Population Viability Models for Salmon Recovery - a Pacific Northwest Perspective

Population viability analysis (PVA) plays a significant role in recovery planning under the U.S. Endangered Species Act (ESA). For Pacific salmon (Oncorhynchus spp.), ESA recovery planning is in progress for 27 listed population units within 5 species, and almost all of these plans include PVA modeling. Recovery planning is being conducted by regional committees, each of which developed local approaches to defining viability and to using PVA. These approaches cover a wide range of methods and complexity, including rules of thumb, linear stochastic matrix models, habitat-structured life-history simulations, and structured Bayesian population simulations. The choice of approach depends on various factors, including the recovery criteria framework (objectives of the analysis), the level of detail needed to link specific management questions, and data availability. An important aspect of model choice is whether absolute or relative predictions are required, for example, whether the model is part of a criterion for delisting or is used to compare alternative recovery actions. While this diversity of approaches limits comparing results across species and population units, it is an inevitable consequence of both life-history diversity among species and the diversity of factors that have led to the decline and listing of various populations.