Fraser River sockeye salmon: data synthesis and cumulative impacts

investigated ecosystems” (Burkhardt-Holm and Scheurer, 2007). This method both integrates theavailable data and facilitates the summary and communication of results.The WOE approach outlined by Burkhardt-Holm and Scheurer (2007) challenges the availableevidence for each potential factor with the following sequential questions. The answers to someof these questions are necessarily site-specific, whereas others may be derived from a broaderrange of similar case studies.1. Plausible mechanism:“Does the proposed causal relationship make sense logically and scientifically?”2. Exposure:“Is there evidence that fish population is, or has been, exposed to be causal factor?• However, presence of a causal factor alone does not indicate exposure• Exposure might not be proven but only suspected• Exposure may be historical as well as current3. Correlation/Consistency:“Is there evidence for association between adverse effects in the population in thepresence of the causal factor, either in time or space?”• Any type of formal relationship may be taken as evidence but statisticalcorrelation is preferable• Recognize that correlation does not imply causation• Acknowledge potential scale issues between potential stressors and ecologicalresponses4. Thresholds:“Do the measured or predicted exposure levels exceed quality criteria or biologicallymeaningful thresholds?”• Both current and historical exceedances of thresholds are relevant5. Specificity:“Is there an effect in the population gnome to be specifically caused by exposure to thestressor?”• Absence of a specific response does not prove a lack of exposure or impact• Presence of a specific response is stronger evidence than absence6. Experiments:“Have the results from controlled experiments in the field or laboratory lead to similareffects?”• Results from controlled experiments are stronger evidence than observationalstudies198