Fraser River sockeye salmon: data synthesis and cumulative impacts

would provide evidence supporting the importance of these stressors. In examining the patternsover 64 Fraser and non-Fraser sockeye populations from Washington to SE Alaska, Petermanand Dorner (2011; pg. 3) comment that: “The large spatial extent of similarities in productivitypatterns that we found across populations suggests that there might be a shared causalmechanism across that large area.”, though they acknowledge that further work is required to testthis hypothesis. The Cohen Commission technical reports do not however include analyses ofthe relationships between stressors at this stage and productivity indices for non-Fraser Riversockeye.4.5.5 Other evidenceThe relevant technical reports do not present any further evidence for factors contributing tolong-term declines in sockeye salmon that fit within the WOE evaluation framework utilized (i.e.thresholds, specificity, experiments, or removals).4.5.6 ConclusionsTable 4.5-1 shows a summary of the results of the weight of evidence evaluation of potentialcontributing factors encountered in this stage of growth in the North Pacific and return to theFraser River. All of the potential factors in this life stage have plausible mechanisms. There arevirtually no data on exposure for pathogens making no conclusion possible. Identical to theprevious stage, the evidence presented suggests that sockeye salmon returning through the Straitof Georgia have little direct exposure to human activities and development, leading to aconclusion that it is unlikely that these factors have contributed to the decline of Fraser Riversockeye salmon. Sockeye salmon have been exposed to predators, marine conditions, andclimate change during this open ocean phase. There has been no evidence presented on anycorrelations between key predators and sockeye salmon survival. However, over the same timeperiod that Fraser River sockeye salmon productivity has been decreasing, some importantpredators appear or are believed to be increasing in abundance, many potentially importantalternate prey have been decreasing, and marine mammals have been increasing substantially(although it is believed there is no relationship with the changes in sockeye salmon population).It therefore remains possible that predators have contributed to the observed declines in sockeyesalmon. Both technical reports addressing marine conditions, as well as the report addressingclimate change, show or reference research that shows correlations with sockeye salmonpatterns, but present no further evidence on thresholds, specificity, experiments, or removals.Marine conditions and climate change remain possible contributors to the long-term decline ofFraser River sockeye salmon. Peterman and Dorner’s analyses of delayed density dependencewere applied to total productivity over the whole life cycle. Therefore, their conclusions thatdelayed density dependence is unlikely to have been a primary factor causing productivity78