Fraser River sockeye salmon: data synthesis and cumulative impacts

3.0 Complexity, Caveats, and Overall Approach,3.1 Complexity of the Ecological SystemOver the 4 to 5 years of their life cycle, salmon encounter largely unmonitored variations inphysical and chemical conditions, food, competitors, predators, and disease, over severalthousand kilometres from high in the Fraser Basin to the Gulf of Alaska, with cumulative andinteractive effects (most unknown), occurring over multiple life history stages in ways that varyfrom year to year. Gaps exist not only in data (limited time series and spatial coverage for manyfactors), but also in fundamental understanding. Under these circumstances, it is extremelydifficult for fisheries managers to accurately predict the expected returns of different salmonstocks in advance of their arrival. Indeed, pre-season predictions of sockeye returns are notreliable for 7 of 18 Fraser sockeye stocks (English et al. 2011; Executive Summary). Previouswork (Walters and Collie 1988, Walters 1989, Myers 1998) has emphasized the difficulties ofpredicting recruitment of fish populations for the purposes of fisheries management, includingthe lack of persistence of environment-recruitment correlations.Rocket science is commonly used as a benchmark when describing the relative difficulty of othersubjects (e.g., “It isn’t rocket science.”). Fisheries science also isn’t rocket science, but it isnonetheless very challenging. Rocket scientists rely on repeatable laws of physics, whereasecological interactions are much more variable over time and space, and much less understood. Ifa rocket scientist had equivalent challenges to a fisheries scientist, s/he would be launching andlanding rockets with all the key variables determining outcomes (gravity, atmospheric pressure,temperature, solar radiation, fuel quality, cosmic rays) radically changing from year to year andplace to place, with little ability to monitor this variation, and considerable uncertainty about thebasic theory behind each of these variables and their interactions.Given the above uncertainties, attributing causes to observed effects is very difficult. Petermanand Dorner (2011, pg. 13-14) express this challenge well:An important concept for readers to keep in mind when considering the evidencepresented in this and other scientific reports to the Cohen Commission is that ecologicalsystems are dynamic and constantly change across time and space. They are composed ofcomplex sets of components that interact to generate responses to concurrently operatingdisturbances arising from both natural processes (e.g., ocean conditions) and humanactivities (e.g., fish farming). Because of such simultaneously occurring natural andhuman processes, it can be very difficult to attribute single dominant causes to observedecological changes, and while it is important to investigate each potential causeindividually, it is important to be aware that it might have been the interaction of severalfactors, rather than one factor per se, that caused the changes. Two well-known case13