Fraser River sockeye salmon: data synthesis and cumulative impacts

4. increased data on biological ocean conditions would increase the ability to determine thebroad scale impacts of variability in physical and ocean conditions and changing climateon the whole ecosystem.5. integrated ecosystem models and bioenergetic models could help increase understandingof relationships among predators, prey, and food resources, under both presumed currentconditions and hypothesized future conditions. In most cases there are not enough basicdata available to accurately develop such models but often they can still offer insight intowhich uncertainties are most important to resolve.6. analyses of differences in the duration of ocean residency as for each of the Fraser Riversockeye salmon stocks with data on recruits by age type would show whether or not theproportions of stocks remaining an extra year in the ocean are changing, and how theseproportions may very among stocks and years.Items 1-5 represent critical gaps in our understanding of the life history of Fraser River sockeyesalmon, where neither the current situation nor historical conditions are well understood.Knowing the natural baseline for these elements would better inform our understanding of howpatterns have changed, but data collected now can only inform our understanding of the currentreality. Item 6 is different in that such analyses could be performed with the available data, buthave not been done within the Cohen Commission scientific projects.4.6 Stage 5: Migration back to SpawnStage 5 includes the period from the time returning adult sockeye enter the Fraser River to thetime that they spawn. En-route mortality is estimated as the difference between spawnerabundance estimates at Mission and on the spawning ground, after accounting for in-riverharvest upstream of Mission. Pre-spawn mortality is the rate of mortality of female spawners thatarrive on the spawning ground but fail to spawn, dying with most of their eggs retained in theirbody.4.6.1 Plausible mechanismsAs illustrated in the conceptual model (Figure 3.3.2-1), the stressors of potential concern include:climate change, which alters temperatures in the Fraser River increasing en-route mortalityand impacts from pathogens; pre-spawn mortality; habitat conditions in both the LowerFraser River and migratory corridors; and contaminants.Some of the above-described mechanisms have well-established interactive effects. Strong riverflows and warm temperatures demand considerable energy expenditures for returning spawners.80