MARINE MAMMALS, EXTINCTIONS OF Glenn R. VanBlaricom,* Leah R. Gerber,† and Robert L. Brownell, Jr.‡ *U.S. Geological Survey and University of Washington, †University of California, Santa Barbara, and ‡National Marine Fisheries Service

I. Introduction principal source for taxonomic nomenclature, includ- II. Patterns and Case Studies of Extinction in ing common names, is the recent review of Rice (1998). Marine Mammals The order Cetacea includes whales, dolphins, and III. Discussion porpoises (Table I). The ‘‘pinnipedia’’ is a group of species in three families in the mammalian order Carni- vora (Table I). The pinnipeds include the seals, fur seals, sea lions, and walrus. The term pinnipedia is no I. INTRODUCTION longer recognized formally by marine mammal taxono- mists, but it continues to appear in the systematic ver- A. Taxonomic Definition of nacular as a matter of tradition and convenience. The order Sirenia includes the extant manatees and dugong ‘‘Marine Mammals’’ and the extinct Steller’s sea cow (Table I). The order The marine mammals include one extinct order and Desmostylia is the only recognized order of marine three major extant taxa that were or are fully aquatic, mammals to become entirely extinct. in most cases occurring entirely in the marine habitats Two largely terrestrial families of the order Carnivora of the major ocean basins and associated coastal seas also include species recognized as marine mammals and estuaries. In addition, a few species of largely terres- (Table I). Sea otters and chungungos (family Mustel- trial taxa are currently regarded as marine mammals. idae) live entirely or primarily in marine habitats. Polar We consider 127 recent mammal species in total to bears (family Ursidae) also spend a significant propor- be marine mammals for purposes of this review. We tion of time at sea. acknowledge that species numbers within any taxon Many other species of mammal utilize aquatic or are subject to revision as new systematic methods and marine habitats, including monotremes, ursids, mustel- philosophies emerge. Our primary bases for defining ids, canids, primates, rodents, bats, and ungulates. Ulti- our list of marine mammal species are the protocols of mately, the distinction among aquatic, marine, and the U.S. federal government, determined largely by the terrestrial taxa is arbitrary. Thus, our reliance on defini- U.S. Marine Mammal Protection Act (MMPA) of 1972 tions and protocols of MMPA, NMFS, and FWS is sub- [16 U.S.C. §§1361-62, 1371-84, and 1401-07 (Supp. jective, although it is consistent with common practice IV 1974)] as amended (MMPA) and managed by two at least in the United States. U.S. federal agencies, the National Marine Fisheries We use the term ‘‘marine’’ to refer to large, contigu- Service (NMFS) and the Fish and Wildlife Service ous aqueous habitats with significant dissolved salt con- (FWS). Our choice of defining criteria is arbitrary. Our tent in ambient waters. Thus, we apply the term marine

Encyclopedia of Biodiversity, Volume 4 Copyright  2001 by Academic Press. All rights of reproduction in any form reserved. 37 38 MARINE MAMMALS, EXTINCTIONS OF

TABLE I TABLE II Major Taxa and Species Numbers of Marine Mammalsa Distinguishing Characteristics of the Major Marine Mammal Taxa Taxon No. of species Characteristic Cetacea Sirenia Pinnipedia Cetacea: Whales 83 Mysticeti: Baleen whales 12 Body streamlined x x x Balaenidae: Right whales 2 Limbs modified x x x Neobalaenidae: Pygmy right whale 1 Rear limbs modified as x Eschrichtidae: Gray whale 1 flippers Balaenopteridae: Rorquals 8 Rear limbs and pelvic girdle x x Odontoceti: Toothed whales 71 absent Physeteridae: Sperm whales 1 Propulsion by caudal spine x x Kogiidae: Pygmy sperm whales 2 and flukes Ziphiidae: Beaked whales 20 Loss of pelage x x Platanistidae: Indian river dolphin 1 Iniidae: Amazon river dolphin 1 Subcutaneous blubber layer x x x Lipotidae: Chinese river dolphin 1 Simplification of dentition x x x Pontoporiidae: La Plata dolphin 1 Expansion of anterior skull x Monodontidae: Beluga and narwhal 2 Development of acoustic capa- xa xa Delphinidae: Dolphins 36 bility for communication Phocoenidae: Porpoises 6 and echolocation Carnivora, ‘‘Pinnipedia’’ 36 Amphibious capability x Otariidae: Sea lions and fur seals 16 Odobenidae: Walrus 1 a Echolocation capability is known only for the odontocete ceta- Phocidae: Seals 19 ceans. Carnivora, other marine taxa 3 Mustelidae: Marine otters 2 Ursidae: Polar bear 1 Sirenia: Manatees, dugongs, and sea cows 5 lated approximately with the duration of the evolution- Trichechidae: Manatees 3 ary history of the major marine mammal taxa. Dugongidae: Dugong and Steller’s sea cow 2 Although marine mammals are largely defined by marked departures from the terrestrial mammalian Total species 127 model, it is instructive to consider major features of

a terrestrial mammals retained in marine mammals. In Following the conventions of Rice (1998). the context of extinction processes in general, and an- thropogenic extinctions in particular, two retained fea- to the world’s oceans, seas, and estuaries. We apply the tures are of particular importance. First, although most term ‘‘aquatic’’ to aqueous habitats without significant marine mammals spend most of their lives immersed measurable dissolved salt concentrations in ambient at sea, they retain largely terrestrial respiratory architec- waters, such as lakes and rivers above the elevation of ture and must surface and breathe in order to exchange significant mixing with marine waters, and to inland respiratory gasses. Second, marine mammals are ho- saline lakes that lack outlet streams connecting to ma- meothermic, with core body temperatures typically near rine habitats. ‘‘Terrestrial’’ habitats are those lacking 38ЊC, like their terrestrial relatives. The need to breathe standing water in normal circumstances. As indicated at the surface and the need for major anatomical adjust- in Table I, our list of ‘‘marine mammals’’ includes ma- ment to minimize rates of heat loss are constraints that rine and aquatic species. foster vulnerability to unsustainable rates of exploita- tion and to certain types of pollution. The significance 1. General Features and Habitat Boundaries of these constraints is developed in the case studies we Compared to terrestrial mammals, marine mammals are present later. characterized by many striking modifications in anat- The diving capabilities of marine mammals define omy, physiology, and ecology (Table II). In some cases, the three-dimensional nature of their habitats at sea. the modifications are sufficiently extreme that phyloge- Nearly all extant marine mammals dive to forage, al- netic linkages to terrestrial ancestry are obscured and though the ranges of diving capability and pattern difficult to resolve. The degree of modification is corre- are broad. Most marine mammals also spend signifi- MARINE MAMMALS, EXTINCTIONS OF 39 cant time submerged while traveling, socializing, or with small breathing holes, beluga whales and narwhals breeding. are also taken as food by polar bears. Thus, the extent Among cetaceans, sperm whales and beaked whales to which the at-sea habitat of marine mammals is truly likely dive the deepest and longest compared to other three-dimensional varies widely among the major taxa species. Sperm whales can dive to 1500 m, remaining and the individual species. Within species, there is also submerged for 20 min or more. The diving behavior of marked ontogenetic variation in diving capability and beaked whales is poorly known, but there is emerging pattern. evidence that beaked whales may also routinely make The marine mammals are geographically ubiquitous repetitive dives of long duration to great depth. Baleen in the world’s oceans, seas, and estuaries. Cetaceans whales may make long deep dives during breeding sea- occur in marine environments at all latitudes. For exam- son. Foraging dives of baleen whales normally are rela- ple, killer whales and minke whales may have the largest tively shallow and brief. Many of the smaller cetaceans natural geographic ranges of the earth’s mammals. Most commonly dive for less than 10 min at a time to depths of the mysticetes and some of the larger odontocetes no greater than a few hundred meters. have global ranges or are distributed antitropically. Among pinnipeds, elephant seals (Phocidae) have Smaller cetaceans are widely dispersed as well, although maximum diving capabilities comparable to the sperm individual populations typically concentrate in regions whales, and they are known to make remarkably long of predictably high local biological productivity. Several sequences of repetitive deep (to 1500 m), long (20 min species of small cetacean, including two delphinids, a or more) dives with surface intervals of only 2 or 3 phocoenid, and the four monotypic families of river min. These sequences may be maintained day and night dolphins, are found in major river systems in South for tens of days at a time. Many other phocid seals are America and Asia. Beluga whales also spend significant thought to have similar capabilities. The sea lions and time in river habitats. Pinnipeds occur in all the world’s fur seals (Otariidae), in contrast, usually dive for only major marine habitats, but most species are concen- a few minutes at a time, and usually to maximum depths trated in middle or high latitudes, in close association of a few hundred meters, although many otariids are with regions of high productivity. In addition, there known to be capable of continuous sequences of repeti- are several pinniped species or populations confined to tive shallow dives of 10–12 hr or more. Walruses are isolated large lakes in Europe, Asia, and North America. known to dive as deep as 80 m, with maximum dura- Most sirenians are limited to tropical or subtropical tions of 10 min. latitudes, in shallow seas that provide adequate macro- In contrast to cetaceans and pinnipeds, sirenians are phytic food and refuge from predation, and are ther- weak divers, normally remaining in shallow water (Ͻ20 mally tolerable. The sea otter is confined to the coastal m) and diving for only 2 or 3 min when active. Deeper North Pacific Rim and the chungungo to the temperate dives (to 70 m) may occur on occasion, and dive dura- coastal southeastern Pacific. Polar bears occur only in tion can be quite long (up to 24 min) when animals the Arctic and subarctic, rarely traveling south of 60ЊN are resting at the bottom. Sea otters are capable of latitude except in the relatively frigid northwestern At- diving to 100-m depth and remaining submerged for a lantic and Hudson Bay. maximum of approximately 5 min, although most dives are to 30 m or less and last only for 1 or 2 min. To our knowledge, there are no data available on the diving 2. Cetacea capabilities of the chungungo. The distinguishing anatomical and functional features Few field observations of Steller’s sea cow were made of the cetaceans are summarized in Table II. The two prior to extinction, but morphological analysis suggests major taxonomic subdivisions of cetaceans are the sub- that sea cows were unable to dive below the sea surface, orders Odontoceti, or ‘‘toothed whales,’’ and Mysticeti, surviving instead by foraging on macroalgae floating or ‘‘baleen whales.’’ The odontocetes are the most di- on the surface. Polar bears are able to make shallow verse of the major marine mammal taxa, with 10 fami- dives but do not typically engage in the extended repeti- lies and 71 species (Table I). The best known families tive dive sequences typical of many marine mammals. are the Delphinidae and Phocoenidae. In ecological They apparently do not forage while diving. Polar bears terms, the family Ziphiidae is among the most sparsely instead use stealth, quickness, and great strength to studied groups of mammals on Earth. The mysticetes capture seals, their primary prey, at seal breathing holes (Table I) include species that, by a wide margin, are on the ice surface. When confined in ice-bound seas the largest animals in the earth’s history. The blue 40 MARINE MAMMALS, EXTINCTIONS OF whale, largest of all, reaches 30 m in length and 200 abnormal, even pathological, behavior typically re- tons in mass. sulting in death or serious injury. Most cetaceans dwell in the open sea or in the seas and estuaries of the continental margins. The excep- 3. Pinnipedia tions are two delphinids, a phocoenid, and four odonto- Although pinnipeds and cetacea often use similar aque- cete species known as river dolphins (Table I). Of the ous habitats, the pinnipeds have many obvious differ- river dolphins, one species, the Franciscana or La Plata ences from the cetacea in form and function. Features dolphin, is found mainly in coastal marine waters of shared by most pinnipeds, including the phocids, ota- Brazil, Uruguay, and Argentina. The other three river riids, and odobenids, are summarized in Table II. The dolphins are exclusively aquatic. One of these, the boto, largest pinnipeds are adult males of the highly dimor- is known to leave river channels and travel within the phic southern elephant seal, exceeding 5 m in length adjacent flooded forests of the Amazon basin during and reaching 3700 kg in mass. Adult male northern the wet season. The Irrawaddy dolphin, a delphinid, elephant seals are only slightly smaller. Walruses are occupies coastal marine habitats and major river sys- also quite large, reaching 3.5 m and 1500 kg. tems in southeastern Asia, some Indo-Pacific islands, Despite many anatomical, physiological, and ecolog- and the northeastern coast of Australia. The tucuxi, ical features obviously associated with life at sea, pinni- another delphinid, occupies the Amazon watershed and peds are best regarded as amphibious. All species utilize coastal marine habitats of tropical Atlantic South solid substrata for breeding or for postbreeding mater- America and southern Central America. The finless por- nal care. Solid substrata are also used as short-term poise, a phocoenid, occurs in the Yangtze River water- resting sites and for protracted periods in some species shed and other large southern Asian rivers and coastal during molting of the skin and pelage. Although the marine habitats from the Persian Gulf to Japan. proportion of time spent on land (‘‘hauled out’’) over Mysticetes often segregate feeding and breeding ac- the long term varies significantly among species and tivities, both in time and space, connecting the two age and sex categories, generally the pinnipeds spend categories of activity with extensive seasonal migration. a major portion of their lives on land near shore or on Feeding is done primarily at high latitude during sum- pack or shorefast ice at sea. mer, and breeding and parturition are done primarily at Otariids use terrestrial habitats near shore for breed- low latitude during winter. Thus, a significant poleward ing, postpartum maternal care, molting, and resting. migration is required during spring, and an equator- Preferred hauling sites are those near areas of high ward return trip is necessary in autumn. The segrega- oceanic productivity and those free of large terrestrial tion of feeding and breeding, and the associated migra- predators. Thus, hauling grounds for otariids typically tory behavior, is best developed and understood in the are islands or mainland locations protected by cliffs or largest cetaceans. However, some large mysticetes, such rough terrain from land predators. Often, the hauling as the bowhead whale of the Arctic region and the grounds are localized at high latitude or the upwelling Bryde’s whale of tropical and subtropical latitudes, un- zones of mid-latitude eastern boundary currents, such dertake only modest seasonal migrations in contrast to as the Humboldt, California, and Benguela currents, species such as the humpback whale or gray whale. The where production of preferred food species is high and smaller cetaceans, including most of the odontocetes, temporally predictable. Optimal hauling grounds for appear to disperse primarily on the basis of food avail- breeding otariids are few in number and often limited ability and productivity at sea. Odontocetes typically in size. Breeding activities of otariids are highly syn- do not engage in the dramatic seasonal migrations chronous, occurring during a narrow time window known for some of the mysticetes, although there are when food availability for lactating females and newly exceptions among the larger odontocetes. produced juveniles is seasonally optimal. As a conse- Healthy mysticetes never leave the water in favor of quence of the various spatial and temporal constraints, land. A few odontocetes occasionally strand intention- pinniped breeding typically involves conditions of ex- ally on beaches or river banks for brief periods while treme crowding on haul-out sites. in pursuit of prey. Perhaps the most familiar example Phocids and walruses haul out for the same purposes is the brief intentional stranding of individual killer as otariids. Unlike otariids, phocids and walruses use whales while foraging on pinnipeds in the surf zone of two very different kinds of substrata. About half of the Argentine beaches. In general, however, the cetaceans phocid species use coastal land for hauling grounds, are not functionally amphibious. Aside from the noted selecting sites for largely the same reasons described exceptions, strandings of cetaceans can be considered for otariids. Thus, timing and location of breeding for MARINE MAMMALS, EXTINCTIONS OF 41 land-breeding phocids and otariids are generally simi- large plants growing on the bottom, in midwater, at lar. As a consequence, reproductive activities for many the surface, or closely overhanging the surface. They land-breeding phocids also occur under conditions of forage exclusively in shallow habitats. Manatees utilize extreme crowding. Known exceptions include some freshwater, estuarine, and fully marine habitats, often populations of harbor seals with spatially dispersed, interchangeably. Use of rivers by manatees is influenced largely aqueous breeding systems and the three recent by rainfall patterns and river discharge rates. Manatees species of monk seal (one now extinct) with temporally generally concentrate in habitats that are relatively asynchronous breeding systems at low latitude. The warm and physically protected from extremes of walrus and the remaining phocids breed or care for weather and sea. Dependence on relatively warm-water young, rest, and molt on ice at high latitudes rather temperatures may result from the combination of obli- than on land. Ice as a substratum varies widely over gate homeothermy and a relatively low basal metabolic time and among locations in stability, vulnerability to rate compared to that of other marine mammals. The predators, and provision of access to the surrounding limited tolerance of low water temperature likely con- sea. Thus, among ice-breeding pinnipeds there are sig- tributes to seasonal migration and a tendency to concen- nificant resultant variations in social and breeding strat- trate at high density in warm-water refugia during the egies and in the degree of crowding at hauling sites. A winter. Manatees may also congregate near sources of major predator of ice-hauling phocids, the polar bear, fresh water, although fresh water is not a physiological is present in ice-covered marine habitats of the Arctic requirement. The smallest of the modern sirenians, the region but not the Antarctic. This pattern has many Amazonian manatee, occurs only in the freshwater habi- interesting consequences for interhemispheric differ- tats of the Amazon River watershed of South America. ences in the ecology of ice-hauling pinnipeds. Dugongs are fully marine and forage primarily on ben- Some phocid species or subspecies occur only in thic seagrasses in shallow coastal tropical marine habi- aquatic habitats. Two subspecies of ringed seal occur tats. Steller’s sea cow, known only from isolated parts only in Lake Saimaa, Finland, and Lake Ladoga, Russia, of the subarctic North Pacific, was the most aberrant respectively. The Caspian seal is found only in the Cas- of the holocene sirenians. Sea cows likely foraged exclu- pian Sea and the Baikal seal only in Lake Baikal, both sively on kelps and other large algae along exposed in Russia. A population of harbor seals occurs year- shores. round in Lake Iliamna, Alaska, but the degree of ex- change, via river connection to populations of harbor 5. Desmostylia seals in nearby Bristol Bay, is unknown. Desmostylians are the only known extinct order of ma- rine mammals. The small number (Ͻ10) of recogniz- 4. Sirenia able species in the fossil record are of Oligocene and Several of the defining anatomical and functional fea- Miocene age and are confined geographically to the tures of the sirenians are convergent with those of the North Pacific region. Desmostylians were quadrupedal cetaceans (Table II). However, in contrast to the ceta- amphibians sharing common evolutionary ancestry ceans there are few Holocene sirenians (Table I). The with the sirenians. Habitats of desmostylians probably sirenians are the only extant herbivorous marine mam- were shallow waters supporting productive populations mals, sharing common ancestry with desmostylians and of algae and aquatic vascular plants, their primary food, terrestrial subungulates (e.g., aardvarks, elephants, in latitudes ranging from subtropical to cool temperate. and hyraxes). In habits and superficial morphology, desmostylians Sirenians are large in body mass and linear dimen- often are characterized as similar to the modern hippo- sion compared to most terrestrial mammal species. The potamus. Some have argued that at least some of the Steller’s sea cow was the largest of the modern species, desmostylians fed on clams and other benthic inverte- reaching 7 m in length. To our knowledge, body mass brate prey, but the consensus is that they were primar- of the Steller’s sea cow was never directly measured, ily, if not strictly, herbivores. but the estimated maximum is 10,000 kg. Maximum adult lengths and masses of the three manatee species 6. Marine Otters range from 3 to 4 m and from 450 to 1600 kg, respec- There are 13 recognized extant species of otters world- tively. Adult dugongs reach maxima of 3.3 m in length wide, comprising the mustelid subfamily Lutrinae. and 400 kg in mass. Here, we consider 2 species, the sea otter of the North All modern sirenians are fully aquatic or marine and Pacific Rim and the chungongo of Peru, Chile, and are incapable of leaving the water. Sirenians feed on southernmost Argentina. Both are marine species with 42 MARINE MAMMALS, EXTINCTIONS OF amphibious characteristics. Other otter species may uti- polar bears may have a diverse diet. They are the only lize marine environments, but they also have obligatory recognized species of marine mammal that travels ex- associations with aquatic and terrestrial habitats. The tensively on land away from the shoreline and the only sea otter and chungongo do not appear to utilize fresh- species that consumes both plant and animal species water habitats, except occasionally and facultatively. as a regular part of the diet. In addition, polar bears The sea otter is arguably the most derived of the are unique among marine mammals in producing altri- lutrines. It is the largest of the mustelids, with some cial young. adult males reaching 45 kg in mass and 1.6 m in total length, but among the smallest of the marine mammals. Sea otters are relatively weak divers compared to most B. Synopsis of Evolutionary Histories of marine mammals, and they feed almost entirely on Major Marine Mammal Taxa large-bodied, sessile or slow-moving benthic in- vertebrates. Sea otters often haul out on coastal beaches 1. Cetacea and reefs to rest and conserve heat, especially in the The oldest recognized cetaceans are Eocene fossils of northern portions of their geographic range during peri- the cetacean suborder Archaeoceti. Archaeocete fossils ods of harsh weather or reduced sea surface tempera- are found primarily in rocks of present-day Egypt, Paki- ture. Sea otters are not known to utilize freshwater stan, and India in strata thought to be associated with habitats for any purpose. the Tethyan Sea of ancient times. Thus, it is presumed The smallest of the marine mammals, the chun- that cetaceans originated in the Old World Tethyan gongo, reaches maxima of 6 kg in mass and 1.1 m in environment. Cetaceans share common ancestry with length. Chungongos are morphologically similar to the an extinct terrestrial ungulate taxon known as the seven congeneric species of otters. The ecological char- mesonychia. The earliest recognizable cetacean fossils acteristics of chungongos are not well known. They date to approximately 55 million years ago (Ma). The feed primarily on small crustaceans, mollusks, and fish archaeocetes included many ‘‘missing link’’ fossils, dis- taken during dives in nearshore marine habitats along playing intermediate forms with regard to progressive open coasts. They may also forage in fresh water, taking reduction and loss of the hindlimbs, elongation of the small crustaceans. They haul out between foraging peri- anterior skull, and modification of dentition. ods on exposed rocky shores and appear to maintain Archaeocetes were largely extinct at the beginning shoreline dens that are focal areas for social and repro- of the Oligocene, approximately 38 Ma. The first precur- ductive behavior. sors to the modern suborders Odontoceti and Mysticeti appear in the fossil record during the Oligocene, but the 7. Polar Bears first fossils linked unambiguously to modern cetacean Polar bears are one of seven recognized bear species. families appear primarily during the Miocene. For ex- Several of the other bear species utilize marine and ample, the earliest sperm whales appear in early Mio- aquatic habitats for foraging, but polar bears are more cene strata. Beaked whales appeared first in the middle dependent on marine habitats for food than are other Miocene, and the earliest dolphins and porpoises ap- bears. Although generally similar to other bears mor- peared in the late Miocene approximately 11 Ma. In phologically, polar bears have several distinguishing the mysticetes, the earliest rorquals and right whales features that reflect their associations with frigid terres- also are in Miocene strata. The oldest gray whale fossils trial and sea ice habitats and with Arctic marine ecosys- are from the Pleistocene. Thus, there are no known tems. Polar bears are small compared to many marine fossils providing insight to the early evolution of the mammals but large compared to most other bears. Adult modern gray whales. There is general agreement that males reach 2.5 m in length and 800 kg in mass. Along the cetaceans are monophyletic. with chungongos, polar bears are perhaps the least mod- It is apparent from the fossil record that the modern ified morphologically, compared to terrestrial mam- taxa of cetaceans have been preceded by many extinct mals, of the world’s recognized marine mammal species. species, likely outnumbering extant species by a consid- Although polar bears do not dive repetitively in the erable number. For example, an early mysticete group, manner typical of many marine mammals, they are effi- the family Cetotheriidae, contains about 60 known spe- cient swimmers, able to traverse large expanses of open cies dating from the Oligocene. The existence of extinct water. Polar bears also cover large distances at sea by large taxa implies significant episodes of diversification walking or running across sea ice. Although primary and subsequent extinction well before the modern fami- prey are pinnipeds taken from the surface on sea ice, lies of cetaceans appeared. The record also suggests a MARINE MAMMALS, EXTINCTIONS OF 43 dynamic pattern of biogeographic variation, such as the include significant numbers of monachine (phocid sub- occurrence of ancestral monodont fossils in Miocene family Monachinae) seals (ancestral to the modern strata of Mexico. The Monodontidae now include only monk seals), elephant seals, and Antarctic ice seals. the belugas and narwhals of high northern latitudes. Ancestry and relationships of the more derived forms, The dynamic evolutionary record almost entirely pre- including the modern phocine (phocid subfamily Pho- dates homonid evolution and the emergence of anthro- cinae) seals of northern temperate and polar latitudes, pogenic influences on pattern of extinction. have not been resolved definitively. As with the ceta- ceans, the pinniped fossil record indicates significant 2. Pinnipeds episodes of diversification and extinction before the The earliest known pinnipeds are represented by fossils emergence of the modern forms, clearly predating an- of the late Oligocene or early Miocene, approximately thropogenic influences. 25 Ma. The two major recognized lineages culminate in the modern Phocidae and the modern superfamily 3. Sirenians Otarioidea, the latter including the Otariidae and the The earliest fossil sirenians are from early Eocene strata, Odobenidae. The earliest fossils of both lineages are of approximately 55 Ma. Significant radiation into at least similar late Oligocene or early Miocene age. In contrast three families of sirenians had occurred by the time the to the cetaceans, there are recognized linkages of good earliest cetacean fossils appeared in the Eocene. Thus, quality between the earliest pinniped fossils and the sirenians appear to be the oldest order of living marine major modern pinniped taxa. mammals on Earth. The fossil record does not provide The traditional view of pinniped evolution is that clear evidence of the ancestral groups that gave rise to the phocids and otarioids evolved independently. Pho- the sirenians, although studies of modern forms indi- cids are said to have emerged in the North Atlantic cate common ancestry with other subungulates. The region from ancestral forms linked to modern muste- oldest sirenian fossils are from Jamaica, but the sireni- lids. Appearance of phocid species in the Pacific likely ans are thought to have emerged first in the Old World occurred much more recently, possibly during events Tethyan environment. The early radiations of the sireni- related to the extinction of early Pacific otariids and ans appear to share common ancestry with the extinct odobenids. Otarioids are thought to have evolved from family Protosirenidae. Protosirenids appear to have ancestral ursids in the North Pacific. The diphyletic given rise to the modern families Trichechidae (mana- model is supported by traditional analyses of cranial tees) and Dugongidae (dugongs and sea cows). Dugon- morphology and by the absence of early fossil otarioids gids probably first appeared in Mediterranean waters from strata of the North Atlantic region. Recent analyses during the Eocene, whereas trichechids apparently first of postcranial material and of molecular data support evolved along the South American coast during the an alternative model in which the pinnipeds are a mono- Miocene. Sea cows first appeared in the southeastern phyletic lineage sharing common ancestry with the Pacific during the early Miocene, later radiating modern mustelids. Current consensus favors the mono- throughout the Pacific basin. Some sea cows were un- phyletic model. usual among sirenians in their great body size and use Recently published evidence indicates controversy of relatively exposed cold-water habitats. They occurred regarding the affinities of the Odobenidae. Some analy- along the coasts of California, Japan, and the subarctic ses indicate that odobenids are in fact more closely North Pacific Rim during the Pliocene and Pleistocene. related to phocids than otariids, whereas others favor Although the predominant sirenian family in the Holo- the more traditional view, with odobenids closely allied cene, trichechids have a relatively poor fossil record. to otariids in the Otarioidea. We follow the traditional The allopatric distribution of the three modern species view here but acknowledge the evidence in support of apparently resulted from temporary geological isolation the alternative scenario. of the Amazonian watershed and from a chance coloni- Ancestral taxa of otariids and odobenids show a high zation of West African coastal waters from an ancestral level of diversity compared to modern forms. The recog- Caribbean population. nized modern genera of odobenids and otariids ap- peared primarily during the late Pliocene or the Pleisto- 4. Desmostylians cene. The fossil record for phocids is not well developed, As noted previously, desmostylians apparently first especially in some North Atlantic regions thought to appeared in the Oligocene, approximately 35 Ma. The be important in understanding early evolution in the oldest known fossils are from the coasts of Washington group. Miocene fossils from the Southern Hemisphere and Oregon in the northeastern Pacific, and all desmo- 44 MARINE MAMMALS, EXTINCTIONS OF stylian fossils come from the North Pacific. Desmostyli- changes of gas volumes contained in their lungs, in ans share common ancestry with sirenians and terres- order to set the biochemical stage for successful subse- trial subungulates, although many details of these quent dives. relationships are unknown. Human travel in watercraft at the sea surface is rela- tively efficient and advanced. By understanding the re- 5. Marine Otters and the Polar Bear spiratory behavior of marine mammals, people can posi- The sea otter, chungungo, and polar bear represent tion themselves to facilitate close contact with surfacing three separate, relatively recent entries into marine en- animals. The result is high vulnerability of marine mam- vironments by largely terrestrial or aquatic taxa. Chun- mals at sea to human hunters. gongos still resemble other otters so closely that a meaningful fossil record of their evolution as marine 2. Large Body Mass and Linear Dimensions mammals does not exist to our knowledge. There are The marine mammals, on average, are large compared some Pleistocene fossils of polar bears, but neither fossil to most other animals. Large body size probably evolved nor modern forms represent significant departures from in response to certain constraints associated with life the ancestral ursid morphology. Thus, for both chun- at sea, most notably those associated with thermoregu- gongos and polar bears, the history of adaptation to latory and hydrodynamic efficiency, foraging ecology, marine life is best inferred from modern biological data. reproductive ecology and physiology, and habitat pref- The sea otter appears to have a somewhat more ex- erence. tensive fossil ancestry in the marine environment than The energetic return to the consumer per unit of the polar bear or chungongo. There are two extinct hunting effort will increase with the mean size of the genera of sea otters in the fossil record. Species of Enhy- prey, all other factors being equal. Among the marine driodon have been found in Africa and Europe in late mammals, all the mysticetes and many of the odonto- Miocene and Pliocene strata. Enhydritherium lluecai is cetes, pinnipeds, and sirenians are large enough in body known from the late Miocene of Europe, and Enhydri- mass to be highly desirable as targets by human hunters. therium terraenovae is known from the late Miocene With twentieth-century refinements to the technology through the middle Pliocene in Florida and California. of marine mammal hunting at sea, pursuit of even the Enhydritherium is thought to be ancestral to Enhydra. most mobile and dangerous of the marine mammals Enhydra is confined to the North Pacific region. The produced highly desired rates of economic return as extinct Enhydra macrodonta is known only from the long as stocks were not depleted. Thus, large body size, late Pleistocene. The single surviving species of sea per se, increases the vulnerability of marine mammal otter (Enhydra lutris), dates from the early Pleistocene. populations to extinction simply by improving the eco- nomic return on investment in hunting activity. C. General Factors Contributing to the 3. Relatively High Predictability of Spatial Vulnerability of Marine Mammals and Temporal Distributions in to Overexploitation and Extinction Association with Regions of High Biological Productivity at Sea 1. Obligatory Dependence on the Sea With certain exceptions, marine mammals are rarely Surface for Respiration far removed from locations in which they can forage Marine mammals must exchange respiratory gasses di- efficiently. The metabolic generation of heat, fueled rectly with the atmosphere, in the same manner as by food consumption at high rates, is the only option their terrestrial relatives. Thus, unlike marine fishes available to marine mammals at sea for replacing heat and invertebrates, marine mammals at sea are never lost continuously in a heat-consumptive environment. entirely free of their association with the sea surface. In species with significant annual migrations to food- Marine mammals must return periodically to the surface poor areas for breeding, high rates of intake during the to breathe. The process of breathing at the surface is feeding season are vital for survival of extended travel often associated with conspicuous activities, such as and for maximizing rates of reproductive fitness. In splashing, exhalations audible over long distances, and species whose breeding systems include extensive sea- the production of clearly visible clouds of condensed sonal fasts, seasonal hyperphagy, requiring proximity water vapor associated with exhalations. Marine mam- to abundant food, may be crucial to reproductive fitness mals are often physiologically obligated to remain at and to long-term survival of both sexes. the surface for several minutes, allowing multiple ex- Most marine mammals feed on planktonic inverte- MARINE MAMMALS, EXTINCTIONS OF 45 brates and small schooling fishes. Over the long term, tended disruption of breeding activity and social inter- seasonal and spatial patterns of production of zooplank- action among exploited pinnipeds in addition to di- ton and forage fish are relatively predictable. Successful rected harvest. The stampeding of panicked animals tracking of resources that vary predictability in space can lead to premature births, trampling of small pups, and time is vital to survival and reproductive success. disrupted dominance hierarchies, permanent abandon- Accumulated ecological data for marine mammals indi- ment of haul-outs by adults, and other forms of distur- cate that most populations successfully track food re- bance. The net added result of hunter-associated disrup- source productivity most of the time. The result is an tions is increased mortality and reduced birth rate in array of stereotypical seasonal and spatial movements the short term. Repeated disruptions associated with by marine mammals that, in many cases, are readily human activity can lead to increased long-term risk of identified. Clearly, an understanding of movements of local extinction for populations at particular hauling marine mammal stocks over time reduces the invest- sites. ment risk in developing strategies for efficient hunting Sea otters are awkward when hauled out. Thus, they of marine mammals. Thus, spatial and temporal predict- are also vulnerable to harvest and disturbance by peo- ability in marine mammal foraging facilitates efficient ple. However, hauling patterns of sea otters are less hunting by humans and adds to the risk of anthropo- predictable in time and space than patterns for pinni- genic extinction as a result of direct exploitation of peds. Polar bears are highly mobile on land and are marine mammal populations. dangerous to human hunters. Nevertheless, time spent on land increases the vulnerability of polar bears to 4. Impaired Mobility, Contagious hunting and disturbance by people. Dispersion, and Temporal and Spatial Predictability When Hauled 5. Subsistence and Commercial Market Out on Land Demand for Oil, Blubber, Meat, Baleen, Pinnipeds, the two marine otters, and polar bears are Pelts, Ivory, and Other Body Parts amphibious marine mammals. Hauling behavior of pin- By virtue of their frequently large size, morphology, nipeds is particularly synchronous and predictable, pro- physiology, and chemical composition, the harvested ducing seasonally dense hauled-out aggregations that carcasses of marine mammals provide many products can be anticipated readily in space and time. These significant in subsistence and commercial contexts. patterns are most extreme for some of the land-breeding Harvested marine mammals provide large quantities of pinnipeds that dwell at middle or subpolar latitudes, meat, organs, and blubber per unit of hunting effort but they are prevalent in many other pinniped species invested. Meat and organs are used directly for human as well. Two primary factors contribute to the pattern. consumption or to feed domestic animals, such as sled First, good hauling sites that are near seasonally predict- dogs, on which human enterprise may depend. Meat able foraging locations, and that are free of the disrup- may also be marketed commercially for human con- tive effects of terrestrial predators such as bears or sumption or as pet food. Blubber is also consumed wolves, are typically few in number and small in size. directly, but traditionally the majority of blubber is Pinnipeds depending on such hauling sites have evolved rendered and refined into products such as oil or fuel, high site fidelity and strong navigational capabilities in used both for subsistence and as commercial commodi- order to minimize the risk that good hauling sites will ties. In the case of the odontocetes, oil taken from the be overlooked when needed for breeding, molting, and organs of acoustic transmission may be refinable to resting. Second, in the case of pinnipeds at middle and high-quality lubricants that, until recent decades, could high latitudes, highly productive foraging locations near not be duplicated synthetically. good hauling sites tend to be strongly seasonal in Skeletal material from hunted marine mammals has food availability. been used traditionally by subsistence cultures for tools, Pinnipeds are awkward on land and can be captured boat construction, dwelling construction, and as raw easily by human hunters on hauling sites, even if meth- material for handicrafts and objects of ceremonial sig- ods are primitive. Because seasonal hauling patterns are nificance. Hand-crafted articles made from marine easily recognized in space and time, human hunters mammal skeletons often have significant commercial can plan highly efficient hunting of hauled pinnipeds value as well. Mysticete baleen and the vibrissae of wal- with a very low risk of poor return on invested effort. ruses and other pinnipeds have, been marketed com- In addition to directed harvest, human activity on mercially as components of clothing or toiletry articles, preferred hauling grounds can cause significant unin- although such uses are largely in the past. Hides and 46 MARINE MAMMALS, EXTINCTIONS OF pelts may be used for clothing and for construction of and sea otters. Exceptional cases, both higher and lower boats or dwellings. The pelts of sea otters and fur seals than mean rates, are known for both groups. Realized have been sought for centuries as commodities of high rates of growth, affected by variations in food supply commercial value for clothing or as adornments for and the effects of disturbance, predation, competition, ceremonial robes and artifacts. Teeth and other body and possibly other factors, often are much closer to parts from sea otters are also known to have had cere- zero and may be constrained to negative values. Given monial significance to indigenous peoples. Specialized these patterns, recovery from depletion associated with tusks in narwhals and walruses are extremely valuable excessive exploitation or disturbance may require many and have put these species at continued risk during years, and intervening additional harvest or disturbance much of the past two centuries. Polar bears and walruses can increase the risk of extinction to high levels. have been hunted for meat, oil, hides, and pelts by subsistence cultures for millennia and were targets of 7. Morphological, Physiological, trophy hunters through much of the nineteenth and and Ecological Predisposition twentieth centuries. Much of the demand for marine mammal products for Bioaccumulation of Lipophilic centers on tissues involved in thermoregulation. The Anthropogenic Contaminants blubber of cetaceans, pinnipeds, and sirenians and the and Toxins pelts of fur seals, sea otters, and polar bears are the Most marine mammals utilize a well-developed subcu- respective primary organs of heat retention, allowing taneous blubber layer as the primary means of thermo- the preservation of homeothermy in a chilling environ- regulation. The blubber layer is also a primary organ ment. Thus, the homeothermic physiology of marine for energy storage, as are fat deposits in polar bears. mammals underlies their desirability as commodities The blubber layer consists of lipids, fatty acids, and and is a significant contributor to the vulnerability of connective tissues. Relative proportions vary by species, marine mammals to anthropogenic extinctions. age, and reproductive status of individuals and by loca- tion on the body. 6. Low Demographic Potential for Many species of cetaceans and pinnipeds, the Ama- Rapid Recovery from Disturbance zonian manatee, and some polar bears have an extensive or Overexploitation seasonal fast each year, relating to migration away from The marine mammals are significantly convergent in primary feeding areas, an extended haul-out or denning many aspects of life history. Mean litter size is one for period in association with reproductive activity, or all species except polar bears and chungongos, and shifts in habitat structure. During such fasts a significant multiple simultaneous births are rare in all species of proportion of the blubber layer or fat deposits is meta- cetaceans, pinnipeds, sirenians, and in sea otters. The bolically mobilized to meet energy and water demands age of first reproduction is often relatively high, espe- during the fasting period. Following the fast, animals cially in sirenians and the larger odontocetes. None of return to the feeding grounds and forage intensively to the extant marine mammals has a birth interval of less reconstitute the reduced blubber layer or fat deposits. than 1 year, and for many species the birth interval is In the case of the odontocete cetaceans, the acoustic at least several years. In all species, parental care is melon is a second concentration of lipid-based tissue. entirely maternal, and the energetic costs of lactation Odontocetes, pinnipeds, the two marine otters, and and other forms of care are extensive for the adult polar bears occupy high trophic levels in marine food female. Reproductive success of newly mature females webs. Many stable lipophilic contaminants are transmit- is often very low in marine mammals, increasing only ted through food webs, such that top-level consumers with experience. Survival rates of weaned offspring may may be exposed to high levels of contaminants. Such be low during the first few years of independence. patterns are particularly well-known for environmental The combined effects of the previously discussed contaminants such as organochlorines, a group includ- characteristics are low potential rates of growth in ma- ing the polychlorinated biphenyls (PCBs) and the vari- rine mammal populations, even when free of the con- ous derivatives of dichlorodiphenyltrichloroethane straints imposed by food limitation, competition, preda- (DDT). In this context, many marine mammals face tion, or natural disturbance. Maximum potential annual ‘‘double jeopardy.’’ First, a high position in their respec- rates of population growth typically are 2–8% for the tive food webs confers the risk of high exposure to cetaceans and sirenians and 10–15% for the pinnipeds stable lipophilic contaminants. Second, extensive, met- MARINE MAMMALS, EXTINCTIONS OF 47 abolically active lipid-based tissues are vital to their result in population-level effects if reduction in rates survival but vulnerable as sites for accumulation of of taking is inadequate, or if parties affected by displace- contaminants. In several cases, lipophilic contaminants ment of fishing effort resort to illegal taking of involved have been correlated with reduced immune compe- marine mammals as a form of retribution. Thus, both tence, disease outbreaks, and significant mass mortali- types of problems may contribute to increased risks of ties in marine mammal populations. There is also extinction, especially in cases in which the involved evidence that contaminants may cause endocrine dis- marine mammal population is small at the time that ruption and reproductive malfunctions such as prema- conflicts are recognized. ture deliveries of pups. Thus, the combination of lipophilic contaminants in the marine environment, D. General Factors Hindering Effective the pattern of foraging at high trophic levels by marine mammals, and lipid-based tissues that are Identification and Monitoring of Marine functionally significant and metabolically active in Mammal Populations Vulnerable many marine mammals results in increased vulnerabil- to Extinction ity of marine mammals to anthropogenic extinction. 1. Availability Bias 8. Overlap of Diet or Habitat with Marine mammals at sea spend most of their time Commercial or Recreational Fisheries below the sea surface. Depending on water clarity, Marine mammals often feed preferentially on prey spe- typical depth of dive, angle of observation, and plat- cies also sought by commercial, recreational, or sub- form of observation (i.e., surface vessel or aircraft), sistence fisheries, or they forage in habitats in which a varying proportion of individual marine mammals significant commercial fishing activity occurs. These in a field of view cannot be seen and thus cannot patterns create two types of problems that may enhance be enumerated in a population survey. The proportion the vulnerability of marine mammals to anthropogenic of animals not visible because of submergence is the extinction. In the first case, marine mammal popula- availability bias of the survey. Availability bias reduces tions are viewed by commercial, recreational, or subsis- both accuracy and precision of population estimates, tence fishers as competitors for a common resource. As and it reduces the statistical power of a survey effort a consequence, legal recourse may be sought to actively to detect population trends correctly. Availability bias reduce the range or numbers of marine mammals by can be estimated with detailed information on water killing, translocation, or harassment in order to reduce clarity in the survey area, diving characteristics of the intensity of competition in favor of harvesting inter- target species, and detection characteristics of survey ests. Illegal activities may also result, including unau- observers. Estimates of bias allow the effects of the thorized killing or harassment also intended to reduce bias to be incorporated into calculations of correction the intensity of competition between marine mammal factors and coefficients of variation (CVs) for popula- populations and fisheries. Such circumstances can lead tion estimates. Elimination of availability bias generally to conflicting management goals by interested parties, is not possible for surveys at sea. particularly if the involved marine mammal populations Availability bias may also be a problem for surveys are small. From the perspective of the involved marine directed to hauled animals on shore. For example, topo- mammal species, competition from harvesting interests graphic irregularities such as overhangs may obscure may alter the quantity or distribution of food availability animals that are present in the defined survey area, and may produce significant consequences at the popu- and animals at high density may obscure one another. lation level. Judicious timing and modified survey angles may some- The second type of problem is inadvertent or inci- times reduce availability bias in surveys of hauled ani- dental take of marine mammals by entanglement in mals to nearly zero. fishing gear. Such taking may include injury or death of individual animals, again producing possibly significant 2. Observer Bias effects at the population level. Potential responses to Observer bias, also known as detection bias, results such problems include tolerance of taking by manage- from the inability of survey observers to correctly enu- ment authority, changes to fishing techniques or effort merate the number of animals visible in a field of view. to reduce rates of taking, or displacement of fishing Unlike availability bias, observer bias can be either a effort to other locations. Such interactions may still high or low bias. Observer bias has the same implica- 48 MARINE MAMMALS, EXTINCTIONS OF tions for population estimation as summarized pre- Many marine mammal surveys have characteristics viously for availability bias. Observer bias can be a that reduce the probability of correctly detecting trends. significant source of error in both surveys at sea and Weak trends may portend significant conservation con- surveys of hauled animals on shore. Observer bias can cerns for marine mammals but are inherently difficult be reduced with increased experience of individual ob- to detect if CVs are large and replication is minimal. servers, and it can be estimated using double-counting Large CVs are common in all types of marine mammal techniques with paired independent observers or by population surveys, although CVs are gradually being comparing observer counts in the field with counts from reduced by the extraordinary efforts of involved re- aerial photographs taken at the same time and place. searchers and managers. The level of replication gener- An important form of observer bias involves errors ally is directly dependent on levels of funding. Imple- in estimates of group size in marine mammal surveys. mentation of field surveys in marine mammal science Typically, marine mammal surveys involve counting of is often compromised by the challenge of limited fund- groups in the survey area. The group count is then ing and competing priorities. Well-executed marine multiplied by the mean group size, often based on a mammal population survey programs generally detect separate survey effort, as the first step in population strong population trends successfully. However, many estimation for the survey area. Estimates of group size surveys lack the statistical power to detect weak trends are subject to observer bias, contributing to an increase that may nevertheless be important in the context of in the CV for population estimates. Observer bias in avoiding eventual extinction of marine mammal popu- group size estimates can be assessed under good condi- lations. The only solution is to extend survey effort over tions by comparing group size counts by observers many years, thus improving the odds of recognizing a with group size counts based on aerial photographs of trend. Such an approach carries the obvious risk of the same group of animals taken during the surveys. potentially delaying the recognition of a significant con- servation problem for the target population and inevita- 3. Low Statistical Power of Population bly increases the overall monetary cost of the monitor- Survey Data to Detect Trends in ing effort. In many cases, there is no alternative to Population Size extension of the timescale of the monitoring project. In many cases, the single most important type of infor- Policies that require decisions about trends over a short mation for assessing the status of a marine mammal time frame are likely to fail in providing appropriate population is the trend in population size over time. A management if trends are weak. trend is simply a time series of counts in which the slope of a fitted line is significantly different from zero. 4. Inadequate Understanding of Vital In a statistical context, the ability to detect a trend Demographic Parameters and correctly is influenced by four factors. The first is the Population Structure strength of the trend. Strong trends are those in which Determination of effective measures to eliminate a nega- the absolute value of the slope of the fitted line is large. tive trend in a marine population often depends on a When other factors are constant, strong trends are more reasonable understanding of the demographic charac- likely to be detected correctly than weak trends. The teristics of the subject population. Such an understand- second factor is estimation error. Other factors being ing improves the odds that limited resources for conser- equal, trends in survey-based estimates of population vation work will be applied where the greatest benefits size over time are more likely to be detected correctly will accrue. The demographic parameters of marine if the associated CV is small than if it is large. The third mammal populations are often known only with poor factor is the number of replicate surveys available for levels of accuracy or precision. In such cases, conserva- a given time period, to be used to calculate a single tion effort can be readily misdirected. For example, estimate of population size. Increased replication re- measures to reduce preweaning mortality in a marine duces the CV associated with a given estimate. Thus, mammal population will be ineffective if the larger the probability of correctly detecting a trend increases problem is a high rate of adult female mortality ob- with the number of replicate surveys used to calculate scured by imprecise or inaccurate estimates of adult each point in the population time series, other factors female survival rate. Misdirection of limited resources being equal. The fourth factor is the number of years for conservation has obvious effects on extinction prob- in which surveys are done. The probability of correctly abilities for populations in jeopardy. detecting a trend, with other factors being equal, is Accurate, precise measurements of population pa- increased with an increasing number of survey years. rameters in marine mammals are difficult to obtain. MARINE MAMMALS, EXTINCTIONS OF 49

Because marine mammals are long-lived species, the wind and ocean current patterns, with major large-scale time line necessary to obtain good parameter estimates effects on patterns of biological productivity. Although is always lengthy, and the best data come from studies often drastic, local changes in productivity typically are that extend beyond a decade in duration. One of the temporary, returning to normal levels over time periods important results of long-term demographic research from a few months to a few years. ENSO events have on marine mammals is evidence, in some cases, of stochastic characteristics regarding both the frequency marked interannual variability in demographic parame- and the intensity of occurrence and may be variable in ters. Such patterns further emphasize the critical need their effects on survival rate and population trajectory of for a long timescale in such studies. For many species, marine mammals. Both of the referenced ENSO events good estimates of demographic parameters require tag- caused significant reduction in some pinniped popula- ging of individuals, an invasive process that can impose tion sizes and in mortality rates in pups of the year. risks of reduced survival for the tagged individual and There have been very few opportunities to observe the risks of disturbance to groups of animals such as pinni- effects of stochastic disturbance during other time peri- ped breeding colonies on haul-outs. In some cases, tag- ods or on other marine mammal taxa. ging has the potential to bias the demographic data In the context of extinction, the major problem in recorded from the tagged individual. Finally, because incorporating naturally occurring stochastic events into of the lengthy duration and labor intensity involved, conservation planning is the lack of good quality data demographic studies may be quite costly and therefore from an adequate number of events. Thus, it is not difficult to implement. possible to generalize about effects of stochastic events, Population structure is poorly understood in many nor is it possible to reasonably consider mitigation mea- marine mammal species. Species with large geographic sures to minimize increased extinction risks associated ranges and high mobility may appear to be genetically with stochastic events. panmictic. However, recent data suggest significant within-species genetic structure in several cases. Exam- 6. High Cost of Survey Efforts ples include several delphinids and baleen whales. Despite their obvious conservation value, survey efforts Uncertainties about population structure impose a risk for marine mammal populations often are compromised of inappropriate scale in the application of management or eliminated by funding constraints. The central prob- policies. For example, bycatch in fishing nets may occur lem is the high cost per unit effort of a good-quality at high rates only in one portion of the geographic survey for marine mammals at sea. Most surveys at sea range of a delphinid. If the population is panmictic use either aircraft or large surface vessels as observation across the entire range, management authorities may platforms. Both types of platforms are extremely costly deem the bycatch rate acceptable. Such a policy would, to operate at the level of rigor and safety necessary to however, increase extinction risk if the area of high obtain statistically defendable estimates of target popu- bycatch rate supports a population genetically distinct lation size. Indeed, the monetary costs of good at-sea from the remainder of the species’ range. surveys may be a significant proportion of the research and management budgets of resource-oriented govern- 5. Inadequate Understanding of Effects ment agencies, even in wealthy countries such as the of Environmental Uncertainty on United States. In most cases, low-cost alternatives sim- Dynamics of Populations ply do not exist. Thus, only the most serious issues of There is limited evidence that apparently stochastic en- population trend in marine mammal conservation can vironmental fluctuations may have important effects on reasonably attract a quantitatively rigorous level of sur- the dynamics of marine mammal populations. The best vey effort. These funding realities increase the risks of known cases involve the pinnipeds, primarily because extinction by improving the odds that trends of concern pinnipeds breed or care for young on solid substrata will be overlooked for lack of the necessary survey and therefore have more readily observed and better effort. known population dynamics than most other marine 7. Lack of Consensus and Consistency in mammal taxa. For example, during the early 1980s and mid-1990s, food supplies for many temperate pinniped Definition of Objective Criteria for the populations in the North Pacific were disrupted by Determination That Particular global-scale oceanographic disturbances generally Populations Are Vulnerable known as ‘‘El Nin˜ o Southern Oscillation’’ (ENSO) There are many forms of institutional or organizational events. ENSO events involve a suite of changes in global protocols designed to provide protection for depleted 50 MARINE MAMMALS, EXTINCTIONS OF populations of wildlife, including marine mammals. however important, is well beyond the scope of Many such protocols originate from and have the back- this article. ing of government agencies. However, few protocols for the protection of species in peril include explicit, objective criteria for determining the level of jeopardy II. PATTERNS AND CASE STUDIES OF or for specifying recovery from jeopardy status. More- over, those cases in which objective criteria are specified EXTINCTION IN MARINE MAMMALS rarely accommodate the quantitative uncertainties in population estimation, demographic parameterization, A. Extinction or Near Extinction of Major characteristics of ecological disturbance, and related Taxa over Evolutionary Time issues that are universal problems in population data for depleted wildlife. Surveys of criteria for status deter- 1. Odobenidae mination of wildlife in peril reveal little consistency, Odobenids have a fossil record of striking diversity, and often only minimal consideration of fundamental including some species resembling modern walruses biological patterns, even within particular political ju- and others superficially similar to the modern sea lions risdictions. and fur seals. The odobenids seem to have diverged Resolution of the problem of objective criteria will from the otariids in the early Miocene. Peak fossil diver- be difficult. Different taxa of organisms have different sity is in strata from the late Miocene and early Pliocene. population characteristics and may warrant different Diversity declined abruptly during the late Pliocene and approaches to the development of objective criteria for Pleistocene. The single surviving species, the modern jeopardy and recovery. Differences in culture, values, walrus, appeared in the fossil record during the Pleisto- and political traditions among jurisdictions also compli- cene. Extinct odobenids were also broadly distributed cate any effort to establish common objective criteria. across latitude. The modern walrus is limited to high However, the separation of jeopardy criteria from arbi- northern latitudes and is a distributionally aberrant rela- trary judgments, often intertwined with political con- tive to the extinct odobenids. siderations, is crucial to ensure that extinction risk is The fossil record indicates that modern walruses are measured by biological criteria. A failure to achieve the single relict of a largely lost taxon. Most extinctions such separation may increase the odds of extinction for of odobenids seem to be associated with global-scale some populations in peril. cooling and related large-scale habitat change during the Pliocene. However, ecological characteristics of the E. Problems in Distinguishing ‘‘Natural’’ extinct odobenids are in many cases difficult to under- stand because the surviving contemporary model seems from ‘‘Unnatural’’ Extinction atypical. Thus, it is difficult to develop meaningful func- As indicated previously, marine mammals have been tional models of extinction in the odobenids. present on Earth since the early Eocene. The majority of the marine mammals that have evolved on Earth 2. Sirenia are now extinct, and virtually all extinctions occurred Sirenian diversity clearly peaked during the Miocene, a before the evolution of the homonid primates, particu- period of warm global climate coincident with extensive larly Homo sapiens. In the context of conserving warm shallow coastal marine habitats. Dugongids, now the earth’s biodiversity, however, we are primarily represented by a single surviving species, were the most concerned about anthropogenic loss of species. Thus, diverse family of sirenians through the fossil record. our time window is narrowed to the Pleistocene and Sirenian diversity declined sharply during the relatively Holocene and our conceptual focus to extinctions cool Pliocene and Pleistocene, and modern forms are that result from conscious human action rather than relicts of a largely extinct order. Two of four recognized from other, natural processes such as changing habitat, sirenian families are now fully extinct. disturbance and catastrophe, or displacement of one The surviving sirenians seem to provide good ecolog- species by another. We suggest that not all anthropo- ical models for the extinct forms. Modern sirenians genic extinctions are necessarily unnatural. However, typically consume macrophytes in shallow waters and, separating the natural from the more philosophically except for Steller’s sea cow, clearly prefer warm pro- objectional unnatural is a great challenge, much bur- tected waters. Thus, it is likely that Pliocene cooling dened by the complicating considerations of values, and the coincident widespread loss of warm shallow culture, politics, and economics. Thus, the distinction, seas were major factors in the decline of the sirenia. MARINE MAMMALS, EXTINCTIONS OF 51

Surviving species were those able to retreat to low- middle of the twentieth century. The last confirmed latitude refugia or, in the case of Steller’s sea cow, a sighting of a Caribbean monk seal was at Seranilla Bank, subpolar refuge with abundant food and no signifi- west of Jamaica, in 1952. Directed surveys for seals in cant predators. the later 1950s and 1960s found no living animals.

3. Desmostylia b. Steller’s Sea Cow: Hydrodamalis gigas Desmostylians did not diversify to nearly the extent of (Zimmerman, 1780) the other major marine mammal taxa, and they did not Steller’s sea cow was first observed by a scientist in 1741, survive beyond the end of the Miocene. Lacking modern at which time it occurred only along the shorelines ecological models, we prefer not to speculate on specific of the Commander Islands, east of Kamchatka in the ecological mechanisms of extinction in the desmostyli- Russian Far East. At the time of discovery, sea cows ans. However, loss of the taxon coincided in time with probably numbered no more than a few thousand indi- the decline of sirenians, with which desmostylians share viduals in total, but population surveys were never common ancestry. Thus, habitat needs and associations done. There are reports that the sea cow had previously may have been similar between late Miocene sirenians occurred along the eastern shore of mainland Kam- and desmostylians, and loss of optimal habitats dur- chatka and in the Near Islands of the Aleutian Archipel- ing Pliocene cooling could have had similar effects on ago, but the primary evidence is stranded material that both groups. could have resulted from the drift of carcasses. Sea cows were subject to intensive hunting, soon after discovery, by crews of sea otter hunters working in the Com- B. Modern Anthropogenic Extinctions of mander and Aleutian Islands. Harvest of sea cows pro- Species, Subspecies, and vided high-quality meat and blubber in great quantity Major Populations and facilitated extended harvesting expeditions by otter hunters. The last sea cow observation was recorded in 1. Species Level the Commander Islands in 1767. The only scientific Following the taxonomic format of Rice (1998), three observations of living Steller’s sea cows were made by species of modern marine mammal are known to G. W. Steller while shipwrecked at Bering Island in be extinct. In all cases, the probable causes are the Commander Islands during the winter of 1741– anthropogenic. In addition, there is evidence that a 1742. recent species of pinniped, undescribed and entirely Three factors probably contributed to the extinction unknown to science, once occurred in the Chagos of Steller’s sea cow. First, directed hunting was intensive Archipelago and Seychelles Islands of the tropical and unmanaged. Second, at the time living sea cows southwestern Indian Ocean (Rice, 1998). If such a were observed by Steller, they occurred only on islands species occurred, it is now extinct as a result of lacking aboriginal human populations. The pattern sug- unknown factors. There is substantial skepticism that gests that aboriginal hunters may have previously re- such a species ever existed. duced the range and numbers of sea cows, predisposing them to extinction when hunting intensified. Third, sea a. Caribbean Monk Seal: Monachus tropicalis cows foraged on nearshore benthic kelps. The rapid (Gray, 1850) depletion of sea otter populations by otter hunters in The Caribbean monk seal is one of three recent species the Commander Islands may have allowed sea urchins, of Monachus. All occur in tropical or subtropical lati- the primary prey of otters in the region, to overgraze tudes. The preexploitation range of M. tropicalis in- their preferred food, the same kelps utilized by sea cluded the islands of the Caribbean Sea, the coastal cows. Thus, catastrophic loss of food supply could have regions of Venezuela and Caribbean Colombia, south- facilitated the rapid extinction of sea cows after reduc- ern Florida, the east coast of Mexico south of the Bay tion of population size(s) and range. of Campeche, and the Caribbean coasts of Belize, Guate- mala, Honduras, Nicaragua, Costa Rica, and Panama. c. Japanese Sea Lion: Zalophus japonicus Estimates of preexploitation population sizes are not (Peters, 1866) available. Intensive hunting of seals for meat and oil The Japanese sea lion is sometimes considered a subspe- began with the arrival of Columbus in 1492. Seal popu- cies (Z. californianus japonicus) of the California sea lations were reported as depleted as early as the seven- lion. Rice (1998) regards the Japanese sea lion as a teenth century, but a few animals survived into the separate species. The Japanese sea lion originally ranged 52 MARINE MAMMALS, EXTINCTIONS OF along the shores of Japan and Korea and the southern 2. North Pacific and North Atlantic Pacific shores of Russia. The species was subject to a Populations of the Right Whale, long history of hunting for meat and oil. No population Balaena glacialis Mu¨ ller, 1776 surveys were done. The sea lion was thought to be Right whales occur in three major regions: the North extinct at the end of the nineteenth century, but a group Pacific, the North Atlantic, and the Antarctic Ocean, of animals was reported from a Japanese island in 1952. together with adjoining regions of the South Pacific, There have been no subsequent sightings and the spe- South Atlantic, and South Indian Oceans. Because of cies is now considered extinct. All available data indi- intervening landmasses and the antitropical distri- cate that directed harvest was the primary factor con- bution of the species, rates of migration and genetic tributing to extinction, but other unreported factors exchange among the three regions are very low. The could have facilitated loss of the species. primary conservation problem for the northern popula- tions is very low population sizes, imposed largely by 2. Subspecies or Population Level centuries of unregulated commercial whaling. a. North Atlantic Gray Whale: Eschrichtius Right whales were identified by the earliest whalers robustus (Lilljeborg, 1861) as targets of choice because of their abundance, large Whaling records and subfossil remains indicate that a size, high yields of meat and blubber, relatively docile population of gray whales (Eschrichtius robustus), ap- behavior, and relative buoyancy postmortem. Historical parently not taxonomically distinct from North Pacific records suggest that significant exploitation of the populations, once occurred along both coasts of the North Atlantic populations began along the European North Atlantic. Available evidence suggests that gray coast early in the second millennium A.D. Changes in whales occurred along the Atlantic coast of North hunting effort over time and space followed the stereo- America into the seventeenth century but probably not typical pattern of overexploitation. As coastal European beyond. We are not aware of any available data on stocks of whales were depleted, whalers expanded ef- population size, foraging or breeding habitats, or migra- forts westward to Greenland, Newfoundland, and Lab- tory corridors. Subfossil specimens have been found rador beginning in the fifteenth century. Subsequent in Europe from the central Baltic coast of Sweden to stock depletion led to further expansion southward in Cornwall in the United Kingdom. In North America, the seventeenth century to the waters of Nova Scotia subfossil finds range from New York to South Carolina. and the United States. Right whale populations off the In our opinion, the most likely explanation for extinc- northeastern United States were depleted to low num- tion is prolonged excessive harvest by the whaling in- bers after the middle eighteenth century. The historical dustry, but a definitive explanation for extinction does record of right whale harvest is less lengthy for the not exist. North Pacific, but it almost certainly followed the same general pattern. Commercial whaling was most inten- sive in the nineteenth century. What ever recovery of C. Species, Subspecies, and Populations North Pacific right whales occurred during the twenti- in Imminent Peril of Extinction eth century was damaged by substantial illegal harvest by whalers from the USSR during the 1960s. 1. Synopsis Approximately 300 individual right whales are Here, we summarize the status of 11 marine mammal thought to be currently present in two populations in taxa or populations that in our opinion face a substantial the North Atlantic. The eastern population, off the coast probability of extinction during the twenty-first century of Europe, probably contains only a few individuals (Table III). We provide more detailed summaries for and is in extreme jeopardy of extinction. The western five examples of the category, chosen arbitrarily based population is found mainly along the coast of Canada on our relative familiarity with the cases. In all but and the United States. During the twentieth century, one of the eleven cases, available data suggest total estimated annual growth rates of the western popula- abundances of less than 1000 individuals. Most of the tion have never exceeded 2.5%, and the population is taxa or populations considered in this category have now declining. The two populations recognized in the several significant past or current anthropogenic North Pacific are also quite small, although estimates sources of mortality that facilitate extinction risk. In of size and trend have not been made. The western nearly all cases, the scope of operational resource invest- population, ranging from the Sea of Okhotsk to main- ment and human societal adjustment necessary to avoid land China, is thought to be somewhat larger than the extinction seems to us very high. eastern population, which ranges from the eastern Be- MARINE MAMMALS, EXTINCTIONS OF 53

TABLE III Species, Subspecies, or Populations Thought to Be in Imminent Peril of Extinction

Population identity Taxon or population Range/habitat structure Estimated population size Primary risk factors

Eastern population of the Pelagic, eastern margins of One population No survey data, perhaps a Commercial whaling, in- North Pacific right North Pacific at middle few hundred animals cluding illegal Soviet whale: Balaena glacialis and high latitudes whaling; incidental take Mu¨ ller, 1776 in fishing nets North Atlantic right whale: Pelagic, eastern and west- Two populations—eastern 300 Commercial whaling, ship Balaena glacialis Mu¨ ller, ern margins of north At- and western strikes, incidental take in 1776 lantic at middle and high fishing nets latitude Davis strait, Hudson Bay, Coastal and pelagic, in re- Four separate populations Davis Strait and Hudson Commerical whaling, dis- Spitsbergen Barents Sea, gions as indicated Bay, about 450 com- turbance from offshore and Sea of Okhotsk pop- bined; Spitsbergen, less petroleum exploration ulations of the bowhead than 50; Okhotsk, a few and development whale: Balaena mysticetus hundred Linnaeus, 1758 Western North Pacific gray Coastal, western Pacific, One population Ͻ100 Commerical whaling, off- whale: Eschrichtius ro- northern Sakhalin Island, shore petroleum explora- bustus (Lilljeborg, 1861) Russia, during summer; tion and development in winter range thought to summer range be off Korea or China Vaquita: Phocoena sinus Coastal, Northern Gulf of One population 567 (95% CI: 177–1073) Incidental take in fishing Norris and McFarland, Mexico, California in 1997 survey nets 1958 Baiji: Lipotes vexillifer Aquatic in lower and mid- Population structure un- Ͻ100 Incidental take in setline Miller, 1918 dle Yangtze River, China known fisheries, directed harvest for oil, contaminants, wa- tercourse impoundments and diversions, habitat loss for prey Indus River population of Aquatic in main channels Population structure un- No data; population is Incidental take in fishing the Indian river dolphin: and tributaries of the known; populations in thought to be very small gear, directed harvest for Platanista gangetica (Rox- Ganges, Indus, Brahma- different watersheds are meat and oil, contami- burgh, 1801) putra, and Karnaphuli isolated from one an- nants, watercourse im- Rivers of India, Bangla- other poundments and diver- desh, Nepal, and Bhutan sions, habitat loss for prey Gulf of Alaska population Coastal marine habitats and One population Approximately 350 Hunting by indigenous peo- of beluga whale: Delphi- river mouths, primarily ples, commercial whal- napterus leucas (Pallas, in Cook Inlet, Alaska; ing, contaminants, habi- 1776) also along the coast of tat disturbance the central Gulf of Alaska Gulf of St. Lawrence popu- Estuarine and coastal, St. One population 1238 (standard error ϭ Commerical whaling, cull- lation of beluga whale: Lawrence River estuary 119) in 1997 ing to protect fisheries, Delphinapterus leucas and Gulf of St. Lawrence, contaminants (Pallas, 1776) Canada Mediterranean monk seal: Coastal in Mediterranean At least two populations 275–460 total Directed harvest for meat Monachus monachus (Her- Sea and eastern warm- likely: Cabo Blanco in and skins, illegal hunt- mann, 1779) temperate North Atlan- Mauritania, western Sa- ing, habitat destruction, tic; currently limited pri- hara, and eastern Medi- overfishing of prey, con- marily to coastal areas of terranean taminants Turkey, Greece, western Sahara, and Mauritania Lake Saimaa ringed seal: Aquatic in Lake Saimaa, One population Approximately 200 Incidental take in fishing Pusa Hispida saimensis Finland; river connection nets (Nordquist, 1899) to the Gulf of Finland is thought to be too swift to allow passage of seals 54 MARINE MAMMALS, EXTINCTIONS OF ring Sea to southern Baja California, Mexico. The east- offshore oil development in the current summer feeding ern population may have suffered irreparable damage range of the population. from the illegal Soviet whaling noted previously. Most of the available information on the western Failure of northern right whale populations to re- gray whale population comes from recent studies sum- cover from the cessation of commercial whaling has marized by Weller et al. (1999). Western gray whales been difficult to understand, excepting the obvious forage on benthic invertebrates during summer months damage from recent illegal whaling in the eastern North in shallow coastal waters off northeastern Sakhalin Is- Pacific. Southern right whale populations protected land, Russia. Foraging activity is particularly intensive from exploitation have grown at rates estimated as high in a small nearshore area off the entrance channel to as 6 or 7% per year, and there is no evidence of major Piltun Lagoon (52Њ 50Ј N, 143Њ 20Ј E). Data from photo- differences in fundamental vital rates between northern identification studies indicate high fidelity of foraging and southern populations. Thus, other factors must be gray whales to the area north and south of the lagoon, retarding population growth in the north. The current within and among years, during the period 1995 to consensus view is that two factors, incidental entangle- 1999. ment in fishing gear and inadvertent collisions with Analyses of photographic data indicate that as few as large commercial ships, are the primary causes for fail- 90 individual whales regularly use the summer foraging ure of North Atlantic populations to grow in recent area off northeastern Sakhalin Island. Based on current decades. These right whales tend to be concentrated in data, the population numbers near 100 individuals. regions that support productive and highly capitalized Data from the recent studies indicate that the crude fisheries, facilitating damaging rates of incidental entan- birth rate in the Sakhalin summering aggregation was glement. Right whales are also concentrated in areas 4.3% in 1997 and 13.2% in 1998. Adult females with frequently transited by large ships. Vulnerability to ship calves show particularly high fidelity to the feeding strikes is enhanced by the apparent tendency of right area near Piltun Lagoon, suggesting that the area is whales to rest quietly at the surface for long periods. important to calf rearing and weaning. Given the long period of depletion, factors in addition The summer feeding area near Piltun Lagoon has to bycatch and shipstrikes may have contributed to been subject to intensive exploration in recent years failed recovery over the long term. For example, social and production of oil began in 1999 at offshore petro- dysfunction resulting from inability to find potential leum production facilities. Offshore petroleum explora- mates (the Allee effect) may diminish the growth poten- tion involves frequent use of intensive low-frequency tial of a small population. sounds, and development of located petroleum re- Survival of northern right whale populations beyond sources involves increased shipping activity, placement the twenty-first century requires a major reduction of of structures, modification of adjacent sediments and all forms of directed harvest and the largest possible benthic communities, and the risk of unintended spills reductions in rates of incidental taking and ship strikes. of drilling fluids, vessel and machinery fuels, and ex- Eastern populations in the North Atlantic and North tracted crude oil. Pacific may be destined for extinction within the cen- The western North Pacific population of gray tury regardless of actions taken. whales is in imminent peril of extinction. Recovery planning for the population will benefit from acquisi- 3. Western North Pacific Gray Whale, tion of significant additional data. The winter range, Eschrichtius robustus (Lilljeborg, 1861) calving grounds, and migratory corridors of the popu- The western North Pacific population of gray whales lation must be determined, and the associated risk summers in the Sea of Okhotsk and probably migrates factors must be identified and analyzed for significance south to winter habitats in southern China. Very little with regard to extinction. The affinity of summering is known about the ecology of the population, and animals, and particularly females with dependent focused studies have been done only within the past 5 calves, for the feeding grounds off Piltun Lagoon years. The western gray whale population is among the must be better understood. Activities associated with smallest of large whale populations in the world and is development of petroleum resources in the coastal one of the most vulnerable to extinction in the twenty- zone of northeastern Sakhalin Island must be carefully first century. The principal conservation concerns for evaluated in the context of risks to gray whales using western gray whales are the very small population size, the area for feeding. All forms of harvest of western resulting from both commercial whaling and subsis- gray whales must be prevented indefinitely if extinc- tence harvests in previous centuries and risks posed by tion is to be avoided. MARINE MAMMALS, EXTINCTIONS OF 55

4. Gulf of Alaska Beluga Whale, est commercial whaling in previous decades. Third, the Delphinapterus leucas (Pallas, 1776) cultural characteristics of native harvest of belugas in The Gulf of Alaska population of beluga whales has Cook Inlet differ from those of all other locations in always concentrated primarily in Cook Inlet on the Alaska where native whaling occurs. In all locations southern mainland coast of Alaska. Animals have been except Cook Inlet, native whaling is done from single coastal villages using practices consistent with lengthy seen on occasion in coastal waters of the Kodiak Archi- tradition, subject to stringent oversight by village elders, pelago, in Prince William Sound and Yakutat Bay, and and based on the subsistence needs of the village. In along the outer coastal waters of the central Gulf of contrast, most native whalers working in Cook Inlet Alaska. However, it is not known if these animals are have moved from their home villages to the relatively part of the Cook Inlet population. Historically, belugas large and secular city of Anchorage. Thus, it appears have been widely distributed in Cook Inlet, a well- that cultural norms and limits on whaling activity char- mixed, turbid, highly productive marine inlet that re- acteristic of native Alaskan villages have been lost in ceives runoff from several large river systems. The the case of Cook Inlet. The consequence has been loss whales concentrate seasonally near and in the river of traditional control over the harvest. mouths to forage on migrating anadromous fish. There is concern about risks of contaminants and Belugas in Cook Inlet were hunted at low levels marine oil activity for belugas in Cook Inlet. However, in previous decades by commercial whalers, although despite substantial offshore oil production activity, commercial harvest no longer occurs. Passage and im- there is no firm evidence of negative effects of oil pro- plementation of MMPA in 1972 ensured the rights of duction on belugas in Cook Inlet, nor is there sub- native peoples in Alaska to pursue the traditional prac- stantive evidence of negative effects of chemical con- tice of hunting beluga whales, including those in Cook taminants. We suggest that the primary conservation Inlet. Hunting of belugas in Cook Inlet by natives in- concern for Cook Inlet belugas at the present time is the creased in the 1980s and 1990s compared to earlier risk of excessive harvest by native hunters disconnected decades. During the 1990s, it was recognized that the from the cultural regulation of their respective home geographic range of beluga whales, based on opportu- villages. In our opinion, harvests of belugas in Cook nistic observations from research vessels, was much Inlet must remain suspended until population recovery smaller than it had been in the 1970s. Few sightings is apparent and a pragmatic harvest comanagement plan of belugas in other locations of the Gulf of Alaska have supported by tribal and agency authorities is in place. been made in recent years. Intensive surveys in the Otherwise, extinction is likely within the century. 1990s confirmed that the population was declining. The population estimate for 1998, determined by NMFS, 5. Vaquita, Phocoena sinus Norris and was 347 (CV ϭ 0.29). Based on known whale kills by McFarland, 1958 native hunters and evaluation of survey data, it was The vaquita is a small porpoise limited to the northern determined that native harvest of belugas may be exces- part of the Gulf of California, Mexico. The vaquita has sive, possibly placing the Cook Inlet beluga population the smallest natural geographic range of any marine at risk of extinction. As a result, a temporary morato- cetacean, and the single population probably has never rium on native harvest of belugas in Cook Inlet was contained a large number of individuals. Numbers were implemented in 1999. Native tribal leaders and U.S. estimated at about 600 individuals based on a compre- federal agencies are now planning for recovery actions hensive survey in 1997 (Table III). The population biol- and a more carefully managed harvest. ogy of the vaquita is poorly known, and the very best The Cook Inlet beluga population is the first known surveys of the vaquita population have low precision. modern case in which excessive harvest by indigenous Thus, trends in the population are difficult to discern North American peoples has placed a population of with confidence, but available data indicate that the marine mammals in jeopardy. Other populations of be- population may be declining. Studies of DNA in sam- lugas are exploited regularly by natives in Alaska, but pled vaquitas indicate the complete absence of poly- none other than the Cook Inlet population is in peril. morphisms in the hypervariable region of the mito- The tenuous status of Cook Inlet belugas, compared to chondrial genome. other Alaskan populations, probably results from three During the last two decades, the primary concerns factors. First, the Cook Inlet population has probably for vaquita conservation have been high rates of inci- always been the smallest of the Alaskan beluga popula- dental take in gillnet and shrimp trawl fisheries, effects tions. Second, Cook Inlet belugas were subject to mod- of contaminants, effects of reduced genetic diversity, 56 MARINE MAMMALS, EXTINCTIONS OF and effects of diversion of the Colorado River away Africa. For years, monk seals have been perceived as from the northern Gulf of California on regional rates direct competitors of fisheries and have been harassed of biological productivity. The significance of the listed and killed in substantial numbers, often illegally, as a risk factors has been evaluated by Rojas-Bracho and result. Harassment has included directed destruction of Taylor (1999). Losses due to incidental take were iden- caves and other shoreline locations favored by seals for tified as the primary conservation problem for the breeding and resting. Monk seals likely have also been vaquita. Concentrations of organochlorines, including affected by loss of prey due to overfishing and to various PCBs and DDT congeners, were found to be low in forms of contamination of the habitat and food webs. vaquita tissues, low in other consumer species within In 1997, a mass mortality event was observed in the the vaquita range, and low in the vaquita habitat. Or- colony at Cabo Blanco, reducing the local seal popula- ganochlorine levels in the region are generally below tion to about 100 individuals. The cause and magnitude minimum levels considered harmful to human health of the event have not been determined to our knowl- and are presumed to be innocuous for vaquitas we well. edge. Although comprehensive demographic and popu- The levels of reduced genetic variability in vaquitas do lation survey data are lacking, the consensus opinion not necessarily result in genetically based reduction of is that the total number of Mediterranean monk seals reproductive rates, particularly in the context of popula- is probably declining over time. tions such as vaquitas that probably have always been In addition to the small size of the two known popu- small. Biological productivity in the upper Gulf of Cali- lations, two factors add great difficulty to the prospects fornia is high compared to other coastal marine ecosys- for implementation of a successful recovery strategy tems despite diversion of the Colorado River. Although for Mediterranean monk seals. First, the habitat of the other risk factors may be detrimental to vaquita conser- monk seal is bounded by many culturally disparate vation over the long term, mortalities due to incidental political jurisdictions. Historically, the political and take are the primary current problem. cultural diversity has interfered with cooperation Continued incidental take of vaquitas will cause ex- across jurisdictions. Thus, the attainment of consistent, tinction of the species during the twenty-first century, broadly supported conservation priorities for monk given even the most conservative estimates of the cur- seals may be an unrealistic political objective. Second, rent rate of take. Elimination of the risk of anthropo- ongoing damage to the monk seal populations appar- genic extinction requires significant reduction in the ently results from many factors acting in concert rather level of fishing effort or changes in gear design or de- than one clearly predominant problem. Thus, agree- ployment strategy to reduce take rates in fisheries re- ment on conservation priorities and actions may be sponsible for incidental take. difficult even within jurisdictions. Mediterranean monk seals appear to be destined for 6. Mediterranean Monk Seal, Monachus extinction, possibly within the twenty-first century, un- monachus (Hermann, 1779) less marine conservation authorities in countries bor- The Mediterranean monk seal was found originally in dering seal habitat can agree on two issues. First, risk the western Black Sea, throughout the Mediterranean factors for the seals must be evaluated dispassionately Sea, and along the coast of northwestern Africa from and placed in order of significance. Second, involved the Strait of Gibralter to about 21ЊN latitude. Currently, authorities must agree on a plan for recovery of seal there are thought to be no more than 275–460 individu- populations based on the assessment of risk factors and als, occurring primarily in two populations. Prior to convince the human populations of their respective 1997, the largest group of approximately 300 seals oc- jurisdictions that seal conservation is a worthwhile ob- curred in a small population at Cabo Blanco, at the jective. border of the western Sahara and Mauritania, on the outer coast of northwestern Africa. A second population of unknown size occurs in the eastern Mediterranean, D. Species, Subspecies, and Populations primarily in the coastal waters of Turkey and Greece. of Significant Concern with Regard Mediterranean monk seals probably have been sub- to Extinction ject to directed subsistence harvest for meat, oil, and hides for several millennia. The precarious status of 1. Synopsis modern populations seems to result from many factors Here, we consider a group of taxa and populations that, associated with the large, multicultural human popula- we believe, are of significant concern with regard to tions of southern and eastern Europe and northern extinction (Table IV). In contrast to the discussion in MARINE MAMMALS, EXTINCTIONS OF 57

TABLE IV Species, Subspecies, and Populations of Significant Concern with Regard to Extinction

Population identity/ Estimated population Taxon or population Range/habitat structure size Primary risk factors

Blue whale: Balaenoptera Pelagic Three subspecies—two 2000 in eastern North Commercial whaling, in- musculus (Linnaeus, in Southern Hemi- Pacific, 400–2000 in cluding illegal Soviet 1758) sphere, one in North- eastern North Atlan- whaling, ship strikes ern Hemisphere; five tic; others unknown populations in North Pacific, two in North Atlantic, one in north- west Indian; number in Southern Hemi- sphere unclear Hawaiian monk seal: Mo- Coastal leeward Hawai- Five primary breeding Approximately 1500 Directed harvest for nachus schauinslandi ian Archipelago sites on different is- meat, oil, and skins; (Matschie, 1905) lands; some exchange disturbance by mili- of individuals among tary conflict and peace- islands time human activity; entanglement in ma- rine debris; declining ecosystem productiv- ity; aberrant breeding behavior associated with anomalous sex ra- tio; natural toxins in prey Baltic Sea ringed seal: Coastal, in areas with Probably one population Unknown Pollution and contami- Pusa hispida botnica pack or shorefast ice nants (Gmelin, 1788) at least part of the year Lake Ladoga ringed seal: Coastal, in areas with Probably one population Unknown Pollution and contami- Pusa hispida ladogensis pack or shorefast ice nants (Nordquist, 1899) at least part of the year Western North Pacific Coastal along the shores Population structure un- Unknown Incidental take in fishing harbor seal: Phoca vi- of the western Aleu- known; island breed- nets tulina stejnegeri Allen, tian and Commander ing colonies probably 1902 Islands, southeastern somewhat isolated, al- Kamchatka Penin- though exchange sula, Kuril Islands, Sea among colonies may of Okhotsk, and Hok- occur kaido Western North Pacific Coastal and pelagic, is- Thought to be a single Approximately 40,000 in- Unknown; primary possi- Steller’s sea lion: Eu- lands and isolated population; some isola- dividuals; decline in bilities are large-scale metopias jubatus rocky shores of the tion of breeding colo- numbers of approxi- declines in ocean pro- (Schreber, 1776) western Gulf of nies probably occurs; mately 65% since the ductivity, changes in Alaska, western North exchange among mid-1970s the species composi- Pacific, and Bering Sea breeding colonies is tion and diversity of thought to be minimal prey species, and com- petition for prey with commercial fisheries Australian sea lion: Neo- Coastal and continental Population structure un- Approximately 5000 indi- Commercial sealing, inci- phoca cinerea (Pe´ron, shelf waters of south- known; long-distance viduals dental take in fishing 1816) ern and southwestern movements are uncom- nets, illegal directed Australia mon, so separate killing, entanglement breeding colonies may in anthropogenic be isolated debris continues 58 MARINE MAMMALS, EXTINCTIONS OF

Continued

Population identity/ Estimated population Taxon or population Range/habitat structure size Primary risk factors

Hooker’s sea lion: Pho- Coastal waters of New Probably one popula- 10,000–12,000 indi- Commercial sealing, inci- carctos hookeri (Gray, Zealand tion, breeding primar- viduals dental take in fishing 1844) ily at the Auckland Is- nets lands Guadalupe fur seal: Arcto- Coastal and continental Probably one popula- 3000–4000 individuals Commercial sealing cephalus townsendi Mer- margin habitats off tion, breeding only at riam, 1897 Baja California, Mex- Guadalupe Island, ico, and southern Cali- Mexico fornia Juan Fernandez fur seal: Coastal and pelagic habi- Population structure un- 7000–10,000 individuals Commercial sealing Arctocephalus philippii tats of the Juan Fer- known (Peters, 1866) nandez Archipelago, Chile Atlantic walrus: Odobe- Coastal habitats with ex- Four separate popula- Unknown Commercial hunting, ille- nus rosmarus rosmarus tensive pack ice in the tions are recognized gal hunting (Linnaeus, 1758) Arctic North Atlantic, from eastern Canada to the Kara Sea Laptev Sea walrus: Odobe- Coastal habitats of the Probably one population Unknown Commercial hunting nus rosmarus laptevi eastern Kara, Laptev, Chapskii, 1940 and western Eastern Siberian Seas Amazonian manatee: Aquatic habitats of the Population structure un- Unknown; thought to be Commercial hunting, Trichechus inunguis Amazon watershed, known declining hunting by indigenous (Natterer, 1883) South America peoples, watercourse impoundment and di- version, sedimenta- tion associated with forest modification, contaminants associ- ated with mining, inci- dental take in fishing nets West African manatee: Warm shallow coastal Population structure un- Unknown Commercial hunting, Trichechus senega- marine habitats and known hunting by indigenous lensis Link, 1795 rivers of West Africa peoples, killing to re- from Senegal to duce damage to fishing Angola gear and rice crops West Indian manatee: Warm shallow coastal Two subspecies—one in Approximately 2000– Habitat destruction, mod- Trichechus manatus marine habitats and the southeastern 3000 in Florida; trend ification, and distur- Linnaeus, 1758 rivers of the Georgia United States, espe- in Florida populations bance associated with Bight, Florida, the Ca- cially in Florida, and unclear; numbers else- growing human popu- ribbean, and northeast- the other along the where unknown lations in Florida; ern South America mainland east coast of commercial hunting; southward to central central America from hunting by indigenous Brazil northern Mexico to peoples; contami- central Brazil, and in nants; incidental take the islands of the Ca- in fishing nets; inges- ribbean Sea tion of debris California sea otter: Enhy- Shallow marine habitats One primary mainland 2000–2500 individuals; Commercial hunting, in- dra lutris nereis (Mer- along exposed outer population, plus small numbers declining at cidental take in fish- riam, 1904) coast of California separate colony at San 1 or 2% per year ing nets, contami- Nicolas Island nants, disease, parasites

continues MARINE MAMMALS, EXTINCTIONS OF 59

Continued

Population identity/ Estimated population Taxon or population Range/habitat structure size Primary risk factors

Marine otter: Lutra felina Shallow marine habitats Population structure un- Unknown Commercial harvest for (Molina, 1782) and coastal aquatic known; most individu- pelts, killing to reduce habitats along the ex- als occur in southern competition with fish- posed outer coasts of Chile; locally extinct eries, incidental take Peru, Chile, and south- in Argentina in fishing gear, con- ern Argentina taminants

a Some taxonomists consider the southern right whale a separate species, Balaena australis (Desmoulins, 1822). Here we follow the convention of Rice (1998), regarding the northern and southern right whales as one species.

Section II,C, we do not regard entries in this group to marine habitats distant from human population centers. be in imminent peril of extinction during the twenty- Thus, they were beyond the technological capabilities first century. In most cases, population sizes are large of commercial whalers prior to the twentieth century. enough and conservation issues tractable enough that Blue whales became priority targets of whalers only less dire predictions seem reasonable. However, we sug- after the development of the steam engine, factory ships, gest that vigilance and positive action will be required explosive harpoons, and air compressors to inflate car- to prevent taxa and populations in this group from casses after killing. Thus, the harvest and depletion of falling to a more precarious status. We list 17 taxa or blue whales occurred primarily during the twentieth populations (Table IV), providing more detailed sum- century. At least 360,000 blue whales were killed in the maries for four arbitrarily selected examples. Antarctic region before commercial whaling declined in the 1960s, and other populations were exploited as 2. Blue Whale, Balaenoptera musculus well. Illegal harvests by Soviet whalers occurred after (Linnaeus, 1758) a moratorium was imposed, taking at least 8000 addi- Blue whales occur in all the world’s coastal and pelagic tional pygmy blue whales. marine habitats. Currently, three subspecies are known. The current consensus opinion is that blue whale The pygmy blue whale (Balaenoptera musculus brevi- populations are now but a fraction of preexploitation cauda) occurs in southern cool-temperate and subpolar size, but there are few data available to defend the latitudes. The ‘‘true’’ southern blue whale (B. m. interme- perception. Recent data indicate that the eastern North dia) summers in the Antarctic Ocean, and the northern Pacific population numbers approximately 2000 indi- blue whale (B. m. musculus) is found in the North Pacific viduals and may be increasing. The eastern North Atlan- and North Atlantic. Eastern and western populations tic population has been estimated at 400–2000 indi- are known in the North Atlantic, and at least five popu- viduals. A circumpolar survey of the Antarctic Ocean lations have been described in the North Pacific. The estimated 710 (CV ϭ 0.64) individuals. There are pub- population structure in the Southern Hemisphere is lished arguments that blue whale populations off south- unclear. However, ‘‘true’’ blue whales must have differ- ern Japan and in the eastern Gulf of Alaska are locally ent populations in the southern Indian, Atlantic, and extinct or very small. Because of small population sizes Pacific oceans, respectively. Available data suggest that and large CVs associated with surveys, it is not possible blue whales migrate seasonally, utilizing higher latitude to identify trends in most blue whale populations. Thus, habitats in summer for feeding, primarily on euphausiid the status of the world’s blue whale populations is gen- crustaceans, and lower latitude habitats during winter erally unknown, and prospects for confidently under- for courtship, breeding, and parturition. standing the size of populations in the foreseeable fu- Blue whales are an obvious target of choice for com- ture are virtually nil. mercial hunting because of their great body size. How- The current status of blue whale populations seems ever, blue whales are swift swimmers and are negatively to be entirely the result of excessive past commercial buoyant postmortem. Prior to exploitation, blue whales harvests. There is evidence that ship strikes may cause were most abundant in the Antarctic Ocean and other some mortality of blue whales off the California coast, 60 MARINE MAMMALS, EXTINCTIONS OF but current anthropogenic mortalities are probably lion numbers. Prey species composition has changed, minimal. Recovery of small blue whale populations will dietary diversity has declined, and there have been mea- require indefinite suspension of all forms of harvest and surable shifts in the spatial distributions of preferred prompt detection and elimination of emerging sources prey during the past three decades. Numbers of other of anthropogenic mortality. piscivores in the habitat, including seabirds and harbor seals, have declined over a similar timescale in many 3. Western North Pacific Steller’s Sea Lion, parts of the sea lion range. However, fishing activity Eumetopius jubatus (Schreber, 1776) may be intensive near important sea lion breeding loca- Steller’s sea lions occur in coastal waters of the North tions, and it has not been possible to eliminate competi- Pacific Rim from southern California to northern Japan tion with fisheries as a potential cause of the decline. and in the Bering Sea and Sea of Okhotsk. Recent genetic Recent rulings in U.S. courts have restricted fishing data are the basis for dividing the species into two activity in some locations and seasons for the purpose populations, western and eastern, with the boundary at of reducing the rate of decline, thus intensifying the Cape Suckling, Alaska (144ЊW longitude). The eastern associated political debate. population is dispersed along the west coast of North Several viability analyses have been applied to Stel- America, numbers more than 20,000 individuals, and ler’s sea lion population data. Model results lead to is increasing gradually, particularly in southeastern extinction of the western population in all cases. Median Alaska. The western population occupies the Bering estimates of time to extinction range from 62 to 160 Sea, Aleutian and Commander Islands, and remote loca- years. The combination of ongoing decline, projected tions of the Russian Far East. The western population extinction risks, and uncertainty about primary risk numbered approximately 150,000 animals in the 1950s factors leads to significant concern about the persistence but has since declined precipitously, with current num- of the western population. Because natural oceano- bers estimated at approximately 39,500. The rate of graphic changes can neither be predicted nor con- decline has varied over time, with highest rates (approx- trolled, management authorities have no choice but to imately 15% per year) from 1985 until 1990. The de- focus on understanding and minimizing anthropogenic cline currently continues. risk factors, despite the political consequences, in order The cause or causes of decline in the western popula- to reduce the probability of eventual extinction. tion of Steller’s sea lions are not understood. Possible risk factors include incidental take in fishing gear, com- 4. West Indian Manatee, Trichechus petition with fisheries for prey in common, hunting manatus Linnaeus, 1758 by indigenous peoples, illegal hunting or harassment, West Indian manatees occur in coastal habitats and inadvertent rookery disturbance, disease or parasitism, the lower reaches of rivers in the southeastern United predation by killer whales, contaminants, and changes States, the islands of the Caribbean Sea, and the main- in the structure and productivity in the marine ecosys- land shores of the Gulf of Mexico, Central America, tems of which Steller’s sea lions are a part. Based on and northeastern South America. Two subspecies are extensive research since the decline was first recog- recognized. The Florida manatee [Trichechus manatus nized, the current consensus opinion is that ecosystem latirostris (Harlan, 1824)] is found in U.S. coastal wa- change or competition with fisheries are the most likely ters, especially in Florida. The Antillean manatee (T. factors driving the decline. Resolution of the question manatus manatus Linnaeus, 1758) occupies the remain- of cause has become the focus of intensive political der of the range of the species. The current population interest because of the potential economic conse- in Florida is the largest of the species, numbering 2000– quences. The groundfish fisheries of the Gulf of Alaska 3000. Despite a broad perception of increasing numbers and the Bering Sea are the most valuable and highly in Florida, population data lack the statistical power to capitalized of the fisheries in the coastal waters of the document a positive trend with confidence. Population United States. Steller’s sea lions feed extensively on structure, numbers, and trends in other locations are groundfish species, such as walleye pollock, targeted not well-known, but most populations probably num- by fisheries. Determination that competition with fish- ber no more than a few hundred animals. eries is contributing to the decline could result in forced Manatees have been hunted by indigenous peoples reduction of fishing effort, with great economic loss for meat and other products for centuries. Commercial and political discord. hunting probably contributed to a reduction of popula- Several lines of evidence favor the argument that tion sizes, but apparently there are few data available ecosystem change has contributed to the decline in sea to assess the rates or significance of commercial harvest. MARINE MAMMALS, EXTINCTIONS OF 61

Manatees have been protected from all forms of directed 5. California Sea Otter, Enhydra lutris harvest in Florida since the 1960s, but subsistence har- nereis (Merriam, 1904) vest for meat and oil and for ceremonial purposes con- Sea otters originally ranged throughout the coastal wa- tinues in other populations. During the twentieth cen- ters of California, including San Francisco Bay and the tury many risk factors for manatees emerged, all in southern California islands. The population was origi- association with an expanding human population in nally contiguous with other otter populations ranging immediate proximity to manatee habitat. The primary from the central outer coast of Baja California, Mexico, problems are a variety of modifications and ongoing through the North Pacific Rim to northern Japan. Sea disturbances of habitat. The latter include watercourse otters in California comprise one of three subspecies diversions and impoundments in aquatic manatee habi- currently recognized. tat and disturbance and collision risk associated with Sea otters have probably been hunted by indigenous recreational boating in aquatic and marine manatee hab- peoples of the North Pacific Rim for several millennia itats. There is also continuing concern about increased for meat and pelts and for ceremonial purposes. Obser- levels of contaminants. vations of the Bering Expedition of 1741 and 1742 and Long-term studies of stranded carcasses indicate other voyages of exploration in the North Pacific found three major sources of mortality in Florida manatees. abundant sea otters throughout their range. Commer- Perinatal mortalities are newborn animals with the cial harvest of sea otters for pelts began with the Bering proximate cause of death uncertain but possibly linked Expedition. In California the hunt was pursued by Rus- to contaminants. Significant mortality rates are also as- sians, often utilizing enslaved Aleut hunters, and by sociated with entrapment in dam floodgates and colli- sion with recreational powerboats. Manatees clearly hunters from Spain, Mexico, and the United States. All prefer areas without significant powerboat traffic. The commercial hunts for sea otters were terminated in ongoing expansion of human populations and associ- 1911 with approval of the Treaty for the Preservation ated demand for recreational opportunities inevitably and Protection of Fur Seals (37 Stat. 1542, T.S. No. leads to continuing reduction in the size of available 542) by Japan, Russia, Great Britain, and the United manatee habitat. States. The treaty included a passage affording protec- Manatees are sensitive to water temperature and typi- tion to sea otters. However, in California and Mexico cally congregate in warm-water refugia during winter, the sea otter populations were depleted commercially especially when ambient sea surface temperatures drop by the 1860s. By 1900, only two small populations below approximately 18ЊC. Refugia include natural survived. One was along the Big Sur coast south of the warm aquatic springs and lagoons associated with ther- Monterey Peninsula, numbering approximately 50–100 mal effluent from electrical generating plants. The lim- animals. The second, of unknown size off the San ited size and number of natural refugia may be threat- Benito Islands, Mexico, was extinct by the 1920s. The ened by the encroaching effects of human development Big Sur population grew at a rate of approximately 5% and activity. Use of power plant lagoons may be risky per year through much of the twentieth century and if plant operations dictate precipitous shutdown, re- now numbers approximately 2000–2500 animals, rang- sulting in cutoff of thermal effluent and rapid chilling ing from San Francisco southward to Point Conception. of lagoons. The observed rate of growth in California has been Manatees in Florida have experienced several sig- much lower than rates commonly observed in more nificant mass mortalities in recent years. The mortality northerly populations with protection from harvest and events apparently result from an interaction of compro- available adjacent vacant habitat. In the late 1980s a mised immune systems, disease, and natural toxins as- new colony was established by translocation at San sociated with phytoplankton blooms. Nicolas Island off southern California. The colony now Habitat loss and disturbance is the primary conserva- numbers approximately 20 animals and persistence re- tion problem for all populations of West Indian mana- mains uncertain. tee, and subsistence or illegal harvest remain significant Several risk factors are known for sea otters in Cali- risk factors for populations outside of Florida. Over the fornia. Nearshore net fisheries are responsible for long term, avoidance of extinction will require cessation significant rates of incidental take. Changes in fishery of all forms of human harvest and an effective, broadly regulations have reduced but not eliminated incidental supported strategy for balancing the habitat needs of take. Sea otters are known to compete with nearshore manatees with the consequences of human population marine shellfish fisheries in California, particularly for growth, especially in Florida. abalones, sea urchins, clams, and crabs. Concern about 62 MARINE MAMMALS, EXTINCTIONS OF interactions of sea otters and shellfisheries is sufficient currently unknown do not appear. We present case that it was until recently the policy of the U.S. federal summaries for five taxa, selected arbitrarily, to illustrate government to actively remove and relocate individual patterns typical of the group. otters found along the California coast south of Point Conception in order to minimize damage to shellfish- eries. The management effort was done despite the 2. Western Arctic Population of the small size of the sea otter population, its precarious Bowhead Whale, Balaena mysticetus status, and various state and federal legal protections Linnaeus, 1758 including a listing as ‘‘Threatened’’ under the auspices Bowhead whales occur in at least five populations in of the U.S. Endangered Species Act of 1973 (ESA) [16 northern habitats characterized by frequent sea ice. U.S. Code §§1531-43 (Supp. IV 1974)] as amended. Four of the five populations are small and at risk of Relocation efforts were inefficient and costly, and extinction (Table III). The western Arctic population alternative management protocols are now in active is by far the largest of the bowhead populations, num- development. There is also concern about illegal killing bering approximately 8000 individuals with annual of sea otters to protect shellfisheries, but little direct growth rates averaging 2%. The population ranges in evidence of a significant problem. The California sea the Bering, Chukchi, and Beaufort Seas, migrating otter population is also regarded to be at high risk northeasterly to the Beaufort Sea in spring and returning of potential damage from oil spills, although oil spills to the Bering and Chukchi Seas in the fall. have yet to cause sea otter mortality in California. The western Arctic population of bowhead whales Oiling mats the pelage and eliminates thermoregula- probably numbered approximately 23,000 individuals tory function, rapidly leading to chilling and death. when first exploited by U.S. whalers during the late Oiling is also known to cause other respiratory and 1840s. By the demise of the commercial harvest in 1919, physiological pathologies. approximately 20,000 whales had been taken, and During the 1990s, the growth of the population the population was thought to include approximately slowed, and currently the population is declining at 1 1000 individuals. or 2% per year. A clear consensus on the cause of the Bowhead whales have been hunted for subsistence decline has not emerged, but primary risk factors are and ceremonial purposes by the indigenous peoples of thought to be ongoing incidental taking in fishing nets, Alaska, western Canada, and Russia for many centuries. effects of contaminants, and the emergence of mortali- Russian and Alaskan native villages continue to harvest ties from diseases and exotic parasites not previously whales from the western Arctic population based on a associated with sea otters. The long-term survival of the quota approved by the International Whaling Com- sea otter population in California will require ongoing mission (IWC) and, in Alaska, managed jointly by research to more effectively characterize current risk representatives of native villages and U.S. federal agen- factors and the development of strategies to minimize cies. Management policies have been successful, allow- associated mortalities. The large and growing human ing continued growth of the population despite annual population in California is a major underlying cause of hunts for whales by several villages. In recent years, the jeopardy status of sea otters, and broad popular the annual native harvest has been 20–50 whales in support, including economic compromise by shellfish- Alaska. For many years, there has been concern about ery and marine oil interests, likely will be required if effects of marine petroleum exploration and develop- recovery is to be successful. ment activities in the habitat of bowhead whales, espe- cially in the Beaufort Sea. Offshore oil activity is known to influence movement patterns of whales during migra- E. Species, Subspecies, and Populations tion, but demographic effects have not been demon- Once Thought to Be Near Extinction But strated to our knowledge. Now Showing Evidence of Recovery The western Arctic bowhead whale population ap- pears to be recovering while other bowhead whale pop- 1. Synopsis ulations are not. The most likely reason is that other Here, we summarize data for eight species, subspecies, populations were pushed much closer to extinction by or populations of marine mammals that have been near commercial whaling, limiting the capacity for recovery. extinction in the recent past but are now either recov- It appears that the western Arctic population will con- ered or en route to recovery (Table V). We regard the tinue to recover as long as harvests by native villages taxa or populations in this group as unlikely to become are regulated conservatively and other significant risk extinct in the foreseeable future as long as risk factors factors do not emerge. MARINE MAMMALS, EXTINCTIONS OF 63

TABLE V Species, Subspecies, or Populations Once Thought to Be Near Extinction But Now Showing Evidence of Increasing Numbers

Population identity/ Estimated population Taxon or population Range/habitat structure size Primary risk factors

Western Arctic population Coastal and pelagic, Arctic One population Approximately 8000 Commercial whaling, dis- of the bowhead whale: and subarctic turbance from offshore Balaena mysticetus Lin- petroleum exploration naeus, 1758 and development Humpback whale: Megapt- Coastal and pelagic in all Five populations in the Recent surveys in the Commercial whaling, inci- era novaeangliae (Borow- oceans and seas except Southern Hemisphere, North Pacific indicate dental take in fishing ski, 1781) the Arctic polar region three in the North Pa- 6000–8000 individu- nets, habitat distur- cific, one in the North als, with aggregate pop- bance from recreational Atlantic, and one in the ulation growth rates of vessels Arabian Sea approximately 7% per year; numbers are not well-known for other populations Eastern North Pacific gray Coastal from the Bering One population 25,000–30,000 individu- Commercial whaling, inci- whale: Eschrichtius ro- and Chukchi Seas south- als; population growth dental take in fishing bustus (Lillje- ward to the southern rate may be declining nets, habitat distur- borg, 1861) Gulf of California, Mex- as the population ap- bance from industrializa- ico, along the west proaches carrying ca- tion and recreational coast of North America pacity boating in and near breeding lagoons in Mexico and along migra- tion route Northern elephant seal: Breeding and molting sea- Separate breeding colonies Approximately 200,000 in- Commercial sealing, dis- Mirounga angustirostris sons: coastal, on island at each of the major dividuals, increasing at turbance of breeding (Gill, 1866) and mainland haul-outs haulouts; exchange approximately 6% per colonies along the Pacific coast among colonies is year of northern Mexico and known to occur California: Other sea- sons: Pelagic in cool- temperate and subpolar latitudes of the North Pacific Galapagos fur seal: Arcto- Coastal and pelagic habi- Separate breeding colonies Approximately 30,000– Commercial sealing, habi- cephalus galapagoensis tats of the Galapagos Ar- at each of the major 35,000 individuals; tat disturbance Heller, 1904 chipelago haulouts; exchange thought to be increas- among colonies is ing in numbers known to occur Subantarctic fur seal: Arcto- Subantarctic islands north Separate breeding colonies Approximately 300,000– Commerical sealing, habi- cephalus tropicalis of the Antarctic conver- at each of the major 400,000 individuals; tat disturbance (Gray, 1872) gence zone in the Ant- haulouts; population thought to be increas- arctic Ocean structure is otherwise ing in numbers unknown Antarctic fur seal: Arcto- Subantarctic islands south Separate breeding colonies Approximately 1,200,000 Commercial sealing, habi- cephalus gazella (Peters, and, in a few cases, at each of the major individuals; thought to tat disturbance, entan- 1875) slightly north of the haulouts; population be increasing in glement in marine Antarctic convergence structure is otherwise numbers debris zone in the Antarctic unknown Ocean Northern and Russian sea Shallow marine habitats Northern subspecies Approximately 100,000 in- Commerical hunting, inci- Otter: Enhydra lutris ken- along the exposed outer ranges from western Al- dividuals in Alaska and dental take in fishing yoni Wilson, 1991, and coast eutian Islands to the Co- approximately 20,000 nets, contaminants, in- E. l. lutris (Linnaeus, lumbia River mouth; individuals in Russia; creased predation rates 1758) Russian population data for many Alaskan by killer whales ranges through the locations are obsolete; Commander and Kuril populations in the Aleu- Islands, southern Kam- tian Archipelago may chatka, and northern be declining rapidly Hokkaido 64 MARINE MAMMALS, EXTINCTIONS OF

3. Humpback Whale, Megaptera region during summer to the shallow protected coastal novaeangliae (Borowski, 1781) lagoons of Baja California, Mexico, during winter Humpback whales are distributed globally in marine months. The annual migration of this population is habitats. At least five populations are recognized in the among the lengthiest of the world’s mammals and is Southern Hemisphere, three in the North Pacific, and the best documented and most familiar of the cetaceans. two in the North Atlantic. An unusual nonmigratory Eastern gray whales were hunted intensively by com- population occurs in the Arabian Sea. Humpback mercial whalers from the eighteenth through the early whales often are found near shore. Lengthy seasonal twentieth centuries. Preexploitation estimates of popu- migrations between high-latitude summer feeding areas lation size are inconsistent and difficult to interpret. and low-latitude winter breeding areas are well docu- The population may have reached a minimum of ap- mented for all populations except as noted. proximately 4000 individuals in the late 1890s. The Humpback whales were among the earliest target population numbered approximately 11,000 individu- species of commercial whalers because of their abun- als when regular quantitative surveys were begun in dance, large size, and coastal distribution. During twen- 1967. Based on 19 surveys over a span of 30 years, tieth-century commercial hunts in the southern ocean, the current population is thought to be about 27,000 several hundred thousand individuals were taken. Ille- individuals. Patterns in population trend, observed gal harvest by whalers from the USSR was extensive adult mortality rates, and the number of whales in un- and damaging to populations following the decline of usual locations during summer all support the percep- large-scale legal commercial whaling. Subsistence har- tion that the population is approaching carrying capac- vest by indigenous peoples was common in previous ity. In 1994, the eastern gray whale was the first marine centuries. Additional modern risk factors include inci- mammal to be removed from the ESA ‘‘List of Endan- dental take in fishing nets and habitat disturbance by gered Species.’’ large recreational cruise ships. Several issues are of current concern for eastern gray Although trends in most populations have not been whales. Modest rates of incidental take in fishing nets confidently documented, there is a broad perception are reported. Disturbances by boats supporting ‘‘whale- that humpback whale numbers are increasing on a watching’’ activities are of concern, both in migratory global scale. Recent estimates are 9000–12,000 individ- corridors along the heavily populated west coast of uals in the North Atlantic and a combined total of North America and in the breeding and calving lagoons 6000–8000 individuals in the North Pacific. Data from in Mexico. Recently suspended plans to expand salt the Southern Hemisphere and the Arabian Gulf are not extraction industries at Mexican lagoons drew substan- sufficient to develop confident population estimates. tial opposition from those interested in gray whale con- There is concern that the population wintering near servation. Possible demographic damage to gray whales Tonga, in the western South Pacific, may have experi- by existing saltworks remains a matter of speculation. enced excessive subsistence harvests in recent decades, Eastern gray whales are subject to ongoing annual although the hunt has been stopped. The eastern and subsistence harvests by indigenous peoples in Russia, western North Pacific population remain small enough Alaska, and Washington state. The subsistence harvests to be of ongoing concern. The relatively small Arabian are authorized by IWC quota and, in the United States, Gulf population came to be known because of extensive are comanaged by village elders and government agen- Soviet whaling in the 1960s. Recent concerns have been cies. Subsistence hunts have taken over 100 whales expressed over sustainability of current levels of inci- per year for several decades, with 95% of the harvest dental taking by local fisheries. We suggest that pros- occurring along the Russian coast of the Bering and pects for survival of humpback whales, as a species, are Chukchi Seas during summer months. In 1998, the good as long as commercial harvests are not resumed, Makah tribe of northwestern Washington state was allo- incidental taking is reduced, and habitat disturbance cated a harvest quota of 5 whales per year for 4 years by human activities continues to be restricted and care- in exchange for a comparable reduction of the quota fully monitored. for Russian and Alaskan hunts. The allocation of harvest quota to the Makah people was consistent with the Treaty of Neah Bay of 1855 (12 Stat. 939) between the 4. Eastern North Pacific Gray Whale, Makah tribe and the U.S. government. One whale was Eschrichtius robustus (Lilljeborg, 1861) taken in 1999 by Makah hunters. The eastern North Pacific population of gray whales In our opinion, the eastern gray whale population ranges from the Bering and Chukchi Seas of the Arctic is no longer at risk of extinction in the foreseeable MARINE MAMMALS, EXTINCTIONS OF 65 future. The status of the population should remain good harvests. In contrast, several of the southern elephant as long as subsistence harvests are conservative and seal populations currently in decline have much higher carefully managed in the context of emerging knowl- levels of measured genetic diversity than those of the edge of population structure. Increasing problems with northern species. incidental taking, disturbance by boats, and industrial- The elimination of commercial harvest has allowed ization at the calving/breeding lagoons in Mexico must northern elephant seals to recover fully from near ex- be monitored and regulated to ensure that these issues tinction despite a loss of genetic diversity. Most current are specifically managed. management concerns for the species involve perceived problems of overabundance rather than rarity. Indefi- 5. Northern Elephant Seal, Mirounga nite survival should be ensured as long as harvests and angustirostris (Gill, 1866) disturbances to habitat can be monitored and con- Northern elephant seals breed and molt on coastal trolled. islands of Baja California, Mexico, and southern and 6. Northern and Russian Subspecies of the central California. Since 1975, at least four mainland breeding and molting colonies have developed in cen- Sea Otter, Enhydra lutris kenyoni tral California. When not hauled out, northern elephant Wilson, 1991, and E. lutris lutris seals forage in pelagic habitats of the temperate and (Linnaeus, 1758) subpolar North Pacific. Two complete migrations are The northern subspecies of sea otter ranges from the made each year between hauling sites and foraging habi- Aleutian Archipelago eastward and southward along tats. Seals pup, nurse, and wean young and breed from the coasts of Alaska, British Columbia, and Washington December through mid-March at the hauling sites, then to the mouth of the Columbia River. The Russian sub- they swim north to forage. They return to haulouts to species ranges from northern Hokkaido, Japan, through molt during spring and early summer, and then return the Kuril Archipelago to southern Kamchatka and the again to foraging areas. Schedules for migration vary Commander Islands. Preexploitation estimates of popu- among age and sex categories. When hauled out, ele- lation size are not available. As noted in Section II,D,6, phant seals are concentrated at high density. Hauled large-scale commercial hunting of sea otters for pelts seals are easily approached by humans, even more so began in 1741. By the time legal hunting ended in 1911, than other land-breeding pinnipeds of North America. the combined number of individuals in both subspecies Northern elephant seals have been utilized for food was probably less than 2000 individuals, scattered and oil over the centuries by native peoples of North among 10 isolated remnant populations from the Queen America. Intensive commercial harvests for oil began Charlotte Islands, Canada, to the Kuril Islands. The early in the nineteenth century. Most colonies of seals Queen Charlotte population was extinct soon after. The were severely depleted by 1850, but commercial har- two subspecies of sea otter have been subject to ongoing vests continued until 1884, at which point the species subsistence harvest by native peoples for meat and pelts, was considered extinct. Subsequent discoveries of small probably for many centuries. numbers led to continued harvests by scientific collec- Populations from Prince William Sound westward tors working for museums of natural history, including have largely recovered without assistance, other than the Smithsonian Institution. Scientific collecting con- prohibition of harvest, during the twentieth century. tinued until at least 1911. The total number of surviving Observed annual population growth rates have been as seals is thought to have been as low as 20–100 in high as 10–15% in some cases. From the 1950s through 1890. At the time harvests finally ended, elephant seals the early 1970s, several translocation projects were at- survived only at Guadalupe Island off the west coast of tempted, moving groups of animals from Prince Wil- Baja California. liam Sound and Amchitka Island eastward to the Pribi- Northern elephant seals numbered approximately lof Islands, southeastern Alaska, British Columbia, 127,000 individuals in 1991. The total is probably now Washington, and Oregon. The projects in the Pribilofs approaching 200,000. They occupy at least 16 major and Oregon failed, but all others succeeded, producing hauling sites in Mexico and California. Population large populations in southeastern Alaska and small but growth has been approximately 6% per year through rapidly growing populations off British Columbia and the latter half of the twentieth century. Recent studies Washington. indicate a marked lack of genetic diversity at examined Illegal commercial harvest of sea otters has been loci, almost certainly a result of the severe population an occasional problem throughout the range. Poaching ‘‘bottleneck’’ associated with commercial and museum increased in Kamchatka with the development of eco- 66 MARINE MAMMALS, EXTINCTIONS OF nomic crises following the fall of the Soviet Union in the past and usually for commercial purposes, reducing 1991. The current scope of the poaching problem is numbers to a small fraction of preexploitation status. unknown. Legal subsistence harvest by native villages In this category we find taxa or populations from all in Alaska has averaged approximately 500 animals per marine locations on Earth, including many that are year since the mid-1980s. The harvest is concentrated distant from human population centers. The second primarily in Prince William Sound and southeastern is a combination of risk factors strongly linked to a Alaska. The Exxon Valdez oil spill of 1989 killed several proximate and encroaching human population. The fac- thousand sea otters in Prince William Sound and nearby tors include habitat loss or chronic habitat disturbance, coastal areas. Despite the intensive public interest and incidental taking in fishing gear, and contaminants as media coverage that facilitated apocalyptic scenarios, it well as directed harvests. The second category primarily appears that sea otter numbers in the sound did not includes taxa or populations restricted ecologically to a experience long-term reduction, with the possible ex- limited geographic range in nearshore marine or aquatic ception of a few local areas most heavily affected by habitats. Here, we consider the vulnerabilities of taxa the oil spill. Some effects on sea otter prey populations or populations in the two categories. and habitats may persist to the present, but sea otter The first category primarily involves excessive di- numbers are large and increasing in most areas affected rected harvest. All species of mysticetes, the larger by the spill. odontocetes, nearly all pinnipeds, the marine otters, Currently, Russian sea otter populations include ap- and the polar bear have been hunted extensively at least proximately 20,000 individuals and are viewed as stable during the past few centuries, in most cases in order and near carrying capacity. Alaskan populations num- to obtain articles of commerce. Most exploited taxa lack ber approximately 100,000 individuals, although many the necessary demographic features to sustain viable of the survey data are obsolete. Recently, some popula- populations at the level of harvest experienced (see tions in the Aleutian Islands have declined rapidly for Section I,C,6). There are two important results. First, unknown causes. There has been speculation about such exploitation has often reduced populations to possible effects of contaminants and of increased rates small sizes. Second, populations so affected require de- of predation on sea otters by killer whales. A clear cades or even centuries to recover to levels free of the understanding of the scope and causes of the apparent risks of extinction. Directed, commercial-scale harvests declines will require new survey data and more defini- of marine mammals ended for most species during the tive studies of population risk factors. twentieth century, and many species are now subject We are confident that northern and Russian sea ot- to rigorous protection. However, the risk of extinction ters have largely recovered from the excessive harvests persists for reduced populations despite relaxation of of the eighteenth and nineteenth centuries and are free harvest activity. of significant extinction risk for the twenty-first cen- Small populations are vulnerable to any factor that tury. For sea otters to remain out of jeopardy, legal reduces survival or collective reproductive success. Sur- harvests must be conservatively regulated, and all possi- vival and reproduction can be impaired by anthropo- ble efforts must be made to reduce or eliminate inciden- genic factors, such as contaminants or disturbance to tal taking, poaching, contaminants, and oil spills. The critically important breeding locations, or by natural recent population declines in the Aleutian Islands are fluctuations in the biological habitat. Anthropogenic a concern and must be evaluated carefully. factors should be controllable in principle by the appro- priate management actions, but in reality effective risk management is difficult and often fails. Natural fluctua- tions are effectively stochastic in timing, duration, and III. DISCUSSION intensity and cannot be anticipated or controlled by any form of management authority. Precautionary A. Synopsis of Factors and Processes management can, however, reduce risks associated with Known to Be Facilitating Modern stochastic events in some cases. Anthropogenic Extinctions of Once marine mammal populations are reduced, they recover slowly and are therefore at risk of the damaging Marine Mammals effects of anthropogenic or natural disturbances over In our review of taxa and populations of marine mam- an extended period even under the most rigorous pro- mals currently in jeopardy of anthropogenic extinction, tection. For example, North Atlantic right whales have there are two major, recurring categories of vulnerabil- not been harvested for decades, but the harvest reduced ity. The first is prolonged excessive harvest, primarily in them to low numbers. Now, even modest rates of ship- MARINE MAMMALS, EXTINCTIONS OF 67 strike mortality or incidental take in fishing gear are peoples is without question a serious risk factor for adequate to hold the population at a dangerously small Cook Inlet beluga whales, and it may have been a crucial size. A major change in ocean productivity, however precursor to the extinction of Steller’s sea cow. How- brief, could easily push the populations to virtual ex- ever, the western Arctic bowhead whale population has tinction without any possibility of effective human in- been increasing steadily for years despite regular annual tervention. subsistence harvest. Thus, subsistence harvests are The second category involves a group of factors asso- manageable risk factors and need not be regarded uni- ciated with increasing human populations in coastal versally as unacceptable practice. None of the other regions, interacting with taxa or populations con- listed factors are alone causing widespread extinction strained to life in the coastal zone. Species in this cate- risk, although there are isolated examples for each. Of gory include the sirenians, river dolphins, and several greater concern here is the problem of significant coastal odontocetes. The essential problem here is that effects from the interaction of multiple factors. The increasing human populations produce a suite of ef- best known cases involve mass mortalities that result fects, each damaging to proximate marine mammal pop- from disease outbreaks. Such outbreaks often result ulations. Reduction of the effects often requires a delib- from immunosuppression, which in turn may result erate curtailment of economic enterprise such as fishing from contaminants or from natural disturbances such or of institutional infrastructure such as waste disposal, as the toxic by-products of certain phytoplankton. flood control, or the provision of drinking water. The Interacting factors are often a problem near human emergent dilemma is the perception by political institu- population centers and are difficult, if not impossible, tions that there must be a choice between human wel- to manage. Thus, we believe that the danger of many fare and the welfare of nearby marine mammals. Our risk factors discussed here is not the direct effect of case studies suggest that, given the choice, human cul- a single factor but rather the synergistic effects of tures of major population centers act in favor of human multiple factors that may be less damaging when needs. Thus, for example, recreational boating activities separated from one another. continue to crowd needed habitat for manatees in Flor- The detection of extinction risks for both categories ida despite 20 years of documentation that manatees of species will continue to be confounded by the inher- do not tolerate powerboat activities. Fishing interests ent uncertainties of population data for marine mam- continue to set nets in vaquita habitat despite general mals. Several kinds of errors are possible in the future, recognition that incidental take is driving the popula- although predictions of error rate are beyond the scope tion to extinction. The latter case is complicated by the of this review. Populations that are numerically stable lack of economic alternatives for the artisanal fishers may be categorized incorrectly as declining and will of the region. receive unwarranted research effort. Declining popula- Species in our first category have reasonable proba- tions may be categorized incorrectly as stable and may bility of survival, given some luck. Sea otters and north- be denied attention from survey efforts necessary to ern elephant seals have escaped the window of vulnera- detect problems and plan recovery actions. Recovery bility associated with small population size, and other efforts may be directed to one component of life history, taxa seem well on their way. Some taxa or populations such as juvenile survival, when similar efforts toward probably will not persist. Northern right whales and other components, such as adult female survival, could western gray whales will survive the new century only produce far greater return for the same effort. All the with good fortune and the most rigorous imaginable error types will be more likely to influence perceptions protection. We are less optimistic about species in our of small populations in remote locations, where the second category. Their ultimate survival depends on incremental cost of survey effort is prohibitively large. conscious economic restraint by human cultures and a possible reevaluation of values regarding the survival of marine mammals and other species in habitats also B. Geographic Regions of Greatest used or coveted by people. Concern with Regard to Anthropogenic Excessive subsistence harvests, anthropogenic noise, contaminants, oil spills, and depletion of genetic diver- Extinctions of Marine Mammals sity are issues that have at least occasionally been in- As previously suggested, marine mammal taxa and pop- voked as risk factors for extinction of marine mammals. ulations constrained to life near human population cen- We find that there are relatively few taxa or populations ters are in general most vulnerable to anthropogenic clearly falling toward extinction as the direct result of extinction. Extinction risks will be greatest where hu- any one of these factors. Subsistence harvest by native man cultures have the fewest economic options when 68 MARINE MAMMALS, EXTINCTIONS OF confronted with the need for restraint in order to solve pinnipeds, sea otters, and polar bears. Many small ceta- conservation problems. Such circumstances are most ceans, some pinnipeds, and some sirenians are not ac- likely in ‘‘developing’’ countries at lower and middle tively and explicitly protected at the national or interna- latitudes in which large concentrations of people face tional level. Second, many of the populations subject ongoing economic shortfalls. During the next century, to active protection are very small and as a consequence we anticipate the greatest extinction risks for coastal will be subject to risks associated with stochastic events, marine or aquatic marine mammals off southern and both natural and anthropogenic, for many decades. southeastern Asia, eastern Europe, Central America, Thus, some extinctions are possible because not all and central Africa. High rates of per capita resource species are equally protected, and because the most consumption in the ‘‘developed’’ countries are also aggressive protection cannot eliminate all risk factors. linked to risk factors for marine mammal populations. Third, the crucial process of detecting trends in small Thus, extinction risks are a significant concern for distant populations is so costly that errors are likely coastal marine mammals off North America and western in determining which populations are most seriously Europe. Example cases include manatees in Florida, sea jeopardized. Thus, despite the best of human intentions, otters off California, and ringed seals in Lake Saimaa, protective effort may be directed inadvertently to the Finland. wrong taxa or populations. Marine mammals in the Southern Hemisphere gener- The group of risk factors associated with human ally should be at lower risk of extinction during the population growth will almost certainly cause some next century than those in the north. Most major human extinctions of coastal marine mammals in the next population centers and most cases of coastal habitat century. Here, we believe that the outcome is more degradation occur in the Northern Hemisphere. How- certain, and the methods of prevention more intracta- ever, some southern populations remain small because ble, than in the simpler cases of small populations dis- of past excessive harvests. Thus, distantly located south- tant from major concentrations of people. Effective pro- ern taxa and populations will be removed from the risk tection of imperiled species requires that human of extinction only to the extent that all forms of harvest cultures forego economic benefits for the good of jeop- are regulated with extreme caution and conservatism. ardized marine mammals. Such sacrifices must extend Moreover, small distant populations are at risk of incor- indefinitely to be effective, given the demographic limi- rect conclusions about number of individuals, trend in tations of most marine mammals. The acceptance of numbers, or demographic characteristics because of the foregone benefits is most needed in cultures least able statistical limitations associated with survey and demo- (‘‘developing’’ countries) or most unwilling (‘‘devel- graphic data. oped’’ countries) to accommodate the loss. Cultural acceptance of economic loss motivated by a conserva- tion ethic will require education, reorientation, and C. General Approaches toward provision of meaningful economic alternatives at a level Minimizing the Rate of Anthropogenic of effectiveness that we find difficult to imagine. We conclude with the reminder than both evolution Extinctions of Marine Mammals and extinction of species have been characteristic fea- Excessive directed harvests have caused more cases of tures of the history of marine mammal taxa on Earth jeopardized marine mammal taxa and populations than since the early Eocene. Although the anthropogenic any other single factor. Thus, the most direct and loss of species is both regrettable and inevitable, there straightforward approach to the control of extinction is no reason to deny that new species will evolve as risk for marine mammals is a precautionary approach well. For example, killer whales off Washington and to the concept of marine mammal harvest on a global British Columbia occur in three distinctive social con- scale. Fortunately, this is the approach currently figurations that correlate with subtle but reliable mor- adopted by many governments, and by international phological differences. Individuals in the different cate- regulatory cooperatives such as IWC, for some species. gories have entirely different diets, different acoustic In this context, we offer three points of caution. First, repertoires, rarely co-occur in space, and do not inter- the protections provided by international treaties and breed. Some have characterized these patterns as a step conventions such as the IWC, and by individual govern- in the process of speciation, although there are alterna- ments, do not necessarily extend to all marine mam- tive viewpoints. The human mind can easily perceive mals. 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