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DECLINE OF THE STELLER SEA LION IN ALASKAN WATERS UNTANGLING FOOD WEBS AND FISHING NETS Committee on the Alaska Groundfish Fishery and Steller Sea Lions Ocean Studies Board Polar Research Board Division on Earth and Life Studies NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES The National Academies Press Washington, D.C. www.nap.edu
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THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This study was supported by Contract/Grant No. SSL-01-B between the National Academy of Sciences and the North Pacific Fishery Management Council. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project. Library of Congress Control Number: 2003101402 International Standard Book Number: 0-309-08632-9 Cover art was created by Emma Wilson. Ms. Wilson is the founder and principal of the Emma Wilson Design Company in Seattle, Washington. She has worked with many Seattle area companies on the design of annual reports, promotions, posters, corporate and retail branding, and environmental graphics. Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu Copyright 2003 by the National Academy of Sciences. All rights reserved. Printed in the United States of America
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THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council. www.national-academies.org
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COMMITTEE ON THE ALASKA GROUNDFISH FISHERY AND STELLER SEA LIONS ROBERT T. PAINE (Chair), University of Washington, Seattle DANIEL W. BROMLEY, University of Wisconsin, Madison MICHAEL A. CASTELLINI, University of Alaska, Fairbanks LARRY B. CROWDER, Duke University, Beaufort, North Carolina JAMES A. ESTES, U.S. Geological Survey/University of California, Santa Cruz JACQUELINE M. GREBMEIER, University of Tennessee, Knoxville FRANCES M.D. GULLAND, The Marine Mammal Center, Sausalito, California GORDON H. KRUSE, University of Alaska, Fairbanks NATHAN J. MANTUA, University of Washington, Seattle JAMES D. SCHUMACHER (a.k.a. Two Crow), Two Crow Environmental, Inc., Silver City, New Mexico DONALD B. SINIFF, University of Minnesota, St. Paul CARL J. WALTERS, University of British Columbia, Vancouver Staff SUSAN J. ROBERTS, Study Director NANCY A. CAPUTO, Senior Project Assistant The work of this committee was overseen by the Ocean Studies Board and the Polar Research Board of the National Research Council (See Appendix G).
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Preface The National Research Council (NRC) has often been called on to provide unbiased and nonjudgmental evaluation of issues that are simultaneously significant and vexing. The Steller sea lion committee was assembled to address just such a challenge. Populations of these sea lions, especially in the western Gulf of Alaska and Bering Sea, have been in decline since about 1970. They were listed as endangered in 1997 under the Endangered Species Act. This enormous region is also the site of the nation’s most valuable groundfish industry, yielding a dockside value approaching $700 million in 2000. Since sea lions eat groundfish, it is not illogical to suspect a causal relationship between their decline and industry removals of about 4 billion pounds of their potential prey per year. This possibility was explored in earlier analyses, including the first “Is It Food?” conference, which concluded that food availability likely contributed to the decline. Data gathered since 1990 suggest that alternative hypotheses deserve equal scrutiny, and the sea lion committee undertook this task. It is not that these hypotheses are new or unanticipated; nor has the older food limitation hypothesis been ignored. Instead, the committee has tried to sift through the enormous but still frustratingly limited database relevant to resolving the question of why these sea lions continue to decline despite the imposition of substantial constraints on fishers. In the past decade, some analyses supported the ecologically plausible possibility of food limitation (a bottom-up control hypothesis), but this committee’s numerous consultations, evaluation of recent data, and modest modeling efforts
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suggest that mortality imposed on sea lions by their enemies, including humans (top-down hypotheses), could also constitute elusive but convincing explanations. Both viewpoints embody generalizations: both the bottom-up and top-down perspectives can be addressed by scientific evidence. Emotion, taxonomic advocacy, and regulatory roadblocks to legitimate research have constrained a science-based understanding of why sea lions continue to decline. Good science may not be able to save sea lions from regional extinction, but it is certain that without the understanding that focused research provides, the causes of the decline can neither be understood nor addressed. So with much of the above understood a priori, the committee chose to address the issue of data gaps, historical trends in the mass of fishes caught and their species composition, the intimate details of sea lion biology, and to offer a collective opinion on what actions should be taken next. That the committee has done, although the advice may please neither fishing industry nor sea lion advocates. The committee met four times: twice in Seattle where the National Marine Fisheries Service’s Alaska Fisheries Science Center and many of the relevant scientific experts are located, once in Anchorage, largely to gather information from interested and involved nongovernmental organizations and Alaska natives, and once in Florida to complete the writing of the report. I know that all scientists willing to join committees like this one lead busy and complex lives. The same must surely hold true for the NRC staffers and presenters at our three public committee meetings. The organizational challenge, which must be like the proverbial “herding cats,” was superbly managed by study director Susan Roberts and project assistant Nancy Caputo. On behalf of the committee, I thank them. It is also appropriate here to acknowledge the willingness of the committee’s members to work toward the common goal of meeting the statement of task despite their disparate backgrounds and opinions. It is a rare privilege to listen to experts debate issues as complex as this one characterized by substantial data gaps. It is even more gratifying to participate in an effort where numerous potential pitfalls and strongly polarized opinions have been minimized. The committee strove to develop a constructive analysis of a continuingly contentious issue. I believe we succeeded. Robert T. Paine, Chair Committee on the Alaska Groundfish Fishery and Steller Sea Lions
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Acknowledgments This report was greatly enhanced by the contributions of many people. We would like to thank the sponsor of this study, the North Pacific Fishery Management Council, executive director, Chris Oliver, and staffers, David Witherell, Jane DiCosimo, and Gail Bendixen, who provided valuable assistance and information. We also thank Thomas Loughlin and Anne York of the National Marine Mammal Laboratory, Alaska Fisheries Science Center, for providing data and figures for this report. John Sease, Lowell Fritz, and Patsy Bearden of the National Oceanic and Atmospheric Administration kindly sent us electronic figures that are reproduced here. Alison Rieser of the Marine Law Institute, University of Maine School of Law, Portland, Maine, provided the committee with valuable information on marine law and policy. The committee also wishes to acknowledge the efforts of those who gave presentations at one of the three public committee meetings. These presentations gave the committee up-to-date information on research relevant to the issues addressed in this study. D. Lee Alverson, Natural Resources Consultants, Inc., Seattle Russel Andrews, Institute of Marine Science, University of Alaska, Fairbanks, and the Alaska SeaLife Center, Seward Kerim Aydin, Alaska Fisheries Science Center, National Marine Fisheries Service, Seattle Vernon Byrd, Alaska Maritime National Wildlife Refuge, U.S. Fish and Wildlife Service, Homer
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Vladimir Burkanov, Natural Resources Consultants, Inc., Seattle Shane Capron, National Marine Fisheries Service, Juneau Helen Chythlook, Bristol Bay Native Association, Dillingham, Alaska David Cline, retired, formerly with World Wildlife Fund, Anchorage Larry Cotter, Aleutian Pribilof Island Community Development Association, Juneau Douglas DeMaster, Alaska Fisheries Science Center, National Marine Fisheries Service, Seattle Douglas Eggers, Alaska Department of Fish and Game, Juneau David Fraser, owner and captain, F/V Muir Milach, Port Townsend, Washington Lowell Fritz, Alaska Fisheries Science Center, National Marine Fisheries Service, Seattle Fritz Funk, Alaska Department of Fish and Game, Juneau Thomas Gelatt, Alaska Department of Fish and Game, Anchorage Daniel Goodman, Montana State University, Bozeman Karl Haflinger, Sea State, Inc., Vashon, Washington Oliver Holm, fisherman, Kodiak, Alaska George Hunt, Jr., School of Biological Sciences, University of California, Irvine Linda Larson, Sandler, Ahern & McConaughy, Seattle Frank Logusak, Togiak Traditional Council, Togiak, Alaska Thomas Loughlin, National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service, Seattle Herbert Maschner, Department of Anthropology, Idaho State University, Pocatello Chris Oliver, North Pacific Fishery Management Council, Anchorage Kenneth Pitcher, Alaska Department of Fish and Game, Anchorage Timothy Ragen, Marine Mammal Commission, Bethesda, Maryland Alan Springer, Institute of Marine Science, University of Alaska, Fairbanks Jack Sterne, Trustees for Alaska, Anchorage Kenneth Stump, consultant for Greenpeace, Seattle Jack Tagart, Washington Department of Fish and Wildlife, Olympia, and the North Pacific Fishery Management Council, Scientific and Statistical Committee Gary Thomas, Prince William Sound Science Center, Cordova, Alaska Andrew Trites, Fisheries Centre, University of British Columbia, Vancouver Glenn VanBlaricom, School of Aquatic & Fisheries Sciences, University of Washington, Seattle
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Terrie Williams, Center for Ocean Health, University of California, Santa Cruz David Witherell, North Pacific Fishery Management Council, Anchorage Boris Worm, Biology Department, Dalhousie University, Halifax, Canada Kate Wynne, Sea Grant Marine Advisory Program, University of Alaska, Kodiak Anne York, National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service, Seattle This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s (NRC) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: D. Lee Alverson, Natural Resource Consultants, Inc., Seattle David R. Cline, retired, formerly with the World Wildlife Fund, Anchorage Richard B. Deriso, Inter-American Tropical Tuna Commission, La Jolla, California Thomas Gelatt, Alaska Department of Fish and Game, Anchorage Daniel Goodman, Montana State University, Bozeman, Montana Susan M. Henrichs, Institute of Marine Science, University of Alaska, Fairbanks Henry P. Huntington, Huntington Consulting, Eagle River, Alaska Andrew A. Rosenberg, University of New Hampshire, Durham Douglas Wartzok, Florida International University, Miami Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by May R. Berenbaum, University of Illinois, Urbana, Illinois, and by Kenneth Brink,
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Woods Hole Oceanographic Institution, Woods Hole, Massachusetts. Appointed by the NRC, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
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Contents EXECUTIVE SUMMARY 1 1 INTRODUCTION 14 Challenges in Understanding the Cause of Population Declines, 14 The Policy Context, 18 History of ESA Listings and Court Challenges, 22 Scope and Organization of the Report, 24 2 THE ENVIRONMENTAL SETTING 26 The Physical Environment, 26 The Biological Environment, 32 3 IDENTIFIYING CLUES AND TESTING HYPOTHESES 39 Population Models, 40 Ecosystem Models, 44 Evaluating Hypotheses for the Cause of the Steller Sea Lion Decline, 52 Evaluating Mechanisms in Relation to Sea Lion Population Dynamics, 54 Summary, 55 4 REVIEW OF STELLER SEA LION BIOLOGY 57 Biogeography and Evolution, 57 Population Structure of Steller Sea Lions, 59
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Population Trends, 62 Vital Rates, 66 Physiology, Behavior, and Feeding Ecology, 67 Steller Sea Lion Diet, 71 Challenges/Logistics of Working with Sea Lions, 74 5 FISHERIES 77 Groundfish Fisheries, 77 State-Managed Fisheries, 101 Management Measures to Mitigate Potential Adverse Fishing Effects, 109 6 STELLER SEA LION DECLINE: ENVIRONMENTAL CONTEXT AND COMPENDIUM OF EVIDENCE 112 Food Web Concepts, 113 Multiple Working Hypotheses, 115 Food Limitation—Bottom-Up Hypotheses, 116 Food Quality, 125 Predation and Takes by Humans—Top-Down Hypotheses, 128 Deliberate and Incidental Mortality from Human Activities, 132 Infectious Disease, 141 Toxins, 143 Weight of Evidence, 145 Synopsis, 150 7 INFORMATION NEEDS AND RECOMMENDATIONS 152 Current and Future Information Needs, 152 Retrospective Analyses, 156 Monitoring to Evaluate Management Efficacy, 156 REFERENCES 161 APPENDIXES A Committee and Staff Biographies 181 B Acronyms 186 C Glossary 188 D Early Account of Steller Sea Lions 190 E Federal Funding Summary 193 F Meeting Agendas 194 G National Research Council Project Oversight Boards 200 H Guide to the Common and Scientific Names of Marine Mammal, Fish, Invertebrate, and Bird Species 203