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Report of the Workshop on Assessing the Population Viability of Endangered Marine Mammals in U.S

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Report of the Workshop on Assessing the Population Viability of Endangered Marine Mammals in U.S Report of the Workshop on Assessing the Population Viability of Endangered Marine Mammals in U.S. Waters 13–15 September 2005 Savannah, Georgia Prepared by the Marine Mammal Commission 2007 This is one of five reports prepared in response to a directive from Congress to the Marine Mammal Commission to assess the cost-effectiveness of protection programs for the most endangered marine mammals in U.S. waters TABLE OF CONTENTS List of Tables ..................................................................................................................... iv Executive Summary.............................................................................................................v I. Introduction..............................................................................................................1 II. Biological Viability..................................................................................................1 III. Population Viability Analysis..................................................................................5 IV. Viability of the Most Endangered Marine Mammals ..............................................6 Extinctions and recoveries.......................................................................................6 Assessment of biological viability...........................................................................7 V. Improving Listing Decisions..................................................................................10 Quantifying the listing process ..............................................................................10 A theoretical decision tree for listing under the Endangered Species Act.............10 VI. Improving Other Management Decisions..............................................................11 VII. Acknowledgments..................................................................................................12 VIII. Literature Cited......................................................................................................12 Appendix I. Examples of Existing Marine Mammal Population Models......................19 North Atlantic Right Whales .....................................................................19 Southern Resident Killer Whales...............................................................20 Cook Inlet Beluga Whales .........................................................................21 Florida Manatees........................................................................................22 Hawaiian Monk Seals ................................................................................24 Steller Sea Lions — Western Stock...........................................................25 Steller Sea Lions — Eastern Stock ............................................................26 California Sea Otters..................................................................................27 Appendix II. Workshop Attendees..................................................................................29 Appendix III. Workshop Agenda .....................................................................................30 iii LIST OF TABLES Table 1. Summary of the biological status of 22 marine mammal species and stocks currently listed as endangered or threatened under the Endangered Species Act or designated as depleted under the Marine Mammal Protection Act .............................15 Table 2. Examples of wild populations that have recovered from extremely low population sizes............................................................................................................16 Table 3. A theoretical decision tree and analytical recommendations for listings under the Endangered Species Act ..............................................................................18 iv EXECUTIVE SUMMARY Congress, in its 2004 Omnibus Appropriations Act, directed the Marine Mammal Commission to “review the biological viability of the most endangered marine mammal populations and make recommendations regarding the cost-effectiveness of current protection programs.” As part of its response to the directive, the Commission convened a workshop to examine the state of science regarding population viability analysis (PVA) for marine mammal populations. The workshop was held 13–15 September 2005 in Savannah, Georgia. Its goals were to (1) review estimates of the viability of the most endangered marine mammals, (2) review the status of ongoing modeling efforts, particularly PVA, for endangered marine mammals, and (3) develop recommendations to improve listing and management decisions based on explicit consideration and improved estimation of population extinction risk. The workshop focused on the 22 marine mammal taxa occurring in U.S. waters and either listed as threatened or endangered under the Endangered Species Act or designated as depleted under the Marine Mammal Protection Act. Participants agreed that, with two or possibly three exceptions, all those taxa—with appropriate management—appear to have the potential for persisting into the future. The first exception is the Caribbean monk seal, which has not been observed and documented since 1952 and is presumed to be extinct. The second is the AT1 stock of killer whales, which numbers fewer than 10 individuals, has not produced a single surviving calf for more than 20 years, and is highly unlikely to persist beyond the lifetimes of existing individuals. The possible third exception is the eastern population of North Pacific right whales, which has been a matter of concern based largely on the rarity of sightings, lack of information on the population, and its history of commercial exploitation. That concern has been tempered somewhat by recent evidence of successful reproduction (observations of cow-calf pairs). In addition to these obvious exceptions, the stock structure of many marine mammal species is poorly known, and participants noted that some additional stocks, yet to be identified, may be unlikely to persist into the future. For the taxa that were considered to be potentially viable, the available published analyses at the time of the workshop were not sufficient for a systematic and consistent quantification of their respective viabilities. The workshop identified methodological issues that need to be addressed to allow meaningful quantitative comparisons among viability estimates. Participants reviewed the current state of PVA for marine mammals and other wildlife. For candidate species or species that are already listed, the growing trend is to use PVA to support listing and management decisions. PVA provides a mechanism for integrating all relevant data into a quantitative assessment to produce an estimate of extinction risk over a defined period of time. Such analyses are more objective than the qualitative listing approaches used to date, more amenable to explicit inclusion of all relevant data, more transparent with respect to assumptions and uncertainties, more easily standardized, and more conducive to the kind of structured decision-making that is needed to improve listing and management of endangered, threatened, and depleted taxa. v Participants also highlighted several common impediments to quantitative analyses for many marine mammal taxa. These include poor understanding of stock structure, insufficient biological data for recognized taxa, insufficient data for characterizing potential relationships between specific threats or management actions and population responses, and difficulty in predicting future threats and management actions that may affect their risk of extinction. Further, participants expressed a need for caution when using commercially available analytical software without proper documentation and without an understanding of the structure, function, and assumptions incorporated into the software. Participants generally agreed with the findings of the Quantitative Working Group convened by the National Marine Fisheries Service and the U.S. Fish and Wildlife Service (DeMaster et al. 2004) to develop quantitative criteria for listing decisions. Among other things, those findings included the need for (1) performance testing of models used in the listing process to determine the likelihood of correct vs. incorrect decisions, given the life histories of species involved and uncertainties in the data or analytical results, and (2) clear links between policy decisions and quantitative models, particularly with regard to interpreting the uncertainty reflected in model results. Finally, participants in the Savannah workshop considered and expressed support for a proposed decision tree incorporating simple PVAs to assess the status of poorly known taxa and guide listing decisions. The decision tree would use available data on the species of interest; default values where data are lacking; a structured, standardized, and simple analytical framework; and explicit guidelines for interpreting results. With appropriate development, the decision tree might be used to structure listing decisions in much the same manner as the potential biological removal concept is used to identify strategic stocks in the management of marine mammal/fishery interactions under the Marine Mammal Protection Act. vi I. INTRODUCTION In its 2004 Omnibus Appropriations Act, Congress directed the Marine Mammal Commission to “review the biological viability of the most endangered marine mammal populations and make recommendations regarding the cost-effectiveness of current
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