Fraser River sockeye salmon: data synthesis and cumulative impacts

more important question is: what is the net impact of Steller sea lions on sockeye salmon?However, predation is a major part of sockeye salmon's natural lifecycle; substantial exposure topredation should be expected even if predation has not substantially contributed to the decline ofFraser River sockeye salmon.Very little is known about the exposure of Fraser River sockeye salmon to pathogens anddisease. Relatively few outbreaks of disease have ever been documented in BC sockeye salmon(Kent, 2011). However, this is not strong evidence against exposure to potentially importantdiseases because there is simply very little research on wild fish; most research focuses onhatchery fish and there is minimal data on the marine phase at all (Kent, 2011). There iscurrently poor understanding of the prevalence, geographic distribution, and virulence ofpathogens that wild sockeye salmon might be exposed to in the marine environment (Kent,2011).Johannes et al. (2011, Section 4) have concluded that the potential exposure of sockeye salmonin the Strait of Georgia to impacts from human activity and development 12 (evaluated in termsof geographic overlap and magnitude of interaction) are “nil” to “low” for the followingcategories of potential stressors: population growth and urbanization; agriculture and forestryland use; large industrial and infrastructure projects; solid and liquid waste; and dredging, diking,and disposal at sea; contaminated materials; and, nonindigenous species introductions. Thegeographic overlap is evaluated as a moderate only for shipping and vessel traffic, but themagnitude of interaction is still only evaluated as low (Johannes et al., 2011).Another poorly understood factor is the extent to which the Strait of Juan de Fuca isoccasionally used by post-smolts leaving the Strait of Georgia, and how this behavior may varyover time and among specific stocks. McKinnell et al. (2011) provide a summary of the availableevidence on the use of this alternate migration route. Any sockeye salmon that use this routemight avoid exposure to potential stressors in the northern Strait of Georgia and Johnstone Strait,but it appears that the use of this route has been relatively rare in sockeye salmon.McKinnell et al. (2011, section 7.1.1) explain how the resolution of most marine data does notcorrespond with the fine scale variability that sockeye salmon actually experience as theymigrate up the coast. Regional data is often inferred from only a single or relatively few point12 “Human activities and development” refers specifically to those activities and developments considered withinTechnical Report #12 (Fraser River Sockeye Habitat Use in the Lower Fraser and Strait of Georgia), which do notinclude salmon farms. Exposure to salmon farms will be covered in the technical report on aquaculture, which iscurrently in progress. The present report does not provide any conclusions regarding salmon farms.60