Marine Mammals, Extinctions of Glenn R Van Blaricom, US Geological Survey and University of Washington, Seattle, WA, USA Leah R Gerber, Arizona State University, Tempe, AZ, USA Robert L Brownell Jr., National Marine Fisheries Service, Pacific Grove, CA, USA r 2013 Elsevier Inc. All rights reserved. Glossary Mysticeti The suborder of cetacean that includes the four Baiji The species of marine mammal also known as the families of baleen whales. Most mysticetes are quite large, Yangtze River dolphin or Chinese river dolphin, Lipotes including the blue whale which reaches 33 m in length and vexillifer Miller, 1918, the sole member of the odontocete is recognized as the largest animal in the earth’s history. cetacean family Lipotidae. The last living baiji was seen in Approximately 9% of the known modern species of marine 2002, and the species was reported by experts to be extinct mammals are mysticetes. in 2007. This was the first known extinction of a cetacean Odontoceti The suborder of the cetacean that includes the species in recorded human history, and the fourth known 10 families of toothed whales, including sperm whales, extinction of a marine mammal species since the eighteenth beaked whales, dolphins, porpoises, belugas, narwhals, and century AD. river dolphins. Approximately 56% of the known modern Baleen Modified, hardened epithelial structures species of marine mammals are odontocetes. suspended from the upper jaws of the mysticete whales. Pinnipedia An obsolete but frequently used taxonomic Baleen is in the form of multiple elongate plates within term for the three families that comprise the seals, sea lions, mysticete whale mouths, with a fibrous fringe on the inside fur seals, and walrus. Approximately 28% of the known edge that allows whales to filter zooplanktonic or fish prey modern species of marine mammals are pinnipeds. All from sea water. pinnipeds are in the mammalian order Carnivora. Cetacea The order of mammals that includes the whales, Scientific whaling Whaling activity currently undertaken dolphins, porpoises, and allies. by the Institute of Cetacean Research (Japan) with the stated Delphinidae The family of odontocete cetaceans that goal of improved understanding of relationships of large includes the dolphins. Delphinids are the most diverse whales and marine ecosystems in the world’s oceans. The family of marine mammals with 36 species currently activity is permitted under a procedural exception to recognized, approximately 28% of the known modern the moratorium on commercial whaling as managed by the species of marine mammals. International Whaling Commission. Scientific whaling is Desmostylia The only known fully extinct order of highly controversial and under ongoing intensive debate marine mammals, closely related to the sirenians. among scientists, management organizations, conservation Desmostylians were large herbivorous quadripedal advocacy groups, government agencies, politicians, and the animals living in shallow waters during Oligocene and public at large, and there is widespread concern that the Miocene times, possibly resembling the modern activity may facilitate development of illegal trade and hippopotamus superficially in ecology, behavior, and export of whale products, possibly leading to uncontrolled appearance. Desmostylians are known in the fossil and damaging illegal harvests of whales. record only from coastal regions of Washington and Sirenia The order of mammals that includes the Oregon, USA. manatees, dugongs, and sea cows. Introduction marine mammal species are the protocols of the US federal government, defined by the US Marine Mammal Protection Taxonomic Definition of ‘‘Marine Mammals’’ Act (MMPA) of 1972 (16 USC yy1361–62, 1371–84, and 1401–07 (Supp. IV 1974)) as amended (MMPA) and managed The ‘‘marine mammals’’ include one extinct order and three by two US federal agencies: the National Marine Fisheries major extant taxa that were or are fully aquatic, in most cases Service (NMFS) and the Fish and Wildlife Service (FWS). Our occurring entirely in the marine habitats of the major ocean principal source for taxonomic nomenclature, including basins and associated coastal seas and estuaries. In addition, a common names, is the review of Rice (1998). few species of largely terrestrial taxa are currently regarded as The order cetacea includes the whales, dolphins, porpoises, marine mammals. We consider 127 Holocene mammal spe- and their allies (Table 1). The ‘‘pinnipedia’’ is a group of cies in total to be marine mammals for purposes of this review species in three families in the mammalian order carnivora (Rice 1998; see also Reeves et al., 2002, and Jefferson et al., (Table 1). The pinnipeds include the seals, fur seals, sea lions, 2008, for excellent non-technical accounts). We acknowledge and allies. The order sirenia includes the extant manatees and that species numbers within any taxon are subject to virtually dugong, and the now-extinct Steller’s sea cow (Table 1). The continuous revision as new systematic methods and phil- order desmostylia is the only recognized order of marine osophies emerge. Our primary bases for defining our list of mammals to become entirely extinct. 64 Encyclopedia of Biodiversity, Volume 5 http://dx.doi.org/10.1016/B978-0-12-384719-5.00187-8 Marine Mammals, Extinctions of 65 Two largely terrestrial families of the order carnivora (family ursidae) spends a significant proportion of time at sea include species recognized as marine mammals (Table 1). as well. The sea otter and chungungo (family mustelidae) live Many other species of mammal utilize aquatic or marine entirely or primarily in marine habitats. The polar bear habitats, including monotremes, ursids, mustelids, canids, primates, rodents, bats, and ungulates, among others. Ultim- ately, the distinction among aquatic, marine, and terrestrial Table 1 Major taxa and species numbers of marine mammals, taxa is arbitrary. Thus, our reliance on definitions and proto- following the conventions of Rice (1998) cols of MMPA, NMFS, and FWS is subjective, although largely consistent with common practice among most specialists. Taxon Number of species We use the term ‘‘marine’’ to refer to large, contiguous Cetacea: whales 83 aqueous habitats with significant dissolved salt content in Mysticeti: baleen whales 12 ambient waters, including the world’s oceans, seas, and estu- Balaenidae: right whales 2 aries. We apply the term ‘‘aquatic’’ to aqueous habitats without Neobalaenidae: pygmy right whale 1 significant measurable dissolved salt concentrations in ambi- Eschrichtidae: gray whale 1 ent waters, such as lakes and rivers above the point of sig- Balaenopteridae: rorquals 8 nificant mixing with marine waters, and to inland saline lakes Odontoceti: toothed whales 71 that lack outlet streams connecting to marine habitats. ‘‘Ter- Physeteridae: sperm whales 1 restrial’’ habitats are those lacking standing water under Kogiidae: pygmy sperm whales 2 Ziphiidae: beaked whales 20 normal circumstances. Platanistidae: Indian river dolphin 1 Iniidae: Amazon river dolphin 1 General Features and Habitat Boundaries Lipotidae: Chinese river dolphin 1a Marine mammals are characterized by a number of striking Pontoporiidae: La Plata dolphin 1 Monodontidae: beluga and narwhal 2 modifications, as compared with terrestrial mammals, in Delphinidae: dolphins 36 anatomy, physiology, and ecology (Table 2). In some cases, Phocoenidae: porpoises 6 the modifications are sufficiently extreme that phylogenetic Carnivora, ‘‘pinnipedia’’ 36 linkages to terrestrial ancestry are obscured, difficult to resolve, Otariidae: sea lions and fur seals 16b and matters of controversy among scientists. The degree of Odobenidae: walrus 1 modification is correlated with the duration of the evo- c Phocidae: seals 19 lutionary history of the major marine mammal taxa as marine Carnivora, other marine taxa 3 organisms. Mustelidae: marine otters 2 Although marine mammals are largely defined by marked Ursidae: polar bear 1 departures from the terrestrial mammalian model, it is in- Sirenia: manatees, dugongs, and sea cows 5 Trichechidae: manatees 3 structive to consider the major features of terrestrial mammals Dugongidae: dugong and sea cow 2d retained in marine mammals. In the context of extinction Total species 127 processes in general, and anthropogenic extinctions in par- ticular, two retained features are of particular importance. a The indicated species was last observed in natural habitat in 2002 and is considered First, although most marine mammals spend most of their extinct. lives immersed at sea, they retain a largely terrestrial respira- bOne of the indicated species, the Japanese sea lion, was last observed in natural habitat in 1951 and is considered extinct. tory architecture and must surface and breathe in order to cOne of the indicated species, the Caribbean monk seal, was last observed in natural allow for exchange of respiratory gases. Second, marine habitat in 1952 and is considered extinct. mammals are homeothermic, with core body temperatures dOne of the indicated species, the Steller’s sea cow, was last observed in natural habitat typically near 38 1C, like their terrestrial relatives. The need to in 1767 and is considered extinct. breathe at the surface and the need for major anatomical Table 2 Distinguishing characteristics of the major marine mammal taxa Characteristic Cetacea Sirenia Pinnipedia Body streamlined X X X Limbs modified X X X Rear limbs modified as flippers X Rear limbs and pelvic girdle absent X X Propulsion by caudal spine and flukes