As part of the Water Quality Benefits Evaluation, experts built a model to estimate potential effects of King County water quality projects on the future health of the Southern Resident Killer Whale (SRKW) population. This model was developed to provide King County planners with a transparent and consistent way to evaluate whether local water quality projects under consideration (e.g., stormwater management, source control, etc.) have the potential to improve the population health of SRKWs. The model uses information about the quantity of salmon coming from King County watersheds into the Salish Sea, and King County’s relative contribution to the amount of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in SRKW’s diet to estimate potential effects of King County water quality projects on the future health of the SRKW population. Though noise disturbance is present in the model, it is not a focus because it is not influenced by water quality projects.

Subject matter experts from a variety of related backgrounds guided the SRKW model development. Our team used a robust expert elicitation process to create the structure and probability estimates used in the model. All the conditional probability tables within the SRKW model are based on expert-derived estimates, not empirical data. Considering the numerous data gaps and uncertainties inherent in this type of model, its output should not be treated as a reliable forecast of future SRKW population health. Instead, it should be used to make general predictions about whether local water quality projects under consideration could potentially improve SRKW population health and set reasonable expectations about the direction and magnitude of their impacts on SRKWs.