Guidance on the Use of Best Available Science under the U.S. Endangered Species Act

The Endangered Species Act’s best available science mandate has been widely emulated and reflects a Congressional directive to ensure that decisions made under the Act are informed by reliable knowledge applied using a structured approach. We build on a standing literature by describing the role of the best science directive in the Act’s implementation and best practices that can be employed to realize the directive. Next we describe recurring impediments to realizing determinations by the federal wildlife agencies that are based on the best available science. We then identify the types of data, analyses, and modeling efforts that can serve as best science. Finally, we consider the role and application of best available science in effects analysis and adaptive management. We contend that more rigorous adherence by the wildlife agencies to the best available science directive and more assiduous judicial oversight of agency determinations and actions is essential for effective implementation of the Act, particularly where it has substantial ramifications for listed species, stakeholder segments of society, or both.