Behavior and Ecology of the Northern Fur Seal. - Review - book reviews

by Daryl J. Boness

Gentry, Roger L. 1998. Princeton University Press, Princeton, New Jersey. xiii 392 p. $69.50, ISBN: 0-691-03345-5 (acid-free paper).

In the last decade a number of books have been published on pinniped behavior and ecology but none has been a detailed single-species account nor as focused as this book. In his position as a research biologist with the National Marine Fisheries Service, Gentry has had the opportunity and resources to accumulate the kind of data sets that most academics can only dream about. In this book he describes a 19-year study of the northern fur seal, a heavily managed species, that was aimed at addressing very specific behavioral questions about a nearly 40-year decline in fur seal pup production.

The book is more heavily weighted to the reproductive behavior of northern fur seals than to its ecology. The predominant coverage of fur seal ecology is in examining the influence of climatic regime shifts (e.g., the Aleutian Low and El Nino-Southern Oscillations) and width of the continental shelf around breeding islands on breeding success and population trends. The book consists of 15 chapters that are organized into five parts. The first part sets the scene for the rest of the book. It provides a short introduction to the natural history of the northern fur seal and of pinnipeds in general. It also describes population changes in this species over the past 40 years, emphasizing the period from 1974-1986 in more detail. The last chapter in this section highlights the importance of various temporal scales in the behavior and ecology of northern fur seals (e.g., several-day foraging cycles, annual breeding cycles, decadal climatic cycles). The next two parts deal with the mating system and male and female reproductive behavior. Part two presents the details of male competition (e.g., establishment and maintenance of territories, energetics of male reproductive effort, and lifetime copulation rates), addresses the question of female mate choice, and examines the use of space and grouping behavior of females. Part three deals in more detail with three aspects of behavior that Gentry feels are especially important to understanding the fur seal mating system: site fidelity and philopatry, estrus behavior, and ontogeny of male territorial behavior. Part four describes maternal behavior, its consequences in terms of pup growth, and variation resulting from environmental factors and individual tendencies. The last part summarizes the findings in relation to some of the initial management questions that drove the research, provides some comparisons with other otariids, and raises further questions to be addressed with future research.

Gentry started out with a particularly difficult challenge because he not only wanted to address the questions raised about this species by wildlife managers, he wanted to make the book useful to academics with general theoretical interests and to provide enough detail for comparative purposes for other seal researchers. These somewhat divergent goals have led to compromises in style and content that make the book harder to use for some readers than for others. For example, a deliberate decision to exclude a general theoretical framework in which to interpret the data will mean that an academic (behavioral ecologists, ethologists, comparative psychologists, etc.) who wishes to understand the northern fur seal mating system in a broader context will get minimal help from the book. A specialist interested in evaluating and using the extensive empirical results for their own synthesis, may become frustrated by the constant need to turn to the "notes" at the end of the book to obtain details about methodology or statistical analysis. This style is similar to the reference notes in a Science paper, which on a small scale is not so bad. Here, the problem is you end up with over 30 pages of pertinent information for which you have to jump between your place in the book and the notes at the back. The book seems best suited for what is perhaps its primary purpose, an account of the role reproductive behavior and ecology has played in the fur seal population in light of the numerous years of planned annual kills of juvenile males.

Having noted these relatively minor difficulties, I am merely giving you forewarning, not suggesting you avoid the book if your interest is for one of the first two reasons. One strong aspect of the studies reported in this book is a mix of observational and experimental approaches to investigate specific questions. Experimental approaches are almost non-existent in research on mating systems in marine mammals, or for that matter, in most large mammals. The most elegant and enlightening experiments described are those associated with estrus behavior. By controlling access of females to males and by using what amounted to a "chastity belt" to prevent copulation, Gentry investigated questions about stimuli sufficient or necessary to trigger or terminate estrus. Other experimental studies involved removing males from their territories and observing resettlement on territories, withholding pups from sucking for periods of time or artificially feeding them to change their level of demand for milk in order to examine the consequent effects on attendance periods, and moving females and pups of different ages to determine the potential for changing breeding sites.

If you have read Gentry's previous book with Gerald Kooyman on maternal strategies in pinnipeds you will find the section on maternal strategy in this book updates the original ideas. The notion of a latitudinal cline and overall species-specific strategies are discounted here and greater importance is given to local ecological conditions, particularly with respect to maternal attendance and foraging patterns. In the case of the northern fur seal, excellent data are presented on attendance-foraging cycles at several colonies in which the marine environments are very different. Likewise, the multiple years of study at the same environments produced variation in cycles resulting from climatic changes.

One disappointment in the book, to which I alluded above, is the limited extent to which the fur seal data are integrated into broader contexts of reproductive behavior and behavioral ecology, and even into marine mammalogy. The references to other pinniped literature are fairly selective and references to more general literature are minimal. On a more mundane note, the final proofreading of the manuscript could have been better. Clearly there was a problem with certain character recognition in the software used to set the book text since all degree symbols for temperatures show up as blanks, and "X"s used in dimensions show up as infinity symbols.

In short, this book has something for a wide range of readers but its efforts to reach such a wide audience will result in some grumbling by each type of reader. You have heard a bit of mine (a behavioral ecologist specializing in pinniped reproductive strategies) but I would have purchased the book for its detailed analysis of reproductive behavior of male and female fur seals. It is an excellent case study for wildlife managers and conservation biologists, illustrating the need for long-term studies of managed species and of the value of studying behavior in various ecological contexts, not just monitoring population trends. For the theoretically oriented academic who is not a marine mammal specialist the species is particularly interesting as a highly polygynous one in which opportunities for female choice appear to be very limited. The nature of interactions between males and females before females become receptive can be extremely aggressive on the part of males and lead to the injury or even death of females. The ontogeny of territorial behavior, philopatry, and site fidelity in combination provide for the potential for cooperative behavior in male territory turnovers that would not be readily apparent without detailed studies of the nature of those described in this book. Lastly, the data presented in this book will lead to many interesting ideas that will hopefully stimulate students to pursue them either in this species or others that are appropriate.