Fraser River sockeye salmon: data synthesis and cumulative impacts

Relative Likelihood of Alternative HypothesesWorkshop participants were asked to examine the PSC Report Probability of, or relativelikelihood of, alternative hypotheses (i.e. Table E-1, Peterman et al. 2010). Working insubgroups, they were asked to compare the PSC conclusions to participants’ own research andthe findings presented during the workshop. When participants were in disagreement with thePSC report, they were asked to give a new rating to each of the hypotheses. Since the ninealternative hypotheses from the PSC report did not exactly correspond to the twelve areas ofresearch presented here, participants also added new hypotheses and ratings when appropriate.Given the available evidence, participants judged the relative likelihood that a given hypothesiscontributed to both the poor returns in 2009 and the long-term decline in productivity of FraserRiver sockeye salmon. Participants used qualitative terms (very likely, likely, possible, unlikely,or very unlikely) to rate the hypotheses. The colour of shading reflects the degree of importanceassociated with each factor (dark=major contributing factor, light=contributing, but not majorfactor). After some discussion about how to interpret Table E-1, participants clarified that thistable only considered whether or not the alternative hypotheses were likely to be contributingfactors (i.e., multiple factors are likely to be involved in the observed declines). For summarypurposes and simplification of results, the entire range of values given by participants areindicated in the updated table, whether or not there was a consensus. There are three importantcaveats regarding this exercise:o the PSC Panel had several days to carefully review and debate evidence which led togreater convergence on ratingso participants at the Cohen Commission workshop had only 1.5 hours for this exercise,with each subgroup doing their ratings independently, leading to a greater variation injudgments; ando only a few participants attended both the PSC and Cohen Commission workshop, andwere able to weigh both sets of presented evidence.There was some variation in support of hypotheses, which is reflected in the updated table(Appendix D). Overall, there was a greater range of variation in ratings within each hypothesis:14 of 22 hypothesis/timeframe combinations were given relative likelihoods that spanned 3 ormore rankings. Of all the rankings assigned by workshop participants, 21 hypothesis/likelihoodratings were in agreement with the conclusions of the PSC panel and 28 ratings were indisagreement.The main conclusions and differences about the relative likelihoods of each hypothesis are asfollows: