Fraser River sockeye salmon: data synthesis and cumulative impacts

7. Removal:“Has the removal of the stressor led to an amelioration of the effects in the population?”• Response to a removal may be delayed rather than immediate• Lack of improvement does not disprove the importance of a causal factor• Affirmative results are stronger evidence than negative resultsAdaptation of the Methodology to the Present ProjectWe have adapted this methodology as necessary in current circumstances. One of the importantlimitations to our ability to apply this methodology in full is that we are applying this approachretrospectively to a series of projects that themselves did not utilize such a framework. Thereforeit is not possible to satisfactorily answer all of the WOE questions within this framework becauseit is not possible to answer questions that were not asked in the projects themselves.Consequently, we have modified the structure by grouping questions 4-7 into a single questioncovering all other evidence beyond question 1-3, as shown in Figure A3.5-1.Within each life stage we examine the major potential causative agents identified within theother Cohen commission technical research projects. For each stressor, we synthesize: 1) theplausibility of each mechanism, 2) the evidence that Fraser River sockeye salmon have beenexposed to the stressor, 3) the evidence for any spatial or temporal correlation between thestressor and the observed patterns in the Fraser River sockeye salmon and, where possible, theobserved patterns in non-Fraser River sockeye salmon, and 4) other evidence regarding thepotential impact of the stressor on Fraser River sockeye salmon (especially including anyinformation on question 4-7 above). Within each step of this evaluation, we emphasize both whatis known and what is not known, and within each life stage we identify the key things that needto be known better. Based on the evidence available, a relative likelihood is assigned to eachbroad category of stressor (e.g., contaminants, predators, etc.) at each life stage, according to theframework shown in Figure A3.5-1. The conclusions from each life stage apply to thecontribution of each broad impact factor to the overall in the observed Fraser River sockeyesalmon. There may be cases in which the relative likelihoods of particular stressors do not allalign perfectly with the relative likelihood assigned to the parent stressor category. For example,the evaluation of the overall impact of predators may not match the evaluation of particularpredators. There may also be cases in which the results from this evaluation framework might bedifferent for individual stocks. However, the focus of the present project is to evaluate thelikelihood that each broad factor has made a significant contribution to the overall observeddecline in the Fraser River sockeye salmon stock complex.199