Fraser River sockeye salmon: data synthesis and cumulative impacts

Table 4.4-6. Evaluation of the relative likelihood that potential stressors encountered by Fraser River sockeyesalmon during their coastal migration and migration to ocean rearing areas have contributed to overalldeclines in productivity in recent decades. See section 4.7 for further statistical analyses relevant to thecorrelation/consistency column.Factor Mechanism Exposure Correlation/Consistency Other LikelihoodEvidencePathogens Yes Few data - - NoconclusionpossiblePredators Yes Yes No data No data PossibleMarine Yes Yes Yes Yes LikelyConditionsHuman Yes No - - UnlikelyActivity andDevelopment(SoG)ClimateChangeYes Yes Yes Yes LikelyThe only technical report to present evidence from this life stage specifically associated with the2009 returns was the report on marine factors, which outlined a set of extreme conditionsencountered by this cohort that demonstrates plausibility, exposure, correlation, the exceedanceof the observed historical range of variability for several metrics, and the differential survival ofcertain stocks and age-types. The conclusion is thus that it is very likely that marine conditionsduring the coastal migration life stage contributed to the poor returns observed in 2009.4.4.7 Key things we need to know betterThere are several major elements about the life history of Fraser River sockeye salmon that arepoorly understood and prevent a better understanding of the contribution of key stressors in thislife stage to the overall decline in the population. These include:1. estimates of number of smolts leaving the Fraser River (preferably by stock) wouldindicate how many sockeye salmon might actually be dying during their outmigrationbefore even encountering the stressors they face in their marine environment. Presently,there are only some estimates available for Chilko and Cultus.2. information on the health and condition of smolts leaving the Fraser River, includingsize, contaminant and disease burdens, signs of temperature stress, would providevaluable insight into the contribution of freshwater stressors prior to reaching the ocean.Even if a high proportion of smolts survive until the ocean, they may be extremelyvulnerable to only small changes in the stressors they will face during their coastalmigration if they are already in poor condition when they arrive.70