Fraser River sockeye salmon: data synthesis and cumulative impacts

and therefore the total recruits in the following generation (though perhaps not recruits/spawner).It is also possible that sub-lethal but stressful conditions could affect the quality of eggs and fryof the next generation, which could affect recruits/spawner, though results to date exploring thisquestion are limited and equivocal. Therefore, en-route mortality is clearly correlated with thedecline in the Fraser fishery, though not with indices of productivity.With respect to conditions in 2009 and 2010, Hinch and Martins (2011) note that rivertemperatures were well above average in 2009, exceeding 18 o C during the period from a fourweek period from late July to late August, and that at least 50-60% migrated in-river earlier thantheir historical timing. While data are not yet available on 2010 en-route mortality, rivertemperatures were also warm, though not as stressful as in 2009. The big difference between2009 and 2010 was in the number of returning spawners, which is assessed prior to en-routemortality.Hinch and Martins (2011) found no clear indication that pre-spawn mortality, at the run-timinglevel, has been increasing over the recent few decades in concordance with increasing en routemortality, with the possible exception of the past 25-year trend in Late-run pre-spawn mortalitythat shows a general increase but with high variability.There are not sufficient data to examine correlations between disease in returning spawners andvarious productivity indicators, or with en-route mortality. Hinch and Martins (2011) note thatmortality rates from a parasitic kidney disease increase in Weaver Creek Late-run sockeye asthey are exposed to higher temperatures (measured as accumulated degree-days), and thatbacterial infections causing gill damage are more common as temperatures increase. Thus, Frasertemperature data may be a useful proxy indicator of both en-route mortality and disease impacts.As for Stages 1 and 2, the available evidence does not support the hypothesis that exposure towater contaminants during the upstream spawning migration could be a contributing factor todeclines in Fraser sockeye productivity (MacDonald et al. 2011, Section 5.4). The post-juvenileindex of sockeye productivity declined with increasing values of a water quality index for theupstream migration period (i.e., the opposite pattern from what one would expect if contaminantswere a cause of the productivity declines). There was no relationship between the water qualityindex and the full life cycle index of productivity.When examining correlations between life cycle productivity and summer air temperatureacross adult migration, Nelitz et al. (2011; Section 4.2; Table 17) found that 16 stocks of 18Fraser stocks had negative correlations (i.e., years with warm summer air temperature along themigration corridor tended to be associated with years of lower total productivity), though only 184