Fraser River sockeye salmon: data synthesis and cumulative impacts

annual data points can be interpolated.Hasn't the total sockeye return been increasing along a similar trend to the diversionrate? Is it possible that the average diversion rate (~0.4-0.5) was actually typical backwhen there were a lot more sockeye around (i.e., prior to Hell's Gate slide), and so thispattern is a return to normal migration patterns?Response: We have not attempted to provide any explanation for theses apparent changes.We simply identify diversion rate and age-type proportions as other potential responsevariables that appear to have also experienced changes over recent decades and suggestthat work to increase our understanding of these patterns would likely be beneficial. Theycould be responding to the same factors that have been driving changes in productivity, orsimilar factors, or completely different factors. The reviewer asks an excellent question tobe explored in further research – are these patterns shifting away from “normal” patternsor returning toward “normal” patterns in a long recovery following the catastrophic Hell’sGate slide in 1913? This question is worth further investigation but the time series availableto us cannot offer any insights for that question.We have not conducted any quantitative analyses for this question, but offer the followingqualitative observations based only on a visual examination of the data. First, the diversionrate data appears to indicate a possible shift in the late 1970s to a state of higher diversionrates on average but with greater variability rather than a gradual increase. The “trend”line in Figure 4.5-2 was present in the original figure extracted from Levy (2006); since weonly had access to this figure and did not have access to the original data, we were unableto remove this trend line (but have removed it in this final report). Second, the patterns insockeye salmon returns (e.g. Figure 4.1-5 shows total returns by brood year cycle) do notappear (based on visual inspection) to correspond with the diversion rate pattern. Sockeyereturns were increasing over the 1960s, 1970s, and 1980s (i.e. the pattern starts well beforeany notable changes in diversion rate) and have been decreasing since approximately 1990(i.e. the pattern reverses with no notable change in diversion rates). However, these areonly preliminary qualitative observations and this deserves further quantitativeexamination.P65: it is not clear what the "definitive correlation" compares.Response: This sentence has been rewritten to be a clearer reflection of the idea itreferences.There is considerable repetition of information/review under Stages 3 and 4: can thesebe combined into one section?Response: We recognize that there is some repetition between these stages. In some casesthe information, analyses and knowledge presented in other technical reports did not, orwas not able to, clearly distinguish between these two marine-based life stages andtherefore similar evidence was available for both stages. We have tried to highlight the146