Fraser River sockeye salmon: data synthesis and cumulative impacts

2.0 Cumulative Impacts or Effects2.1 What are Cumulative Impacts or Effects?One of the primary goals of this project is to examine the potential cumulative impacts on FraserRiver sockeye salmon productivity, of multiple stressors acting at different times and places. Theterms cumulative effects and cumulative impacts are frequently used interchangeably. In Section2.0 we use the term “cumulative effects” to respect the convention of the literature to which werefer; however, throughout the rest of the report, we generally use the term “cumulative impacts”to respect the language with which our original assignment from the Cohen Commission wasdescribed.We start by exploring what is meant by “cumulative effects”. Unfortunately, while there is nouniversal definition of “cumulative effects”, there are some general concepts worthy of review.What is an effect? Greig (2010) defines an environmental effect as, “a change in a component,property or function of an ecosystem.” In the present project we are concerned specifically withadverse environmental effects that “diminish a desirable component, property, or function of anecosystem” (Greig 2010), namely, the ecosystems that support Fraser sockeye, and the sockeyestocks themselves.What is it that is being affected? To assess the consequences of particular stressors, we need todefine the Valued Ecosystem Component (VEC), the focal component that society wishes toprotect, conserve or enhance. These are the sockeye stocks occupying the 36 Conservation Unitsin the Fraser River watershed.Which effects are being examined cumulatively? There are various conceptualizations relevant tothis question. Cumulative effects could be conceived as:• the total impact of a single type of stress that has occurred repeatedly over time,possibly increasing in frequency or magnitude (e.g., the cumulative effect of waterpollution in the Fraser River estuary over the past four decades);• the total impact of a single type of stress that occurred repeatedly over space (e.g.,the cumulative effect of multiple mountain pine beetle outbreaks across the entire FraserRiver watershed);• the total impact of many different types of stressors at one point in time or over aperiod of time (e.g., the cumulative effect of changing climate, increased mammalpredation, and increased harmful algal blooms).Even when multiple stressors are examined together, there is a distinction between examining therelative magnitude of impacts of each stressor, versus examining the mechanisms by which5