The Community Ecology of Sea Otters

260 Pages·1988·10.12 MB·English

by  G. R. VanBlaricom, J. A. Estes (auth.), Professor Dr. Glenn R. VanBlaricom, Professor Dr. James A. Estes (eds.)

Ecological Studies, Vol. 65
Analysis and Synthesis
Edited by
W D. Billings, Durham, USA
F. Golley, Athens, USA
0. L. Lange, Wiirzburg, FRG
J. S. Olson, Oak Ridge, USA
H. Remmert, Marburg, FRG
Ecological Studies
Volume 52 Volume 59
Air Pollution by Photochemical Acid Deposition and the Acidification
Oxidants Formation, Transport, Control of Soils and Waters
and Effects on Plants By J.O Reuss and D.W. Johnson
Edited by Robert Guderian 1986. VIII, 120p., 37 figures. cloth
1985. XI, 346p., 54 figures. cloth ISBN 3-540-96290-5
ISBN 3-540-13966-4
Volume 53
Volume 60
The Gavish Sabkha
Amazonian Rain Forests
A Model of a Hypersaline Ecosystem
Edited by C.F. Jordan
Edited by G.M. Friedman and
1987. X, 133p., 55 figures. cloth
W.E. Krumbein
ISBN 3-540-96397-9
1985. X, 484p., 246 figures. cloth
ISBN 3-540-15245-8
Volume 54 Volume 61
Tidal Flat Ecology Potentials and Limitations of
An Experimental Approach to Species Ecosystem Analysis
Interactions Edited by E.-D. Schulze and H. Zw6lfer
By Karsten Reise 1987. XII, 435p., 141 figures. cloth
1985. X, 198p., 69 figures. cloth ISBN 3-540-17138-X
ISBN 3-540-15447-7
Volume 55
Volume 62
A Eutrophic Lake
Frost Survival of Plants
Lake Mendota, Wisconsin
By A. Sakai and W. Larcher
By Thomas D. Brock
1987. XI, 321 p., 200 figures. cloth
1985. XII, 308p., 82 figures. cloth
ISBN 3-540-17332-3
ISBN 3-540-96184-4
Volume 56
Resources and Society Volume 63
A Systems Ecology Study of the Island Long-Term Forest Dynamics of the
of Gotland, Sweden Temperate Zone
By James J. Zucchetto and By Paul A. Delcourt and
Ann-Mari Jansson Hazel R. Delcourt
1985. X, 248p., 70 figures. cloth 1987. XIV, 450 p., 90 figures.
ISBN 3-540-96151-8 333 maps. cloth
ISBN 3-540-96495-9
Volume 57
Forest Ecosystems in the Alaskan Taiga
A Synthesis of Structure and Function
Volume 64
Edited by K. Van Cleve, F.S. Chapin
Landscape Heterogeneity and Disturbance
III,
Edited by Monica Goigel Turner
L.A. Viereck, C. T. Dyrness and
1987. XI, 241 p., 56 figures. cloth
P.W. Flanagan
ISBN 3-540-96497-5
1986. X, 240p., 81 figures. cloth
ISBN 3-540-96251-4
Volume 58 Volume 65
Ecology of Biological Invasions of North The Community Ecology of Sea Otters
America and Hawaii Edited by G.R. VanBlaricom and
Edited by H.A. Mooney and J .A. Drake J.A. Estes
1986. X, 320p., 25 figures. cloth 1987. XVI, 247 p., 71 figures. cloth
ISBN 3-540-96289-1 ISBN 3-540-18090-7
The Community
Ecology
of Sea Otters
Edited by
G.R.VanBlaricom and lA. Estes
With 71 Figures
Springer-Verlag
Berlin Heidelberg New York
London Paris Tokyo
Professor Dr. GLENN R. VANBLARICOM
Professor Dr. JAMES A. ESTES
U.S. Department of the Interior
Fish and Wildlife Service
Institute of Marine Sciences
272 Applied Sciences Building
University of California
Santa Cruz, CA 95064
USA
Legendfor cover motif: A sea otter carries a common prey species, the red sea urchin
Strongylocentrotusfranciscanus, to the ocean surface. Illustration by Jenny Wardrip,
based on an underwater photograph by Richard Mattison.
ISBN-13:978-3-642-72847-1 e-ISBN-13:978-3-642-72845-7
DOl: 10.1007/978-3-642-72845-7
Library of Congress Cataloging in Publication Data. The Community ecology of sea otters.
(Ecological studies; v. 65). Bibliography: p. Includes index. 1. Sea otter - California - Pacific
Coast - Ecology. 2. Animal populations - California - Pacific Coast. 3. Mammals - California-
Pacific Coast- Ecology. 1. VanBlaricom, G. R. (Glenn R.), 1949- . II. Estes, J. A. (James A.),
1945- . III. Series. QL737.C25C66 1987 599.74'47 87-20553.
This work is subject to copyright. All rights are reserved, whether the whole or part of the material
is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation,
broadcasting, reproduction on microfilms or in other ways, and storage in data banks.
Duplication of this publication or parts thereof is only permitted under the provisions of the
German Copyright Law of September 9,1965, in its version of June 24, 1985, and a copyright fee
must always be paid. Violations fall under the prosecution act of the German Copyright Law.
© Springer-Verlag Berlin Heidelberg 1988.
Softcover reprint of the hardcover 1st edition 1988
The use of registered names, trademarks, etc. in this publication does not imply, even in the
absence of a specific statement, that such names are exempt from the relevant protective laws and
regulations and therefore free for general use.
2131/3130-543210
Preface
The impetus for this volume comes from two sources. The first is scientific:
by virtue of a preference for certain large benthic invertebrates as food, sea
otters have interesting and significant effects on the structure and dynamics
of nearshore communities in the North Pacific. The second is political: be-
cause of the precarious status of the sea otter population in coastal California,
the U.S. Fish and Wildlife Service (USFWS) announced, in June 1984, a
proposal to establish a new population of sea otters at San Nicolas Island,
off southern California. The proposal is based on the premise that risks of
catastrophic losses of sea otters, due to large oil spills, are greatly reduced
by distributing the population among two geographically separate locations.
The federal laws of the U.S. require that USFWS publish an Environmental
Impact Statement (ElS) regarding the proposed translocation of sea otters
to San Nicolas Island. The EIS is intended to be an assessment of likely bio-
logical, social, and economic effects of the proposal. In final form, the EIS
has an important role in the decision of federal management authority (in
this case, the Secretary of the Interior of the U.S.) to accept or reject the
proposal.
As a result of our positions with USFWS and our experience in the study
of sea otter-community interactions, the authors of the draft EIS for the
above proposal (USFWS 1986) solicited our views on predicted effects of
sea otters on the nearshore benthic communities of San Nicolas Island. Many
of our views were incorporated into an early draft of the EIS, which was
then made available for review by experts in various relevant disciplines.
Several of the reviewers were intensively critical of portions of the early draft
ElS. Discussions concerning the relationships of sea otters to kelp forest
communities were perceived as particularly contentious, stimulating voci-
ferous accusations of bias and even ulterior motives.
Our response to the above events was to seek a forum wherein the various
views of sea otter-community interactions could be objectively stated, com-
pared, and discussed, in an atmosphere free of political overtones. Thus, we
organized and moderated a half-day symposium on community effects of
foraging by sea otters. The symposium was part of the 66th annual meeting
of the Western Society of Naturalists, held in December 1985 at Monterey,
California. The gathering included presentations by M. Foster, D. Laur,
A. Ebeling, D. Duggins, and S. Levin, in addition to ourselves (see Chaps. 4
through 10, this Vol.). Although the symposium was well attended, well
VI Preface
presented, and well received, the participants agreed that there was much
more to be said, and more topics to be covered. In response to this need, we
solicited the manuscripts which comprise this volume. Selection of contribu-
tors and subject matter was intended to cover all categories of habitat in
which sea otters are known to have biological effects. Thus, Kvitek and Oliver
review interactions of sea otters and soft-sediment communities (Chap. 3),
VanBlaricom presents data on effects of sea otters in rocky intertidal systems
(Chap. 4), and several authors contribute views on relationships of sea otters
and kelp forests (Chaps. 5 through 9). We emphasize kelp forests in this
Volume because more work has been done with sea otters and kelp forests
than with other habitat types influenced by sea otters. In addition (probably
as a consequence of the greater research effort), interactions of sea otters
and kelp forests are quite controversial, especially in California. Our selec-
tion of contributors reflects our desire to have the full range of views in the
controversy represented in this Volume. Finally, we sought the views of
S.A. Levin as a widely recognized theoretical ecologist and applied mathe-
matician, and as one experienced in environmental policy disputes. Dr. Levin's
role was to assess available data on sea otter-community interactions, and to
determine if existing evidence and lines of inquiry are appropriate for the
kinds of answers needed for ecological generalizations and environmental
policy decisions.
With the exception of Chap. 1, all chapters in this volume were subjected
to peer review. We established a panel of 20 scientists to provide the reviews.
Panel members are listed below, with the exception of one member, who
requested anonymity:
Ames, J .A., California Department of Fish and Game, Monterey, Cali-
fornia, USA
Beddington, J .R., Center for Environmental Technology, Imperial Col-
lege of Science and Technology, London, England
Cailliet, G.M., Moss Landing Marine Laboratories, Moss Landing, Cali-
fornia, USA
Dayton, P K., Scripps Institution of Oceanography, University of Cali-
fornia, La Jolla, California, USA
Gaines, S D., Hopkins Marine Station, Stanford University, Pacific Grove,
California, USA
Goodman, D., Department of Biology, Montana State University, Boze-
man, Montana, USA
Hines, A.H., Chesapeake Bay Center for Environmental Studies, Smith-
sonian Institution, Edgewater, Maryland, USA
Hixon, M.A., Department of Zoology, Oregon State University, Corvallis,
Oregon, USA
Jackson, G.A., Scripps Institution of Oceanography, University of Cali-
fornia, La Jolla, California, USA
Jameson, RJ ., US Fish and Wildlife Service, San Simeon, California, USA
Johnson, A.M., US Fish and Wildlife Service (retired), Anchorage, Alaska,
USA
Preface VII
Kenyon, K.W., US Fish and Wildlife Service (retired), Seattle, Washington,
USA
Menge, B.A., Department of Zoology, Oregon State University, Corvallis,
Oregon, USA
North, WJ ., Kerckhoff Marine Laboratory, California Institute of Tech-
nology, Corona del Mar, California, USA
Pearse, J .S., Institute of Marine Sciences, University of California, Santa
Cruz, California, USA
Peterson, C.H., Institute of Marine Sciences, University of North Carolina,
Morehead City, North Carolina, USA
Simenstad, C.A., Fisheries Research Institute, University of Washington,
Seattle, Washington, USA
Sousa, W.P., Department of Zoology, University of California, Berkeley,
California, USA
Suchanek, T .H." Division of Environmental Studies, University of Cali-
fornia, Davis, California, USA
Chapters 2 through 10 were each reviewed by at least two members of
the panel. No panel member reviewed more than one chapter. Chapter 11
(our concluding summary) was reviewed by all of the principal authors of
the contributed chapters. In addition, several authors of contributed chapters
sought additional review comments from colleagues. These reviewers are
acknowledged in the individual chapters as appropriate.
Because of our joint roles as editors and contributors to this Volume, we
established a procedure to avoid conflict of interest in the review process.
For all chapters that we authored or co-authored, Dr. A.W. Ebeling (Uni-
versity of California, Santa Barbara, California, USA) assumed the role of
editor, and held final authority on any matters of disagreement between us
and our reviewers.
The review process outlined above was intended to insure that this Volume
would be as informative, constructive, and objective as is humanly possible.
We believe that the process has been reasonably successful, recognizing that
such goals are, in practice, difficult to obtain. We sincerely hope that this
Volume will contribute to improved knowledge of the ways in which sea ot-
ters influence natural communities. In addition, we hope the Volume will
provide a model for the discussion of sea otter ecology in an atmosphere
relatively free of the heavy constraints of political intrigue.
Santa Cruz, California, USA G.R. VanBlaricom
J.A. Estes
Acknowledgments
We thank the contributors to this Volume for their efforts toward improve-
ment of our knowledge of sea otters and natural communities. We are grate-
ful for the responsiveness and tolerance of the contributors to the review
process, and to deadlines and various other impositions. Likewise, we thank
the members of the review panel, whose prompt and constructively critical
evaluations led to substantial improvements in the quality, clarity, objectivity,
and credibility of the volume.
We are particularly grateful to Dr. A.W. Ebeling for his efforts as an editor
of manuscripts that we contributed. Dr. Ebeling's time and efforts had a
significant positive influence on the quality and objectivity of our chapters.
We thank Dr. David Montgomery for his support and assistance in the
presentation of our symposium at the 1985 annual meeting of the Western
Society of Naturalists, in Monterey, California. The completion of this
volume was, to a large degree, a consequence of the successful presentation
of our symposium.
We thank Dr. Dieter Czeschlik and the editorial staff of Springer-Verlag
for their remarkable support, enthusiasm, and tolerance of this project. We
also thank the editors of Ecological Studies for supporting the inclusion of
this Volume in the Series.
We are grateful for the administrative support and patience of the U.S.
Fish and Wildlife Service and the University of California, San ta Cruz (UCSC),
especially Drs. Robert 1. Brownell, Jr., and William Doyle. The National
Ecology Center of the Fish and Wildlife Service was most helpful in the pre-
paration of graphics for the volume. The office staff of the Institute of Marine
Sciences, UCSC, provided extensive assistance with manuscript preparation,
and David Carlson provided valued help with computers.
Our own research activities on the community ecology of sea otters
probably would not have developed without the support and encouragement
of Dr. Clyde Jones during the time he served as Director of the National Fish
and Wildlife Laboratory and the Denver Wildlife Research Center. We grate-
fully acknowledge his wisdom, friendship and commitment to scientific ex-
cellence.
It is a particular pleasure to express our thanks to Mrs. Patti Himlan for
her contributions to the completion of this volume. In the face of an end-
less stream of manuscripts, letters, unreasonable deadlines, and self-destruct-
ing hard discs, she has maintained her patience, good humor, and a steady
commitment to the completion of this volume.
Finally, we thank our families for their continuous support and patience
throughout the project.
G.R. VanBlaricom and J.A. Estes
Contents
1 Introduction
G.R. VanBlaricom and J.A. Estes ......................... .
2 A Review of the History, Distribution and Foraging Ecology
of Sea Otters
M.L. Riedman and J .A. Estes (With 12 Figures)
2.1 Introduction ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4
2.2 Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4
2.3 History, Distribution and Present Status of Populations . . . . . . .. 7
2.4 Diet and Foraging Behavior .......................... 12
2.4.1 Habitat .................................... 12
2.4.2 Diet ...................................... 13
2.4.3 Foraging Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15
2.4.4 Activity ................................... 16
2.4.5 Class and Individual Variation ..................... 19
2.5 Summary ...................................... 20
3 Sea Otter Foraging Habits and Effects on Prey Populations and
Communities in Soft-Bottom Environments
R.G. Kvitek and 1.S. Oliver (With 5 Figures)
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22
3.2 Soft-Bottom Foraging Habits ......................... 23
3.2.1 Epifaunal Prey Communities. . . . . . . . . . . . . . . . . . . . .. 28
3.2.1.1 Prey Populations ....................... 28
3.2.1.2 Prey Communities ...................... 29
3.2.2 Shallow-Burrowing Infaunal Prey. . . . . . . . . . . . . . . . . .. 30
3.2.2.1 Prey Populations ....................... 30
3.2.2.2 Prey Communities ...................... 31
3.2.3 Deep-Burrowing Infaunal Prey .................... 32
3.2.3.1 Prey Populations ....................... 32
3.2.3.2 Prey Communities ...................... 37
3.3 Prey Vulnerability and Patch Dynamics .................. 38
XII Contents
3.3.1 Prey Resistance .............................. 38
3.3.2 Prey Resilience ............................... 41
3.4 Substrate Disturbance .............................. 41
3.5 Rocky and Soft Substrata ........................... 43
3.6 Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 45
3.7 Summary ...................................... 45
4 Effects of Foraging by Sea Otters on Mussel-Dominated Intertidal
Communities
G.R. VanBlaricom (With 19 Figures)
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48
4.2 Models of Mussel-Dominated Communities ................ 48
4.3 Sea Otters as Predators of Mussels .................... .. 50
4.4 Case 1: Sea Otters and Mussels on the Coast of Central California . 51
4.4.1 Study Location .............................. 52
4.4.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54
4.4.3 Consumption of Mytilus californumus by Sea Otters:
The Basic Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 55
4.4.4 Creation of Gaps in Mussel Cover by Sea Otters: Spatial and
Temporal Aggregation. . . . . . . . . . . . . . . . . . . . . . . . .. 57
4.4.5 Size Distribution of Gaps Created by Sea Otters. . . . . . . .. 61
4.4.6 Mussel Size and Vulnerability to Foraging Sea Otters. . . . .. 63
4.5 Case 2: Sea Otters and Mussels in Prince William Sound, Alaska. .. 65
4.5.1 Study Location .............................. 66
4.5.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 69
4.5.3 Consumption of Mytilus edulis by Sea Otters:
The Basic Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70
4.5.4 Size Distribution of Intertidal Mussels and the Population
Status of Sea Otters ........................... 73
4.5.5 Mussel Size and Vulnerability to Foraging Sea Otters. . . . .. 82
4.6 Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 84
4.7 Summary ...................................... 88
5 Kelp Communities and Sea Otters: Keystone Species or Just Another
Brick in the WaD?
M.S. Foster and D.R. Schiel (With 3 Figures)
5.1 Introduction ............. . . . . . . . . . . . . . . . . . . . . . .. 92
5.2 Kelp Community Structure .......................... 94
5.3 The Otter as a Keystone Species in California: Local or General? .. 95
5.3.1 Approach and Methods .... . . . . . . . . . . . . . . . . . . . .. 95
5.3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 98
5.3.3 Possible Bias ................................ 99
5.4 Otter Effects: Geographic and Historical . . . . . . . . . . . . . . . . . . 102