Fraser River sockeye salmon: data synthesis and cumulative impacts

thermal optimum, with longer exposures to freshwater diseases and parasites. Weaver Creeksockeye, one of the Late Run stocks, have lost of 50 to 100% of their total run due to en-routemortality, with higher mortality rates generally occurring in the years with earliest migration(Hinch and Martins 2011, Figure 2.2).Hinch and Martins (2011; section 1.7.1) cite climate model studies predicting that summer watertemperature in the Fraser River may warm by ~ 2.0 o C over the next 100 years, with a worseningof en-route mortality. Other research studies predict that the number of days per year exceedingsalmonid critical temperatures may triple in the Fraser River over the next 100 years and morethan 90% of a stock may be forced to migrate under suboptimal temperatures for physiologicalperformance.The methods of estimating exposure to contaminants and habitat stressors along the migrationcorridor have already been described in section 4.3 for Stage 2 (smolts).Figure 4.6-1. Daily average temperature in the lower Fraser River averaged among years within two time periods(thick line: 1951-1990; thin line: 1991-2010) over the summer months. The period of entry and passage in the lowerFraser River for the four main run timing groups are indicated by solid lines above the figure. Since 1995, segmentsof all Late-runs have been entering the river much earlier than usual and this is indicated by the dashed line. Source:Hinch and Martins (2011; Fig. 2.8)82