Fraser River sockeye salmon: data synthesis and cumulative impacts

1. The adverse ecological impact has already occurred.The focus of the Cohen Commission technical research projects is inherentlyretrospective – Fraser River sockeye salmon productivity has been declining overrecent decades and 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 contracted scientific and technical projects a range of specific potentialstressors are identified.4. The evidence available to evaluate the likelihood of each possible factor is limited.Collectively, the evidence available with which to evaluate all of the factors thatmay potentially have contributed to the decline of Fraser River sockeye salmonreflect virtually all of the constraints and limitations described above.A Method for Incorporating WOE Concepts into RERAForbes 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 guideadditional analyses to gain further evidence about likely agents as causes of observed harm”,which precisely describes the challenge of the present project as well.To address this challenge, Forbes and Callow (2002) present a framework to incorporate WOEconcepts into a RERA, based on earlier methodological linkages that had been developedbetween human epidemiology studies and ecological studies. Their framework uses sevensequential questions to systematically assess the available evidence on each potential causativeagent. These questions are situated within a flow diagram such that the answers can be used tosystematically assign a categorical likelihood (i.e. unlikely, possible, likely, or very likely) toeach potential factor. The overall approach is thus to: 1) formulate the problem, 2) screenpotential agents, and 3) focus future work. Forbes and Callow (2002) demonstrate theirapproach using case studies of several distinctively different ecological problems. Burkhardt-Holm and Scheurer (2007) use this method to assess the decline of brown trout in Swiss riversover the past several decades, but reconfigure the sequence of questions to better reflect thesituation of fish declines in Switzerland. They describe this approach as “semi-quantitativemethod for identifying causal factors are likely to explain adverse effects occurring in197