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History of Marine Mammal Research
History of Marine Mammal Research
from that of other species of Ursus. Departures of sea otter hind limb anatomy from that of other terrestrial mustelids (Tarasoff 1972; Tarasoff et al., 1972), however, are seen more readily. Externally, the leg is enclosed within the loose body skin to the approximate level of the ankle. The digits are bound together by interdigital webbing, although the fourth and fifth digits are bound more closely together than other adjacent digital pairs. The sea otter is unusual in that in overall length the digits decrease in size from the fifth to the first: V IV III II I. While swimming, sea otters use the hind feet to generate thrust and sweep the leg through the water such that the fifth digit forms the leading edge of the pes. The hair densities for the ankle and interdigital webbing have been estimated at 107,000 and 3300 hairs/cm2, respectively, compared to a density of 125,000 hairs/cm2 for the back. Pads are present on the phalangeal portion of each toe and are variably found ventral to the metatarsals. As with pinnipeds, the fovea capitis is absent from the femur, marking the absence of the teres ligament. The biceps femoris muscle inserts onto the middle of the tibia and maintains the leg in a posterior position. The flexor digit V muscle is very large in the sea otter (relative to other mustelids). This enlargement corresponds to the use of the lateral surface of the pes to lead during the power stroke of the limb. The remaining hind limb anatomy of the sea otter corresponds well with that of terrestrial mustelids (Fig. 2).
Schulte, H. W., and Smith, M.de. F. (1918). The external characters, skeletal muscles, and peripheral nerves of Kogia breviceps (Blainville). A Bull. Am. Mus. Nat. Hist. 38, 7–72. Sedmera, D., Misek, I., and Klima, M. (1997). On the development of cetacean extremities. I. Hind limb rudimentation in the spotted dolphin. Eur. J. Morphol. 35, 25–30. Tarasoff, F. J. (1972). Comparative aspects of the hind limbs of the river otter, sea otter and seals. In “Functional Anatomy of Marine Mammals” (R. J. Harrison, ed.), Vol. 1, pp. 333–359. Academic Press, New York. Tarasoff, F. J., Bisaillon, A., Pièrard, J., and Whitt, A. P. (1972). Locomotory patterns and external morphology of the river otter, sea otter, and harp seal (Mammalia). Can. J. Zool. 50, 915–929. Thewissen, J. G. M., Coh, M. J., Stevens, L. S., Bajpai, S., Heyning, J., and Horton, W. E., Jr. (2006). Developmental basis for hind-limb loss in dolphins and origin of the cetacean body plan. Proc. Natl. Aca. Sci. USA 103, 8414–8418. Uhen, M. D. (1998). Middle to late Eocene basilosaurines and dorudontines. In “The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea” (J. G. M. Thewissen, ed.), pp. 29–61. Plenum Press, New York.
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See Also the Following Articles Forelimb Anatomy ■ Locomotion, Terrestrial ■ Musculature ■ Skeletal Anatomy ■ Swimming
BERND WÜRSIG, WILLIAM F. PERRIN AND J.G.M. THEWISSEN
References Berta, A., and Ray, C. E. (1990). Skeletal morphology and locomotor capabilities of the archaic piniped Enaliarctos mealsi. J. Vertebr. Paleontol. 10, 141–157. Bisaillon, A., and Pierard, A. (1981). Osteologie de morse de 1’Atlantique (Odobenus rosmarus, L. 1758) ceintures et members. zentralbatt Veterinarmedizin. Reihe C Anat. Histol. Embryol. 10, 310–327. Domning, D. P. (1977). Observations on the myology of Dugong dugon (Miller). Smith. Contrib. Zool. 226, 1–57. Domning, D. P. (1991). Sexual and ontogenetic variation in the pelvic bones of Dugong dugon. Mar. Mamm. Sci. 7, 311–316. Fay, F. H. (1974). Comparative and functional anatomy of the vascular system in the hind limbs of the Pinnipedia. “Transactions of the First International Theriological Congress.” pp. 166–167. Nauka Publishers, Moskow. Gambarjan, P. P., and Karapetjan, W. S. (1961). Besonderheiten im Baudes Seelowen (Eumetopias californianus), der Baikalrobbe (Phocasibirica) and des Seeotters (Enhydra lutris) in Anpassung an die Fortbewegung im Wasser. Zool. Jahrbucher (Abteilung Anat. On-tog. Tiere) 79, 123–148. Kaiser, H. E. (1974). “Morphology of the Sirenia: A Macroscopic and X-Ray Atlas of the Osteology of Recent Species.” Karger, Basel, Switzerland. Miller, W. C. S. (1888). The myology of the Pinnipedia. In “Report on the Scientific Results of the Voyage of H. M. S. Challenger during the Years 1873–76.” (C. W. Thomson, and J. Murray), Vol. 26, Order of Her Majesty’s Government. Muizon, C.de (1981). Une interpretation functionelle et phylogene-tique de l’insertion du psoas major chez les Phocidae. Comp. Ren. Acad. Sci. (Paris) 292, 859–862. Nakanishi, T., Yamamoto, M., and Suenaga, Y. (1978). Comparative anatomical studies on the nerves and muscles of the posterior limb of the northern fur seal and cat. Okajimas Fol. Anat. Japon. 54, 317–340.
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f research is the gathering of knowledge, then we can think of marine mammal research to have gone on as long as humans have gazed at whales spouting offshore and seals pupping on beaches. But early observations of nature were largely tied up with myths about animals and legends of their capabilities. A common theme appears to have been the changing of humans to dolphins and whales, and the reverse. This theme is recognized in remaining legends of Australian aborigine “dream time,” boto (Inia geoffrensis) and baiji (Lipotes vexillifer) river dolphin folklore (Sangama de Beaver and Beaver, 1989; Zhou and Zhang, 1991, respectively), tales of the god-like killer whales (Orcinus orca) of Pacific Northwest indigenous tribes (McIntyre, 1974), and many more. Some early writings show remarkable insights in marine mammal biology. Well over 2000 years ago, scholars of China’s Han Dynasty in the annotated dictionary “Er-Ya,” described the baiji as related to marine dolphins, implying that those were known to intellectuals of the time. Even earlier, the Greek philosopher/scientist Aristotle (384–322 bc) differentiated between baleen and toothed whales and described both types in some detail. It is unfortunate but totally understandable in hindsight that he classified cetaceans as fishes, a practice still present in Britain’s term “Royal Fishes” under which all whales and dolphins belong by law to the Crown. The Roman writer/ lawyer/admiral Pliny the Elder (23–79 ad) published a book on dolphins and whales 400 years after Aristotle’s time as part of his 37-volume “Natural History.” Not much scientific inquiry or thought was conducted between Roman times and the western Renaissance, and knowledge, at least written knowledge, of marine mammals languished as well. The modern progression of marine mammal research can perhaps best be
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described as occurring in four general (and not mutually exclusive) phases: (1) morphological description from beach-cast specimens and fossils; (2) descriptions of behavior, anatomy, and distribution as gathered during hunting and whaling activities; (3) studies of physiology and behavior in captivity; and (4) studies of ecology, habitat use, numbers, life history patterns, behavior, and physiology in nature. A fifth phase may be thought of as an ever-increasing sophistication in integrating knowledge from terrestrial situations as well as from different fields of marine mammal endeavors. The phases of research mentioned above follow a rough chronology, with morphology and systematics the main topics pre-1900s; hunting-related habitat, morphological, and behavioral research mainly from the 1850s to the 1970s; scientific captive animal descriptions beginning around 1950; and more ecologically oriented descriptions in nature beginning around the 1970s. All phases are ongoing, with electronic devices helping to elevate in-field research on marine mammal lives to a new level of sophistication. A very readable recent account of the history of marine mammal studies is found in Berta and Sumich (1999). Elsewhere, this volume lists some of the major deceased marine mammal researchers of the past and mentions their classic works in the field (see References). Pierre Bélon was probably the first “modern” marine mammal author since Pliny’s time. He published accurate descriptions and woodcuts of some whales, dolphins, and seals (Belloni, 1553), and these (and also, unfortunately, the less accurate ones) were much copied by others in the next two centuries. The real burst of marine mammal knowledge did not come until later, however. And then it came suddenly, in tune with eighteenth century awakening of scientific thought in the western world. While many authors could be mentioned, three early contemporaries did much to advance cetacean descriptions, taxonomy, and systematics. These were the French zoologist La Cépède (1804) and the Cuvier brothers. Georges Cuvier, who arguably founded modern evolutionary theory, wrote on many topics, including cetaceans; whereas his less-famed brother Frederic published two important works on cetaceans (Cuvier, 1829, 1836). These three were followed by the Belgian zoologist Van Beneden in the latter half of the nineteenth century, with work mainly consisting of compilations of information on fossil whales, and by a host of fine morphologists, taxonomists, systematists, and evolutionary historians in the twentieth century (summaries are provided by Rice, 1998; Thewissen, 1998; Pabst et al., 1999; and Reynolds et al., 1999). While much of the earlier work centered on cetaceans, the British zoologist John Edward Gray described both seals and whales in the British Museum (Gray, 1866), and the American zoologist Joel Allen wrote excellent monographs on whales, pinnipeds, and sirenians (Allen, 1880). Yamase (1760) began the science of marine mammalogy in Japan at about the same time as serious studies began in the west. He presented accurate figures and descriptions of the external morphology of six toothed and seven baleen whale species and distinguished them from fishes. His work was brought to the west in a marine mammal section of “Fauna Japonica” by Siebold (1842). Otsuki began to describe the internal anatomy of cetaceans of Japan in 1808, but his manuscript remains unpublished. A second major phase of information gathering, often linked intricately with that just described, involved descriptions of animals as related to hunting and whaling. Morphological information was at the core of these descriptions, but behavior and the basic society structure of whales and pinnipeds—of course much of the time affected by the hunting activities themselves—were recorded as well. One of the earliest accurate accounts consisted of German-born
and Russian-naturalized Georg Steller’s descriptions of pinnipeds and the soon-after extinct Steller’s sea cow (Hydrodamalis gigas), the largest and only cold-water sirenian known (originally published in Latin in 1751, and republished in English as Steller, 1899). Quite a few books related especially to whaling were produced, but perhaps the most enduring one from the nineteenth century was by the North American whaling captain Charles Scammon, who wrote with feeling and accuracy on behavior and life history habits of marine mammals of the North Pacific (Scammon, 1874). In the twentieth century, one of the most famous works largely relying on whalingaccumulated data consists of Everhard Slijper’s book “Whales and Dolphins” (published in English in 1976). A very readable account of whaling and the literature derived from whaling can be found in “Men and Whales” by Richard Ellis (1991). Modern factory whaling itself helped to usher in excellent research on numbers, habitat use, life history patterns, and morphology/physiology. This was so especially during the Discovery investigations of 1925– 1951, a British research program that was responsible for a wealth of new data, especially on large whales of the southern hemisphere. These investigations consisted in part of extensive long-term tagging (“discovery tags,” shot into the blubber and muscle tissues of whales, and later recovered during actual whale kills). In this manner, migrations of great whales were delineated long before modern radio and satellite tags provided such information (e.g., Allen, 1980). Dozens of fine researchers published hundreds of papers that relied on the Discovery expeditions, and on other whaling data since then (e.g., Laws, 1959) (see also the section “International Whaling Commission” in this voume). As a counterpoint to early cetacean information, the reader interested in pinniped research from the ancient Greeks to about 1983 can consult an excellent annotated bibliography of over 12,000 publications by Ronald et al. (1976, 1983). While whaling, sealing, and other forms of direct hunting are much abated today as compared to in the 1960s, there are still powerful low-level, oft-indigenous hunts, especially in protein-poor areas of the world (Perrin, 1999). As a result, data are being accumulated and analyzed on morphology, genetics, taxonomy, and systematics, life history, prey patterns, and so on. Excellent recent information has become available from results of hunting on, e.g., pilot whales (Globicephala spp.), oceanic dolphins (especially of the genus Stenella), bowhead whales (Balaena mysticetus), sperm whales (Physeter macrocephalus), and several seal, fur seal, and sea lion species (summaries in Berta and Sumich, 1999; Reynolds and Rommel, 1999; and Twiss and Reeves, 1999). A third major research avenue has come about as a result of keeping marine mammals in captivity. Attempts to do so in the early part of the last century usually resulted in the animals’ untimely deaths— due to poor water, incorrect or tainted food, disease, and aggression between individuals in confined spaces. Facilities that housed marine mammals simply replaced dead ones by more captures from nature. However, especially since the 1970s, amazing strides in husbandry have been made for all marine mammals (except large whales), and the better aquaria now keep—and breed—animals very well. Unfortunately, there are still many “primitive” facilities, especially in less-developed parts of the world. At present, there are representatives of all major taxonomic groups in captivity, as show animals and for research: toothed whales and dolphins (only two baleen whales, each time young gray whales, Eschrichtius robustus, have been successfully kept); pinnipeds of all types, but especially California sea lions (Zalophus californianus); sirenians (mainly the West Indian manatee, Trichechus manatus and the dugong, Dugong dugon); and polar bears (Ursus maritimus) and sea otters (Enhydra lutris).
History of Marine Mammal Research
Only through holding animals in controlled situations have researchers learned that dolphins echolocate (Au, 1993); that all marine mammals exhibit reduced heart and general metabolic rates during dives (Ridgway, 1972; Pabst et al., 1999); and that both dolphins and sea lions have remarkably advanced cognitive capabilities (Tyack, 1999). Furthermore, it is now fully appreciated that while pinnipeds and cetaceans are finely tuned underwater swimmers and divers with superbly evolved methods of breath holding, avoiding or reducing lactic acid depth during long submergences, and navigating in dark and cold waters, there is no secret “magic” to their energetic capabilities (Costa and Williams, 1999). One major misstep from studies in captivity took place: the American John Lilly avowed in the 1960s that his research on bottlenose dolphins (Tursiops truncatus) proved that these popular show animals have an intelligence superior even to that of the brightest dogs (Canus lupus familiaris) and chimpanzees (Pan troglodytes), and likely equal to that of humans (Lilly, 1967). Careful studies by others have shown that dolphins are undeniably “smart” (intelligence is very difficult to define and compare, but has something to do with well-developed flexibilities of behavior and of innovative learning), but that there is no reason to believe that dolphins fare better in this “intelligence/cognition” sphere than many other highly social mammals (Herman, 1980, 1986; Tyack, 1999; Wells et al., 1999). While the study of marine mammals dead from the sea and live in captivity continues and grows, a relatively new approach has become the major research avenue since the 1970s. This consists of our fourth phase, of researchers going out into nature to observe the animals in their own milieu; as the animals associate with conspecifics; eat and are being eaten; and mate, give birth, and raise their young. We are learning more about the lives of these generally social creatures as they face storms, heavy years of sea ice, seasons of poor food resources (e.g., caused by “El Niño” southern oscillation climatic events), parasite infestations, adoring but noisy boatloads of whale-watching tourists, crowded shipping lanes, and habitat degradation near shore and in mighty rivers. This information on ecology of marine mammals is vital if we are to help protect them and their natural ecosystems from the depredations of overfishing, habitat pollution by chemicals, heavy metals, and noise; and the results of global climate change and wholescale habitat destruction due to the effects of ozone depletion and global warming (Tynan and DeMaster, 1997; Ferguson et al., 2005). Studies in nature often rely on visual or photographic recognition of individual whales, dolphins, and pinnipeds, often with the help of tags or color marks but also by natural markings (Hammond et al., 1990). Researchers have described movement patterns by tracking animals with surveyor’s transits from shore, and from shore and vessels by small radio tags placed on their bodies (Würsig et al., 1991). Since the early 1990s, satellite tags that relay position information to earth-orbiting satellites have become smaller, less expensive, and ever more popular. As a result, we know that northern elephant seals (Mirounga angustirostris) swim and dive into deep oceanic waters for months at a time, humpback whales (Megaptera novaeangliae) take rapid zigzag courses between their mating and feeding grounds, North Atlantic right whales (Eubalaena glacialis) undergo previously unsuspected jaunts between Greenland and New England during the feeding summer, and much more (Wells et al., 1999). Tags are being fitted not only with depth-of-dive measuring and telemetering devices, but also with ways to ascertain geographic position, swimming velocity, angles of dives, water and skin temperature, individual sound production, heart rate, and, in the future, other physiological measures. Recent advances in small and low-light capable video camera/record systems are even giving data on swimming, socializing,
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and feeding behavior directly from the animals under water (Davis et al., 1999). Physiological research, previously entirely within the realm of captivity, is more and more possible with innovative or sophisticated techniques in nature. Samples of stool, urine, blood, and even mother’s milk are being collected from pinnipeds resting on land or ice. Trained dolphins have been released at sea, commanded to dive, and then told to exhale into a funnel to ascertain oxygen consumption values and to station themselves so that blood can be drawn. Small darts have been developed that are fired from a crossbow or pneumatic pistol and that obtain skin and blubber samples from freeliving cetaceans for analyses of genetics (Dizon et al., 1997), toxin loads, reproductive status, and blubber energy content for relative measurements of health within and between populations. Sloughed skin samples from breaching whales have been successfully collected from the water and genetically sampled for gender, social grouping, and population data. A technique has been developed to harmlessly “skin-swab” bow-riding dolphins, also for genetic analysis (Harlin et al., 1999). In response to an apparent increase in marine mammal strandings and the emergence of new marine mammal diseases in recent years, studies of wild marine mammal disease and ocean chemical contaminants are on the increase. While studies in nature have yielded data on the presence of deadly viruses and contaminant levels in tissues of beached and dying marine mammals (Aquilar and Borrell, 1997), they have provided little insight into immune defense against disease or the biochemical consequences of contaminants. More recently, e.g., species-specific biomarkers have been developed to assess the dolphin immune system (Romano et al., 1999). Because they are readily available for long-term studies requiring serial sampling of tissues and health and reproductive histories, captive marine mammals afford unique opportunities to provide basic insight into the relationships among contaminants, the immune system, and animal health. Once they are developed and tested on animals in captivity, biomarkers can be used with wild marine mammal populations to assess contaminant exposures and their possible effects on immune systems and neurologic responses (Ridgway and Au, 1999), as well as on reproductive success (Ridgway and Reddy, 1995), growth, and development. The sensitive hearing of marine mammals has led to concerns that intense sound or noise pollution generated by humans could impede communication, cause physiological stress, or damage hearing. Marine mammal hearing studies currently underway should help to define mitigation criteria for the effects of human-generated sound in the ocean (Schlundt et al., 2000), and ultimately allow us to find a balance between the ecological needs of marine mammals and the role the ocean plays in commerce, exploration, travel, and defense. Overall, descriptions of marine mammal taxonomy and population biology have shifted from mainly morphological approaches to an increasing reliance on molecular methods. Up through the 1960s, cetologists studied dolphins by harpooning them. For example, the revision of the spotted dolphins (Stenella attenuata and S. frontalis) by Perrin et al. (1987) was based in part on dolphins collected at sea by Francis C. Fraser, Dale W. Rice, William E. Schevill, and Edward D. Mitchell, all eminent scholars and pioneers of modern cetology. Without those specimens, the study would not have been possible; that is the way it was done until protection of marine mammals became the norm in most countries in the 1970s. Another source of specimens has been dolphins that died in oceanaria. The same revision by Perrin et al. (1987) included spotted dolphins
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retrieved from oceanaria by David K. Caldwell through the 1970s and early 1980s. And at that time, there were still a number of accessible directed dolphin fisheries; the spotted dolphin review also included specimens from directed fisheries in the Caribbean, St. Helena, West Africa, Japan, and the Solomon Islands. Today, dolphins, whales, and pinnipeds are stringently protected in the wild in most places. For oceanaria, restrictions have been placed on species and numbers of animals that can be captured for exhibit and the high monetary value of captive marine mammals has resulted in better husbandry and fewer deaths. As a result of these factors, marine mammal biologists practicing morphological approaches became limited to specimens from strandings and bycatch, greatly decreased opportunities for amassing adequate series of specimens for quantitative analysis. But then along came biopsy sampling and ready techniques of amplifying DNA fragments by a technique termed polymerase chain reaction (PCR). Collection of samples by biopsy is legal and doable, so the balance of taxonomic and population studies has shifted from morphology to genetics. And the traditional morphologists have been scrambling to keep up by re-educating themselves in the new techniques or recruiting collaborators who know their way around genetics. The study of marine mammals has now matured into a fifth phase, characterized by the obliteration of boundaries that separated the previous phases. New studies on marine mammals are often integrative, combining methods and ways of thinking largely gleaned from terrestrial animals. This comparison of ideas and research techniques holds great promise for the understanding of the biology of marine mammals. As our understanding of their biology increases, marine mammals become appealing subjects for approaches that are at times laboratory heavy and at times nearly biomedical in scope. In turn, these approaches enrich knowledge of marine mammals. For instance, biochemical analyses of body fats, first championed for humans and other terrestrial animals, give new insights into the functions of different fats in cetaceans (Koopman et al., 2003). Immuno-histochemical staining techniques originally used for non-marine mammal studies allow the identification of genes that significantly affected cetacean evolution, such as those genes responsible for the loss of hind limbs (Thewissen et al., 2006). Our understanding of the social systems of terrestrial mammals, with one major aspect being sperm competition at the physiological level (Kenagy and Trombulak, 1986) has begun to inform us about the relatively non-competitive balaenid whales, gray whales, quite a few species of dolphins, and manatees that have polygynous or polygandrous (multi-mate) societies (Reynolds et al., 2004). Through sophisticated studies with modern techniques, marine mammalogy is beginning to enrich more broad fields of science such as behavioral ecology, physiological ecology, and evolutionary biology. It was recognized long ago that marine mammals represent amazing natural experiments of evolution, and the maturation of the field of marine mammalogy is allowing for these experiments to be explored, and to inform all of biology. Sophisticated electronic and biochemical techniques have recently been and are being developed to study the lives of marine mammals. However, the “tried and true” methods of looking at fossil bones, dissecting and describing pathologies of a net-entangled animal or one cast on shore after a storm, safely and carefully experimenting with animals in captivity, and the dogged gathering of behavioral information by binoculars and notebook are by no means passé. The greatest change since about the 1960s is the ever wider availability of information. This means that there is now a wealth of background knowledge
available to anyone anywhere with a computer and an Internet connection. We are, in this new twenty-first century, in a vibrant phase of marine mammal research, and we see a very bright future for evermore exciting discoveries in our field. Although much of the research landscape looks bright, we would be amiss if we did not cite a note of pessimism as well, as it is undeniable that many populations and some entire species are facing reductions and even extinction due to human-caused habitat degradation, including rapid climate change. For example, the Chinese river dolphin, baiji, is very likely extinct (Turvey et al., 2007), and the vaquita (Phocoena sinus) and Mediterranean monk sea (Monachus monachus) may not be far behind. No amount of modern and multidisciplinary research will be able to wrest information from a species that is gone from the face of the Earth.
See Also the Following Articles Hunting of Marine Mammals ■ Marine Protected Areas ■ InterRational Whaling Commission ■ Popular Culture and Literature
References Aguilar, A., and Borrell, A. (eds) (1997). “Marine Mammals and Pollutants: An Annotated Bibliography.” Foundation for Sustainable Development, Barcelona. Allen, J. A. (1880). History of North American pinnipeds: A monograph of the walruses, sea-lions, seabears and seals of North America. US Geol. Surv. Terr. Misc. Publ. 12, 1–785. Allen, K. R. (1980). “Conservation and Management of Whales.” University of Washington Press, Seattle, WA. Au, W. W. L. (1993). “The Sonar of Dolphins.” Springer-Verlag, New York. Belloni, P. (1553). “De Aquatibilis (Book Two).” Stephan Press, Paris. Berta, A., and Sumich, J. L. (1999). “Marine Mammals: Evolutionary Biology.” Academic Press, San Diego. Costa, D. P., and Williams, T. M. (1999). Marine mammal energetics. In “Biology of Marine Mammals” (J. E. Reynolds, III, and S. A. Rommel, eds), pp. 176–217. Smithsonian Institution Press, Washington, DC. Cuvier, F. (1829). Cétacés. In “Histoire Naturelle des Mamifères.” Roret Press, Paris. Cuvier, F. (1836). “De l’Histoire Naturelle des Cétacés.” Roret Press, Paris. Davis, R. W., et al. (8 authros) (1999). Hunting behavior of a marine mammal beneath Antarctic fast ice. Science 283, 993–996. Dizon, A. E., Chivers, S. J., and Perrin, W. E. (eds.) (1997). “Molecular Genetics of Marine Mammals.” Special Publication No. 3. The Society for Marine Mammalogy, Allen Press, Lawrence, KS. Ellis, R. (1991). “Men and Whales.” Knopf Press, New York. Ferguson, S. H., Stirling, I., and McLoughlin, P. (2005). Climate change and ringed seal (Phoca hispida) recruitment in western Hudson Bay. Mar. Mamm. Sci. 21, 121–135. Gray, J. E. (1866). “Catalog of Seals and Whales in the British Museum,” 2nd Ed. British Museum Press, London. Hammond, P. S., Mizroch, S. A., and Donovan, G. P. (eds.) (1990). “Individual Recognition of Cetaceans: Use of Photo Identification and Other Techniques to Estimate Population Parameters.” International Whaling Commission, Special Issue No. 12, Cambridge University Press, Cambridge. Harlin, A. D., Würsig, B., Baker, C. S., and Markowitz, T. M. (1999). Skin swabbing for genetic analysis: Application on dusky dolphins (Lagenorhynchus obscurus). Mar. Mamm. Sci. 15, 409–425.
Hooded Seal
Herman, L. M. (1980). Cognitive characteristics of dolphins. In “Cetacean Behavior: Mechanisms and Functions” (L. M. Herman, ed.), pp. 363–429. Wiley-Interscience Press, New York. Herman, L. M. (1986). Cognition and language competencies of bottlenosed dolphins. In “Dolphin Cognition and Behavior: A Comparative Approach” (R. J. Schusterman, J. A. Thomas, and F. G. Woods, eds), pp. 221–252. Lawrence Erlbaum Press, Hillsdale, NJ. Kenagy, G. J., and Trombulak, S. C. (1986). Size and function of mammalian testes in relation to body size. J. Mammal. 67, 1–22. Koopman, H. N., Iverson, S. J., and Read, A. J. (2003). High concentrations of isovaleric acid in the fats of odontocetes: Stability in the melon vs. variation and patterns of accumulation in blubber. J. Comp. Physiol. 173, 247–261. La Cépède, Compte de. (1804). “Histoire Naturelle des Cétacé.” Paris. Laws, R. M. (1959). The foetal growth rates of whales with special reference to the fin whale, Balaenoptera physalus Linn. Dis. Rep. 29, 281–308. Lilly, J. C. (1967). “The Mind of the Dolphin.” Doubleday Press, New York. McIntyre, J. (1974). “Mind in the Waters.” Charles Scribner’s Sons, New York. Pabst, D. A., Rommel, S. A., and McLellan, W. A. (1999). The functional morphology of marine mammals. In “Biology of Marine Mammals” (J. E. Reynolds, III, and S. A. Rommel, eds), pp. 15–72. Smithsonian Institution Press, Washington, DC. Perrin, W. F. (1999). Selected examples of small cetaceans at risk. In “Conservation and Management of Marine Mammals” (J. R. Twiss, Jr., and R. R. Reeves, eds), pp. 296–310. Smithsonian Institution Press, Washington, DC. Perrin, W. F., Mitchell, E. D., Mead, J. G., Caldwell, D. K., Caldwell, M. C., van Bree, P. J. H., and Dawbin, W. H. (1987). Revision of the spotted dolphins, Stenella spp. Mar. Mamm. Sci. 3, 99–170. Reynolds, J. E., and Rommel, S. A. (1999). “Biology of Marine Mammals.” Smithsonian Institution Press, Washington, DC. Reynolds, J. E., Odell, D. K., and Rommel, S. A. (1999). Marine mammals of the world. In “Biology of Marine Mammals” (J. E. Reynolds, III, and S. A. Rommel, eds), pp. 1–14. Smithsonian Institution Press, Washington, DC. Reynolds, J. E., Rommel, S. A., and Pitchford, M. E. (2004). The likelihood of sperm competition in manatees—explaining an apparent paradox. Mar. Mamm. Sci. 20, 464–476. Rice, D. W. (1998). “Marine Mammals of the World: Systematics and Distribution.” Special Publication No. 4. The Society for Marine Mammalogy, Allen Press, Lawrence, KS. Ridgway, S., and Reddy, M. (1995). Residue levels of several organochlorines in Tursiops truncatus milk collected at varied stages of lactation. Mar. Pollut. Bull. 30, 609–614. Ridgway, S. E. (1972). “Mammals of the Sea: Biology and Medicine.” Charles H. Thomas Press, Springfield, IL. Ridgway, S. E., and Au, W. W. L. (1999). Hearing and echolocation: Dolphin. In “Encyclopedia of Neuroscience” (G. Adelman, and B. Smith, eds), 2nd Ed., pp. 858–862. Springer-Verlag, New York. Romano, T. A., Ridgway, S. H., Felton, D. L., and Quaranta, V. (1999). Molecular cloning and characterization of CD4 in an aquatic mammal, the white whale, Delphinapterus leucas. Immunogenetics 49, 376–383. Ronald, K. L., Hanley, L. M., Healey, P. J., and Selley, L. J. (1976). An annotated bibliography of the Pinnipedia. International Council for the Exploration of the Sea. Charlottenlund, Denmark. Also: Supplement 1, 1983. Sangama de Beaver, M., and Beaver, P. (1989). “Tales of the Peruvian Amazon.” AE Publications, Largo, FL. Scammon, C. M. (1874). “The Marine Mammals of the North-Western Coast of North America Described and Illustrated Together with an Account of the Whale-Fishery.” John. H. Carmany, San Francisco, CA. Schlundt, C. E., Finneran, J. J., Carder, D. A., and Ridgway, S. H. (2000). Temporary shift in masked hearing thresholds (MTTS) of bottlenose dolphins, Tursiops truncates, and white whales, Dephinapterus leucas, after exposure to intense tones. J. Acoust. Soc. Am. 107, 3496–3508.
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Siebold, P. F. von. (1842). “Fauna Japonica: Les Mammiferes Marins.” Batavia Press, Jakarta. Slijper, E. J. (1976). “Whales and Dolphins.” University of Michigan Press, Ann Arbor, MI. Steller, G. W. (1899). The beasts of the sea. In “The Fur Seals and Fur Seal Islands of the North Pacific Ocean” (D. S. Jordan, ed.), pp. 179–218. US Government Printing Office, Washington, DC. Thewissen, J. G. M. (ed.) (1998). “The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea.” Plenum Press, New York. Thewissen, J. G. M., Cohn, M. J., Stevens, L. S., Bajpai, S., Heyning, J., and Horton, W. E., Jr. (2006). Developmental basis for hind-limb loss in dolphins and the origin of the cetacean bodyplan. Proc. Natl. Acad. Sci. USA 103, 8414–8418. Turvey, S. T., et al. (17 authors) (2007). First human-caused extinction of a cetacean species? Biol. Lett. 3, 537–540. Twiss, J. R., Jr., and Reeves, R. R. (1999). “Conservation and Management of Marine Mammals.” Smithsonian Institution Press, Washington, DC. Tyack, P. L. (1999). Communication and cognition. In “Biology of Marine Mammals” (J. E. Reynolds, III, and S. A. Rommel, eds), pp. 287–323. Smithsonian Institution Press, Washington, DC. Tynan, C. T., and DeMaster, D. P. (1997). Observations and predictions of Arctic climatic change: Potential effects on marine mammals. Arctic 50, 308–322. Wells, R. S., Boness, D. J., and Rathbun, G. B. (1999). Behavior. In “Biology of Marine Mammals” (J. E. Reynolds, III, and S. A. Rommel, eds), pp. 324–422. Smithsonian Institution Press, Washington, DC. Würsig, B., Cipriano, F., and Würsig, M. (1991). Dolphin movement patterns: Information from radio and theodolite tracking studies. In “Dolphin Societies: Discoveries and Puzzles” (K. Pryor, and K. S. Norris, eds), pp. 79–111. University of California Press, Berkeley, CA. Yamase, H. (1760). Geishi [Natural History of Whales]. Osaka Shorin, Osaka, Japan. Zhou, K., and Zhang, X. (1991). “Baiji, the Yangtze River Dolphin, and Other Endangered Animals of China.” Yilin Press, Nanjing, China.
Hooded Seal Cystophora cristata KIT M. KOVACS I. Characteristics and Taxonomy
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he hooded seal is a large phocid that is silver-gray in color with irregular black spots covering most of the body; the face is often completely black (Fig. 1). Adult males are about 2.5 m long and weigh an average of 300 kg; large males can be in excess of 400 kg. Adult females are considerably smaller than males, measuring 2.2 m in length and weighing an average of 200 kg. Hooded seal pups are approximately 1 m long when they are born and weigh about 25 kg. They are blue on their backs and silver-gray on their bellies (Fig. 1). This distinctive “blueback” pelage is maintained for about 2 years (Lavigne and Kovacs, 1988). The most distinctive physical feature of hooded seals is the prominent nasal ornament borne by adult males (Fig. 1). When relaxed the nasal appendage hangs as a loose, wrinkled sac over the front of males’ noses. During the breeding season (in March) males inflate this sac to display to females and to other males, forming a tight, bi-lobed “hood” that covers the front of the face and the top of the head. This structure
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from that of other species of Ursus. Departures of sea otter hind limb anatomy from that of other terrestrial mustelids (Tarasoff 1972; Tarasoff et al., 1972), however, are seen more readily. Externally, the leg is enclosed within the loose body skin to the approximate level of the ankle. The digits are bound together by interdigital webbing, although the fourth and fifth digits are bound more closely together than other adjacent digital pairs. The sea otter is unusual in that in overall length the digits decrease in size from the fifth to the first: V IV III II I. While swimming, sea otters use the hind feet to generate thrust and sweep the leg through the water such that the fifth digit forms the leading edge of the pes. The hair densities for the ankle and interdigital webbing have been estimated at 107,000 and 3300 hairs/cm2, respectively, compared to a density of 125,000 hairs/cm2 for the back. Pads are present on the phalangeal portion of each toe and are variably found ventral to the metatarsals. As with pinnipeds, the fovea capitis is absent from the femur, marking the absence of the teres ligament. The biceps femoris muscle inserts onto the middle of the tibia and maintains the leg in a posterior position. The flexor digit V muscle is very large in the sea otter (relative to other mustelids). This enlargement corresponds to the use of the lateral surface of the pes to lead during the power stroke of the limb. The remaining hind limb anatomy of the sea otter corresponds well with that of terrestrial mustelids (Fig. 2).
Schulte, H. W., and Smith, M.de. F. (1918). The external characters, skeletal muscles, and peripheral nerves of Kogia breviceps (Blainville). A Bull. Am. Mus. Nat. Hist. 38, 7–72. Sedmera, D., Misek, I., and Klima, M. (1997). On the development of cetacean extremities. I. Hind limb rudimentation in the spotted dolphin. Eur. J. Morphol. 35, 25–30. Tarasoff, F. J. (1972). Comparative aspects of the hind limbs of the river otter, sea otter and seals. In “Functional Anatomy of Marine Mammals” (R. J. Harrison, ed.), Vol. 1, pp. 333–359. Academic Press, New York. Tarasoff, F. J., Bisaillon, A., Pièrard, J., and Whitt, A. P. (1972). Locomotory patterns and external morphology of the river otter, sea otter, and harp seal (Mammalia). Can. J. Zool. 50, 915–929. Thewissen, J. G. M., Coh, M. J., Stevens, L. S., Bajpai, S., Heyning, J., and Horton, W. E., Jr. (2006). Developmental basis for hind-limb loss in dolphins and origin of the cetacean body plan. Proc. Natl. Aca. Sci. USA 103, 8414–8418. Uhen, M. D. (1998). Middle to late Eocene basilosaurines and dorudontines. In “The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea” (J. G. M. Thewissen, ed.), pp. 29–61. Plenum Press, New York.
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See Also the Following Articles Forelimb Anatomy ■ Locomotion, Terrestrial ■ Musculature ■ Skeletal Anatomy ■ Swimming
BERND WÜRSIG, WILLIAM F. PERRIN AND J.G.M. THEWISSEN
References Berta, A., and Ray, C. E. (1990). Skeletal morphology and locomotor capabilities of the archaic piniped Enaliarctos mealsi. J. Vertebr. Paleontol. 10, 141–157. Bisaillon, A., and Pierard, A. (1981). Osteologie de morse de 1’Atlantique (Odobenus rosmarus, L. 1758) ceintures et members. zentralbatt Veterinarmedizin. Reihe C Anat. Histol. Embryol. 10, 310–327. Domning, D. P. (1977). Observations on the myology of Dugong dugon (Miller). Smith. Contrib. Zool. 226, 1–57. Domning, D. P. (1991). Sexual and ontogenetic variation in the pelvic bones of Dugong dugon. Mar. Mamm. Sci. 7, 311–316. Fay, F. H. (1974). Comparative and functional anatomy of the vascular system in the hind limbs of the Pinnipedia. “Transactions of the First International Theriological Congress.” pp. 166–167. Nauka Publishers, Moskow. Gambarjan, P. P., and Karapetjan, W. S. (1961). Besonderheiten im Baudes Seelowen (Eumetopias californianus), der Baikalrobbe (Phocasibirica) and des Seeotters (Enhydra lutris) in Anpassung an die Fortbewegung im Wasser. Zool. Jahrbucher (Abteilung Anat. On-tog. Tiere) 79, 123–148. Kaiser, H. E. (1974). “Morphology of the Sirenia: A Macroscopic and X-Ray Atlas of the Osteology of Recent Species.” Karger, Basel, Switzerland. Miller, W. C. S. (1888). The myology of the Pinnipedia. In “Report on the Scientific Results of the Voyage of H. M. S. Challenger during the Years 1873–76.” (C. W. Thomson, and J. Murray), Vol. 26, Order of Her Majesty’s Government. Muizon, C.de (1981). Une interpretation functionelle et phylogene-tique de l’insertion du psoas major chez les Phocidae. Comp. Ren. Acad. Sci. (Paris) 292, 859–862. Nakanishi, T., Yamamoto, M., and Suenaga, Y. (1978). Comparative anatomical studies on the nerves and muscles of the posterior limb of the northern fur seal and cat. Okajimas Fol. Anat. Japon. 54, 317–340.
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I
f research is the gathering of knowledge, then we can think of marine mammal research to have gone on as long as humans have gazed at whales spouting offshore and seals pupping on beaches. But early observations of nature were largely tied up with myths about animals and legends of their capabilities. A common theme appears to have been the changing of humans to dolphins and whales, and the reverse. This theme is recognized in remaining legends of Australian aborigine “dream time,” boto (Inia geoffrensis) and baiji (Lipotes vexillifer) river dolphin folklore (Sangama de Beaver and Beaver, 1989; Zhou and Zhang, 1991, respectively), tales of the god-like killer whales (Orcinus orca) of Pacific Northwest indigenous tribes (McIntyre, 1974), and many more. Some early writings show remarkable insights in marine mammal biology. Well over 2000 years ago, scholars of China’s Han Dynasty in the annotated dictionary “Er-Ya,” described the baiji as related to marine dolphins, implying that those were known to intellectuals of the time. Even earlier, the Greek philosopher/scientist Aristotle (384–322 bc) differentiated between baleen and toothed whales and described both types in some detail. It is unfortunate but totally understandable in hindsight that he classified cetaceans as fishes, a practice still present in Britain’s term “Royal Fishes” under which all whales and dolphins belong by law to the Crown. The Roman writer/ lawyer/admiral Pliny the Elder (23–79 ad) published a book on dolphins and whales 400 years after Aristotle’s time as part of his 37-volume “Natural History.” Not much scientific inquiry or thought was conducted between Roman times and the western Renaissance, and knowledge, at least written knowledge, of marine mammals languished as well. The modern progression of marine mammal research can perhaps best be
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described as occurring in four general (and not mutually exclusive) phases: (1) morphological description from beach-cast specimens and fossils; (2) descriptions of behavior, anatomy, and distribution as gathered during hunting and whaling activities; (3) studies of physiology and behavior in captivity; and (4) studies of ecology, habitat use, numbers, life history patterns, behavior, and physiology in nature. A fifth phase may be thought of as an ever-increasing sophistication in integrating knowledge from terrestrial situations as well as from different fields of marine mammal endeavors. The phases of research mentioned above follow a rough chronology, with morphology and systematics the main topics pre-1900s; hunting-related habitat, morphological, and behavioral research mainly from the 1850s to the 1970s; scientific captive animal descriptions beginning around 1950; and more ecologically oriented descriptions in nature beginning around the 1970s. All phases are ongoing, with electronic devices helping to elevate in-field research on marine mammal lives to a new level of sophistication. A very readable recent account of the history of marine mammal studies is found in Berta and Sumich (1999). Elsewhere, this volume lists some of the major deceased marine mammal researchers of the past and mentions their classic works in the field (see References). Pierre Bélon was probably the first “modern” marine mammal author since Pliny’s time. He published accurate descriptions and woodcuts of some whales, dolphins, and seals (Belloni, 1553), and these (and also, unfortunately, the less accurate ones) were much copied by others in the next two centuries. The real burst of marine mammal knowledge did not come until later, however. And then it came suddenly, in tune with eighteenth century awakening of scientific thought in the western world. While many authors could be mentioned, three early contemporaries did much to advance cetacean descriptions, taxonomy, and systematics. These were the French zoologist La Cépède (1804) and the Cuvier brothers. Georges Cuvier, who arguably founded modern evolutionary theory, wrote on many topics, including cetaceans; whereas his less-famed brother Frederic published two important works on cetaceans (Cuvier, 1829, 1836). These three were followed by the Belgian zoologist Van Beneden in the latter half of the nineteenth century, with work mainly consisting of compilations of information on fossil whales, and by a host of fine morphologists, taxonomists, systematists, and evolutionary historians in the twentieth century (summaries are provided by Rice, 1998; Thewissen, 1998; Pabst et al., 1999; and Reynolds et al., 1999). While much of the earlier work centered on cetaceans, the British zoologist John Edward Gray described both seals and whales in the British Museum (Gray, 1866), and the American zoologist Joel Allen wrote excellent monographs on whales, pinnipeds, and sirenians (Allen, 1880). Yamase (1760) began the science of marine mammalogy in Japan at about the same time as serious studies began in the west. He presented accurate figures and descriptions of the external morphology of six toothed and seven baleen whale species and distinguished them from fishes. His work was brought to the west in a marine mammal section of “Fauna Japonica” by Siebold (1842). Otsuki began to describe the internal anatomy of cetaceans of Japan in 1808, but his manuscript remains unpublished. A second major phase of information gathering, often linked intricately with that just described, involved descriptions of animals as related to hunting and whaling. Morphological information was at the core of these descriptions, but behavior and the basic society structure of whales and pinnipeds—of course much of the time affected by the hunting activities themselves—were recorded as well. One of the earliest accurate accounts consisted of German-born
and Russian-naturalized Georg Steller’s descriptions of pinnipeds and the soon-after extinct Steller’s sea cow (Hydrodamalis gigas), the largest and only cold-water sirenian known (originally published in Latin in 1751, and republished in English as Steller, 1899). Quite a few books related especially to whaling were produced, but perhaps the most enduring one from the nineteenth century was by the North American whaling captain Charles Scammon, who wrote with feeling and accuracy on behavior and life history habits of marine mammals of the North Pacific (Scammon, 1874). In the twentieth century, one of the most famous works largely relying on whalingaccumulated data consists of Everhard Slijper’s book “Whales and Dolphins” (published in English in 1976). A very readable account of whaling and the literature derived from whaling can be found in “Men and Whales” by Richard Ellis (1991). Modern factory whaling itself helped to usher in excellent research on numbers, habitat use, life history patterns, and morphology/physiology. This was so especially during the Discovery investigations of 1925– 1951, a British research program that was responsible for a wealth of new data, especially on large whales of the southern hemisphere. These investigations consisted in part of extensive long-term tagging (“discovery tags,” shot into the blubber and muscle tissues of whales, and later recovered during actual whale kills). In this manner, migrations of great whales were delineated long before modern radio and satellite tags provided such information (e.g., Allen, 1980). Dozens of fine researchers published hundreds of papers that relied on the Discovery expeditions, and on other whaling data since then (e.g., Laws, 1959) (see also the section “International Whaling Commission” in this voume). As a counterpoint to early cetacean information, the reader interested in pinniped research from the ancient Greeks to about 1983 can consult an excellent annotated bibliography of over 12,000 publications by Ronald et al. (1976, 1983). While whaling, sealing, and other forms of direct hunting are much abated today as compared to in the 1960s, there are still powerful low-level, oft-indigenous hunts, especially in protein-poor areas of the world (Perrin, 1999). As a result, data are being accumulated and analyzed on morphology, genetics, taxonomy, and systematics, life history, prey patterns, and so on. Excellent recent information has become available from results of hunting on, e.g., pilot whales (Globicephala spp.), oceanic dolphins (especially of the genus Stenella), bowhead whales (Balaena mysticetus), sperm whales (Physeter macrocephalus), and several seal, fur seal, and sea lion species (summaries in Berta and Sumich, 1999; Reynolds and Rommel, 1999; and Twiss and Reeves, 1999). A third major research avenue has come about as a result of keeping marine mammals in captivity. Attempts to do so in the early part of the last century usually resulted in the animals’ untimely deaths— due to poor water, incorrect or tainted food, disease, and aggression between individuals in confined spaces. Facilities that housed marine mammals simply replaced dead ones by more captures from nature. However, especially since the 1970s, amazing strides in husbandry have been made for all marine mammals (except large whales), and the better aquaria now keep—and breed—animals very well. Unfortunately, there are still many “primitive” facilities, especially in less-developed parts of the world. At present, there are representatives of all major taxonomic groups in captivity, as show animals and for research: toothed whales and dolphins (only two baleen whales, each time young gray whales, Eschrichtius robustus, have been successfully kept); pinnipeds of all types, but especially California sea lions (Zalophus californianus); sirenians (mainly the West Indian manatee, Trichechus manatus and the dugong, Dugong dugon); and polar bears (Ursus maritimus) and sea otters (Enhydra lutris).
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Only through holding animals in controlled situations have researchers learned that dolphins echolocate (Au, 1993); that all marine mammals exhibit reduced heart and general metabolic rates during dives (Ridgway, 1972; Pabst et al., 1999); and that both dolphins and sea lions have remarkably advanced cognitive capabilities (Tyack, 1999). Furthermore, it is now fully appreciated that while pinnipeds and cetaceans are finely tuned underwater swimmers and divers with superbly evolved methods of breath holding, avoiding or reducing lactic acid depth during long submergences, and navigating in dark and cold waters, there is no secret “magic” to their energetic capabilities (Costa and Williams, 1999). One major misstep from studies in captivity took place: the American John Lilly avowed in the 1960s that his research on bottlenose dolphins (Tursiops truncatus) proved that these popular show animals have an intelligence superior even to that of the brightest dogs (Canus lupus familiaris) and chimpanzees (Pan troglodytes), and likely equal to that of humans (Lilly, 1967). Careful studies by others have shown that dolphins are undeniably “smart” (intelligence is very difficult to define and compare, but has something to do with well-developed flexibilities of behavior and of innovative learning), but that there is no reason to believe that dolphins fare better in this “intelligence/cognition” sphere than many other highly social mammals (Herman, 1980, 1986; Tyack, 1999; Wells et al., 1999). While the study of marine mammals dead from the sea and live in captivity continues and grows, a relatively new approach has become the major research avenue since the 1970s. This consists of our fourth phase, of researchers going out into nature to observe the animals in their own milieu; as the animals associate with conspecifics; eat and are being eaten; and mate, give birth, and raise their young. We are learning more about the lives of these generally social creatures as they face storms, heavy years of sea ice, seasons of poor food resources (e.g., caused by “El Niño” southern oscillation climatic events), parasite infestations, adoring but noisy boatloads of whale-watching tourists, crowded shipping lanes, and habitat degradation near shore and in mighty rivers. This information on ecology of marine mammals is vital if we are to help protect them and their natural ecosystems from the depredations of overfishing, habitat pollution by chemicals, heavy metals, and noise; and the results of global climate change and wholescale habitat destruction due to the effects of ozone depletion and global warming (Tynan and DeMaster, 1997; Ferguson et al., 2005). Studies in nature often rely on visual or photographic recognition of individual whales, dolphins, and pinnipeds, often with the help of tags or color marks but also by natural markings (Hammond et al., 1990). Researchers have described movement patterns by tracking animals with surveyor’s transits from shore, and from shore and vessels by small radio tags placed on their bodies (Würsig et al., 1991). Since the early 1990s, satellite tags that relay position information to earth-orbiting satellites have become smaller, less expensive, and ever more popular. As a result, we know that northern elephant seals (Mirounga angustirostris) swim and dive into deep oceanic waters for months at a time, humpback whales (Megaptera novaeangliae) take rapid zigzag courses between their mating and feeding grounds, North Atlantic right whales (Eubalaena glacialis) undergo previously unsuspected jaunts between Greenland and New England during the feeding summer, and much more (Wells et al., 1999). Tags are being fitted not only with depth-of-dive measuring and telemetering devices, but also with ways to ascertain geographic position, swimming velocity, angles of dives, water and skin temperature, individual sound production, heart rate, and, in the future, other physiological measures. Recent advances in small and low-light capable video camera/record systems are even giving data on swimming, socializing,
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and feeding behavior directly from the animals under water (Davis et al., 1999). Physiological research, previously entirely within the realm of captivity, is more and more possible with innovative or sophisticated techniques in nature. Samples of stool, urine, blood, and even mother’s milk are being collected from pinnipeds resting on land or ice. Trained dolphins have been released at sea, commanded to dive, and then told to exhale into a funnel to ascertain oxygen consumption values and to station themselves so that blood can be drawn. Small darts have been developed that are fired from a crossbow or pneumatic pistol and that obtain skin and blubber samples from freeliving cetaceans for analyses of genetics (Dizon et al., 1997), toxin loads, reproductive status, and blubber energy content for relative measurements of health within and between populations. Sloughed skin samples from breaching whales have been successfully collected from the water and genetically sampled for gender, social grouping, and population data. A technique has been developed to harmlessly “skin-swab” bow-riding dolphins, also for genetic analysis (Harlin et al., 1999). In response to an apparent increase in marine mammal strandings and the emergence of new marine mammal diseases in recent years, studies of wild marine mammal disease and ocean chemical contaminants are on the increase. While studies in nature have yielded data on the presence of deadly viruses and contaminant levels in tissues of beached and dying marine mammals (Aquilar and Borrell, 1997), they have provided little insight into immune defense against disease or the biochemical consequences of contaminants. More recently, e.g., species-specific biomarkers have been developed to assess the dolphin immune system (Romano et al., 1999). Because they are readily available for long-term studies requiring serial sampling of tissues and health and reproductive histories, captive marine mammals afford unique opportunities to provide basic insight into the relationships among contaminants, the immune system, and animal health. Once they are developed and tested on animals in captivity, biomarkers can be used with wild marine mammal populations to assess contaminant exposures and their possible effects on immune systems and neurologic responses (Ridgway and Au, 1999), as well as on reproductive success (Ridgway and Reddy, 1995), growth, and development. The sensitive hearing of marine mammals has led to concerns that intense sound or noise pollution generated by humans could impede communication, cause physiological stress, or damage hearing. Marine mammal hearing studies currently underway should help to define mitigation criteria for the effects of human-generated sound in the ocean (Schlundt et al., 2000), and ultimately allow us to find a balance between the ecological needs of marine mammals and the role the ocean plays in commerce, exploration, travel, and defense. Overall, descriptions of marine mammal taxonomy and population biology have shifted from mainly morphological approaches to an increasing reliance on molecular methods. Up through the 1960s, cetologists studied dolphins by harpooning them. For example, the revision of the spotted dolphins (Stenella attenuata and S. frontalis) by Perrin et al. (1987) was based in part on dolphins collected at sea by Francis C. Fraser, Dale W. Rice, William E. Schevill, and Edward D. Mitchell, all eminent scholars and pioneers of modern cetology. Without those specimens, the study would not have been possible; that is the way it was done until protection of marine mammals became the norm in most countries in the 1970s. Another source of specimens has been dolphins that died in oceanaria. The same revision by Perrin et al. (1987) included spotted dolphins
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History of Marine Mammal Research
retrieved from oceanaria by David K. Caldwell through the 1970s and early 1980s. And at that time, there were still a number of accessible directed dolphin fisheries; the spotted dolphin review also included specimens from directed fisheries in the Caribbean, St. Helena, West Africa, Japan, and the Solomon Islands. Today, dolphins, whales, and pinnipeds are stringently protected in the wild in most places. For oceanaria, restrictions have been placed on species and numbers of animals that can be captured for exhibit and the high monetary value of captive marine mammals has resulted in better husbandry and fewer deaths. As a result of these factors, marine mammal biologists practicing morphological approaches became limited to specimens from strandings and bycatch, greatly decreased opportunities for amassing adequate series of specimens for quantitative analysis. But then along came biopsy sampling and ready techniques of amplifying DNA fragments by a technique termed polymerase chain reaction (PCR). Collection of samples by biopsy is legal and doable, so the balance of taxonomic and population studies has shifted from morphology to genetics. And the traditional morphologists have been scrambling to keep up by re-educating themselves in the new techniques or recruiting collaborators who know their way around genetics. The study of marine mammals has now matured into a fifth phase, characterized by the obliteration of boundaries that separated the previous phases. New studies on marine mammals are often integrative, combining methods and ways of thinking largely gleaned from terrestrial animals. This comparison of ideas and research techniques holds great promise for the understanding of the biology of marine mammals. As our understanding of their biology increases, marine mammals become appealing subjects for approaches that are at times laboratory heavy and at times nearly biomedical in scope. In turn, these approaches enrich knowledge of marine mammals. For instance, biochemical analyses of body fats, first championed for humans and other terrestrial animals, give new insights into the functions of different fats in cetaceans (Koopman et al., 2003). Immuno-histochemical staining techniques originally used for non-marine mammal studies allow the identification of genes that significantly affected cetacean evolution, such as those genes responsible for the loss of hind limbs (Thewissen et al., 2006). Our understanding of the social systems of terrestrial mammals, with one major aspect being sperm competition at the physiological level (Kenagy and Trombulak, 1986) has begun to inform us about the relatively non-competitive balaenid whales, gray whales, quite a few species of dolphins, and manatees that have polygynous or polygandrous (multi-mate) societies (Reynolds et al., 2004). Through sophisticated studies with modern techniques, marine mammalogy is beginning to enrich more broad fields of science such as behavioral ecology, physiological ecology, and evolutionary biology. It was recognized long ago that marine mammals represent amazing natural experiments of evolution, and the maturation of the field of marine mammalogy is allowing for these experiments to be explored, and to inform all of biology. Sophisticated electronic and biochemical techniques have recently been and are being developed to study the lives of marine mammals. However, the “tried and true” methods of looking at fossil bones, dissecting and describing pathologies of a net-entangled animal or one cast on shore after a storm, safely and carefully experimenting with animals in captivity, and the dogged gathering of behavioral information by binoculars and notebook are by no means passé. The greatest change since about the 1960s is the ever wider availability of information. This means that there is now a wealth of background knowledge
available to anyone anywhere with a computer and an Internet connection. We are, in this new twenty-first century, in a vibrant phase of marine mammal research, and we see a very bright future for evermore exciting discoveries in our field. Although much of the research landscape looks bright, we would be amiss if we did not cite a note of pessimism as well, as it is undeniable that many populations and some entire species are facing reductions and even extinction due to human-caused habitat degradation, including rapid climate change. For example, the Chinese river dolphin, baiji, is very likely extinct (Turvey et al., 2007), and the vaquita (Phocoena sinus) and Mediterranean monk sea (Monachus monachus) may not be far behind. No amount of modern and multidisciplinary research will be able to wrest information from a species that is gone from the face of the Earth.
See Also the Following Articles Hunting of Marine Mammals ■ Marine Protected Areas ■ InterRational Whaling Commission ■ Popular Culture and Literature
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Hooded Seal Cystophora cristata KIT M. KOVACS I. Characteristics and Taxonomy
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he hooded seal is a large phocid that is silver-gray in color with irregular black spots covering most of the body; the face is often completely black (Fig. 1). Adult males are about 2.5 m long and weigh an average of 300 kg; large males can be in excess of 400 kg. Adult females are considerably smaller than males, measuring 2.2 m in length and weighing an average of 200 kg. Hooded seal pups are approximately 1 m long when they are born and weigh about 25 kg. They are blue on their backs and silver-gray on their bellies (Fig. 1). This distinctive “blueback” pelage is maintained for about 2 years (Lavigne and Kovacs, 1988). The most distinctive physical feature of hooded seals is the prominent nasal ornament borne by adult males (Fig. 1). When relaxed the nasal appendage hangs as a loose, wrinkled sac over the front of males’ noses. During the breeding season (in March) males inflate this sac to display to females and to other males, forming a tight, bi-lobed “hood” that covers the front of the face and the top of the head. This structure
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