U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications
NOAA Technical Memorandum       NMFS-F/NWC-198

Determining MinimumViable       Populationsunder theEndangered Species       Act

byGrant G. Thompson

National Marine Fisheries ServiceAlaska Fisheries       Science CenterResource Ecology and Fisheries Management       Division7600 Sand Point Way NE, Bin C15700Seattle, WA 98115-0070       
June 1991      
U.S. DEPARTMENT OF COMMERCENational       Oceanic and Atmospheric AdministrationNational Marine       Fisheries Service

NOAA NMFS F/NWC-198: Determining Minimum Viable Populations under the Endangered Species Act

NOAA Technical Memorandum NMFS Series

The Northwest Fisheries Science Center of the National Marine Fisheries Service, NOAA, uses the NOAA Technical Memorandum NMFS series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible due to time constraints. Documents published in this series may be referenced in the scientific and technical literature. 

The NMFS-NWFSC Technical Memorandum series of the Northwest Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest & Alaska Fisheries Science Center, which has since been split into the Northwest Fisheries Science Center and the Alaska Fisheries Science Center. The NMFS-AFSC Technical Memorandum series is now being used by the Alaska Fisheries Science Center. 

Reference throughout this document to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.

This document should be cited as follows: 

Thompson, G.G. 1991. Determining Minimum Viable Populations under the Endangered Species Act. U.S. Dep. Commer., NOAA Tech. Memo. NMFS F/NWC-198. 78 p.

This document is available to the public through:

National Technical Information ServiceU.S. Department of Commerce5285 Port Royal RoadSpringfield, VA 221611-800-553-8647orders@ntis.fedworld.gov
ABSTRACT
Conservation biologists have typically viewed population viability as a stochastic phenomenon. Although many factors can influence population viability, this paper focuses on the role of population size. More specifically, the paper addresses the "minimum viable population" question: As population size decreases, at what point does the risk of extinction become unacceptably high? In addition, the paper provides recommendations for conducting population viability analyses pursuant to petitions filed under the Endangered Species Act (ESA).

Three general techniques of population viability analysis are reviewed: rules of thumb, analytic approaches, and simulation approaches. Rules of thumb prescribe single "safe" levels of abundance. Analytic approaches give explicit solutions for quantities such as effective population size, mean time to extinction, and the probability of extinction as a function of time. Simulation approaches provide a flexible method for estimating nearly any quantity of interest.

All three approaches are shown to have advantages and disadvantages. The value of any particular approach is likely to vary from case to case, depending on data availability and other factors. In general, it is advisable to make use of as many methods as possible, recognizing the strengths and weaknesses of each.
CONTENTS
Introduction

Overview of Approaches to Population Viability Analysis
Rules of Thumb
Analytic Approaches

Simulation Approaches

Discussion
Evaluation of Alternative Approaches
The Use of Models in Population Viability Analysis

Determining Appropriate Persistence Criteria

Recommendations

Acknowledgments

Citations
- Appendix A:   
- Evaluation   of Nominal and Expected Utilities From a Minimum Viable Population   
- Appendix B:  
- Elasticity   of Expected Extinction Time in a Special Case of the Birth-and-Death Process   Mode
ACKNOWLEDGMENTS
The following individuals provided helpful comments on an earlier draft of the manuscript: Nic Bax (Pentec Environmental), Jim Berkson (Columbia River Inter-Tribal Fish Commission), Mitch Friedman (Greater Ecosystem Alliance), Jim Lannan (Oregon State University), Bruce Marcot (U.S. Forest Service), Ben Sandford and Robin Waples (National Marine Fisheries Service), and Hal Weeks (Oregon Department of Fish and Wildlife). 

Table of Contents