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Fur Seals

Fur Seals: Maternal Strategies on Land and at Sea

Roger L. Gentry
Gerald L. Kooyman
Copyright Date: 1986
Pages: 310
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  • Book Info
    Fur Seals
    Book Description:

    The contributors to this volume have accomplished a breakthrough in our ability to collect data on ocean-dwelling mammals. In the first large-scale comparison of fur seals, they have employed quantitative methods and a special instrument called a Time-Depth-Recorder to study the strategies used by females in six species of cared seals to rear and wean their young in different environments.

    Originally published in 1986.

    ThePrinceton Legacy Libraryuses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

    eISBN: 978-1-4008-5469-1
    Subjects: Zoology

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
  3. List of Contributors
    (pp. ix-x)
  4. Preface
    (pp. xi-xiv)
    Roger L. Gentry and Gerald L. Kooyman
  5. Acknowledgments
    (pp. xv-2)
  6. 1 Introduction
    (pp. 3-27)
    R. L. Gentry and G. L. Kooyman

    Marine mammal science has always been thwarted by the difficulty of collecting data on free-ranging animals at sea. This problem has hindered research on cetaceans (whales and porpoises) somewhat more than on pinnipeds (seals, sea lions, and walruses) because, except in rare circumstances, all data on cetacean biology must be collected at sea. Since pinnipeds mate and rear young on land where measurements are more easily made, some aspects of their behavior and biology are relatively well known. However, just as the pelagic lives of cetaceans remain obscure, those aspects of pinniped biology that occur at sea, such as feeding...

  7. 2 Methods of Dive Analysis
    (pp. 28-40)
    R. L. Gentry and G. L. Kooyman

    Chapter 1 stated that the maternal strategies of fur seals would be compared largely through data on attendance and dive behavior. Attendance data were obtained with conventional behavioral research methods, already described in an extensive literature (e.g., Altmann, 1974; Fagen and Young, 1979). However, the methods used to measure dive behavior require introduction because the technology evolved along with this research project. The existing literature contains only a brief description of the instrument (Kooyman et al., 1983a) and one kind of result obtainable with it (Kooyman et al., 1976). In this chapter we discuss the design requirements of the Time-Depth-Recorder...

  8. 3 Attendance Behavior of Northern Fur Seals
    (pp. 41-60)
    R. L. Gentry and J. R. Holt

    When we first began this study in 1974 our purpose was to monitor female attendance behavior as a fur seal herd changed in size and age/sex composition. We knew that these changes were imminent because the commercial harvest of fur seal pelts had been terminated at our study site (St. George Island, Alaska) in 1973 specifically to create such changes. Terminating the harvest was part of a research program to investigate the effects of the northern fur seal management program on herd composition, behavior, and size (Anonymous, 1973). Female attendance was only one of many parameters that were to be...

  9. 4 Feeding and Diving Behavior of Northern Fur Seals
    (pp. 61-78)
    G. L. Kooyman and M. E. Goebel

    When we began research on northern fur seal diving in 1975, our goals were modest compared to the global view presented in Chapter 1. Initially, we hoped only to characterize the depth, duration, number, and temporal occurrence of dives made by foraging mothers (Kooyman et al., 1976). Since diving had not previously been measured in any free-ranging otariids, even these modest goals seemed optimistic. But when initial success showed that these goals were easily attained, we shifted from simply describing diving behavior to studying interrelationships among the variables that make up the foraging pattern. For example, some of our newly...

  10. 5 Free-Ranging Energetics of Northern Fur Seals
    (pp. 79-101)
    D. P. Costa and R. L. Gentry

    The two preceding chapters showed the behavior associated with prey capture and subsequent delivery of nourishment to young northern fur seals. From the viewpoint of energetics, this behavior represents two categories in the overall allocation of maternal energy resources: foraging and travel costs. Other categories are the energy expended while avoiding predators, energy loss to parasites and diseases, milk production, and maintenance metabolism. The pattern of energy allocation among these categories has undoubtedly evolved in response to environmental pressures balanced against physiological limitations. Because environmental pressures differ among fur seal species, the allocation of maternal energy resources, or energy budget,...

  11. 6 Attendance Behavior of Antarctic Fur Seals
    (pp. 102-114)
    D. W. Doidge, T. S. McCann and J. P. Croxall

    Over 95% of the Antarctic fur seal population breeds at the island of South Georgia. Very small populations occur elsewhere in the Scotia Arc (Aguayo, 1978; Holdgate and Baker, 1979), at the Prince Edward Islands (Kerley, 1984), Crozet Islands (Jouventin et al., 1982), and McDonald and Heard islands (Budd, 1972).

    Following near extermination by late nineteenth-century sealers, pup production at South Georgia rose from a few hundred in the 1930s to 5,000 by 1957, and to over 100,000 by 1976 (Payne, 1977; Croxall and Prince, 1979). The mean annual rate of increase from 1958 to 1972 was 16.8% (Payne, 1977),...

  12. 7 Diving Behavior of Antarctic Fur Seals
    (pp. 115-125)
    G. L. Kooyman, R. W. Davis and J. P. Croxall

    This study of diving in the Antarctic fur seal is timely, given the recent history of the species. These animals, which have been relatively undisturbed by humans in recent times, are experiencing a phenomenal, worldwide population increase (Chapter 1). Their food during the pup-rearing period is mainly krill,Euphausia superba,a resource that until recently was not exploited by man. Now, however, several countries are developing krill-harvesting capabilities, and soon competition for this resource may develop between man and Antarctic wildlife. Thus it is appropriate to obtain a detailed analysis of the Antarctic fur seal’s feeding behavior—particularly that of females...

  13. 8 Attendance Behavior of South African Fur Seals
    (pp. 126-141)
    J. H. M. David and R. W. Rand

    South African fur seals are distributed around the southeastern and western coasts of southern Africa, from Algoa Bay (lat. 34° S, long. 26° E) in the southeast to False Cape Frio (lat. 18°30' S, long. 12° E) in the northwest. Twenty-three discrete breeding colonies occur along this 3,000 km of coastline, of which seventeen are situated on small, rocky, islands, and six (including the four largest) are on the mainland. This distribution is probably related to the northward flowing Benguela current on the west coast and the southwestward flowing Agulhas current on the south coast (Rand, 1967).

    Regular migratory movements...

  14. 9 Diving Behavior of South African Fur Seals
    (pp. 142-152)
    G. L. Kooyman and R. L. Gentry

    The purpose of this study was to test the newly developed TDR system and to obtain data comparable to that described in previous dive chapters. We selected the South African fur seal because, as the largest of the fur seals, we expected it to dive more deeply than the northern fur seal, the only other species we had studied by 1977 when this project began. The proximity of deep water to the breeding sites was also promising because one of our goals was to test bourdon tubes having greater maximum depths than those used in the northern fur seal work....

  15. 10 Attendance and Diving Behavior of South American Fur Seals during El Niño in 1983
    (pp. 153-167)
    F. Trillmich, G. L. Kooyman, P. Majluf and M. Sanchez-Griñan

    When we studied the diving and attendance behavior of the South American fur seal in Peru in January and February 1983, the strongest El Nino (EN) in over 100 years was in progress (Cane, 1983). Sea surface temperature (SST) at Punta San Juan, our study site, averaged 22.4 ± 0.80C (mean ± SD; range 21.0-24.50C; Pesca Peru, unpubl. data), while in normal years average January SST is 15.5°C and February SST is 16.O0C (Zuta et al., 1978). These high temperatures resulted from a massive influx of warm water coming from the west.

    The warm water influx results from a decrease...

  16. 11 Attendance Behavior of Galapagos Fur Seals
    (pp. 168-185)

    Galapagos fur seals permanently live close to the equator. They are the only fur seals that experience constant day length and minimal fluctuations between seasons. Tropical conditions are ameliorated by the influx of a cold surface current from the east, by the Peru or Humboldt current, and by an upwelling of the Cromwell countercurrent on the west coasts of the archipelago. Strong east winds along the coast of South America drive the Peru current, and this in turn induces the flow of the Cromwell countercurrent. Massive influx of these cooler waters is restricted to the so-called garua (drizzle) season, from...

  17. 12 Diving Behavior of Galapagos Fur Seals
    (pp. 186-195)
    G. L. Kooyman and F. Trillmich

    The purpose of this study was to determine the offshore feeding characteristics of females which were suckling pups. Since this species is not migratory and is one of the smallest marine mammals, it was of particular value to determine the: (1) duration of trips to sea; (2) time to reach the feeding area; (3) common feeding depths; (4) duration of feeding periods; (5) dive frequency rate within bouts; and (6) preferred feeding times for comparison with larger, migratory species.

    The study was done at Cabo Hammond, Fernandina Island (Fig. 1.12), during October and November 1980, the garua or drizzle season...

  18. 13 Attendance Behavior of Galapagos Sea Lions
    (pp. 196-208)
    F. Trillmich

    Galapagos sea lions live under nearly the same environmental conditions as the Galapagos fur seal (Chapter 11) but cope with these conditions quite differently. Sea lions prefer flat beaches that are sandy or rocky, where they have easy access to relatively calm waters and can spend the hot hours around tidepools or, at some colonies, in the shade of vegetation (mostly Cryptocarpus pyriformis). Thermoregulatory problems tend to be less acute for seal lion female and pup pairs than for fur seals because of easy access to calm waters, which are safe even for small pups. Sea lion pups enter the...

  19. 14 Diving Behavior of Galapagos Sea Lions
    (pp. 209-219)
    G. L. Kooyman and F. Trillmich

    The general purpose of this study was to compare, for the first time, the diving behavior of two sympatric otariids, the Galapagos sea lion and the Galapagos fur seal. Because of their sympatry, resource partitioning may be critical to the coexistence of these species. Since both species live in a tropical environment where food resources are not likely to be abundant, and since both species live on the same islands and may feed in overlapping areas, competition for food resources has probably shaped different foraging strategies in the two species. We tried to characterize these patterns by collecting the same...

  20. 15 Synthesis and Conclusions
    (pp. 220-264)
    R. L. Gentry, D. P. Costa, J. P. Croxall, J. H. M. David, R. W. Davis, G. L. Kooyman, P. Majluf, T. S. McCann and F. Trillmich

    We now return to the subject of maternal strategies, the main emphasis of this book. As stated in Chapter 1, these strategies cannot be identified from the study of either attendance behavior or diving behavior alone, nor even from a comprehensive study of a single species. We characterize these strategies by comparing six species according to more than forty different measures. In brief, the comparison shows that latitude correlates with broad suites of traits that are related to rearing pups (hence maternal strategies). Despite differences in taxonomic affinity and diet, seals of comparable latitudes share traits that seals of different...

  21. Literature Cited
    (pp. 265-278)
  22. Author Index
    (pp. 279-282)
  23. Subject Index
    (pp. 283-291)
  24. Back Matter
    (pp. 292-292)