fraser sockeye conservation units(Nelitz et al. 2011) and Technical Report 12 (Johannes et al. 2011) discussing the Lower Fraser. This rowsummarizes all of the rows reported in Table 4.3-1.86