Fraser River sockeye salmon: data synthesis and cumulative impacts

stressors interact or combine to affect sockeye. The first type of analysis might examine allstressors to determine which factors made the largest independent contribution to a change in theVEC. For example, what has had a larger relative effect on sockeye productivity: increases inpredators, increases in diseases and parasites, decreased food resources, or increased competitionfor food? Such a question explores the relative importance of each individual factor.The second kind of analysis looks at how multiple effects might combine (i.e., how multiplestressors might interact to produce a combined impact different (in form or magnitude) fromeach stressor acting independently). For example, how might increasing ocean temperatures haveaffected predators, diseases and parasites in a way that changes their overall impact? There aremany ways in which individual effects might combine to form types of “cumulative effects”.Sonntag et al. (1987) classified cumulative effects into the following types: linear additiveeffects, amplifying or exponential effects, discontinuous effects, and structural surprises. Greig etal. (2003) suggested an alternative categorization of types of cumulative effects: additive,compensatory, synergistic, and masking.2.2 Cumulative Effects Assessment“Cumulative Effects Assessment” (CEA) specifically refers to the process in which the effects ofa proposed project are assessed together with the effects of other past, present or future projectsto determine the overall cumulative effects on Valued Ecosystem Components (VECs). Underthe Canadian Environmental Assessment Act (CEAA) CEA is required for all projects where theAct applies and is thus a part of the project approval process. The issue at hand, a retrospectiveinvestigation into the potential causes underlying the decline of Fraser River sockeye salmon, isin many ways fundamentally different from the forward-looking Environmental ImpactAssessment process. However, there are many important shared concepts about how “cumulativeeffects” are defined and used, or rather how they should be, that are critical to understand.According to current practice, two criteria may be used to determine if CEA is required for aproposed project. First, in some cases it has been argued that the effects of the individual projectmust be significant on their own (L. Greig, pers. comm.). If the effects of an individual projectare insignificant, it is assumed that the project’s contribution to potential cumulative effects willalso be insignificant and a CEA will not be required for project approval. This is inappropriatesince effects that are individually insignificant when combined with other effects can result insignificant impacts. Second, some practitioners take the view the proposed project and otherrelevant developments/projects must have effects of the same type, with the same timing, at thesame location. If multiple projects have effects that differ by type or timing or location, it is6