Fraser River sockeye salmon: data synthesis and cumulative impacts

The two key objectives defining our WOE approach are:1. Use the full breadth of evidence presented within the Cohen Commission projects.2. Synthesize and evaluate the evidence within a logical and systematic framework.Whereas it is not realistic to use every single piece of evidence presented in this body ofscientific work, the intent is to incorporate the breadth of evidence presented, recognizing thatthe weight of evidence synthesis cannot possibly capture the depth of evidence presented withineach project. The framework used to evaluate the evidence is based on publications in the fieldof Retrospective Ecological Risk Assessment (RERA), specifically Forbes and Callow (2002),and Burkhardt-Holm and Scheurer (2007). Their approach is considered appropriate when fourcriteria are met, all of which apply in the case of Fraser sockeye:1. The adverse ecological impact has already occurred.Fraser River sockeye salmon productivity has been declining over recent decadesand the 2009 returns were exceptionally poor.2. The evidence for this impairment already exists.Data on the abundance Fraser River sockeye salmon recruits and spawnersconfirms the declines in both returns and productivity.3. Factors that could potentially be causal agents of this impairment have been identified.The Cohen Commission identified a selection of broad factors that could feasiblyhave contributed to the decline of Fraser River sockeye salmon, and within eachof the Cohen Commission Technical Reports a range of specific potentialstressors are identified. The Pacific Salmon Commission workshop in June 2010(Peterman et al.) identified a similar, though not identical, set of factors.4. The evidence available to evaluate the likelihood of each possible factor is limited.The constraints on the quantity and quality of the evidence available with whichto evaluate potential contributors to the decline of Fraser River sockeye salmonare representative of many ecological problems: 1) quantitative data are usuallyshort, incomplete, sparse, or simply non-existent; 2) where quantitative data doexist, they are likely to be complex, variable, ambiguous, and/or noisy, makingrigorous statistical analysis difficult or impossible; and 3) available evidence iscorrelative at best, and complicated by the interaction of multiple confoundingfactors that are uncontrollable, or even unknown.Forbes and Callow (2002) state that “the primary challenge in retrospective risk assessment is tomake best use of the available evidence to develop rational management strategies and/or guide21