DECLINE OF THE STELLER SEA LION IN ALASKAN WATERS
UNTANGLING FOOD WEBS AND FISHING NETS
The National Academies Press
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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.
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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
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).
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
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
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
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
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,
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.
Challenges in Understanding the Cause of Population Declines,
Evaluating Hypotheses for the Cause of the Steller Sea Lion Decline,
Evaluating Mechanisms in Relation to Sea Lion Population Dynamics,
Management Measures to Mitigate Potential Adverse Fishing Effects,
STELLER SEA LION DECLINE: ENVIRONMENTAL CONTEXT AND COMPENDIUM OF EVIDENCE
H Guide to the Common and Scientific Names of Marine Mammal, Fish, Invertebrate, and Bird Species