Fraser River sockeye salmon: data synthesis and cumulative impacts

Response: We have further emphasized the early marine environment in ourrecommendations for future work, in both the Executive Summary and Section 5.2.2. Wehave further emphasized the importance of the knowledge gap on pathogens, especially inour recommendations. We believe that we have already placed sufficient emphasis onPoint ‘b’, regarding the freshwater environment.2. The following key, inherent weaknesses in the multiple regression approachneed to be more solidly described and highlighted.a. Linearity: By necessity, most of the analyses appear to have assumed thateach factor, on its own, contributes a linear effect. There was an attemptto consider the so-called hockey stick model with a linear effect kicking inafter a threshold was passed, but this approach is a relatively simplisticway to address this issue. There is typically inadequate justification forassuming the presence of a sharp threshold, and data such as in FigureA3.5-3 are inadequate even for distinguishing between a hockey-stickmodel vs. a parabolic relationship let alone identifying the location of athreshold or the start of a downward trend 17 . Additivity: It seems to methat, when assessing cumulative impacts, the potential for nonlinear andnon-additive interactions is key. The authors address a related issue intheir Figure 2.3-1, but this figure seems to be focused primarily on theextent to which multiple, minor stressors might accumulate, potentiallyover several life stages, but in a sort of additive fashion, to produce a largeimpact over the entire fish life cycle. It does not address the potential forsome factor, perhaps a pollutant encountered in the Salish Sea, topossibly combine with a shortage of food in Queen Charlotte Sound toproduce a devastating impact on marine survival when either of thesefactors on its own might not present the fish with a significant challenge.b. Several candidate explanatory variables are in fact functions over time(e.g., sea surface salinity or river discharge). The authors sensiblyattempted to use basic background information, such as the timing of themigration run, to reduce these functions to simple averages over areasonable time window. However, in my work on Rivers Inlet sockeyesalmon, I have found that there can be surprising timing anomalies whosecauses are not immediately clear – sometimes even after they have cometo our attention. I would recommend that this potential be highlighted aswell. In addition, though there is insufficient time for the authors to developa functional regression analysis, this technique can address these sorts ofissues more definitively. 1817 Chiu, G. Lockhart, R. and Routledge, R. 2006. Journal of the American Statistical Association, 101::542–553.18 Ainsworth, L.M., Routledge, R., and Cao, J. 2011. Functional Data Analysis in Ecosystem Research:the Decline of Oweekeno Lake Sockeye Salmon and Wannock River Flow. Journal of Agricultural,Biological, and Ecological Statistics. Available online (DOI: 10.1007/s13253-010-0049-z).151