PREFACE

"If you like superlatives, you will love this animal," a pitchman for elephant seals might say. The list is long and far-ranging. It is the largest seal and one of the most sexually dimorphic marine mammals. It is extremely polygynous by comparison with any other large vertebrate. Females fast while lactating, and the largest breeding males fast for more than one hundred days during the breeding season. Elephant seals dive deeper and longer than any other pinniped, and they spend more time submerged during their long aquatic wanderings than most whales. No other large vertebrate has come so close to extinction as the northern elephant seal did one hundred years ago and made such a rapid recovery.

Although these superlatives make the two elephant seal species in the genus Mirounga ideal subjects for a variety of scientific studies, some of their more mundane attributes are responsible for much of the attention by scientists. Elephant seals breed on open beaches where they are plainly visible. They are unafraid of humans and do not flee when approached or disturbed. Consequently, when sleeping, they can be easily marked or tagged individually. Tagging at weaning, one month after birth, yields a cohort of known-age animals by sex. This is critical for long-term behavior studies and studies of growth, aging, and survival and defines the age and maturation variables in physiological studies in the laboratory. To put this in perspective, a biologist can identify, sex, and age more elephant seals in one afternoon than a student of killer whales might accomplish in a month, if at all. Arrivals and departures on rookeries for breeding and molting are predictable, which has facilitated instrumentation of individuals for the study of diving and at-sea behavior.

Owing in large part to their ease of study, the rudiments of elephant seal natural history, the basis for a good monograph, were provided by the first

systematic observations and studies conducted in the 1940s and 1950s. It was in elephant seal teeth that annual growth layers were first demonstrated as a reliable method of age determination of mammals. George Bartholomew pioneered studies of the northern elephant seal, M. angustirostris , in California and Mexico and one of us (RML) concurrently conducted an intensive study of southern elephant seals, M. leonina , at South Georgia and other rookeries in Antarctic waters. During the next three decades, this information base expanded rapidly as a result of fundamental behavioral, physiological, and population studies conducted by scientists from a number of countries at most places where elephant seals breed. One measure of the ease and depth of study of this animal is that lifetime reproductive success of several cohorts has been estimated by measuring reproductive success annually in identifiable males and females throughout their lifetimes, something that has been accomplished in only a few large vertebrates. Studies of at-sea behavior began in 1983, made possible by the development of small self-contained diving instruments. By 1990, elephant seals were one of the most thoroughly studied and well-known marine mammals.

When there is sufficient knowledge and intellectual activity in a field, it becomes interesting and worthwhile to survey this knowledge, and holding a conference has numerous advantages. In 1990, Gordon Reetz, representing the Minerals Management Service, asked one of us (BJL) to organize and coordinate such a conference. The impetus for the international conference on elephant seals held in Santa Cruz, California, on May 20-21, 1991, was to review and update the status of both the northern and southern elephant seal populations and present current research findings in life history, diving and foraging behavior, and physiological ecology. Because it was apparent that the population of the northern species was expanding rapidly while major colonies of the southern species were in long-term decline, it was hoped that causes of colony decline might be suggested from an examination of behavioral, reproductive, and survival data. Second, there was a great deal of exciting research being done on diving and foraging behavior and energy requirements during feeding and breeding on diverse rookeries, and we thought it would be stimulating to meet, present our findings, and discuss progress in this fast-developing area of research. Third, we aimed to examine factors affecting survival and reproductive success. For both species, we wanted the principal researchers from around the world to present their most recent findings on these topics.

Like the conference, this volume is intended to provide a detailed summary of current knowledge of certain aspects of elephant seal life. It is not an attempt to present all that is known about elephant seals. Everything that was presented orally at the conference is reported here except for two talks. Additional information, acquired after the talks were given, has been

added to many of the chapters, and an introductory chapter was written to provide background information on natural history.

This volume has 40 authors, 39 more than the typical monograph. The advantage of a multiauthor monograph over the more typical single-author volume is breadth of coverage, depth of treatment in each chapter, and multiple perspectives on the same issues. Little effort was made to hold authors to a uniform format or writing style. We hope that the information presented in this volume will be of interest to students of animal behavior, ecology, physiology, and marine science, as well as wildlife managers and administrators linked with government, fisheries, and petroleum assessment and development, that is, people who are concerned with the impacts of activities in our oceans on the animals that live in them.

In this volume, the first section on population ecology contains chapters addressing the history and current status of both species, the impact of southern elephant seals on the Antarctic ecosystem, and possible causes of the decline of some colonies. In the second section, the results of long-term studies of juvenile survivorship, diet, and breeding strategies of the northern elephant seal are presented, basic behavioral and life history data that are intended to elucidate the causes of population growth and decline. The third section deals with at-sea behavior of both species. In chapter 12, Roger D. Hill presents the theory that made it possible to determine the migratory paths and foraging areas of seals treated by Marthan N. Bester and Ian S. Wilkinson (chap. 5), Burney J. Le Boeuf (chap. 13) and Brent S. Stewart and Robert L. DeLong (chap. 16). Other chapters review recent findings in this fast-developing field and explore new directions for elucidating foraging behavior and physiological constraints on diving, such as early development, measurement of swimming speed, and analysis of dive types. The volume closes with a consideration of key elements of foraging economics in southern elephant seals, endocrine changes during development, breath-hold performance during sleep on land and underwater, and the role of hormones in fuel regulation during fasting, a key aspect of the life history strategy of both species.

We are grateful to Gordon Reetz, Carol Fairfield, James Lang, Mark Pierson, and others from the Minerals Management Service for support in acquiring the finances that enabled us to bring this international group together for a stimulating exchange of information in a pleasant setting and for the funding to initiate this volume. We thank John Twiss and Bob Hofman of the Marine Mammal Commission for providing a small grant to help defray travel costs for participants from out of the country. BJL acknowledges the financial assistance of George A. Malloch and the Gerena MacGowan Estate and grants from the National Science Foundation. RML acknowledges a grant from the Royal Society. We thank Daniel Costa and

Christophe Guinet for their oral presentations at the conference and James Estes, Gerald Kooyman, and Joanne Reiter for chairing sessions and acting as discussants. Communication with authors and transmittal of manuscripts to the publisher were facilitated by Gigi Nabors and Marie McCullough. We are grateful to the science editor at the University of California Press, Elizabeth Knoll, for taking on this project and speeding it along.