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Appendix B
An Introduction to Marine Mammals
Three orders of the class Mammalia contain marine mammals: Cetacea, Carnivora, and Sirenia. (There is a section on each of the three orders in this appendix. Each includes a table listing the marine mammals in that order.) The size range of marine mammals is immense, varying from a newborn sea otter weighing perhaps 1 kilogram (kg) to the largest female blue whale weighing about 100,000 kg. Their habitats are also quite varied, encompassing all seas and numerous coastal areas and shores as well as some freshwater lakes and rivers.
All extant Cetacea and Sirenia normally spend their entire lives in water. In contrast, marine mammals of the order Carnivora are semiaquatic, often hauling out on land. Some of these semiaquatic mammals spend considerable periods of time (many months) in the water, often hundreds or even thousands of kilometers at sea away from haul-out or breeding areas. Families of marine mammals of the order Carnivora are these: Otariidae, or eared seals (fur seals and sea lions); Odobenidae (walrus); Phocidae (true seals); Mustelidae (chungungo and sea otter); and Ursidae (polar bear).
In the United States, all marine mammals are legally protected by the Marine Mammal Protection Act of 1972 (MMPA). The species of the order Cetacea and suborder Pinnipedia that live strictly in freshwater are also protected under this law, and thus they are included in this discussion. Under the 1972 act, the U.S. Fish and Wildlife Service (FWS) of the U.S. Department of the Interior is responsible
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for administering regulations concerning polar bears, walrus, sirenians, and sea otters; the National Marine Fisheries Service of the U.S. Department of Commerce is responsible for whales, dolphins, seals, sea lions, and other marine mammals not regulated by FWS. In addition, another independent body established under the MMPA, the Marine Mammal Commission, maintains a scientific committee to advise on issues related to marine mammal conservation. Those species designated as endangered are further protected under the Endangered Species Act of 1973.
Threats to marine mammal populations worldwide are many. They result, for example, from fishing (the use of gillnets, driftnets, ghost nets, long lines, the yellowfin tuna purse seine, rolling hooks), pollution (agricultural runoff, industrial waste, petroleum spills, trash dumping), deforestation and development of the rain forests, damming, oil field development, mining, heavy-vessel traffic, and other human activities.
Twenty species of marine mammals are listed as endangered under U.S. provisions (see the tables in this appendix), although some of them appear to be gaining in population and may be removed from endangered status (Brownell et al., 1989). For example, the eastern or California stock of the gray whale Eschrichtius robustus has apparently recovered from severe exploitation and thus was proposed for removal from the endangered species list by the U.S. Department of Commerce as of 7 January 1993 (Marine Mammal Commission, 1992). Some other marine mammals, such as the Gulf of California porpoise (vaquita) and the Yangtze River dolphin (baiji), appear to be headed for extinction. However, the majority of species are not endangered or seriously threatened.
Cetacea: Whales, Dolphins, Porpoises
The larger cetaceans include Physeteridae (sperm whales), Ziphoidea (beaked whales and bottlenose whales), and suborder Mysticeti (baleen whales) (Table B-1). Eight of the largest species are listed as endangered.
The sperm whale has been on the U.S. List of Endangered and Threatened Wildlife, even though there may be more than a million sperm whales in the world's oceans. Some specific populations are apparently depleted even though the world population is relatively large.
Because of their past exploitation by whalers and recent publicity about this exploitation, most large baleen whales are assumed by the public to be endangered species. However, in the absence of the
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TABLE B-1 Classification of Living Mammals of the Order Cetacea
Suborder, family, genus, species
Common name
I. Suborder Odontoceti
Superfamily Platanistoidea
Family Platanistidae
Platanista gangetica
Ganges River dolphin, Ganges susu
Platanista minor *
Indus River dolphin, Indus susu
Family Pontoporiidae
Subfamily Lipotinae
Lipotes vexillifer * **
baiji, Yangtze, or Chinese River dolphin
Subfamily Pontoporiinae
Pontoporia blainvillei
franciscana, cachimbo, La Plata dolphin
Family Iniidae
Inia geoffrensis **
boto, boutu, bufeo, Amazon River dolphin
Superfamily Delphinoidea
Family Monodontidae
Subfamily Orcaellinae
Orcaella brevirostris
Irrawaddy dolphin, pesut
Subfamily Delphinapterinae
Delphinapterus leucas **
white whale, beluga
Subfamily Monodontinae
Monodon monoceros narwhal
Family Phocoenidae
Subfamily Phocoeninae
Phocoena phocoena **
harbor porpoise
Phocoena spinipinnis
Burmeister's porpoise
Phocoena sinus *
vaquita, Gulf of California harbor porpoise
Neophocaena phocaenoides
finless porpoise
Subfamily Phocoenoidinae
Australophocaena dioptrica
spectacled porpoise
Phocoenoides dalli
Dall's porpoise
Family Delphinidae
Subfamily Steninae
Steno bredanensis
rough-toothed dolphin
Sousa chinensis
Indopacific hump-backed dolphin
Sousa plumbea
plumbeous dolphin
Sousa teuszii
Atlantic hump-backed dolphin
Sotalia fluviatilis
tucuxi
Subfamily Delphininae
Lagenorhynchus albirostris
white-beaked dolphin
Lagenorhynchus acutus
Atlantic white-sided dolphin
Lagenorhynchus obscurus
dusky dolphin
Lagenorhynchus obliquidens
Pacific white-sided dolphin
Lagenorhynchus cruciger
hourglass dolphin
Lagenorhynchus australis
Peale's dolphin
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Suborder, family, genus, species
Common name
Grampus griseus
Risso's dolphin
Tursiops truncatus
bottlenose dolphin
Stenella frontalis
Atlantic spotted dolphin
Stenella attenuata
pantropical spotted dolphin
Stenella longirostris
spinner dolphin
Stenella clymene
clymene dolphin
Stenella coeruleoalba
striped dolphin
Delphinus delphis
common dolphin
Lagenodelphis hosei
Fraser's dolphin
Subfamily Lissodelphinae
Lissodelphis borealis
northern right whale dolphin
Lissodelphis peronii
southern right whale dolphin
Subfamily Cephalorhynchinae
Cephalorhynchus commersonii
Commerson's dolphin
Cephalorhynchus eutropia
black dolphin, Chilean dolphin
Cephalorhynchus heavisidii
Heaviside's dolphin
Cephalorhynchus hectori
Hector's dolphin
Subfamily Globicephalinae
Peponocephala electra
melon-headed whale, electra dolphin
Feresa attenuata
pygmy killer whale
Pseudorca crassidens **
false killer whale
Orcinus orca **
killer whale
Globicephala melas
long-finned pilot whale
Globicephala macrorhynchus
short-finned pilot whale
Superfamily Ziphoidea.
Family Ziphiidae
Tasmacetus shepherdi
Shepherd's beaked whale
Berardius bairdii
Baird's beaked whale
Berardius arnuxii
Arnoux's beaked whale
Mesoplodon pacificus
Longman's beaked whale
Mesoplodon bidens
Sowerby's beaked whale
Mesoplodon densirostris
Blainville's beaked whale
Mesoplodon europaeus
Gervais' beaked whale
Mesoplodon layardii
strap-toothed whale
Mesoplodon hectori
Hector's beaked whale
Mesoplodon grayi
Gray's beaked whale
Mesoplodon stejnegeri
Stejneger's beaked whale
Mesoplodon bowdoini
Andrew's beaked whale
Mesoplodon mirus
True's beaked whale
Mesoplodon ginkgodens
ginkgo-toothed beaked whale
Mesoplodon carlhubbsi
Hubb's beaked whale
Ziphius cavirostris
Cuvier's beaked whale
Hyperoodon ampullatus
northern bottlenose whale
Hyperoodon planifrons
southern bottlenose whale
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Suborder, family, genus, species
Common name
Superfamily Physeteroidea
Family Physeteridae
Subfamily Physeterinae
Physeter macrocephalus *
sperm whale
Family Kogiidae
Kogia breviceps
pygmy sperm whale
Kogia simus
dwarf sperm whale
II. Suborder Mysticeti
Family Balaenidae
Balaena mysticetus *
bowhead whale
Eubalaena austalis *
southern right whale
Eubalaena glacialis *
northern right whale
Family Neobalaenidae
Caperea marginata
pygmy right whale
Family Eschrichtfiidae
Eschrichtius robustus *1
gray whale
Family Balaenopteridae
Subfamily Balaenopterinae
Balaenoptera acutorostrata
minke whale
Balaenoptera borealis *
sei whale
Balaenoptera edeni
Bryde's whale
Balaenoptera musculus *
blue whale
Balaenoptera physalus *
fin whale, finback
Subfamily Megapterinae
Megaptera novaeangliae *
humpback whale
NOTE: * = endangered species; ** = species for which some audiometric information has been published.
1The California stock of gray whales has been recommended for delisting by NMFS.
resumption of full commercial whaling, most of these larger cetaceans, including some species of baleen whales that appear on the Endangered Species List are, as species, in reality not endangered. Some of these species have been completely protected for many years, and all are currently protected by the moratorium on commercial whaling promulgated by the International Whaling Commission. As with the sperm whales, however, some populations of large baleen whales remain depleted. Brownell et al. (1989) suggest that some of these large whales be removed from the Endangered Species List and that some small cetaceans be added. With the possible exception of the northern right whale, none of the large cetacean species is currently in peril of extinction (Perrin, 1988).
There are more than 40 species of smaller cetaceans, dolphins
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and porpoises, found worldwide. While no cetacean species has been driven to extinction by human endeavors (Perrin, 1988), four species of the smaller cetaceans are in jeopardy in the coming decades if certain human activities in their habitats are not changed (Brownell, 1991; Norris, 1992). These include the baiji, Lipotes vexillifer; the Chilean dolphin, Cephalorhynchus eutropia; the Indus River dolphin, Platanista minor; and the vaquita, Phocoena sinus, of the Gulf of California.
The Carnivora: Pinnipeds, Sea Otters, Polar Bears
The marine Carnivora all spend some time on land or sea ice to breed and bear their young. The breeding areas are therefore especially sensitive to human encroachment. A few species live in freshwater. Marine mammals in the order Carnivora include fur seals and sea lions, true seals, walrus, chungungo and sea otters, and polar bears (Table B-2).
Pinnipedia
Pinniped means ''feather footed,'' and the suborder Pinnipedia includes three families: Otariidae (fur seals and sea lions), Odobenidae (walrus), and Phocidae (true seals). Historically, almost all pinnipeds were hunted for fur, meat, oil, or ivory. Brownell (1991) suggests that, although most pinniped species will probably experience an increase in number during the 1990s, at least three species—northern fur seal, Callorhinus ursinus; Steller sea lion, Eumetopias jubatus; and Mediterranean monk seal, Monachus monachus—will continue to decline in the absence of stronger corrective measures. One pinniped species, the Caribbean monk seal, Monachus tropicalis, has apparently become extinct during this century (Kenyon, 1977).
Sea Otters
The sea otter of the North Pacific, Enhydra lutris, is a coastal animal that is often associated with kelp beds just off the coasts of California, British Columbia, and Alaska.
The marine otter off the coasts of Peru and Chile, chungungo, Lutra felina, is severely endangered because the animals are hunted for their prized pelts on the Chilean coast and because Peruvians often shoot them as a menace to fishing (Miller and Rottmann, 1983). Another large otter, Lutra longicaudis of northeast Brazil, is threatened by fishing, clandestine hunting, and habitat degradation (Almeida et al., 1991).
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TABLE B-2 Marine Mammals (Pinnipeds, Otters, Polar Bears) of the Order Carnivora
Family, genus, species
Common name
Family Otariidae of suborder Pinnipedia
Eumetopias jubatus
Steller sea lion, northern sea lion
Zalophus californianus **
California sea lion
Otaria flavescens
South American sea lion
Neophoca cinerea
Australian sea lion
Phocartos hookeri
New Zealand sea lion
Callorhinus ursinus **
northern fur seal
Arctocephalus townsendi *
Guadalupe fur seal
Arctocephalus philippii *
Juan Fernández fur seal
Arctocephalus galapagoensis
Galápalgos fur seal
Arctocephalus australis
South American fur seal
Arctocephalus pusillus
Cape fur seal, South African fur seal, Tasmanian fur seal, Victorian fur seal
Arctocephalus forsteri
New Zealand fur seal, West Australian fur seal
Arctocephalus gazella
Kerguelen fur seal, Antarctic fur seal
Arctocephalus tropicalis
Amsterdam Island fur seal
Family Odobenidae of suborder
Pinnipedia
Odobenus rosmarus
walrus
Family Phocidae of suborder
Pinnipedia
Phoca vitulina **
harbor seal
Phoca largha
larga seal, spotted seal
Phoca hispida **
ringed seal
Phoca sibirica
Caspian seal
Phoca groenlandica **
harp seal, Greenland seal
Phoca fasciata
ribbon seal
Erignathus barbatus
bearded seal
Cystophora cristata
hooded seal, bladdernose seal
Halichoerus grypus **
gray seal
Monachus monachus *
Mediterranean monk seal
Monachus tropicalis ***
West Indian monk seal, Caribbean monk seal
Monachus schauinslandi * **
Hawaiian monk seal
Mirounga leonina
southern elephant seal
Mirounga angustirostris
northern elephant seal
Lobodon carcinophagus
crabeater seal
Ommatophoca rossii
Ross seal
Hydrurga leptonyx
leopard seal
Leptonychotes weddelli
Weddell seal
Family Mustelidae
Lutra felina *
Chungungo, marine otter, gato marino
Enhydra lutris
sea otter
Family Ursidae
Ursus maritimus
polar bear
NOTES: The otters and bear listed in this table are regarded as marine mammals. Of course, most bears and otters are carnivores but not marine mammals.
* = endangered species; ** = species for which some audiometric data are available; *** = extinct species.
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Polar Bears
Polar bears from the family Ursidae may be seen in the water some distance at sea. However, they spend most of the year on sea ice or, in the absence of ice, on land. They prey primarily on ringed seals (Phoca hispida). Polar bears also kill other marine mammals such as bearded seals (Erignathus barbatus), white whales (Delphinapterus leucas), and the narwhal (Monodon monoceros). Ringed seal populations are large, but white whales and narwhals, although not endangered,1 are much less numerous.
The Sirenia: Manatees and Dugongs (Sea Cows)
Although they receive much less attention by the media, the Sirenia are probably more endangered than any of the great whales with the possible exception of right whales. In fact, a sirenian species has become extinct in modern times (in the 1800s)—the great northern sea cow, or Steller's sea cow, Hydrodamalis gigas, of the Bering Sea (Nishiwaki and Marsh, 1985). Dugongs and manatees are the two living genera of Sirenia (Table B-3). They represent two distinct families of plant-grazing marine mammals that are found in separate parts of the world. Dugongs occur in tropical and subtropical shallows of the Indo-Pacific region—northern Australia, the Guangxi coast of China, Indonesia, the Aru Islands, Sri Lanka, India, the Persian Gulf, the Arabian Peninsula, the East African coast, and Madagascar.
Other than the dugong, the elephant and the hyrax are the closest living relatives of the manatee. There are three living species of
TABLE B-3 Living and Recent Members of the Totally Aquatic Order Sirenia (Sea Cows)
Family, genus, species
Common name
Order Sirenia (sea cows)
Family Dugongidae
Dugong dugon *
dugong
Hydrodamalis gigas ***
Steller's sea cow
Family Trichechidae
Trichechus manatus * **
Caribbean manatee
Trichechus inunguis *
Amazonian manatee
Trichechus senegalensis
West African manatee
NOTES: * = endangered species; ** = some auditory information is available; *** = extinct species.
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manatees: the West Indian or Florida manatee, Trichechus manatus; the West African manatee, T. senegalensis; and the Amazonian manatee, T. inunguis. Manatees prefer shallow estuaries and swampy areas where aquatic plants are abundant (Caldwell and Caldwell, 1985). They are at times found in freshwater, brackish water, or marine waters.
West Indian or Caribbean manatees range from Georgia on the coast of the southern United States to the coast of Brazil; however, there is a very patchy distribution over this wide range. The Amazonian manatee is found in the Amazon basin and possibly in parts of the Orinoco River system. The West African manatee is apparently most abundant in the Niger River and its tributaries (Nishiwaki et al., 1982), although there are areas of dense manatee population along the coast of Sierra Leone.
References
Almeida, R.T., G.P. Pimentel, and F.J.L. Silva. 1991. Occurrence of Otter Lutra longicaudis (Mammalia-Mustelidae) in mangrove area, Pernambuco State—NE Brazil. Abstract from: Ninth Biennial Conference on the Biology of Marine Mammals, Chicago Zoological Society, Chicago. p. 1.
Brownell, R.L., Jr. 1991. Marine Mammal Populations in the 1990's: Status, Problems and Research. IBI Reports. 2:1–10. (International Marine Biological Research Institute, Kamogawa, Japan.)
Brownell, R.L., Jr., K. Ralls, and W.F. Perrin. 1989. The plight of the 'forgotten' whales. Oceanus 32(1):5–11.
Caldwell, D.K., and M.C. Caldwell. 1985. Manatees, Trichechus manatus Linnaeus, 1758; Trichechus senegalensis Link, 1795 and Trichechus inunguis (Natterer, 1883). In: S.H. Ridgway and R.J. Harrison (eds.), Handbook of Marine Mammals, vol. 3. The Sirenians and Baleen Whales. Academic Press, London. pp. 33–66.
Kenyon, K.W. 1977. Caribbean monk seal extinct. J. Mammal. 58:97–98.
Marine Mammal Commission. 1992. Annual Report of the Marine Mammal Commission: Calendar Year 1991. A report to Congress. U.S. Marine Mammal Commission, Washington, DC.
Miller, S.D., and J. Rottmann. 1983. Endangered mammals of Chile: Status and conservation. Biol. Conserv. 25:335–352.
Nishiwaki, M., and H. Marsh. 1985. Dugong, Dugong dugon (Muller, 1776). In: S.H. Ridgway and R.J. Harrison (eds.), Handbook of Marine Mammals, vol. 3. The Sirenians and Baleen Whales. Academic Press, London. pp. 1–31.
Nishiwaki, M., M. Yamaguchi, S. Shikota, S. Uchida, and T. Kataoka. 1982. Recent survey on the distribution of African manatee. Sci. Rep. Whales Res. Inst. 34:137–147.
Norris, K. 1992. Dolphins in Crisis. Nat. Geog. 182(3):2–35.
Perrin, W. F. 1988. Dolphins, Porpoises, and Whales: An Action Plan for the Conservation of Biological Diversity: 1988–1992. IUCN, Gland, Switzerland.
Representative terms from entire chapter:
beaked whale