Fraser River sockeye salmon: data synthesis and cumulative impacts

Region Variable M1 M2 M3 M4 M5 M6 M7 M8 M9SoG Chlorophyll X X X X XSoG Temperature X X X X XSoG Salinity X X X X XSoG Discharge X XRank of model 3 9 8 6 2 1 5 4 74.4.6 ConclusionsTable 4.4-6 shows a summary of the results of the weight of evidence evaluation of potentialcontributing factors at this life stage. All of the potential factors in this life stage have plausiblemechanisms. There are almost no data on exposure for pathogens making no conclusionpossible. The evidence presented suggests that sockeye salmon in the Strait of Georgia have littledirect exposure to human activities and development, leading to a conclusion that it is unlikelythat these factors have contributed to the decline of Fraser River sockeye salmon. Sockeyesalmon have been exposed to predators, marine conditions, and climate change during this earlymarine phase. However, there has been no evidence presented on any correlations between keypredators and sockeye salmon survival. Some important predators appear to be increasing inabundance, and some potentially important alternate prey appear to be decreasing, but manyother known predators are decreasing or remaining stable. It therefore remains possible thatpredators have contributed to the observed declines in sockeye salmon. Based on plausiblemechanisms, exposure, consistency with observed sockeye productivity changes, and otherevidence, marine conditions and climate change are considered likely contributors to the longtermdecline of Fraser River sockeye salmon. Peterman and Dorner’s analyses of delayeddensity dependence were applied to total productivity over the whole life cycle. Therefore, theirconclusion that delayed density dependence is unlikely to have been a primary factor causingproductivity declines (discussed in section 4.2 for life stage 1) reflects the net effect across alllife history stages. Aquaculture was not considered in our report as the Commission Technicalreports on this potential stressor were not available, but will be considered in an addendum tothis report.69