Fraser River sockeye salmon: data synthesis and cumulative impacts

The objective of our approach is to use, wherever possible, all the major sources of evidencebrought forth by the investigations and analyses presented in the other Cohen Commissiontechnical projects. Whereas it is not realistic to use every single piece of evidence presented inthis body of scientific work, the intent is to incorporate the breadth of evidence presented,recognizing that the weight of evidence synthesis cannot possibly capture the depth of evidencepresented within each project. However, this approach still requires the compilation andsynthesis of many different types of both qualitative and quantitative evidence (as describedabove), available over varying timeframes. All of these lines of evidence are then examined andpresented within a logical and systematic framework. The structure of this framework is basedon the work of Forbes and Callow (2002) and Burkhardt-Holm and Scheurer (2007) onRetrospective Ecological Risk Assessment (RERA) but further modified where necessary tofunction within the constraints of the present project.Retrospective Ecological Risk AssessmentOne of the obvious but crucial attributes of RERA is that it is applied retrospectively to examineadverse ecological impacts that have already occurred. RERA is intended for situations wherethe evidence for ecological impairment already exists and a number of factors have already beenidentified as possible causal agents. The objective of RERA is thus to evaluate how likely it isthat each of those potential causal factors may have contributed to the adverse ecological impactsobserved. However, there are usually many constraints and limitations on the quantity andquality of evidence available to evaluate such ecological impairments. For ecological problemsthe available evidence is often very limited and predominantly qualitative (Forbes and Callow,2002). Quantitative data is usually short, incomplete, sparse, or simply non-existent, and wherelimited quantitative data does actually exist, it is likely to be complex, variable, ambiguous,and/or noisy, often making rigorous statistical analysis almost impossible (Forbes and Callow,2002; Burkhardt-Holm and Scheurer, 2007). The available evidence is often correlative at best,and further complicated by the interaction of multiple co-existing hypotheses and confoundingfactors that are uncontrollable, or even unknown (Forbes and Callow, 2002; Burkhardt-Holm andScheurer, 2007). Given this context, the objective of incorporating WOE into RERA is thereforeto provide a framework in which to synthesize and evaluate the evidence that is available in amanner that is transparent, systematic, logical, and less subjective (Forbes and Callow, 2002;Burkhardt-Holm and Scheurer, 2007). The WOE RERA approach outlined by Forbes and Callow(2002), which was subsequently adapted by Burkhardt-Holm and Scheurer (2007), thereforeappears to be an extremely suitable basis for the present work due to the following criteria beingwell met:196