Recommendations to NOAA Fisheries: ESA Listing Criteria by the Quantitative Working Group

EXECUTIVE SUMMARY The Endangered Species Act of 1973 (ESA) employs a two-category system: listing species either as endangered (in danger of extinction throughout all or a significant portion of its range) or threatened (likely to become endangered in the foreseeable future). Absence of Congressional guidance on how to interpret the terms used in the statutory definitions of these categories has left the task of defining them to the U.S. Fish and Wildlife Service and NOAA Fisheries (National Marine Fisheries Service). To date, neither of these agencies has developed uniform guidelines for listing, reclassifying, or delisting species. The lack of uniform guidelines for listing decisions has led to inconsistencies and inequities in the listing process. NOAA Fisheries responded to this problem by establishing a Steering Committee and a Quantitative Working Group (QWG) to work toward developing quantitative procedures that will make listing decisions " more transparent, consistent, and scientifically and legally defensible. " The Steering Committee, in turn, has provided the QWG with a set of Guiding Principles which state that these procedures should possess characteristics such as applicability, implementability, transparency, flexibility, and equitability. The QWG offers the present report as a possible roadmap by which NOAA Fisheries could eventually develop uniform guidelines for listing, reclassifying, or delisting species. Briefly, the QWG proposes the following process: (1) overarching definitions for both endangered and threatened should be adopted, (2) values of any policy parameters associated with the overarching definitions (e.g., the level of extinction risk corresponding to " endangered ") should be specified, (3) decision metrics that can be used as proxies for (1) and (2) in data-poor cases should be developed for an appropriate range of taxonomic groups or life history types, and (4) all of the above should be done in the context of performance testing (use of simulations to evaluate how well an alternative performs relative to the objective). These four steps are explained further below. The QWG has developed three alternative overarching definitions for " endangered " (EN). The Probability of Extinction Threshold definition states that a species is EN if its probability of extinction within a specified time horizon exceeds some cutoff percentage. The Depensatory Threshold definition states that a species is EN if its abundance, area of distribution, or other relevant metric falls below the level at which depensatory (Allee) effects are likely to predominate or population processes are largely unknown. The Comprehensive Threshold definition is …