Fraser River sockeye salmon: data synthesis and cumulative impacts

generally better for Alaska sockeye marine survival and worse for Fraser sockeye marinesurvival) and inter-stock variability in other river systems.Hinch hypothesized that thermal (and related) issues play a large role in among and within-stockvariation in en-route and pre-spawn mortality. En route loss observations, lab experiments, andfield telemetry studies showed stock-specific differences in how fish deal with acute and chronicthermal stressors. Most stocks experience substantially elevated mortality rates when migrationtemperatures exceed 18 C˚. The preliminary results and conclusions of the study agree with thePSC findings that en route mortality does not contribute directly to the decline in productivity,defined as recruits per spawner, since en route mortality is already included in the calculation ofrecruits. However, en route mortality clearly reduces the density of spawners, and therefore canhave substantial long term effects on the sockeye fishery. Although there was no overall trend inpre-spawn mortality across all Fraser stocks, Hinch found a trend of increasing pre-spawnmortality in late runs since early migration began in 1995. Migration mortality is likely a greatercontributor to declining trends in spawning abundance for early and late runs, or stocks that donot cope well with high temperatures. Similar to the PSC findings, pre-spawn mortality wasfound to reduce the number of effective female spawners, which could play a role in reducedproductivity for late run stocks. Intergenerational effects are plausible, but the supportingevidence is weak. Overall, climate change is a possible contributor to recent declines in averageFraser River sockeye productivity, given inter-annual and inter-stock variability.There are data gaps that could be improved through future studies (i.e. unknown information thatis “knowable”). There are no direct measures of migration survival, no data on the effects offisheries bycatch on migration mortality, and sparse research on the intergenerational effects.Workshop participants were interested in the earlier timing of the freshet in recent years. There isevidence that zooplankton blooms occur 30 days earlier and for a shorter period. High Fraserdischarge and wind patterns could be linked to the timing of blooms.Data Synthesis and Cumulative EffectsAlex Hall & Darcy Pickard, ESSA TechnologiesThis study seeks to understand the mechanisms by which stressors across all projects interact orcombine. The timeline for this study extends beyond that of the other reports, because it relies ondata from each of the other studies. Using qualitative and quantitative approaches, researcherswill illustrate the potential cumulative impacts of multiple types of stressors through a series ofintegrative frameworks. Qualitative analysis will use a life-history approach with a conceptualmodel of the pathways of different stressors, a spatial life-history diagram illustrating the spatialscale of the sockeye’s life cycle, and an expert evaluation of the relative likelihood of evidence.The latter exercise will build upon findings in the PSC report (Peterman et al. 2010).