Fraser River sockeye salmon: data synthesis and cumulative impacts

possibly even negligible component of the predators diet. This type of predator-prey relationshipmay be fundamentally important to the prey while being of virtually no importance to thepredator.The third challenge (really an extension of the second) is unknowables. We cannot know theexplanatory influence of a factor that has not been monitored in a given year or location. Whenthere are no data, one cannot make any inferences either in favour or opposed to a givenhypothesis.3.3 Current Framework3.3.1 OverviewOur approach to cumulative impacts analysis comprises three components:1. Understand the patterns of change in the productivity of Fraser River sockeye salmonstocks (and other sockeye stocks) over the past several decades. This is the patternthat we are seeking to explain. This component is the primary focus of Project 10(Peterman and Dorner, 2011), and is summarized in section 4.1 of this report.2. Identify factors that could feasibly have contributed to the observed patterns ofchanging productivity in Fraser sockeye salmon. These potential explanatory factorsdo not necessarily need to be mutually exclusive (i.e., there may be multiple causes ofthe observed patterns). The various factors are the focus of other Cohen CommissionTechnical Reports and are covered in much greater detail therein.3. Assess the relative likelihood of feasible explanatory factors and their potentialinteractions, the focus of sections 4.2 to 4.7 of this report. We have compiled theevidence presented within other Cohen Commission Technical Reports into a weightof evidence approach.3.3.2 Conceptual modelWe developed a conceptual model illustrating the factors potentially affecting each life stage(Figure 3.3-1), so as to:1. organize the factors identified within the Technical Reports as being potentialcontributors to the Fraser sockeye productivity declines, and indicate the life stagespossibly affected by each factor;.2. represent some of the key interactions among factors, both within and across TechnicalReports;16