Fraser River sockeye salmon: data synthesis and cumulative impacts

o Can you find the same shared trend in productivity for stocks outside the Fraser? 2Marine Mammal, Fish and Bird PredationAndrew Trites, UBCVilly Christensen, UBCThe overall objective of this study is to evaluate the effects of predators on Fraser River sockeyesalmon, with an extensive review of primary literature. Dr. Trites reported that in generalsockeye salmon is not an important part of marine mammal diets. Among those mammals thateat salmon, sockeye is not a preferred prey species. There is no evidence of significant predationon smolts, only adult sockeye. Data were too sparse to assess the predator impacts on differentsockeye stocks. Evidence agrees with the PSC report on several points including the increase inSteller sea lions since protection 40 years ago, especially in recent years (Peterman et al. 2010).Likewise, sightings of Pacific white-sided dolphins have increased, harbour seal populationshave recovered to historical levels in the Strait of Georgia and humpback whale populations aregrowing in BC and Alaska. Unlike the PSC report findings, the researchers concluded that totalfood consumption by mammals is not large enough to affect sockeye. While the timing ofsockeye declines coincides with increases in Stellar sea lions, sockeye form only a small fractionof their diet (about 2-3%). Information gaps include outdated and seasonally limited data forharbour seals (only available for summer), DNA analysis of prey remains would determinespecies of salmon consumed by predators.Dr. Christensen reported on fish and bird predation in the Georgia Strait, Queen Charlotte Soundand Northeast Pacific Ocean (not addressed in the PSC report). Based on the available data,freshwater predators are not likely to have caused declines in sockeye salmon. Similarly,predation by marine birds does not seem to be a likely contributor to Fraser sockeye declines.Recent declines in other fish species could increase sockeye’s relative importance as prey forocean predators. Specifically, salmon sharks and daggertooth should be considered for furtherstudies.The most important unknown is monitoring the changing abundances of key predators infreshwater and marine ecosystems. In order to explain what happens in these ecosystems, weneed to understand changes in productivity, fisheries and food webs. Information is poor for theopen ocean and in freshwater. DFO’s attempts to implement integrated management have beenvery limited.2 This question was addressed by Peterman and Dorner’s presentation. In general, stocks outside the Fraser do showthe same shared trend in productivity.