Methods of extinction risk assessment developed for US West Coast salmon

In assessing extinction risk for Pacific salmon (Oncorhynchus spp.), a variety of interacting risk factors are considered, some of which can be quantified but many of which are qualitative. In addition to the common measures of population abundance and trends for individual populations, these factors include ecological and genetic effects of hatchery fish, changes in life history traits, selective effects of harvest, trends in freshwater habitat condition, and climate variation. Combining such information into an assessment of the overall degree of risk facing populations and species relies heavily on scientific judgement rather than explicit quantitative criteria. To organize multifactor information and ensure consistency, a risk-matrix method has been implemented in which individual risk factors are scored on a 5-point scale, and then combined into an overall assessment of extinction risk.