Fraser River sockeye salmon: data synthesis and cumulative impacts

was also shown that tagged fish returned to the river suffered much higher mortality if they hadbeen kept in warmer water. It’s still not understood why the fish are migrating earlier but theyare returning in poor physiological condition and then they encounter much higher rivertemperatures.Pre-spawn mortality: There is a long history of information showing that this affects all stocks,with mortality of up to 90%. Occurrences are variable and episodic among years and may behigher and more variable in recent years. There does not appear to be an overall trend for Frasersockeye but it does appear to be higher and more variable in Late-run stocks.There are many causes of PSM, including disease, stress and time spent on spawning grounds.There is evidence that it is simply a continuation of the processes that are killing fish during theirreturn migration.Conclusions: Migration mortality is substantial in many stocks across all run-timing groups inrecent years, particularly when river migration temperatures exceed 18 degrees C. Lab and fieldstudies show there are stock-specific differences in how fish deal with acute and chronic hightemperatures. Migration mortality is likely a contributing factor in declining trends in spawningabundance for stocks that don’t cope well with high temperatures (early and late runs). Prespawnmortality reduces the number of effective female spawners and could be a factor indeclining productivity for some late-run stocks.DFO and others are starting to do studies on possible inter-generational effects, but results todate are limited and equivocal.This study agrees with the three conclusions from the PSC report regarding en-route mortality,pre-spawn mortality and intergenerational effects.Information gaps: These include intergenerational effects, direct measures of migrationsurvival, and effects of bycatch/discard releases on survival. All three of these information needsare knowable.Climate & climate change effects on Fraser sockeye: literature reviewEduardo MartinsThe study objectives were to review the literature on documented effects of climate on sockeyeand to make a qualitative assessment of the role of recent climate change on the decline in Frasersockeye productivity.The presentation discusses how the literature was compiled, climate change and its effects onFraser sockeye habitats, the likelihood of climate change effects on survival, survival by lifestageand the likelihood of changes.A search was undertaken of primary and grey literature specific to sockeye. Most of the papersfocused on freshwater, though there have been more papers on the marine in the past 2 - 3 years.Climate change and Fraser sockeye habitats: Summer temperatures in the Fraser River havewarmed by 2 degrees C since the 1950s, and 13 of the last 20 summers have been the warmest onrecord. There have also been substantial changes in precipitation (an average increase of 22% percentury but highly variable across BC). Fraser River flows show no trend, though the freshet isslightly earlier. For Georgia Strait and the Gulf of Alaska, temperatures have warmed by 0.2563