SUMMARY OF VOLUME 4:
Sea Mammals OTARIIDAE (Eared Seals) ODOBENIDAE (Walrus) PHOCIDAE (Earless Seals) BALAENIDAE (Right and Bowhead Whales) NEOBALAENIDAE (Pygmy Right Whale) ESCHRICHTIIDAE (Gray Whale) BALAENOPTERIDAE (Rorquals) PHYSETERIDAE (Sperm Whale) KOGIIDAE (Pygmy and Dwarf Sperm Whales) ZIPHIIDAE (Beaked Whales) PLATANISTIDAE (South Asian River Dolphin) INIIDAE (Amazon River Dolphins) LIPOTIDAE (Baiji) PONTOPORIIDAE (Franciscana) MONODONTIDAE (Narwhal and Beluga) DELPHINIDAE (Ocean Dolphins) PHOCOENIDAE (Porpoises) TRICHECHIDAE (Manatees) DUGONGIDAE (Dugong)
VOLUME 1: Carnivores VOLUME 2: Hoofed Mammals VOLUME 3: Primates VOLUME 4: Sea Mammals VOLUME 5: Marsupials VOLUME 6: Rodents VOLUME 7: Insectivores VOLUME 8: Bats
Published by Lynx Edicions in association with Conservation International and IUCN Chief editors Don E. Wilson & Russell A. Mittermeier
TECHNICAL DETAILS: 310 x 240 mm 614 pages 30 color plates 667 photographs 147 distribution maps c. 2800 bibliographical references
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Cover photo by Doug Perrine/DRK PHOTO Southern Right Whale (Eubalaena australis)
FAMILY OTARIIDAE Eared Seals
Genetic differences between Australian Sea Lion colonies as little as a day’s swim from one another may be due to foraging specializations that restrict them to particular fine-scale ecotypes. Stable isotope analysis has identified significant variations in adult female Australian Sea Lion food consumption, indicating the use of alternative foraging ecotypes, which appear to remain stable over years. Young sea lions may learn how and where to forage from their mothers and older siblings. A study of Galapagos Sea Lions (Zalophus wollebaeki) suggests that behavioral decisions may be influenced by the degree of kin relatedness. Neophoca cinerea Seal Island, Shoalwater Islands Marine Park, Western Australia, Australia. Photo: Clay Bryce/ Lochman Transparencies
Other than movements to and from the shoreline, these young otariids do not learn how to swim, dive, forage, or travel to foraging areas by example from their mothers. Their behavior and response to weaning are innately programmed. In species with long lactation periods, such as sea lions, weaning can be initiated by aggressive interaction between the mother and her now large juvenile-age offspring, birth of a new offspring, and environmental variables. The highest mortality rates in most species of otariids occur in the first three years before they become sexually mature. The norm for sea lions and some fur seal species is an extended nursing period when females may forage at sea with nursing-age young or yearlings. Female sea lions often tolerate their nursing young right up to the birth of their next offspring, and some allow yearlings to nurse beyond this point. Steller Sea Lions nurse young, yearlings, and even two year olds. Young and juvenile sea lions
would presumably gain advantages from extended maternal care beyond the direct benefit of extra milk, including identifying foraging areas, learning foraging techniques, and gaining experience in diving, holding their breath, and predator identification and avoidance. Otariids, like all pinnipeds, almost invariably give birth to a single offspring per year. Twin births are very rare and usually result in the death of one or both offspring. Otariids have a bicornuate uterus. While one horn and ovary are involved in the development, birth, lactation, and recovery from birth, the other horn and ovary are preparing for ovulation and the pregnancy that almost immediately follows a birth. Reproductive rates are generally high for female otariids. Pregnancy rates vary among species from a low of 63% in Steller Sea Lions to 84% in Subantarctic Fur Seals, with rates in some age classes of certain species reaching as high as 93%.
The Australian Sea Lion feeds by day, on a variety of bottomdwelling fish, mollusks, and crustaceans, including whiting, Australian salmon (Arripis sp.), rays and small sharks, squid and cuttlefish, and small crabs. The sea lions often reach their regular feeding destinations by swimming along the sea bottom. Most feeding dives last between two and four minutes, and reach depths of 40–80 km. This individual has caught a striped cowfish (Aracana aurita), a fish species found on reefs and seagrass meadows at depths of from 10 m to more than 100 m. Neophoca cinerea Carnac Island, Western Australia, Australia. Photo: Tony Wu
FAMILY OTARIIDAE Eared Seals
The lactating female Galapagos Sea Lion feeds both day and night, in contrast to the Galapagos Fur Seal (Arctocephalus galapagoensis), which is exclusively a nocturnal feeder. Feeding at night may enable both species to pursue vertically migrating prey species when they are near the water’s surface. The feeding habits of Galapagos Sea Lions are not well studied, but they are known to eat sardines (Clupeidae), lanternfish (Myctophidae), deep-sea smelts (Bathylagidae), and squid. The individual shown here is pursuing a shoal of black-striped salema (Xenocys jessiae), a fish endemic to the Galapagos. Between bouts of nursing, lactating Galapagos Sea Lions go on foraging trips that last 0·5–3 days during the cool season, but they may be longer during the less productive warm season. The Galapagos Archipelago is a highly variable marine environment, where food shortages occur often, but at unpredictable intervals because of oceanographic changes associated with El Niño events. During these events, water temperatures increase, primary productivity decreases, and rates of sea lion and Galapagos Fur Seal mortality rise dramatically, especially among newborns and pre-weaning youngsters of up to three years old. The black-striped salema, which lives in shallow waters where temperatures rise quickly, has also been observed to be greatly affected by severe El Niño events.
Zalophus wollebaeki Cousin’s Rock, off E Santiago Island, Galapagos Islands. Photo: Norbert Probst/Imagebroker/ FLPA
FAMILY OTARIIDAE Eared Seals
Studies of maternal strategies in Juan Fernandez Fur Seals (Arctocephalus philippii), Subantarctic Fur Seals (A. tropicalis), and Guadalupe Fur Seals show that young of these three species are exposed to the longest periods of fasting of any otariid while the mother is feeding at sea. Mean duration of feeding trips of female Guadalupe Fur Seals was found to be 9–13·5 days, with a maximum of 24 days. Their feeding grounds may be hundreds of kilometers from the rookeries. Probably to compensate for these long fasts, the fat-rich milk of female Guadalupe Fur Seals is higher in energy than that reported for other temperate species. The young are nursed for 9–11 months, and some females with offspring may stay in the vicinity of Guadalupe Island until the following spring.
Arctocephalus townsendi Guadalupe Island, Baja California, Mexico. Photo: Jaime Rojo
Juan Fernandez Fur Seals, 15,000–17,000 Guadalupe Fur Seals, 355,000 California Sea Lions, 20,000–40,000 Galapagos Sea Lions (fluctuates widely), 106,000–118,000 Steller Sea Lions, 250,000–280,000 South American Sea Lions, c.12,000 New Zealand Sea Lions, and 13,800 Australian Sea Lions. All species of fur seals were heavily hunted beginning in the late 18th century, with numbers of most species being severely reduced to the brink of extinction. So decimated was the Guadalupe Fur Seal that it was considered extinct until rediscovered in the 1950s. The story is virtually the same for the Juan Fernandez Fur Seal. Now increasing, Guadalupe Fur Seals are beginning to reoccupy most of their former distribution and are breeding on former rookery islands. Antarctic Fur Seals are a dramatic success story, recovering from extremely low numbers to huge abundance, centered on the colony at South Georgia in the South Atlantic Ocean, where more than 95% of the population breeds. It has been argued that the relatively rapid recovery of the Antarctic Fur Seal is attributable to loss of most of the large whales in the Southern Ocean from earlier commercial whaling. This made huge quantities of the euphausiids (krill), a primary food item, available to fuel the recovery of the Antarctic Fur Seal. The two species of otariids endemic to the Galapagos Archipelago, the Galapagos Fur Seal and Galapagos Sea Lion, experience wide population fluctuations due to environmental changes brought on by cyclical El Niño weather patterns. El Niño events may trigger periods of reduced upwelling and primary productivity that critically reduce availability of marine prey. Production and survival rates of young-of-the-year and juveniles fall to low levels. When El Niño conditions persist for several years, the effect on populations of both species is dramatic. Several other species of otariids with restricted foraging areas are impacted by fisheries operations, low marine productivity, or some combination of both, and they are listed as Endangered or Near Threatened on The IUCN Red List. For example, the Australian Sea Lion breeds on a number of islands across southern Australia, but individuals are non-migratory and forage locally on benthic cephalopods and crustaceans, the latter an important fishery. New Zealand Sea Lions breed primarily on a small number of islands in the New Zealand subantarctic and forage in waters over the adjacent continental shelf. Their limited distribution and relatively small population size have made them vulnerable to diseases and mortality in trawl fisheries. Juan Fernandez Fur Seals breed only in the Juan Fernández Islands, foraging in pe-
lagic areas with low productivity off the west coast of Chile. Female Juan Fernandez Fur Seals have to make some of the longest foraging trips of any otariid; time and effort that females need to replenish their milk stores and feed their new offspring may be contributing factors to the species’ slow recovery. These species, with limited breeding and foraging distributions, are considered more vulnerable to environmental perturbations and direct and indirect conflict with fisheries, concentrated in their limited distributions, and they are at greater risk from disasters such as oil spills. California Sea Lions have benefited from protection, particularly in US waters. As a direct result of public disapproval of whaling and dolphin mortality in tuna fisheries, the USA enacted the Marine Mammal Protection Act in 1972. This law provides blanket protection for all species of marine mammals. Previously killed for vibrissae, reproductive organs, and bounties paid to protect fisheries, the California Sea Lion received immediate, complete protection. The population increased rapidly, and individuals began reoccupying old breeding areas in large numbers. They also began to forage over a larger area. Nevertheless, their increase in numbers and distribution has led to conflicts with both commercial and sport fisheries and their taking over jetties and piers for use as haul outs. Two otariids in the North Pacific Ocean have declined dramatically in the last three to four decades. The Steller Sea Lion and the Northern Fur Seal are imperiled for reasons that are not well understood. Numerous factors have been advanced to explain their declines, which correlate with declines in other marine mammal species in the North Pacific Ocean and Bering Sea ecosystems, such as Harbor Seals and Sea Otters (Enhydra lutris). One factor may be shifts in ocean conditions associated with the Pacific Decadal Oscillation, a cycling of the North Pacific Ocean and its atmosphere that causes marine productivity to increase and decrease, or otariid prey community composition to change, on a multi-decadal time scale. Other factors include overfishing of important prey, particularly those near rookery islands that lactating females depend upon, and predation by Killer Whales. Increased predation on pinnipeds and Sea Otters by Killer Whales has been linked to the decline in large whales due to earlier commercial whaling, forcing Killer Whales to turn to smaller marine mammal species as prey. Several of these factors could work simultaneously in this complex ecosystem, combining to put pressure on these species of otariids, and may compromise them unevenly in parts of their distributions. For
FAMILY OTARIIDAE Eared Seals
The young Australian Sea Lion begins to swim on its own at around two months old, but it remains in sheltered inshore waters to begin with. The mother sea lions accompany their offspring in the sea until after the post-natal molt is completed. The youngsterâ€™s ability to dive increases with age, but development is slow. At six months old, young fitted with time/depth recorders show only minimal diving activity, and even at 23 months, mean dive depth is only 44Â m, or 62% of adult mean depth. Their smaller size means they have to work harder to reach the sea bottom, where they feed. These young sea lions are nursed into their second year, but even so, they are weaned before they have reached their full diving ability. Australian Sea Lions appear to use different foraging grounds at different ages, and expand their ranges as they grow. However, the home range of a 23-month old juvenile has been found to be less than one-half the adult female home range. Female sea lions may forage at sea with their nursing-age and newly weaned offspring. In contrast, the fur seal species of high latitudes must reach independence early. When weaned at four months of age, juvenile Northern Fur Seals (Callorhinus ursinus) head to sea and do not return to their colonies for two to three years. During this time, they remain at sea and do not haul-out on land. Some young fur seals may be weaned forcibly and abruptly because their mothers never return from foraging. These young otariids cannot learn how to swim, dive, forage, or travel to foraging areas by example from their mothers; however, their behavior and response to weaning are innately programmed.
Neophoca cinerea Green Head, Jurien Bay Marine Park, Western Australia, Australia. Photo: Alex Steffe/ Lochman Transparencies
PLATE 1 inches
1 2 young
7 southern Chile form
central Peru to northern Chile form
Plate 1 Species Accounts
Genus CALLORHINUS Gray, 1859
1. Northern Fur Seal Callorhinus ursinus French: Otarie à fourrure / German: Nördlicher Seebär / Spanish: Lobo marino septentrional Other common names: Alaskan Fur Seal, Pribilof Fur Seal
Taxonomy. Phoca ursina Linnaeus, 1758, “Habitat in Camschatcæ maritimis inter Asiam & Americam proximam, primario in insula Beringii.” Restricted by O. Thomas in 1911 to “Bering Island.” This species is monotypic. Distribution. N Pacific, including the Bering Sea, Sea of Okhotsk, and Sea of Japan, S to Japan (Honshu), and N Mexico (Baja California). Descriptive notes. Total length up to 210 cm (males) and 150 cm (females); weight 180–270 kg (males) and 40–60 kg (females). Newborns are 60–65 cm and 5·4–6 kg. Dental formula I 3/2, C 1/1, PC 6/5 (× 2) = 36. Northern Fur Seals are extremely sexually dimorphic. Mature males are 30–40% longer and 4·5–5 times heavier than mature females. Flipper characteristics are unique. Top of foreflipper has bare skin, demarcated by sharp line where fur starts on wrist. Hindflippers are relatively longer than on any other otariids’ due to long thin extensions of cartilage on each toe. In both sexes, muzzle is short and curved downward, and nose is small. Ear pinnae are long and prominent and may become bare as an individual reaches an advanced age. Vibrissae are long, often extending past ears. Mature adult Northern Fur Seals have pale vibrissae, subadults have vibrissae that are a mix of pale and black, and young have black vibrissae. Adult males are stocky and have mane of long guard hairs from head to neck, chest, and upper back. Their foreheads appear to rise steeply because crown is enlarged by skull’s sagittal crest. Adult females and subadults are moderately built, and it is hard to determine gender until males reach 4–5 years of age and exceed size of females. Fur is very thick, with pale-colored underfur. Males are gray to black, or fur may be dark ruddy brown, and mane may show silvery or blonde tints. Adult females and subadults have more variation in fur color but are often dark gray to black above with buff on chest, sides, and neck (where fur may form a pale, contrasting V-shape). Muzzle may be buffy or ruddy colored. Young are born with blackish coat, with some creamy areas on sides and face, and they molt to subadult color by 3–4 months old. Habitat. Highly pelagic, often far from shore or at edge of continental shelf or over continental slope. Terrestrial habitat usually consists of rocks and boulders, but it may also be a beach. Predators include Killer Whales (Orcinus orca), sharks, and Steller Sea Lions (Eumetopias jubatus). Food and Feeding. Dietary shifts of Northern Fur Seals occur depending on season and foraging area; diets often includes vertically migrating species. Off California and Washington, Northern Fur Seals eat anchovy (Engraulidae), hake, saury (Scomberesocidae), squid, rockfish (Sebastidae), and salmon (Salmonidae). Off Alaska, they eat walleye pollock (Theragra chalcogramma), capelin (Mallotus villosus), sand lance (Ammodytidae), herring (Clupeidae), Atka mackerel (Pleurogrammus monopterygius), and squid. Breeding. All fur seals, including Northern Fur Seals, have a polygynous breeding system with the same general features. Males hold territories onshore and fight, vocalize, or make postural displays to maintain them. Mature males arrive first at a breeding rookery to establish a territory, followed by pregnant females. Almost always, more than one female will select a male’s territory and give birth to a single neonate soon after arriving. Non-breeding subadult males, referred to as bachelors, congregate outside territories at the edge of the rookery. Breeding males remain ashore continuously. A few days after parturition, a female leaves her neonate to go to sea on a foraging trip. Young are left alone or in a group of other unattended young, and males have no role in parenting. Territorial males may pose a threat to young, sometimes trampling or attacking them, but their presence can benefit young by keeping bachelors at bay and reducing crowding in the territory. After a female’s milk stores are replenished, she returns to the territory, attracting her offspring with a special high-pitched call. This pattern of nursing bouts and foraging trips repeats itself until the offspring is weaned. Foraging trips tend to be short when offspring are young and become longer as they get older. Soon after a female gives birth, she enters estrus and usually copulates with the male in whose territory she resides. Thus, females are likely to be pregnant and lactating throughout most of their entire adult lives. After conception, development of the fertilized egg is suspended at the blastocyst stage and then resumes a few months later after the blastocyst becomes implanted in the uterus. Breeding of Northern Fur Seals on Pribilof Islands occurs from mid-June through August and c.2 weeks earlier on San Miguel Island. Northern Fur Seals reach sexual maturity at 3–5 years old, but males are not large enough to compete for a territory until they are 8–9 years old. Gestation lasts 51 weeks, including the delayed implantation phase of 3·5–4 months. Pregnant females usually give birth a day after arriving at the breeding territory and enter estrus an average of 5·3 days later. They remain with their neonates for an average of 8·3 days before leaving on the first foraging trip. Subsequent nursing bouts
ashore usually last less than two days. The female will provide 8–12 nursing bouts, each lasting c.2 days, before the offspring is weaned at c.4 months. Life span is c.25 years. Activity patterns. Northern Fur Seals are among the most pelagic of all pinnipeds (seals), with adults remaining at sea for most of the year, except for the breeding season, which lasts 4–5 months for females, including rearing of offspring, and c.45 days for males. They generally avoid hauling-out between breeding seasons, and weaned offspring go to sea and do not touch land until they return to their natal rookery 2–3 years later. At sea, Northern Fur Seals are most likely to be sighted alone or in pairs. When not foraging or traveling at sea, they groom or rest on the water’s surface during the day and usually feed at night or twilight. Typical resting postures at the water’s surface include lying on back or side with one or more flippers extended in the air or held pressed together. They commonly elevate hindflippers, rotate them forward, and drape one or both foreflippers over the top, and hold them above the surface—a posture known as the “jug-handle.” Fur seals groom their pelage by rubbing foreflippers over their bodies and scratching with their three exposed claws on hindflippers. Dives of lactating female Northern Fur Seals lasted 2·2 minutes to an average depth of 68 m; maximum dive lasted 7·6 minutes to a depth of 207 m. Movements, Home range and Social organization. Most Northern Fur Seals breed on the Pribilof Islands in the Bering Sea. Significant numbers also breed on Commander and Kuril islands, Russia; small rookeries occur, on Bogoslof Island in the Bering Sea; Robben Island, Russia; and San Miguel and south-east Farallon Islands off California. Annual migrations of Northern Fur Seals are the longest of any species of otariid, with many individuals traveling from the Bering Sea to winter-feeding areas off California or Japan. Even during the breeding season, lactating females at the Pribilof Islands make longer foraging trips than most other female otariids, lasting 6·9 days on average, to reach the edge of continental shelf. Vagrants have been recorded as far west as the Yellow Sea, near China, south to Taiwan, and north to the Arctic’s Beaufort Sea. Status and Conservation. Classified as Vulnerable on The IUCN Red List. Total population of Northern Fur Seals is 900,000–1·1 million individuals and declining. Breeding population on the Pribilof Islands is c.650,000 individuals. Luxurious pelt of Northern Fur Seal was the target of intensive hunting soon after breeding rookeries were discovered in the 18th century. By 1984, when controlled commercial hunting ended, the population had suffered several cycles of declines and recoveries. In the 1950s, it was estimated to be 2·5 million individuals, and that number may be considerably lower than during the pre-exploitation era. Currently, international treaties and agreements are in place to manage the population. Small numbers of Northern Fur Seals on the Pribilof Islands are still killed in a subsistence harvest by Alaskan Natives; 478 subadults were taken in 2007. Fishing-gear entanglement is known to be a lethal threat to Northern Fur Seals. A high level of mortality occurred during the 1980s when the driftnet fishery in the North Pacific Ocean was at its height. Continuing entanglement, commercial catches of walleye pollock (Theragra chalcogramma)—one of the seal’s main prey species—and possible increased predation by Killer Whales may be contributing to the current population decline of Northern Fur Seals. Bibliography. Call & Ream (2012), Dickerson et al. (2010), Fowler (1987), Gelatt & Lowry (2008a), Gentry (1998, 2009b), Jefferson et al. (2008), Kajimura (1985), Kuhn (2011), Kurle & Worthy (2001), Merrick et al. (1994), NMFS (1993, 2007), Reijnders et al. (1993), Rice (1998), Thomas (1911), Towell et al. (2006), Wickens & York (1997), York (1987).
Genus ARCTOCEPHALUS É. Geoffroy Saint-Hilaire & F. Cuvier, 1826
2. Antarctic Fur Seal Arctocephalus gazella French: Otarie antarctique / German: Kerguelen-Seebär / Spanish: Lobo marino antártico Other common names: Kerguelen Fur Seal
Taxonomy. Arctophoca gazella Peters, 1875, “von Seehunden aus Kerguelenland.” Restricted by V. B. Scheffer in 1958 to “Anse Betsy (49° 09’ S, 70º 11’ E)” (= south-east of Africa, halfway to Antarctica). A. gazella was once considered a subspecies of A. tropicalis. Monotypic. Distribution. Subantarctic and Antarctic waters S of, or just N of, the Antarctic Convergence, and scattered islands in this zone, mainly South Georgia. Regular haul-out areas include the Antarctic Peninsula. Descriptive notes. Total length mean 188 cm but up to 200 cm (males) and 120–140 cm (females); weight 130–204 kg, mean 188 kg (males) and 22–51 kg, mean 40 kg (females) Newborns are 63–67 cm and 6–7 kg. Dental formula I 3/2, C 1/1, PC 6/5 (× 2) = 36. Antarctic Fur Seals are strongly sexual dimorphic. Mature males weigh 4–5 times as much as females and are 1·4–1·5 times longer. Muzzle is of moderate size and length, tapering to slightly pointed nose that reaches just past mouth. Pale ear pinnae are long and conspicuous. Vibrissae are pale and quite noticeable; adult male Antarctic Fur Seals
FAMILY OTARIIDAE Eared Seals
On following pages: 3. Juan Fernandez Fur Seal (Arctocephalus philippii); 4. Guadalupe Fur Seal (Arctocephalus townsendi); 5. Galapagos Fur Seal (Arctocephalus galapagoensis); 6. South American Fur Seal (Arctocephalus australis); 7. New Zealand Fur Seal (Arctocephalus forsteri); 8. Subantarctic Fur Seal (Arctocephalus tropicalis); 9. Afro-Australian Fur Seal (Arctocephalus pusillus).
FAMILY ODOBENIDAE Walrus
A number of Walruses are usually to be found loafing in shallow water offshore of a coastal haul out. When disturbed, for example by low-flying aircraft or boats, all the occupants will take to the water. The length of time an individual Walrus spends at a haul-out site is related to the length of the previous foraging bout. Male Walruses may spend from eight hours to two days, or more, hauled out, after a foraging trip that may last up to six days. They tend to make more frequent, but shorter, trips when using sea ice as the haul-out platform. Odobenus rosmarus divergens Chukchi Peninsula, Chukotka, Russia. Photo: Staffan Widstrand
Seals (Callorhinus ursinus), Bearded Seals (Erignathus barbatus), Ringed Seals (Pusa hispida), and Spotted Seals (Phoca largha). They also scavenge on cetacean carcasses by sucking out blubber and inner organs. Foraging dives last two to seven minutes and occasionally as long as 20 minutes or even more, and foraging depths are correlated directly with distance from the sea surface to the seafloor but are rarely over 100 m. Adult male Walruses apparently fast during the breeding season.
Sexually mature female Walruses enter estrus in winter and are impregnated by adult males in the water. They give birth to a
single offspring (twins are rarely reported) about 15 months later in spring. Consequently, full gestation is about 15 months, but the embryo develops only briefly after the egg is fertilized and then is free-floating and dormant for about four to five months before it attaches to the uterine wall and resumes development. This physiological event is called embryonic diapause or delayed implantation. Females nurse and protect their offspring for up to two, and sometimes three, years. Most females are sexually mature at six to seven years old. Males are generally sexually mature when eight to ten years old but not socially mature until about 14 years old. Walruses are polygynous, with males competing with each other through visual and acoustic displays and occasionally physical battles in the water to defend access to estrous females resting nearby. The males’
The Walrus feeds mainly on invertebrates that live on or just above the seafloor. They feed in the waters of continental shelves, mostly to depths of about 80 m. Walrus stomachs sometimes contain prey and sediments that must have come from depths greater than 100 m, but their prey is most abundant in shallower waters. As this picture shows, Walruses occasionally forage in very shallow water, although less than 6 m is unusual. Odobenus rosmarus Sandøen, Daneborg, Northeast Greenland National Park, Greenland. Photo: Göran Ehlmé
FAMILY ODOBENIDAE Walrus
It was long believed that the Walrus raked the seafloor sediments with its tusks looking for mollusks, and that when it found them, the tusks were used as a kind of oyster-knife to lever them open. The reality is less picturesque: the tusks provide some supplementary support while the Walrus is foraging. Feeding Walruses root with their snouts, rather like pigs, and they use suction to extract the meat from shellfish. The tongue of the Walrus almost fills the buccal cavity and consists mainly of muscle. When it is retracted and depressed, it creates a very low pressure, strong enough to suck bivalve mollusks out of their shells. Their diets are variously supplemented with crustaceans, snails, soft-shelled crabs, and polychaete and sipunculid worms. The proportion of soft-bodied prey in the diet can be easily underestimated because it is more easily digested than tougher or harder prey. Adult male Walruses were radio-tracked in Young Sound, an important summer feeding area off north-eastern Greenland. They made an average of 165 dives deeper than 6 m every 24 hours. Observations suggest that their primary food in Young Sound is bivalve mollusks and that they feed mainly at depths of between 8 m and 34 m. Typically, feeding dives last 2–7 minutes. In an earlier study, measurements of the energy expenditure of “Atlantic Walruses” (shown here) in Greenland, using double-labeled water, indicated that the daily gross food consumption of an adult male was 5–6% of its total body weight. That would equate to 90 kg of mollusks out of their shells for a typical 1500 kg adult male, although its diet would usually include other benthic invertebrates.
Odobenus rosmarus rosmarus Greenland. Photos: Paul Nicklen
FAMILY PHOCIDAE Earless Seals
Both species of elephant seal are regularly seen tossing sand or pebbles onto their backs with alternating strokes of their flippers. One function of “sand flipping” appears to be to help the animals keep cool, by covering the skin in wet material, and at the same time, creating a depression that brings more of the body’s surface into contact with the damp substrate. The Southern Elephant Seal colony on the Valdes Peninsula, Argentina, the location of these pictures, lies in more temperate latitudes than the majority of sites used by this species. Temperatures at midday range around 20°C, and occasionally as high as 30°C, compared to highest temperatures of 5°C at some subantarctic rookeries. The rate of sand flipping increases as temperatures increase, and by noon some individuals will have covered more than one-half their upper body surfaces in sand or pebbles. In Northern Elephant Seals (Mirounga angustirostris), sand flipping is part of a gradient of responses to increasing solar radiation. Individuals first expose their more reflective undersides to the sun, then sand-flip, and finally go into the water. The behavior is innate: neonatal elephant seals perform sand-flipping movements within minutes of birth. Neonates have darker skin that absorbs more heat, and they flip sand at higher rates than their mothers, while mothers have been seen to flip sand over their offspring. Elephant seals also flip sand at night and in cool rainy weather, which indicates that it has other behavioral functions, perhaps as a displacement activity. Males flip sand when disturbed or aroused, and females flip sand continually during copulation. Elephant seals may also go through sand-flipping motions on inappropriate substrates, such as rock. The South American Sea Lion (Otaria byronia), which also breeds on the Valdes Peninsula, is one of a number of sea lion species that flip sand over themselves on hot days. Above: Mirounga leonina Valdes Peninsula, Argentina. Photo: Günter Ziesler
Below: Mirounga leonina Valdes Peninsula, Argentina. Photo: Eberhard Hummel
FAMILY PHOCIDAE Earless Seals
Earless seals scratch and groom using the five well-developed claws on their front flippers. They are unable to bring their hindflippers forward to groom their heads, as eared seals (Otariidae) do. The claws on their hindflippers are short and barely visible in some species. By arching their bodies sideways, they bring their hindquarters within reach of their front flippers. The Ringed Seal and other phocid species are hosts to the “seal louse” (Echinophthirius horridus), which in turn carries parasitic nematode worms of the genus Dipetalonema that burrow into the subcutaneous tissues of mammals. Pusa hispida Svalbard, Norway. Photo: Staffan Widstrand
The comfort behavior of the resting Harbor Seal includes yawning and stretching. Like other mammals, seals also shiver in response to low temperatures, as a way of increasing metabolic heat production through muscular activity. Nevertheless, research indicates that when diving in cold water, seals may be able to inhibit shivering as a way of conserving oxygen. Harbor Seals are not particularly social, and most interactions between individuals are brief visual and vocal threats to maintain distance between them. These increase when haul-out space is limited.
between ice floes (about 41%), both highly correlated with locations of large numbers of departing and arriving Adelie penguins; searching around ice floes (about 6%); stalking under thin ice (about 3%); and searching in open water (about 3%). Near a haul-out site on Bird Island, South Georgia, Gentoo penguins (Pygoscelis papua) were most common in winter diets of Leopard Seals, and macaroni penguins (Eudyptes chrysolopus) were most common in summer diets. At the same location between 1983 and 1995, subadult Antarctic Fur Seals (58%) and macaroni penguins (27·8%) were the main prey of Leopard Seals; other prey included Gentoo penguins (8·6%), young Southern Elephant Seals about c.150–200 cm in length (3·1%), diving petrel (Pelecanoides spp., 1·9%), and Cape petrel (Daption capense, 0·6%).
Perhaps most unique of all is the diet of the Leopard Seal. Unlike most species of earless seals, Leopard Seals regularly prey on warm-blooded species, such as Subantarctic Fur Seals (Arctocephalus tropicalis), Antarctic Fur Seals (Arctocephalus gazella), Australian Sea Lions (Neophoca cinerea), New Zealand Sea Lions (Phocarctos hookeri), Weddell Seals, Crabeater Seals, Ross Seals, and Southern Elephant Seals, with a focus on young Crabeater Seals and Weddell Seals. Leopard Seals are known to prey on penguins. From mid-October to midFebruary (summer) in Prydz Bay, Antarctica, male and female Leopards Seals used five different hunting styles to prey on a seasonally available breeding colony of Adelie penguins (Pygoscelis adeliae): patrolling fast-ice edges (about 47% of 32 observations of five Leopard Seals) and ambushing from
Phoca vitulina California, USA. Photo: Roland Seitre
PLATE 6 inches
ssp vitulina dark morph
ssp stejnegeri dark morph
14 ssp vitulina light morph
ssp richardii dark morph
young ssp saimensis
FAMILY PHOCIDAE Earless Seals
Plate 6 Species Accounts
Genus HALICHOERUS Nilsson, 1820
11. Gray Seal Halichoerus grypus French: Phoque gris / German: Kegelrobbe / Spanish: Foca gris Other common names: Atlantic Seal, Horsehead
20th century. They were killed for bounties in several places to reduce perceived competition with commercial fisheries. Hunting is now regulated in most areas. Numbers of Gray Seals are actually increasing at most locations (e.g. continental Europe, British Isles, USA, and Sable Island in Canada), but they are declining in a few localities such as Iceland or the Gulf of Saint Lawrence in Canada. Recent estimates for births throughout their distribution are c.100,000 offspring, translating to global population of perhaps 400,000–500,000 individuals. Bibliography. Hall & Thompson (2009), Hammond et al. (1994a, 1994b), Harwood & Greenwood (1985), Mansfield (1988), McConnell et al. (1999), Pomeroy et al. (1994), Scheffer (1958), Thompson & Härkönen (2008a), Wiig et al. (1990).
Genus HISTRIOPHOCA Gill, 1873
12. Ribbon Seal Histriophoca fasciata French: Phoque rubané / German: Bandrobbe / Spanish: Foca listada
Taxonomy. Phoca fasciata Zimmermann, 1783, “Wohnt um die Kurilischen Inseln” (= Russia, Kuril Islands). This species is monotypic. Distribution. E Siberian, Chukchi, W Beaufort, and Bering seas, and Sea of Okhotsk, and high latitudes of the N Pacific Ocean, from Hokkaido and the N Sea of Japan to Alaska. Descriptive notes. Total length c.150– 175 cm; weight 70–110 kg. Newborns are c.90 cm in length and weigh c.10 kg. Ribbon Seals are relatively small, with large eyes and exceptionally striking body coloration. Young Ribbon Seals are uniform color, but a banding pattern begins to develop during the first couple of years of life. Adult males have broad white bands around their necks, front flippers, and body just in front of pelvis against a dark brown to black background. Adult females have a lighter brown to gray general background and fainter bands. Front flippers of Ribbon Seals are small but have robust, strong claws that appear to be adapted to help them haul-out in fast ice (ice fastened to land) and pack ice. Habitat. Mostly restricted to the Bering Sea and Sea of Okhotsk, although recent studies have revealed that they range widely into the North Pacific Ocean during spring, summer, and autumn after the breeding season and after the fast ice melts and packice habitats recede. During winter and early spring, Ribbon Seals are mostly found in coastal fast-ice and near-shore, pack-ice habitats off eastern Russia and Japan and in pack-ice habitats of the central Bering Sea and north-western Alaska (USA). As ice melts and recedes, Ribbon Seals appear to be mostly pelagic, roaming over large areas in the Bering Sea, near the Aleutian Islands, into the Beaufort and Chukchi seas, and south into the central North Pacific Ocean. Food and Feeding. In spring, Ribbon Seals have a relatively diverse diet of shrimp, squid, and fish such as Arctic cod (Boreogadus saida and Arctogadus spp.), saffron cod (Eleginus gracilis), walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), capelin (Mallotus villosus), and flatfish. Off Japan, walleye pollock can be a primary prey in winter and spring. In a 2008 summary by the US National Marine Fisheries Service, Ribbon Seals were reported, across many studies, to select prey from 20 genera of at least twelve fish families, eight genera from four cephalopod families, and eleven genera of eight crustacean families. They forage relatively deep to 500 m or more. Breeding. Offspring are born on fast ice or pack-ice floes in March–April and are weaned at c.3–4 weeks of age. Nothing is known of the breeding system of the Ribbon Seal, although their sparse distribution during the breeding season suggests they are not polygynous. Adult males do make a variety of underwater noises that have been suggested to be involved with attracting females or repelling other adult males from breeding opportunities. Ribbon Seals are sexually mature at c.3–5 years old. Maximum life span is probably 25–30 years. Activity patterns. There is little specific information available for this species because Ribbon Seals breed in relatively inaccessible pack-ice habitats and then appear to live solitarily in pelagic ocean areas the rest of the year. Movements, Home range and Social organization. Ribbon Seals appear to be solitary most of their lives and mostly asocial even when they occur in small groups on ice. Recent studies have documented large movements and seasonal migrations of Ribbon Seals throughout the Bering Sea and the Aleutian Islands and into the central North Pacific Ocean. Status and Conservation. Classified as Data Deficient on The IUCN Red List. Soviet sealers harvested substantial numbers of Ribbon Seals for oil, skins, and food in the Bering Sea from the early 1960s through at least the mid-1990s when quotas were reduced to 10,000–15,000 ind/year because of signs of overharvest and population declines. Native villagers in Alaska and eastern Russia kill a few Ribbon Seals each year, but they are generally inaccessible to them throughout the year. Conservation threats include loss of sea ice from caused by climate change, oil and gas development in the Bering Sea
Taxonomy. Phoca grypus Fabricius, 1791. No type locality given. Listed by V. B. Scheffer in 1958 as “Greenland.” There are three populations isolated geographically. Some authors recognized two subspecies (grypus in the western Atlantic Ocean and macrorhynchus in the eastern Atlantic Ocean), and the Baltic population was formerly referred to as the subspecies baltica; none of them are recognized here. Monotypic. Distribution. N Atlantic in subarctic to temperate waters, from S Labrador to Gulf of Maine, including Gulf of Saint Lawrence in NE North America, also in Iceland, Faroe Is, Norway, NW Russia, Baltic Sea, British Is, and North Sea and Atlantic coasts S to NW France (Brittany). Descriptive notes. Total length 195–230 cm (males) and 165–200 cm (females); weight 170–310 kg (males) and 100–190 kg (females). Newborns are 90–110 cm in length and weigh 11–20 kg. Gray Seals in the western Atlantic Ocean are significantly larger (males more than 400 kg and females more than 250 kg) than those in the eastern Atlantic Ocean. Adult Gray Seals are sexually dimorphic in body size and shape of heads and necks. Chests, necks, and shoulders of adult males are more massive than those of adult females, with many folds and wrinkles in skin and are heavily scarred from battles with other males during the breeding season. Nose of adult males is also longer and broader than that of adult females. Color of pelage varies substantially from black to brown to dark gray and even pale white, with darker blotches scattered dorsally and laterally and some ventrally. Adult females are generally lighter colored than males. Neonates have a silky white or yellow lanugo (fine, soft hair) that is molted at 2–3 weeks old into a lighter phase of the adult pelage. Habitat. Coastal areas of the northern North Atlantic Ocean and Baltic Sea. Breeding rookeries of Gray Seals are on rocky coasts and sandy beaches, or in caves, usually on remote beaches and uninhabited islands. Gray Seals also uses fast ice (ice fastened to land) in the Baltic Sea and the Gulf of Saint Lawrence. Coastlines exposed to the open sea, intertidal flats, and estuaries are used to haul-out. Food and Feeding. Gray Seals are shallow, short-duration divers, and most of their foraging activity is focused at or near the seafloor. Their diet can be diverse, but they mostly eat sand eel (Ammodytes sp.), which can make up 70% of the diet at some locations and in some seasons. Other prey includes squid, octopus, and fish such as Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), capelin (Mallotus villosus), Atlantic wolffish (Anarhichas lupus), dab (Limanda limanda), North Atlantic flounder (Platichthys flessus), European plaice (Pleuronectes platessa), saithe (Pollachius virens), whiting (Merlangius merlangus), and sole (Solea solea). Breeding. Timing of breeding of Gray Seals varies among populations, but it generally occurs from September through early March, either on offshore islands and reefs or on sea ice. Females aggregate in large concentrations, give birth to single offspring, and then remain ashore fasting while they nurse their offspring for c.17–20 days. Adult male Gray Seals assemble at these sites and compete with each other, using visual and vocal threat behaviors to monopolize access to estrous females. Females mate, either on land or in the water, c.15 days after giving birth and then wean their offspring soon after that. Female Gray Seals are sexually mature at 3–5 years old and males at 4–8 years old, although most males are not socially mature and capable of breeding until they are about ten years old. Activity patterns. Gray Seals spend most of their time after the breeding season in the water foraging, but they haul-out again to molt in April–June. Offspring are highly mobile and wander considerably in the North Atlantic Ocean during their first year of life. When foraging, Gray Seals dive to and forage near the seafloor at 60–100 m, occasionally to more than 300 m, and most dives last 4–10 minutes, although some can last as long as 30 minutes. Movements, Home range and Social organization. During the non-breeding and nonmolting seasons, Gray Seals make regular foraging trips of one to several days or more to offshore sites within c.40 km of haul-out sites and often repeatedly visit the same sites to hunt. Gray Seals are polygynous, and sometimes, large aggregations of females occur at particular breeding sites, although they are not particularly social then or at any other time of the year. Vagrant Gray Seals are known from as far south as New Jersey (USA) in the western Atlantic Ocean and Portugal in the eastern Atlantic Ocean. Status and Conservation. Classified as Least Concern on The IUCN Red List. A key population of Gray Seals occurs in eastern Canada and Nova Scotia, including Sable Island south to the Gulf of Maine and Cape Cod. There is another small population in the Baltic Sea, and larger ones around the British Isles, Iceland, and Finland. Gray Seals were hunted extensively throughout most of their distribution beginning in the late 1600s near Nova Scotia and then more intensively there and elsewhere for most of the
On following pages: 13. Harp Seal (Pagophilus groenlandicus); 14. Harbor Seal (Phoca vitulina); 15. Spotted Seal (Phoca largha); 16. Caspian Seal (Pusa caspica); 17. Baikal Seal (Pusa sibirica); 18. Ringed Seal (Pusa hispida).
FAMILY BALAENIDAE Right and Bowhead Whales
Despite being a bulky and slowmoving species, the Southern Right Whale sometimes engages in energetic behavior at the water’s surface. This species is frequently observed breaching, rising out of the water, sometimes as far as the tailstock, before falling onto its side or back (as seen in the bottom image) on the water’s surface with a tremendous splash into the water that is can be heard from great distances. Southern Right Whales have been reported breaching multiple times in succession. Breaching has been observed in solitary individuals, in pairs, and as part of socio-sexual surface activity. In July 2010, during the austral winter, when the whales come close to the shore to breed, a couple sailing off Cape Town, South Africa, had a lucky escape when a breaching Southern Right Whale landed on their yacht. After snapping the mast, the whale slid down the side of the boat and back into the water. The Bowhead Whale (Balaena mysticetus)— even larger than the Southern Right Whale—is also known to breach, often energetically. For example, one individual observed in the Beaufort Sea in August interspersed 49 tail slaps between six breaches during eleven minutes of observation. As it surfaced after its final breach, a second Bowhead Whale began breaching about 300 m away. During the next 75 minutes, this whale made 64 breaches, 36 tail slaps, and 48 flipper slaps.
Eubalaena australis Puerto Pirámides, Valdes Peninsula, Argentina. Photos: Darío Podestá
FAMILY BALAENIDAE Right and Bowhead Whales
Breaching is an activity that likely imposes a heavy energetic cost on the whale. The purpose for breaching is unknown. It is frequently observed on the mating and birthing grounds of the Southern Right Whale, perhaps suggesting a display of strength by males competing for the attention of females. Breaching may be a form of visual communication, and the sound resulting from the whale hitting the water’s surface may also serve some purpose in communication. Underwater, however, the sound of breaching is audible for only a few hundred meters, compared with the longer distances that baleen whales’ long wavelength, low-frequency calls are transmitted. Eubalaena australis Reserva Natural Turística Punta Pirámides, Valdes Peninsula, Argentina. Photo: Juan Carlos Muñoz
Many tourists visit coastal breeding grounds of the Southern Right Whale to observe behaviors like breaching. While this increasing interest may provide an important incentive for whale conservation, studies at Valdes Peninsula, Argentina, have indicated that whale-watching activities result in short-term changes in the behavior of individual whales approached by whale-watching boats. Disturbed Southern Right Whales approached by whale-watching boats, including mothers with their young, appear to spend less time resting and engaging in social behavior and more time traveling.
Calanus finmarchicus in the North Atlantic Ocean, but they have also been observed feeding on Centropages and Pseudocalanus spp. In the North Pacific Ocean, they feed on Calanus marshallae and Neocalanus spp. Krill (Euphausia superba) is a prominent prey species for right whales in the Southern Hemisphere. Bowhead Whales feed mainly on Calanus hyperboreus and C. glacialis. They also consume smaller quantities of a variety of other planktonic and benthic invertebrates, including euphausiids, tiny shrimps-like mystids, amphipods, isopods, pteropods (tiny snails), and larval stages of barnacles and crustaceans. Fish are occasionally ingested while feeding.
each side of the mouth. The balaenid head and mouth have been compared to an immense plankton net that is propelled forward, rather than pulled, through the water. Feeding occurs at all levels of the water: at the surface, in the water column, and also near the seafloor. The long, thin baleen plates are fringed with very fine, long bristles and are well suited to efficient filtering of very small prey items, the smallest ingested by any cetacean species. Stomach contents have included prey approximately 3·5 mm long. Balaenids feed on zooplankton, mainly small copepods and euphausiid crustaceans. Right whales primarily consume adult stages of the copepod species
Eubalaena australis Valdes Peninsula, Argentina. Photo: Daniel Alarcón
FAMILY ESCHRICHTIIDAE Gray Whale
throughout their distribution from prehistoric to historic times, first by indigenous people using primitive harpoons and lances and later by European and Yankee (north-eastern coast of the USA) whalers who established shore-based stations and pursued whales with sailing ships equipped with steel harpoons and hand lances. In the 20th century, industrial whalers used motorized vessels with deck-mounted, canonfired explosive harpoons to kill whales. Historical accounts suggest that Basque, Icelandic, and Yankee whalers killed the last Gray Whales in the North Atlantic Ocean in the late 17th
or early 18th century. Whether coastal whaling was solely responsible for or only hastened the extinction of Gray Whales in the North Atlantic is unknown. Gray Whales in the western North Pacific Ocean were hunted off Russia, Japan, and Korea from 1600 into the 19th century until the population was extirpated. From 1600 to 1860, European and American whalers pursued Gray Whales in the Sea of Okhotsk, and whales migrating near the shore along Japan were caught in nets and killed with harpoons and lances. During the “modern” period from 1860 to 1900, Russian, European, and American catcher boats pursued western Gray Whales, which were killed and brought to the shore-based stations for processing. From 1890 to 1966, Gray Whales were taken off the Korea Peninsula and Japan and in the Yellow Sea. Occasional catches were recorded off China from 1916 to 1958. Commercial whaling on the eastern population of Gray Whales began in 1845–1846 when whalers entered Magdalena Bay in the southern Baja California to pursue the Gray Whale during the winter as an alternative to hunting Sperm Whales (Physeter macrocephalus) in the Pacific Ocean during the summer. Word spread of the wintertime concentrations of Gray Whales in the bays and lagoons of Baja California, and lagoon whaling reached its peak in the mid-1800s. From 1854 to 1901, Gray Whales also were hunted from at least 15 shore-based whaling stations located from northern California to Baja California. By the 1870s, the hunt of the Gray Whale in the eastern population was no longer economically viable, and the fishery was largely abandoned. A period of “modern commercial whaling” involving whaling ships from the USA, Japan, Norway, and the former Soviet Union operated from 1914 to 1946 and targeted several species of Pacific whales, including Gray Whales. During this period, Gray Whales declined to critically low numbers, and they finally received international protection from commercial whaling by the International Whaling Commission in 1946. A subsistence hunt by Native Arctic communities of up to 140 Gray Whales per year continues and is regulated by the International Whaling Commission and its Scientific Committee. Today, Gray Whales in the eastern North Pacific Ocean support an ecotourism-based whale watching industry centered off the west coast of North America and in the breeding lagoons in Baja California, Mexico. One unexpected feature of whale watching in the breeding lagoons is the appearance of
On her southward migration, the late-pregnant female Gray Whale usually passes the south-western coast of the USA alone, and ahead of other whales. By this stage in her 11–13-month pregnancy, she will weigh 25–30% more than other adult females and will be conspicuously wide-bodied. The point of maximum girth is further back on the bodies of pregnant whales. While most offspring will be born in the lagoons around Baja California, Mexico, some female Gray Whales give birth en route. Studies in the late 1990s identified 4–5% of southbound migrating Gray Whales as newborns. Eschrichtius robustus Channel Islands National Park, California, USA. Photo: Hiroya Minakuchi/GETTY
The newborn Gray Whale is 4·5–5 m long and weighs about 800 kg. On the North American coast, births occur from the end of December to early March, with a peak in late January. Based on weaning and separation times observed off Sakhalin Island, Russia, the birth peak of the Asian coastal population probably also occurs in January. Low birth-weight or premature neonates appear to be more prone to stranding: the average length of stranded neonates is 4·4 m. Eschrichtius robustus Magdalena Bay, Baja California, Mexico. Photo: François Gohier/ardea.com
FAMILY ESCHRICHTIIDAE Gray Whale
The female Gray Whale establishes an affectionate and often playful bond with her offspring. A youngster will gently butt or nuzzle its mother’s head to gain her attention. When nursing, the youngster approaches her from below and nudges her abdominal area, whereupon her teat is extruded. Young Gray Whales consume about 200 l of milk a day and grow rapidly. During a 5-year study, young Gray Whales photographed on their northward migration during April, at the age of about three months, averaged 7·1 m in length. Eschrichtius robustus Laguna San Ignacio, Baja California, Mexico. Photo: Tui de Roy/The Roving Tortoise
Mother Gray Whales will support their swimming or resting offspring on their heads and backs. When the young Gray Whale reaches 2–4 months old, mothers in the breeding lagoons begin to mix and perhaps socialize, and their offspring play together. Young Gray Whales also play with objects such as pieces of kelp. Mother–offspring pairs are the last to leave the wintering area on the northward migration, allowing the young to develop in size and strength before the journey. First to leave the breeding grounds are newly pregnant females, which need to maximize the time they spend feeding in northern waters in preparation for the rigors of gestation and lactation.
the conservation of protected species is evident; however, Gray Whales are wild animals, and as with any wildlife, it is imperative that the whales be treated with caution and respect.
Status and Conservation Absent formal scientific surveys, pre-whaling abundance estimates for populations of Gray Whales were extrapolated from the number of barrels of whale oil landed and ranged
curious or “friendly” Gray Whales, first reported by R. M. Gilmore in 1975 from Laguna San Ignacio. He reported that Gray Whales solicited human attention by deliberately approaching whale-watching skiffs, apparently curious about the engine sound, and allowed passengers to pat them. This phenomenon continues, suggesting that if not threatened, Gray Whales are curious and will investigate boats emitting low-frequency sounds—apparently not all human interactions are disturbing to Gray Whales. The educational, recreational, and economic importance of controlled and responsible whale watching for
Eschrichtius robustus Mexico. Photo: François Gohier/VWPics.com
FAMILY BALAENOPTERIDAE Rorquals
The Blue Whale is generally stenophagous (restricted to a single kind of food), feeding almost exclusively on krill. Krill generally have a patchy distribution, occurring in areas of high primary productivity, such as where ocean currents converge and diverge and in regions of localized upwelling. To take advantage of these ephemeral high-productivity hotspots, Blue Whales must move over long distances. In the summer, the Blue Whales that visit the eastern North Pacific Ocean off the coast of California appear to favor waters with steep submarine topographic features that enhance upwelling. Balaenoptera musculus California, USA. Photo: Doc White/naturepl.com
the net to concentrate the fish, rorquals engulf watery aggregations of prey species in their greatly expanded and tonguelined, ventral throat pouch and upon closing the jaws, contract the throat pouch, expelling water and concentrating prey in the mouth. Thus, rorquals have enlarged the volume of their oral cavity by evolving mechanisms for expanding the ventral portion of their mouths. In contrast, balaenid mysticetes (the Bowhead Whale and right whales) have increased the volume of their oral cavity through the evolution of a dorsally arched rostrum that enlarges the dorsal portion of their mouths, while the eschrichtiid mysticete, the Gray Whale, has increased the
volume of the oral cavity by evolving a moderately dorsally arched rostrum and a weakly expandable buccal region. Expansion of the rorqual oral cavity is accommodated via a series of soft anatomical features including a large and flaccid tongue; a cavum ventrale (a seam in the throat musculature that receives the expanding, bag-like tongue during engulfment); stretchy and accordion-like ventral groove blubber marked by a series of external longitudinal ridges and grooves that extend from the chin to the umbilicus; and highly mobile, fibrocartilaginous, temporomandibular and mandibular symphyseal jaw joints that allow for a remarkable degree of
The “ventral groove blubber” of the Blue Whale has 55–88 pleats that extend from the chin to just behind the umbilicus. When the whale lunges, this accordion-like blubber unfolds, with the elastic tissues expanding to up to four times their resting size. At the same time as its throat pouch is expanding and filling with water, the Blue Whale is accelerating at rates of up to 4 m/s. The energy cost of a lunge is consequently very high. However, it has been calculated that the Blue Whale’s foraging efficiency is higher than that of other marine mammals by nearly an order of magnitude, but only if lunges target extremely high densities of krill. Balaenoptera musculus Gulf of California, Baja California, Mexico. Photo: François Gohier/Bios
FAMILY BALAENOPTERIDAE Rorquals
This sequence of photographs shows a Bryde’s Whale lungefeeding on a mixed baitball of sardines and Pacific chub mackerel (Scomber japonicus) off Baja California, Mexico. In the top left picture, the whale approaches the baitball, which has also attracted the attention of a California Sea Lion (Zalophus californianus) and a striped marlin (Kajikia audax). In the second picture in the sequence (below left), the whale is lunging toward the baitball, with its mouth open and its throat pouch expanded, displaying the elastic properties of its ventral groove blubber. During a lunge, a rorqual’s laterally bowed lower jaws first rotate outward, and then begin to drop, eventually reaching a gape angle with the palate of close to 90°. The lower jaws form the “rim” of the expanding buccal cavity as the lunging whale’s body “collides” with the prey-laden seawater. Bryde’s Whales are considered opportunistic feeders, switching their prey preference depending on prey availability, geographical location, and season. Seasonal variations of prey preference were recorded from the population of “ordinary” Bryde’s Whales in the western North Pacific Ocean, where krill and pelagic schooling fish such as the Japanese anchovy (Engraulis japonicus) are commonly consumed in May–June, the Pacific saury (Cololabis saira, another member of the mackerel family Scombridae) in July–August, and krill again in September.
Balaenoptera edeni Baja California, Mexico. Photos: Doug Perrine/naturepl.com
FAMILY BALAENOPTERIDAE Rorquals
In the third picture of this sequence (top right), the Bryde’s Whale has engulfed the water containing most of the baitball of fish. When fully expanded, the ventral throat pouch imparts a tadpole-like appearance to a feeding rorqual, with the pouch spanning up to 60% of the body length. The flaccid tongue acts like a sack, lining nearly the entire inflated buccal cavity. As the whale’s body begins to slow down, the engulfed water starts to move forward, and at the same time, the lower jaws rotate inward and close. Under this dynamic process, water flows across and through the baleen racks and out of the mouth, trapping prey species in the deflating buccal cavity. In the lower right picture, the throat pouch can be seen deflating as the whale expels the water. Baleen whales are known for their seasonal “feasting and fasting,” gorging themselves while on their feeding grounds in summer and hardly eating at all while on the winter breeding and birthing grounds. However, it appears that this pattern is typical only of certain rorqual species and populations, including Common Minke Whales (B. acutorostrata), Antarctic Minke Whales (B. bonaerensis), Humpback Whales (Megaptera novaeangliae), Sei Whales (B. borealis), and offshore Bryde’s Whales. Blue Whales (B. musculus) and Fin Whales (B. physalus) feed throughout the year, and this year-round feeding strategy has also been reported for the population of inshore Bryde’s Whales that lives in the coastal waters off South Africa. Whales of the Bryde’s Whale complex are unique among rorquals in that they do not undergo long-distance migrations into high-latitude summer feeding grounds. A population of Bryde’s Whale reportedly lives year-round in the Gulf of California.
Balaenoptera edeni Baja California, Mexico. Photos: Doug Perrine/naturepl.com
FAMILY BALAENOPTERIDAE Rorquals
Compared with the Blue Whale (B. musculus), the Fin Whale eats a relatively varied diet, feeding on krill or schooling fish as available. The Fin Whale’s baleen reflects the color asymmetry of the rest of its head. The entire left baleen rack and the rear twothirds of the right rack are dark blue-gray, with vertical streaks of yellow or white, while the baleen plates at the front of the right rack are white or yellow. Estimates suggest that during a lunge, the Fin Whale’s throat pouch fills at the rate of around 20 m3/s. The mouth is completely closed after only six seconds, by which time it may hold as much as 70,000 l of seawater. In less than a minute, all the engulfed water passes out, trapping as much as 10 kg of prey behind the baleen. Balaenoptera physalus Canada. Photo: François Gohier/VWPics.com
Rorquals use a number of techniques to herd fish into tighter concentrations for more efficient lunge feeding. The most remarkable of these has evolved in the Humpback Whale and is know as bubble-net feeding. The whales begin diving below the schooling fish, and one swims in a narrowing circle around them while blowing a ring of bubbles. As the curtain of bubbles rises toward the surface, reflections and noise from bubbles scare fish into an ever-tighter formation. When the resulting bait ball is near the surface, the whales ascend through the bubble net and lunge-feed.
forward, and at the same time, the lower jaws rotate inward and close. Under this dynamic process, water flows across and through the baleen racks and out of the mouth, trapping prey species in the deflating buccal cavity. A single lunge and engulfment sequence in a foraging Fin Whale may last only six seconds, during which time the whale’s speed decreases from 3 m/s to just 1 m/s, with the buccal cavity filling at a rate of 20 m3/s to eventually hold up to 70,000 l of sea water and perhaps more than 10 kg of krill. When fully expanded, the ventral throat pouch imparts a tadpole-like appearance to the feeding rorqual, with the pouch spanning up to 60% of
mandibular mobility. When deployed during feeding, the expandable ventral throat pouch of rorquals begins to fill with seawater as the laterally bowed, lower jaws first rotate outward and then begin to drop, eventually reaching a gape angle with the palate of close to 90°. The massive lower jaws form the “rim” of the inflating buccal cavity as the lunging whale’s body “collides” with the prey-laden seawater. The resulting drag is somewhat mitigated by a physiological feedback loop between mechanoreceptors in the accordion-like, grooved throat blubber and the engulfed water mass. As the whale’s body begins to slow down, the engulfed water starts to move
Megaptera novaeangliae Gulf of Maine, USA. Photo: Robert Harding/Bios
FAMILY BALAENOPTERIDAE Rorquals
Away from the rough-and-tumble of male–male competition, the male and female Humpback Whale engage in gentler courtship behaviors that include rubbing or touching one another with their pectoral flippers. A male may also escort a solitary female, or more frequently, a female and her offspring. The escorting male typically remains within a body length of the female and appears to synchronize his breathing and dive patterns with hers. Females reportedly give birth every 2–3 years, although several examples are known of individual females giving birth nearly annually. Postpartum estrus may occur on a regular basis, which may explain why males escort mother–offspring pairs late in the breeding season. Studies in the Hawaiian breeding grounds suggest that as many as 86% of mother–offspring pairs have been accompanied by an adult male escort in a given season. The adult female Humpback Whale is 40–70 cm longer than the male. Otherwise, the only externally observable difference is in the urogenital area. Females have a hemispherical lobe at the rear end of the genital slit, which is absent in males, while the separation between the genital slit and the anus is greater in males than females.
Megaptera novaeangliae Tonga, Polynesia. Photo: Tony Wu
FAMILY BALAENOPTERIDAE Rorquals
The courtship of the male and female Humpback Whale can include actions that are used in other contexts, such as flipper slapping. The whales may also assume a vertical head-up posture in water, and a male that does this may extrude his penis while close to the female. Penis extrusion also has other contexts and may occur during aggressive encounters between males in the presence of females. It has been suggested that a flipper-slapping female may be demonstrating dissatisfaction with an escorting male and attempting to attract other males. Megaptera novaeangliae Tonga, Polynesia. Photo: Tony Wu
The act of copulation has still not been reliably observed in decades of Humpback Whale studies, although they have been observed swimming in close synchrony, with their ventral surfaces in close contact. Male Humpback Whales have smaller testes than might be expected from their body size, and relatively short penises—especially when compared with the three species of right whales (Eubalaena spp.) and the Bowhead Whales (Balaena mysticetus), all in the family Balaenidae, species in which reproductive success is thought to be determined largely by sperm competition rather than aggression. A study around Hawaii suggested that male Humpback Whales preferentially expend energy competing over females without offspring, because these are most likely to conceive and are therefore the best investment for their limited sperm supplies.
ian Islands suggest that Humpback Whales have a polygynous mating system that grossly resembles a lek (males gathering to attract females). Although this mating system does not involve establishment of defensible territories, male Humpback Whales do exhibit aggressive competitive behaviors. Males are also known to form temporary “coalitions” to drive away males in other competitive groups. Besides these male–male competitive behaviors, male Humpback Whales are known to perform male–female courtship behaviors. In addition to the showy and powerful physical displays executed by males on winter breeding grounds, males are famously known to perform elaborate vocal songs. Within the context of a modified lek-mating
pressures of commercial overexploitation in the 20th century. In most rorquals, mating occurs in the respective austral or boreal winter, and gestation typically lasts 10–11 months. Birth of a single offspring is the norm, although twins have been reported in some species such as the Common Minke Whale or the Fin Whale. Young nurse for 5–7 months and typically remain with their mothers for up to a year. Sexually mature females generally reproduce on a two-year cycle, although some species appear to have shifted to an annual reproductive cycle. The reproductive biology of the Humpback Whale is the best studied of the rorqual species. Ongoing research conducted since the 1970s in the warm waters around the main Hawai-
Megaptera novaeangliae Tonga, Polynesia. Photo: Tony Wu
5 ssp brevicauda
7 right side
8 Southern Hemisphere
PLATE 11 inches
Plate 11 Species Accounts
5. Blue Whale Balaenoptera musculus French: Rorqual bleu / German: Blauwal / Spanish: Rorcual azul Other common names: Blue Rorqual, Sibbald’s Rorqual, Sulphur-bottom Whale; Northern Blue Whale (musculus); Pygmy Blue Whale (brevicauda); Antarctic Blue Whale, Southern Blue Whale (intermedia); Northern Indian Ocean Blue Whale (Northern Indian Ocean population)
Taxonomy. Balæna musculus Linnaeus, 1758, “Habitat in mari Scotico” (Scotland, United Kingdom). The type specimen was stranded in the Firth of Forth, a fjord on the eastern coast of Scotland in the North Sea. A possible fourth subspecies, the “Northern Indian Ocean Blue Whale” (indica) named by Blyth in 1859, is recognized by some workers. Genetic support for recognition of distinct subspecies of Blue Whales currently is relatively weak. Three subspecies recognized. Subspecies and Distribution. B. m. musculus Linnaeus, 1758 – N Atlantic and N Pacific. B. m. brevicauda Ichihara, 1966 – Indian Ocean and SW South Pacific around Australia. B. m. intermedia Burmeister, 1871 – Southern Ocean. Descriptive notes. Total length 3170–3260 cm; weight 113,000–150,000 kg. Adult female Blue Whales are larger than males and represent the largest animals, past and present, to ever live on Earth. Total body length and weight estimates are up to 3260 cm and 145,000 kg for the “Antarctic Blue Whale” (B. m. intermedia), 2800 cm and 113,000 kg for the “Northern Blue Whale” (B. m. musculus), and 2300 cm and 69,000 kg for the “Pygmy Blue Whale” (B. m. brevicauda). Although older scientific literature reports total body lengths of up to 3300 cm for Antarctic Blue Whales, these measurements are questionable because they were taken by nonstandard methods at whaling stations. The same can be said for body weights of 190,000 kg in some reports. Computing accurate weights of animals as large as Blue Whales is a challenge, and because an entire individual cannot be weighed at the same time, the most accurate estimates of weights have been made at whaling stations or onboard factory whaling ships where the different parts of a dead whale are weighed separately and then totaled. This method, however, also has problems because weight of body fluids, especially blood, is not included in the calculation. In general, head of the Blue Whale is uniformly gray, while body is generally light bluish-gray with extensive gray-to-grayish white mottling. Ventral surface is lighter gray to yellowish-white. Pectoral flippers are generally bluish-gray above and whitish below, with a thin white border. Caudal flukes are light bluish gray above and below, although a radial pattern of pale striations on undersurface of flukes is often present and has been used to identify different groups of individuals. In cold, high-latitude polar waters, some foraging Blue Whales have a yellow-green–to–brown hue during summer, which is caused by a surface film of diatoms (Cocconeis ceticola). This diatom film is responsible for the name “sulfur-bottom whale,” a term that is variably applied to Blue Whales. A submerged individual seen from the deck of a ship appears to be slate gray on cloudy days and silvery or turquoise blue on sunny days. Head is 22–27% of total body length. External surface of head has a single, prominent median rostral ridge, extending from blowholes to tip of rostrum. A prominent, fleshy “splash guard” is immediately in front of blowholes. This splash guard expands impressively when an individual is about to take a breath, and the blow that follows is typically tall, slender, and distinctly vertical (9–12 m high). Lateral margin of rostrum is broadly rounded and U-shaped as viewed from above, in contrast to the more sharply triangular rostra of other rorquals such as the Fin Whale (B. physalus) and the Sei Whale (B. borealis). In lateral view, rostrum of the Blue Whale has a distinctly flattened profile. Dorsal fin is proportionally tiny (c.35 cm) compared with other species of rorquals and is located well posterior on body, approximately three-quarters of the body length from tip of rostrum. Shape of dorsal fin varies from distinctly triangular to broadly rounded or smoothly falcate. Pectoral flippers are relatively long (c.15% of body length), slender, and bluntly pointed, with an anteriorly convex leading edge. As with all species of rorquals, there are only four elongate digits in the flipper (digit I is lost). Caudal flukes are broad (c.24% of body length) and can measure up to 700 cm across, with straight-to-slightly sinuous trailing edges marked by median notches. Fluke tips are distinctly pointed. Ventral groove blubber has 55–88 pleats that extend from chin to just posterior of umbilicus. Baleen plates are surprisingly thin for their length (up to 100 cm) and uniformly black, with numerous, coarse black bristles extending from lingual margins. Baleen laminae number 270–395/side or rack. Individual baleen laminae are broadly triangular and relatively broad compared with those in Fin Whales. When observed at sea, Blue Whales slowly rise to the surface, first showing head and blowholes, then their broad back, and finally their diminutive dorsal fin. Unlike Fin Whales, Blue Whales sometimes raise their flukes above the water when sounding. Habitat. Epipelagic regions of all ocean basins, except the Arctic, and sometimes in neritic coastal areas of continental shelves. Blue Whales occur in coastal areas of continental shelves such as the Gulf of Saint Lawrence, Gulf of California, and Southern California Bight and in submerged oceanic plateaus and volcanoes (Madagascar Plateau, Crozet Plateau, and Kerguelen Plateau). Habitat preferences of Blue Whales are related to feeding grounds, which appear to be localized and the consequence
of strong oceanographic interactions between currents and seafloor topographic features or convergence of surface currents that form cyclonic circulation and a shallow thermocline. This pattern is reflected in the population of Blue Whales that summers in the eastern North Pacific Ocean off central California, where individuals appear to prefer coastal habitats marked by steep submarine topographic features that enhance upwelling (shelf-slope break, borderland basin margins, etc.). These Blue Whales feed almost exclusively on krill during boreal summer and early autumn as far north as the Farallon Islands and Monterey Bay before moving south to waters around the Channel Islands to continue feeding during autumn. During boreal winter, individuals move further south into the Gulf of California and continue to feed on krill in protected waters of Bahia de Loreto. Some members of this population are even reported to migrate during boreal winter to the Costa Rica Dome (10° N) in the tropical eastern Pacific Ocean, where upwelling and a shallow thermocline result from a combination of cyclonic surface current circulation and large-scale wind patterns. In contrast, austral summer foraging habitat of the Blue Whale in high-latitude regions of the Southern Ocean is generally associated with areas of sharp oceanographic density interfaces, such as those caused by convergence of cold, northward flowing surface waters from Antarctica and relatively warmer surface waters of the subantarctic region (Antarctic Convergence). Whaling records indicate that the neritic waters off the south-western coast of South Africa were formerly frequented by Blue Whales during austral winter. Food and Feeding. Information on diets of Blue Whales is primarily based on studies of stomach contents from individuals killed by whalers. In recent years, however, at-sea collection of feces from Blue Whale has also provided reliable dietary information. Mortality-based dietary studies indicate that Blue Whales are generally stenophagous, feeding almost exclusively on euphausiids (krill). Other species of meso-zooplankton and larger nektonic animals are occasionally eaten, but these are probably unintentionally ingested. Antarctic Blue Whales primarily consume Euphausia superba, a relatively large species of krill reaching up to 6 cm in length with an average mass of c.1 g. Pygmy Blue Whales primarily consume E. vallentini, a smaller species of krill measuring 1·3–2·8 cm. Blue Whales in the North Pacific Ocean feed on several different species of euphausiids including E. pacifica, Thysanoessa inermis, T. longipes, and Nematoscelis megalops, but they also eat copepods (Calanus spp.). Blue Whales in the North Atlantic Ocean also eat a variety of different euphausiids including T. inermis, T raschii, and Meganyctiphanes norvegica, but they also feed on copepods (Temora longicornis). It has been estimated that a feeding Blue Whale consumes up to 6000 kg of krill in a single day. Blue Whales, like all species of rorquals, are lunge feeders, and information on their feeding behavior from direct observations and deployment of temporary digital tags on foraging individuals provide an impressive array of data including dive depth, roll, pitch, and even acceleration. Such studies show that Blue Whales feed at water depths of up to 100 m during daytime and follow diel vertical movements of prey to feed at shallower depths up to the surface during the night. One study found that foraging dives of Blue Whales in the Gulf of Saint Lawrence had higher feeding rates during the night and occurred at water depths typically less than 20 m. The feeding rate at night averaged one feeding lunge every 2·1 minutes vs. one every 4·2 minutes during the day. Daytime dives were generally of longer duration (up to 23 minutes), and individuals dove to greater depths (up to 134 m). Maximum number of lunges in a single dive was 15. Not all daytime dives, however, were deep, and some individuals preferred to forage at shallower depths in areas where topographic or oceanographic conditions resulted in prey aggregating near the water’s surface. Surface lunges were also noted and, as observed elsewhere, often involved individuals feeding on dense surface patches of krill while swimming on their sides with one flipper and parts of their flukes out of the water. At a broader ecological scale, it is interesting to note that krill generally have a patchy distribution in pelagic ecosystems and occur in areas of ephemeral, high primary productivity such as regions of ocean current divergences and convergences and regions of localized upwelling, fronts, and eddies. Localized aggregations of krill also occur in areas where strong interactions between currents and topographic features of the seafloor result in predictable areas of high primary productivity of phytoplankton. To take advantage of these ephemeral high-productivity hotspots, epipelagic mesopredators like Blue Whales must range over long distances. In viewing Blue Whales as “capital” breeders, researches have traditionally thought that the annual migration cycle of the Blue Whale is similar to that of other species of rorquals, with whales feeding at high latitudes (either austral or boreal depending on the hemisphere) during summer and fasting at low latitudes during winter, while giving birth and breeding. Several recent studies, however, suggest that Blue Whales likely continue to feed during winter, given the clustering of Blue Whales in areas with locally dense concentrations of krill and other planktonic crustaceans at this time of year. This behavior may be a consequence of the extremely large size of Blue Whales and an inability on the part of individuals to maintain sufficient energy stores through a long winter fast. Breeding. Not a great deal is known about breeding behavior of Blue Whales except that such activities are generally synchronized with the annual migration cycle. In this scheme, breeding typically occurs during winter—austral winter in the Southern Hemisphere and boreal winter in the Northern Hemisphere. Thus, reproductive seasons for northern and southern populations are c.6 months out of phase, which suggests an allopatric condition that leaves little opportunity for interbreeding among populations from opposite hemispheres. Blue Whales have a 2-year interbirth interval characterized by a 10–12-month gestation, a 6–7-month lactation period, and a 6–7-month anestrous. Shipboard observations of Northern Blue Whales near the Costa Rica
FAMILY BALAENOPTERIDAE Rorquals
On following pages: 6. Omura’s Whale (Balaenoptera omurai); 7. Fin Whale (Balaenoptera physalus); 8. Humpback Whale (Megaptera novaeangliae).
PLATE 16 inches
Plate 16 Species Accounts
15. Gray’s Beaked Whale Mesoplodon grayi French: Baleine-à-bec de Gray / German: Gray-Zweizahnwal / Spanish: Zifio de Gray Other common names: Scamperdown Whale, Southern Beaked Whale
Taxonomy. Mesoplodon grayi Von Haast, 1876, New Zealand, “the Chatham Islands…from specimens stranded…on the Waitangi beach of the main island of that group.” This species is monotypic. Distribution. Ranges from temperate waters of the S Atlantic, Indian, and S Pacific oceans to waters of Antarctica. A single specimen stranded on the Dutch coast is thought to have been a vagrant individual. Descriptive notes. Total length 450–500 cm; weight c.900 kg (unconfirmed). Body of Gray’s Beaked Whale is spindle-shaped, with greatest girth around its midpoint. Flukes are wide in relation to body length, and tailstock is compressed laterally. Dorsal fin is small and set approximately two-thirds the distance between tip of the beak and end of the tail. Coloration is typically dark brown, dark gray, or black and paler on the ventral surface. Tip of rostrum is often colored white, especially in adult males. Rostrum and lower jaw form a long distinct beak, and there are two grooves on the throat. Adult males have a single tusk on each side of the lower jaw; tusks are positioned about halfway along the jaw line. Tusks are approximately triangular but may become heavily worn over time. Habitat. Waters greater than 200 m deep. In common with other species of Mesoplodon, Gray’s Beaked Whale may be more common in areas of complex seabed topography, but this still has to be confirmed. Food and Feeding. While it is often assumed that Gray’s Beaked Whales consume deep-water cephalopods, analyses of stomach contents suggest that they may primarily consume deep-water fish species. In common with other species of beaked whales, Gray’s Beaked Whales likely forage at depths greater than 500 m for much of their lives. Breeding. Almost nothing is known about the reproductive biology of Gray’s Beaked Whale. Females give birth to a single offspring after gestation that is likely twelve months. Offspring likely remain dependent on their mothers for at least one year. Activity patterns. There is no information available for this species. Movements, Home range and Social organization. There is no specific information available for this species, but sightings of Gray’s Beaked Whales at sea tend to be of relatively small groups of five or fewer individuals. Nothing is known about the typical composition of these groups. Status and Conservation. CITES Appendix II. Classified as Data Deficient on The IUCN Red List. There are no estimates of global population size of Gray’s Beaked Whale. It may be one of the more abundant species of Mesoplodon and may be relatively common in some areas, such as waters to the south of New Zealand. Like other species of beaked whales, Gray’s Beaked Whale is potentially affected by ingestion of plastic debris and noise pollution, and individuals can be caught as bycatch in driftnet fisheries. As a species restricted to cooler waters, it may also be vulnerable to effects of climate change. Nevertheless, nothing is known about the form or extent of these potential impacts. Bibliography. MacLeod, Perrin et al. (2006), MacLeod, Santos & Pierce (2003), Mead (1989b), Rice (1998).
16. Ginkgo-toothed Beaked Whale Mesoplodon ginkgodens French: Baleine-à-bec du Japon / German: Japan-Zweizahnwal / Spanish: Zifio de dientes de Ginkgo Other common names: Japanese Beaked Whale
Taxonomy. Mesoplodon ginkgodens Nishiwaki & Kamiya, 1958, Japan, “Oiso Beach, Sagami Bay, near Tokyo.” Historically, there has been confusion about the number of species or subspecies contained in the classification of M. ginkgodens. It was originaly described in 1958 from an animal which stranded in Japan, while a second similar species, M. hotaula, was described independently in 1963 from an animal which stranded in Sri Lanka. Based on morphological similarities, these two species were synonymized under the name M. ginkgodens by J. C. Moore and R. M. Gilmore in 1965. However, recent molecular analysis, published in 2014, has resulted in these two species being separated again. Monotypic. Distribution. Warmer waters of the Pacific and Indian oceans in an area ranging from S India and Sri Lanka to Taiwan, Japan, SE Australia, Galapagos Is, and California. Exact distribution remains unclear due to the small number of known strandings, and the taxonomic confusion between the Ginkgo-toothed Beaked Whale and the Deraniyagala’s Beaked Whale (Mesoplodon hotaula).
Descriptive notes. Total length 470–528 cm; weight c.1000 kg (unconfirmed). Body of the Ginkgo-toothed Beaked Whale is spindle-shaped, with greatest girth around its midpoint. Flukes are wide in relation to body length, and tailstock is compressed laterally. Dorsal fin is small and set approximately two-thirds the distance between tip of the beak and end of the tail. Coloration is typically dark brown, dark gray, or black. Female and juvenile Ginkgo-toothed Beaked Whales may be paler on ventral surface. Rostrum and lower jaw form a beak that is indistinct from the low sloping forehead. There are two grooves on the throat. Adult males have a single tusk on each side of the lower jaw. Tusks are positioned approximately one-third of the way along the mandibles, but only the very tips of tusks emerge from gums. Male Ginkgo-toothed Beaked Whales are unusual because they seem to lack any of the long, pale, linear scars caused by tusks of other males that are found on males of most species of beaked whales. Habitat. Primarily waters greater than 200 m deep. Nothing further is known about habitat preferences of Ginkgo-toothed Beaked Whales. Food and Feeding. There is no specific information available for this species, but in common with other species of beaked whales, Ginkgo-toothed Beaked Whales are thought to consume deep-water squid and, to a lesser extent, deep-water fish. They likely forage at depths greater than 500 m. Breeding. There is no information available for this species. Activity patterns. There is no information available for this species. Movements, Home range and Social organization. There is no specific information available for this species, but Ginkgo-toothed Beaked Whales likely occur in small groups. Status and Conservation. CITES Appendix II. Classified as Data Deficient on The IUCN Red List. There are no estimates of global population size of the Ginkgo-toothed Beaked Whale. Like other species of beaked whales, the Ginkgo-toothed Beaked Whale is potentially affected by ingestion of plastic debris and noise pollution, and individuals can be killed as bycatch in driftnet fisheries. Nevertheless, nothing is known about the form or extent of these potential impacts. Bibliography. Dalebout et al. (2014), MacLeod et al. (2006), Mead (1989b), Moore & Gilmore (1965), Rice (1998).
17. Deraniyagala’s Beaked Whale Mesoplodon hotaula French: Baleine-à-bec de Deraniyagala / German: Deraniyagala-Zweizahnwal / Spanish: Zifio de Deraniyagala
Taxonomy. Mesoplodon hotaula Deraniyagala, 1963, Sri Lanka, washed ashore “in a dying condition” on 26 January 1963 at Ratmalana (6° 49’ N, 79° 52’ E), approxiately 8 km south of Colombo, on the west coast of Sri Lanka. Historically, there has been confusion about whether or not M. hotaula represents a species in its own right. It was originally described in 1963 from an animal which stranded in Sri Lanka, but based on morphological similarities, J. C. Moore and R. M. Gilmore synonymized it with M. ginkgodens in 1965. However, recent molecular analysis, published in 2014, has resulted in M. hotaula being resurrected as a species in its own right. Monotypic. Distribution. Warmer waters of the Pacific and Indian oceans in an area ranging from E Africa, S India and Sri Lanka to Galapagos Is, and possibly as far as Central and South America. Exact distribution remains unclear due to the small number of known strandings, and the taxonomic confusion between the Deraniyagala’s Beaked Whale and the Ginkgo-toothed Beaked Whale (M. ginkgodens). Descriptive notes. Total length c.400–450 cm; weight c.1000 kg (unconfirmed). Body of the Deraniyagala’s Beaked Whale is spindle-shaped, with greatest girth around its midpoint. Flukes are wide in relation to body length, and tailstock is compressed laterally. Dorsal fin is small and set approximately two-thirds the distance between tip of the beak and end of the tail. Coloration is typically dark on top and light ventrally, with a pale lower jaw and chin. Rostrum and lower jaw form a beak that is indistinct from the low sloping forehead. There are two grooves on the throat. Adult males have a single tusk on each side of the lower jaw. Tusks are positioned approximately one-third of the way along the mandibles. In common with Ginkgo-toothed Beaked Whales, male Deraniyagala’s Beaked Whale may lack any of the long, pale, linear scars caused by tusks of other males that are found on males of most species of beaked whales, but this is based on information from a single individual. However, broken tusks on two specimens suggests that aggressive male–male combat (the cause of such scars) may occur. Habitat. Primarily waters greater than 200 m deep. Nothing further is known about habitat preferences of Deraniyagala’s Beaked Whales. Food and Feeding. There is no specific information available for this species, but in common with other species of beaked whales, Deraniyagala’s Beaked Whale are thought to consume deep-water squid and, to a lesser extent, deep-water fish. They likely forage at depths greater than 500 m. Breeding. There is no information available for this species. Activity patterns. There is no information available for this species. Movements, Home range and Social organization. There is no specific information available for this species, but Deraniyagala’s Beaked Whales likely occur in small groups.
FAMILY ZIPHIIDAE Beaked Whales
On following pages: 18. Sowery’s Beaked Whale (Mesoplodon bidens); 19. Blainville’s Beaked Whale (Mesoplodon densirostris); 20. Andrews’s Beaked Whale (Mesoplodon bowdoini); 21. Spade-toothed Whale (Mesoplodon traversii); 22. Gervais’s Beaked Whale (Mesoplodon europaeus).
FAMILY INIIDAE Amazon River Dolphins
Populations of the Amazon River Dolphin throughout its distribution have been observed to carry objects in their beaks, in behavior that resembles play but is actually sociosexual display. These objects are of natural origin and include branches and sticks, floating vegetation, lumps of hard clay, and large seeds (as in the lower picture here). Object-carrying is predominantly performed by adult males and less often by subadult males. Adult females and young botos rarely carry objects. An object may be repeatedly thrashed against the water’s surface, or thrown with a violent movement of the head. In a form of the behavior exclusive to adult males, the boto grasps a large lump of hard clay in his open mouth, while rising slowly above the surface, and then sinking again with his body held vertically. He may spin languidly on his own axis while holding the object above the water. Carrying behavior is most frequent in large groups with a number of adult males and increases with the number of adult females in the group. During a three-year study, carrying was observed in 221 groups (3·7%) out of 6026 groups encountered. But while aggression was observed in just 15 of the 5815 “non-object” groups, it was seen in 22 out of the 210 object-carrying groups, a 40-fold difference. With few exceptions, aggression was between adult males. Object-carrying may be a form of lekking behavior, with males competing to gain the attention of mate-seeking females. The use of non-edible inanimate objects in displays is unknown in any other aquatic mammal, or indeed any other mammal apart from humans. Above: Inia geoffrensis Pacaya-Samiria National Reserve, Loreto, Peru. Photo: Heinz Plenge
Below: Inia geoffrensis Brazil. Photo: Kevin Schafer
FAMILY INIIDAE Amazon River Dolphins
This extraordinary picture shows the attempted copulation of captive Amazon River Dolphins, an event that some dedicated field researchers have been unable to witness in thousands of hours of work. Births of Amazon River Dolphins occur throughout the year, with a small peak in the lowwater season. This peak occurs in September in Brazil’s Mamirauá lake system. Object-carrying (previous pictures), which is thought to be a sociosexual display, also takes place throughout the year in Mamirauá, with higher occurrences in March and June– August. Length of gestation in botos is not accurately known, but it is probably 11–12 months. Inia geoffrensis Duisburg Aquarium, Germany. Photo: Roland Seitre
Movements, Home range and Social organization As with other aspects of their biology of botos, most of our knowledge comes from work on the Amazon River Dolphin, but the Bolivian and the Araguaian Botos are expected to be
The newborn Amazon River Dolphin is 80–90 cm long and weighs 10–13 kg. Young botos often have sparse, bristly hairs on their beaks that may persist into adulthood. Mothers and their dependent offspring often remain alone, but they sometimes form groups. Long-term relationships other than mother–offspring pairs are unknown. During the low-water season, when lakes are inaccessible, mother–offspring pairs tend to be found in the parts of rivers and channels least exposed to fast currents. Inia geoffrensis Cuyabeno Wildlife Reserve, Ecuador. Photo: Pete Oxford/Minden Pictures/ FLPA
similar. Studies in Brazil relied mostly on the multiple sightings of individual botos or, in one case, the close-range detection of very high frequency (VHF) radio signals. Although long-range movements are almost certainly underrepresented in these studies, they are likely to occur in at least some seasons of the year. Daily movements of up to 20 km are normal, and individuals can move at sustained swimming speeds of 3–6 km/h. About one-half of the botos occurring at the entrance of the Mamirauá Lake system in the central Brazilian Amazon were “residents,” defined as being seen there in at least seven months of the year, and 90% of the botos seen further inside the system met that definition. The “non-residents” demonstrated a range of fidelity to the area, with 10% of the hundreds marked permanently with freeze-brands never encountered again. Seasonal changes in water level and habitat availability resulted in major
males that have asserted their dominance through fighting and display. The evidence for this is that males are much larger than females, with among the most extreme sexual dimorphism of all cetaceans. Adult males always have multiple scars and wounds caused by intraspecific fighting. Finally, the most compelling evidence for female choice is the fact that adult males use objects such as rocks and clumps of vegetation in socio-sexual displays.
FAMILY MONODONTIDAE Narwhal and Beluga
Class Mammalia Order Cetacea Suborder Odontoceti
Family MONODONTIDAE (NARWHAL AND BELUGA) • Medium-sized toothed whales, with blunt heads, fusiform bodies narrowing toward tails, short beaks, mouths curving upward toward eyes, and no dorsal fins; rostrums have globe-like melons containing fatty tissue used in echolocation. • 300–500 cm.
• • • •
The family Monodontidae is composed of two genera, each with a single species: the Narwhal (Monodon monoceros) and the Beluga (Delphinapterus leucas). This whale family is related to families of odontocetes, or toothed whales, which includes dolphins, porpoises, pilot whales, and the Killer Whale (Orcinus orca). The fossil record on monodontids is poor, but the family appears to have differentiated from other odontocetes in the late Miocene. A precursor, Denebola brachycephala, is thought to have lived five million or more years ago. Monodontid-like fossils found along Pacific coasts of North and South America are thought to be from animals that lived two or five million years ago. Fossil remains suggest that monodontids ranged farther south than they do now, in what are now Atlantic and Pacific waters. They are presently only found in Arctic and subarctic regions. There is no evidence of further differentiation at the specific or even subspecific level in monodontids, but there is genetic differentiation among populations of Narwhals and Belu-
Arctic and subarctic regions. Circumpolar, mainly Arctic and subarctic seas. 2 genera, 2 species, 2 taxa. No species threatened; none Extinct since 1600.
gas. This is particularly evident in variable mitochondrial DNA among Beluga populations. Based on genetics or distinct seasonal distributions, there are at least 16 populations of Belugas that are recognized as management units around its circumpolar distribution. Most of these Beluga populations are found in Canadian, Alaskan, or Russian Arctic and subarctic waters. Five Canadian subarctic populations are found in the Gulf of Saint Lawrence, Cumberland Sound (east Baffin Island), James Bay, and eastern and western Hudson Bay. The latter is the largest Beluga population in the world, estimated at more than 50,000 individuals. An additional population in Ungava Bay, Quebec, Canada, would probably be considered eradicated if it were not for occasional sightings in the area. In the Canadian Arctic, there are two other Beluga populations, one centering in the Arctic Archipelago and the other, arguably the second largest in the world, estimated at about 40,000 individuals, summers in the eastern Beaufort Sea. Alaska has four populations of Belugas, starting in Cook Inlet where there is an endangered population of about 350 individuals and followed further north of the Aleutians by three other populations numbering in the
The Beluga has a visible neck region, which in healthy adults, and particularly males, give the appearance of shoulders. Unlike those of most other whales, the Beluga’s cervical vertebrae are not fused and they can move their heads. The Beluga and the Narwhal (Monodon monoceros), the only other species in this family, both have small, blunt heads with narrow short beaks, and their mouths curve upward toward their eyes. Their bulging foreheads contain fatty tissue that is used in echolocation. This structure is known as the melon. Delphinapterus leucas Somerset Island, Nunavut, Canada. Photo: Günter Ziesler
FAMILY MONODONTIDAE Narwhal and Beluga
The Narwhal is more streamlined and torpedo-shaped than the Beluga (Delphinapterus leucas), with little or no narrowing in the neck area. Most male Narwhals have a single long tooth, or tusk, that protrudes forward from the left side of the upper jaw. This tusk can grow to 3 m in old males and is very straight, with a spiraled ivory shaft tapering to a smooth tip. A few females also have a single short, slender tusk. Monodon monoceros Arctic Ocean. Photo: David Fleetham/VWPics.com
Monodontids are toothed whales (Odontoceti), like ocean and river dolphins, porpoises, sperm whales, and beaked whales. However, Narwhals (Monodon monoceros) have no erupted teeth except for the tusk, or occasionally two tusks, of the male and rarely the female. The Beluga has 8–11 blunt, uniform-looking teeth on each side of both its upper and lower jaws, up to a total of 40. Toothed whales can usually be aged by the successive layers of dentine in their teeth.
found in the Greenland Sea and north of Svalbard and the Kara Sea, but there are no estimates of their numbers.
Morphological Aspects Monodontids are medium-sized (300–500 cm long) toothed whales with a blunt head and a fusiform body that narrows toward the tail. Narwhals are more streamlined and torpedoshaped, with little or no constriction in the neck area. Belugas are more rotund than Narwhals, displaying bulging midsections when well fed. They also have narrower neck regions that give healthy adults the appearance of having “shoulders,” particularly males. Both species have a small blunt head with a short beak, and their mouths curve upward toward their eyes. The rostrums of Narwhals and Belugas have globe-like melons containing fatty tissue that aid in echolocation. Their blowhole opens behind the melon, just above the eyes. Both species have a dorsal ridge that runs along the mid-back, starting some distance behind the head and flattening toward the tailstock.
low to mid-thousands. The latter are found in Bristol Bay, the eastern Bering Sea, and the eastern Chukchi Sea. Finally, Russia has three to perhaps six or seven populations of Belugas across its distribution in the White, Barents, Kara, and Laptev seas; the Anadyr Bay (Chukotka); and the Okhotsk Sea. There are no estimates of their numbers, except for the population in the Okhotsk Sea estimated at about 4000 individuals. There are no genetic or distributional studies to suggest segregation among Belugas in the Barents, Kara, and Laptev seas. Data on genetic diversity in Narwhals are not extensive, but information to date suggests that their mitochondrial DNA is less diverse than that of Belugas. In contrast to Belugas, only three populations of Narwhals have been identified to date, although current research in Canada and Greenland suggests that there may be reasons to subdivide them into smaller geographically segregated management units. The largest Narwhal population is named after its wintering distribution in Baffin Bay and numbers in excess of 60,000 individuals. It segregates into several summering stocks in West Greenland and Canada. A second Canadian population of more than 5000 Narwhals centers in northern Hudson Bay in summer. Narwhals are also
Delphinapterus leucas White Sea, Karelia, Russia. Photo: Andrey Nekrasov/VWPics.com
FAMILY MONODONTIDAE Narwhal and Beluga
This group of Beluga mothers with offspring includes at least one yearling or older young of around three-quarters of its mother’s body length. A small young in the top right part of the group is apparently being carried on its mother’s tailstock and lower back. Most dives in coastal areas are shallow, but when offshore, Belugas of both sexes frequently dive through the water column down to the seabed to depths of at least 500 m; some dives even range down to 800 m. Young are not able to do these long dives and remain near the surface while their mothers are foraging. Adult males are capable of deeper dives; a record dive of about 1000 m has been measured. Delphinapterus leucas Somerset Island, Nunavut, Canada. Photo: Art Wolfe
Cumberland Sound of Canada; Cook Inlet Alaska; and Anadyr Bay and the Okhotsk and White seas of Russia. Narwhals and Belugas are most often seen in pods of 2–10 individuals. Pods are often segregated by sex, composed only of males or only females and offspring. Larger mixed-sex pods, which can reach dozens of individuals, are also seen. Both species will also form mixed groups numbering many hundreds or even a few thousand individuals. Such groups are often seen during migrations in spring and fall, but they are also common for Belugas along the coast and in estuaries in summer. Narwhals form large groups when fleeing an area from Killer
Whales. During winter, Narwhals and Belugas can be found aggregating in cracks and leads within the pack ice that covers their winter home ranges.
Relationship with Humans Narwhals and Belugas have been hunted by Arctic People, primarily Inuit, for millennia and are an important part of their lipid-rich diet in this cold environment. Inuit are fond of the “maqtaq” or skin and outer layer of dermal fat. It not only
Polar Bears (Ursus maritimus) are predators both of the Beluga (Delphinapterus leucas) and the Narwhal. They catch the whales when they surface to breathe in narrow holes in the ice, or when they are close inshore during the summer. Polar Bears will also scavenge on the carcasses of these species. In Lancaster Sound, Baffin Bay, and Gulf of Boothia, Polar Bears were found to derive 20–35% of their ingested biomass from Beluga. In the spring and summer, bears from those populations also showed a slight increase in their consumption of Narwhals, but that species is relatively rare in their diet. The loss of pack-ice cover because of climate change may lead to increased predation on both monodontid species by its other main nonhuman predator, the Killer Whale (Orcinus orca).
Monodon monoceros Admiralty Inlet, Baffin Island, Nunavut, Canada. Photo: Paul Nicklen/National Geographic Creative
FAMILY MONODONTIDAE Narwhal and Beluga
The Beluga (Delphinapterus leucas) and the Narwhal have been hunted by Arctic people for millennia. Their skin and blubber make an important contribution to the fat-rich traditional diet and also provide essential vitamins. The cash value of Narwhal ivory provides incentive for the hunting of adult males. In Canada, the annual Narwhal take is co-managed by Regional Wildlife Management Boards and the Department of Fisheries and Oceans. In Greenland, an annual quota is set by the Ministry of Fisheries and Wildlife. While the Beluga does not qualify for threat status at the global level, there is uncertainty about Narwhal numbers and trends, and it is classified as Near Threatened on The IUCN Red List. Monodon monoceros Greenland. David McLain/GETTY
Status and Conservation A number of threats may potentially affect populations of Narwhals and Belugas. They include hunting, fisheries competition or bycatch, disturbance due to vessel traffic, environmental contaminants, climate-induced changes to their seasonal habitats, increased competition with other marine species, and increased predatory pressure. Considering the large numbers of Narwhals and Belugas worldwide, neither species is presently considered threatened. Nevertheless, because there is uncertainty in the population size and trend of many exploited populations, and conservation measures are not being implemented in some parts of their distributions, The IUCN Red List
classifies the Beluga and the Narwhal as Near Threatened. This reflects the possibility that they could be listed as threatened in the near future. Declines of some populations of Canadian Beluga have been documented, and there are proposed or enacted listings of threatened or endangered under the Species at Risk Act (SARA) in Canada. The Beluga population in the Alaskan Cook Inlet is also listed under the US Endangered Species Act. Greenland has documented a large decline in its winter population of Belugas in Davis Strait. Conservation measures are the responsibility of national governments. Population recovery plans are in effect or are being planned for some of the listed populations in Canada and the USA. General Bibliography Angliss & Outlaw (2005), Bailey & Zinger (1995), Boltunov & Belikov (2002), Brennin et al. (1997), Brodie (1967, 1970), COSEWIC (2004), Dietz & HeideJørgensen (1995), Dietz, Heide-Jørgensen, Born & Glahder (1994), Dietz, Heide-Jørgensen, Richard & Acquarone (2001), Dietz, Heide-Jørgensen, Richard, Orr et al. (2008), Finley & Gibb (1982), Finley et al. (1990), Fordyce (2009), Frost & Lowry (1990), Garde et al. (2007), Gjertz & Wiig (1994), Gurevich (1980), Hazard (1988), Heide-Jørgensen (1990, 1994, 2009), Heide-Jørgensen & Acquarone (2002), Heide-Jørgensen & Laidre (2006), Heide-Jørgensen & Rosing-Asvid (2002), Heide-Jørgensen et al. (2001), JCNB (2004, 2006), Jefferson et al. (2008a, 2008b), Laidre & Heide-Jørgensen (2005a, 2005b, 2011), Laidre, Heide-Jørgensen, Dietz et al. (2003), Laidre, Heide-Jørgensen, Jørgensen & Treble (2004), Laidre, Heide-Jørgensen, Logsdon, Hobbs, Dietz & VanBlaricom (2004), Laidre, Heide-Jørgensen, Logsdon, Hobbs, Heagerty et al. (2004), de March & Maiers (2001), de March & Postma (2003), de March & Stern (2003), de March, Maiers & Friesen (2002), de March, Stern & Innes (2004), de March, Tenkula & Postma (2003), Martin & Reeves (2000), Michaud (1993), Mitchell & Reeves (1981), Moore & DeMaster (2000), NAMMCO (2000, 2006), O’Corry-Crowe (2009), O’Corry-Crowe, Dizon et al. (2002), O’Corry-Crowe, Suydam et al. (1997), Ognetov (1981), Reeves & Tracy (1980), Reeves et al. (2011), Remnant & Thomas (1992), Richard (2010a, 2010b), Richard & Pike (1993), Richard & Stewart (2008), Richard, Heide-Jørgensen, Orr et al. (2001), Richard, Heide-Jørgensen & St. Aubin (1998), Richard, Martin & Orr (1997, 2001), Richard, Orr, Dietz & Dueck (1998), Richard, Orr & Postma (1990), Richard, Weaver et al. (1994), Seaman et al. (1982), Sergeant (1973), Sjare & Smith (1986a, 1986b), Stewart, B.E. & Stewart (1989), Stewart, D.B. et al. (1995), Stewart, R.E.A. et al. (2006), Suydam (2009), SWG-JCNB (2005), Thomsen (1993), Tomilin (1957), Van Parijs et al. (2003a), Vergara (2011), Vladykov (1946), Wagemann et al. (1996), Welch et al. (1993), Westdal et al. (2009).
c ontains sought-after lipids but when eaten raw, it provides several vitamins essential to people who live in an environment almost devoid of fruits and vegetables. Inuit also eat some of the dark meat, particularly the back-straps. References to the Narwhal tusk go back several thousand years in Chinese written texts, where a unicorn-like creature is described. Crafty tusk traders in Medieval Europe probably perpetuated this myth. As commercial whaling for Bowhead Whales (Balaena mysticetus) expanded throughout Arctic regions from the 17th to the 20th century, harvests of Belugas and Narwhals were taken periodically by whalers who had not filled their ship holds with Bowhead Whale oil. Trading companies established in Arctic regions, such as the Royal Greenland Company and the Hudson Bay Company, traded in Narwhal tusks in the 19th and 20th centuries. In the early 20th century, trading posts of the Hudson Bay Company even organized hunts for Belugas in various parts of the Canadian subarctic. Skins and oil were sold on European markets. Presently, products from legal hunts of Belugas and Narwhals by Native People, particularly maqtaq, are either consumed directly by Inuit hunters and their extended families, or they are sold in local food markets, particularly in Greenland and, to a lesser extent, the Canadian Arctic. The valuable tusk of the Narwhal is also sold to collectors in Greenland, Canada, and elsewhere. Permitting systems designed to track the origin of traded Narwhal tusks regulates hunting and sale of tusks in Canada and Greenland. International trade is regulated under permits issued by the Convention on the International Trade in Endangered Species of Fauna and Flora (CITES).
FAMILY DELPHINIDAE Ocean Dolphins
The skin pigmentation of the Indo-Pacific Humpback Dolphin varies throughout its distribution and also at different ages. Individuals in the east, such as those in the eastern Indian and Pacific oceans, are born with darkgray pigmentation and become paler with age. Dark young off South-east Asia and Australia, like those shown here, also tend to become paler with age, but they retain dark spotting and blotches. Some, however, lose all their dark pigmentation and are completely white, with a pinkish tinge. Conversely, pale-colored young off South Africa, in the west of their distribution, darken with age. The dorsal fin and associated hump also vary distinctly between the extremes of the Indo-Pacific Humpback Dolphin’s distribution. In the east, the dorsal fin is short and slightly recurved, with a wide, laterally sloping hump. In the west, the dorsal fin is sharply recurved and smaller, with a broad hump. Although the species is here considered monotypic, S. chinensis consists of at least two types, plumbea in the western Indian Ocean and from South Africa to the east coast of India, and chinensis, from the eastern coast of India to China, and Australia. Some researchers consider the two forms to be distinct species. Mitochondrial DNA differences suggest that humpback dolphins in northern Australian waters may also represent a separate species. The second Sousa species recognized here, the Atlantic Humpback Dolphin (S. teuszii) does not seem to attract much controversy, because its western African distribution is distant from other populations of Sousa and because genetic studies and morphological studies of skulls have determined that it is a distinct species. Above left: Sousa chinensis Hong Kong, China. Photo: Jonas Livet Above right: Sousa chinensis Guangxi, China. Photo: Yilun Qiao Below left: Sousa chinensis Hong Kong, China. Photo: Roland Seitre
Below right: Sousa chinensis Queensland, Australia. Photo: Rohan Clarke
FAMILY DELPHINIDAE Ocean Dolphins
The species of the genus Stenella are primarily small, slender dolphins, with prominent, long beaks containing numerous teeth. Five species are currently included. However, molecular studies indicate that the Pantropical Spotted Dolphin is not closely related to three other members of the genus, and similarities in appearance are likely the result of convergence. Of the two subspecies, the “Coastal Pantropical Spotted Dolphin” (S. a. graffmani) tends to be slightly larger and more robust than the “Offshore Pantropical Spotted Dolphin” (S. a. attenuata), but with a slightly thinner beak. Stenella attenuata Kona, Hawaii, Hawaiian Islands. Photo: Andre Seale/VWPics.com
Spots begin to appear as the Atlantic Spotted Dolphin ages, showing first on the back and belly. Adults are heavily spotted. The spots are white and tend to be larger than those on the Pantropical Spotted Dolphin (Stenella attenuata, picture above). Immature Atlantic Spotted Dolphins are unspotted and have a color pattern like the bottlenose dolphins (Tursiops sp.). According to molecular studies, the Atlantic Spotted Dolphin is most closely related to the Striped Dolphin (S. coeruleoalba) and Clymene Dolphin (S. clymene), followed by the common dolphins (Delphinus spp.) and the Indo-Pacific Bottlenose Dolphin (T. aduncus). Stenella frontalis Little Bahama Bank, The Bahamas. Photo: Norbert Wu/Minden Pictures/ ASA
Dolphin are recognized: the nominate form (T. t. truncatus) and the “Black Sea Bottlenose Dolphin” (T. t. ponticus). Presently, there are no subspecies of the Indo-Pacific Bottlenose Dolphin. Based on mitochondrial cytochrome-b sequences, the Indo-Pacific Bottlenose Dolphin shares a closer affinity to some species of Stenella and Delphinus than to the Common Bottlenose Dolphin (i.e. the two bottlenose dolphins are not sister taxa). Nevertheless, more recent analyses of multiple independent molecular markers indicated monophyly of this genus, albeit with low support. The monophyly hypothesis is consistent with the very similar morphologies (external and both cranial and post-cranial osteology) shared by the two species.
reproductive isolation in sympatry, based on consistent morphological and molecular differences, have resulted in the recognition of at least two species: the Common Bottlenose Dolphin (Tursiops truncatus) and the Indo-Pacific Bottlenose Dolphin (Tursiops aduncus). Based only on mitochondrial DNA, a third species of Tursiops in South African waters was also suggested, but it is not presently accepted. More recently, a small population of bottlenose dolphins in south-eastern Australia was proposed to be a new species, the so-called Burrunan dolphin (T. australis), but inadequate supporting evidence also rendered this possible species provisional. It would not be too surprising if more species were recognized in the near future. Two subspecies of the Common Bottlenose
FAMILY DELPHINIDAE Ocean Dolphins
Like the Short-beaked Common Dolphin (Delphinus delphis), schools of Long-beaked Common Dolphin work together to herd fish into “bait balls.” The dolphins are able to detect large gatherings of fish from a distance and rush toward them, often “porpoising” or leaping above the surface. As they approach, they adopt a U-shaped formation, perhaps using echolocation to pinpoint the position of the shoal. They surround the shoal rapidly, some swimming in circles around it, while others dive beneath to drive it to the water’s surface. Delphinus capensis East London, Eastern Cape, South Africa. Photo: Chris Fallows
lived and slow to mature. Delphinid longevity varies greatly from about 20 years to more than 60 years, and Killer Whales may live as long as 90 years. Females usually live longer than males, by as much as 20–30 years in larger delphinid species. The age at sexual maturity varies from about 2–3 years for the Short-beaked Common Dolphin to as late as 15 years or more for the Killer Whale, Short-finned Pilot Whale, and Melonheaded Whale. For most delphinids, females reach sexual maturity a few years earlier than males; the difference in the age of maturation appears to be much greater for species in which males are much larger than females. Maternal care is exceptionally lengthy, even for mammals, and investment of resources is considerable, with long gestation, lactation, and extended post-weaning care in several species. Only in a few rare cases do males provide some parental care for their
offspring (e.g. the Killer Whale and the Short-finned Pilot Whale). Gestation for most delphinids lasts for about twelve months, but there is great variation across species, populations, and individuals; gestation is about nine months for the Spinner Dolphin but about 17 months for the Killer Whale. In general, it appears that larger delphinid species have longer maximum gestation lengths and produce larger neonates. Delphinid offspring are proportionately large and precocial, capable of swimming and breathing almost immediately after birth, which occurs completely in the water. Neonates can be 40–45% of the asymptotic length and 8–10% of the mass of female delphinids. Lactation in delphinids varies greatly in length across species. Most of the small delphinids lactate for 2–3 years, but in the extreme case of the Short-finned Pilot Whale, lactation
The Pacific White-sided Dolphin lives in groups of hundreds to thousands, which split into smaller units when foraging. Groups can consist of as few as two individuals, but 10–50 is more typical. Larger groups are more successful at herding shoals of fish, like these herring (Clupea), into “bait balls.” Near the western coast of North America, Pacific Whitesided Dolphins prefer epipelagic (near-surface) species such as herring, hake (Merluccius spp.), salmon (Oncorhynchus spp.), and cod (Gadidae), but offshore populations of the dolphins prefer more mesopelagic prey (species from deeper water that move nearer the surface at night). Lagenorhynchus obliquidens Queen Charlotte Strait, SW British Columbia, Canada. Photo: Paul Nicklen
FAMILY DELPHINIDAE Ocean Dolphins
During the “Sardine Run” along the coast of the Eastern Cape, South Africa, the Long-beaked Common Dolphin can be found in “superpods” of more than 5000 individuals. These dolphins are present in smaller numbers off the stretch of coast between East London and Port Elizabeth in most months of the year. When the sardines (actually the South African pilchard, Sardinops sagax ocellatus) begin their northward migration to breed, dolphins that are resident for the rest of the year in cooler waters to the south begin to follow them. Long-beaked Common Dolphins from further offshore may also move in to the continental shelf to take advantage of this superabundance of food. The “sardines” migrate along a corridor of cool water between the coast and the warm offshore Agulhas Current, which flows in the opposite direction. Sardine shoals can be several kilometers in length and more than 1 km wide. Working cooperatively and making use of the sardines’ instinct to crowd together when threatened, the dolphins cut out a portion of the shoal and surround it, forming a “bait ball” 10–20 m in circumference. Among other cooperative techniques, the dolphins are reported to produce clouds or curtains of bubbles that corral the fish into ever-tighter formations. Above: Delphinus capensis Wild Coast, Eastern Cape, South Africa. Photo: Alexander Safonov/GETTY
Below: Delphinus capensis East London, Eastern Cape, South Africa. Photo: Chris Fallows
FAMILY DELPHINIDAE Ocean Dolphins
Dolphins are the mainstay of whale-watching tourism in areas where they are easily and reliably encountered. This and similar activities, including dolphin feeding and swimming with dolphins, can have short and long-term disturbance effects, especially on dolphins in small, isolated populations. Chronic exposure to disturbance has been linked to habitat displacement, increased levels of stress hormones, and reduced reproductive success and survivorship in Indo-Pacific Dolphins (Tursiops aduncus) and Common Bottlenose Dolphins, among other species. Tursiops truncatus Sado Estuary, Portugal. Photo: Pedro Narra
and their future is precarious. These include five populations of Irrawaddy Dolphins, one subspecies and one population of Short-beaked Common Dolphins, one population of the IndoPacific Humpback Dolphin, one population of the Striped Dolphin, one subspecies of the Spinner Dolphin, one subspecies and two populations of Common Bottlenose Dolphins, and one subspecies of Hector’s Dolphin. All species of Sousa, Orcaella, and Sotalia are listed under CITES Appendix I, and all other delphinids are under Appendix II. Hector’s Dolphin is the only delphinid species that is listed as Endangered on The IUCN Red List. It is endemic to the coastal waters of New Zealand and has the most limited distribution of any species of marine cetaceans, with the exception of the Critically Endangered Vaquita, only found in the upper Gulf of California, Mexico. The total population of Hector’s Dolphin has
decreased to about 7400 individuals, and the decline is projected to continue at a rate of more than 50% over three generations (about 39 years). One subspecies of Hector’s Dolphin, Maui’s Dolphin, is found only in a restricted area along the west coast of the North Island of New Zealand. It numbers slightly more than 100 individuals, and a continuing decline of more than 80% over three generations is projected; thus, it is classified as Critically Endangered on The IUCN Red List. The main threat to Hector’s Dolphins is bycatch in gillnets, but trawl fishing is also responsible for some mortality. Conservation efforts include the establishment of two protected areas. These areas appear to have reduced mortality but do not seem to be sufficiently large to ensure continued survival of the subspecies. The Atlantic Humpback Dolphin has a limited distribution in coastal waters along western Africa from southern Angola
Like several other ocean dolphin species, Hector’s Dolphin seems actively attracted to moving boats. This behavior has led to the development of a number of commercial dolphin watching and swimming-with-dolphins operations in New Zealand. During summer weekends, dozens of recreational boats also approach the dolphins, and swimmers enter the water to interact with them. In recent decades, the dolphins have changed their behavior. Instead of moving away from human swimmers, they approach them. Cephalorhynchus hectori New Zealand. Photo: Brian J. Skerry
FAMILY DELPHINIDAE Ocean Dolphins
A scuba diver encounters a habituated False Killer Whale. This is possibly a rehabilitated stranded individual now kept in â€œnaturalâ€? conditions, although far from normal environment for this intensely social species. No overall population estimates or trends are available for the False Killer Whale, and IUCN lists it as Data Deficient. It seems naturally uncommon, making it vulnerable to localized threats. Incidental catch in gillnet, purse seine, and long-line fisheries is probably the most serious threat. False Killer Whales are hooked or injured, sometimes seriously, when attempting to remove fish from hooks, and they may be persecuted by fishermen. Unknown numbers are hunted for meat and oil in the China Seas and Caribbean.
to Morocco. Although total abundance of the Atlantic Humpback Dolphin is unknown, it is likely no more than a few thousand and certainly fewer than 10,000 individuals. A continuing decline is inferred or suspected from the limited information that is available about its mortality levels and threats that occur within its distribution. As such, it is classified as Vulnerable on The IUCN Red List. The most serious threat, as with most delphinids, is bycatch in fishing gear, primarily gillnets, and this threat has been increasing in recent decades as fishing pressure intensifies. Fishing pressure may have also resulted in a decrease in food availability for the Atlantic Humpback Dolphin. Some direct hunting of these dolphins for food may also occur. Other threats include habitat destruction as a result of agricultural and industrial development, especially in and near areas with high human densities such as oil and gas exploration and development, vessel disturbance and collisions, and environmental contaminants. Although information about the Atlantic Humpback Dolphin is limited, it raises sufficient concern to make this a high priority species for research and conservation attention. The Irrawaddy Dolphin has experienced a significant contraction of its distribution and, in most regions where it has been studied, seems to exist in small numbers, except in coastal waters off Bangladesh where a few thousand are found. It is particularly vulnerable to bycatch in fishing gear, especially gillnets, and limited data on fisheries-related mortality indicate high and unsustainable levels. Total abundance is unknown (with no reliable estimate being expected in the near future), and no information exists on mortality levels. It is suspected that a 30% decline has occurred over three generations (45â€“48 years) given observed distributional contractions, declining abundance of several isolated populations, and increasing number and intensity of anthropogenic threats. These threats are varied and include increasing intensity of fisheries that use harmful gear such as gillnets, stow nets, electro-fishing, and blast-fishing; increasing vessel traffic that increases noise disturbance to the animals and collisions; habitat loss, degradation, and fragmentation because of fixed fishing gear, coastal development, freshwater extraction, and river alterations; deforestation and mining that have led to large inputs of mercury and increased sedimentation, reducing the depth of some rivers and adjoining lakes inhabited by isolated populations; prey depletion due to overfishing and compounded by habitat loss; and intensive inputs of agrochemicals. For some small populations, captures for live display can also be a major threat. The
Irrawaddy Dolphin is classified as Vulnerable on The IUCN Red List, but there are five Critically Endangered populations that are isolated and have highly restricted distributions: Malampaya Sound, Palawan Island, Philippines; Mekong River, Vietnam, Laos, and Cambodia; Mahakam River, East Kalimantan, Indonesia; Irrawaddy River, Burma; and Songkhla Lake, Thailand. These populations all number less than 100 individuals (with fewer than 50 mature individuals) and are declining, mainly due to unsustainable bycatch in fishing gear and habitat loss. Two other populations in Chilika Lagoon in eastern India and the central Visayas in Philippines also appear to be threatened. Although a lack of information has prevented assessment of their current conservation status, they appear to be similarly few in number and are facing several serious threats as the five critically endangered populations. In many regions, local decrees and laws protect Irrawaddy Dolphins, which has a conservation action plan, but their effectiveness seems to be quite limited due to issues with implementation and enforcement. As numbers continue to decline and distributions shrink further, it is likely that at least some, and perhaps all, of the Critically Endangered populations will be lost in the near future. Although the Indo-Pacific Humpback Dolphin is listed as Near Threatened on The IUCN Red List, the taxonomy within the genus Sousa is quite confused. At least two morphological forms (plumbea- and chinensis-type) of this species exist, and some researchers believe that they represent two distinct species. Even within what is termed the chinensis-type, there is growing evidence that the humpback dolphins of northern Australia may represent a distinct species from those in southeastern and eastern Asia. If assessed separately, both forms would qualify as vulnerable on The IUCN Red List. Some localized direct hunting for food exists, but the primary problem is bycatch in fishing gear (including anti-shark nets set to protect bathers), especially in areas where there is heavy fishing pressure in coastal and estuarine waters. Other serious threats facing local populations include habitat loss and degradation due to coastal development, loss of freshwater input to estuaries, chemical pollution; noise from coastal construction, shipping, seismic surveys, resource extraction, military activities and increasing vessel traffic. Population fragmentation due to loss of important habitat may have occurred in some regions. There is no global population estimates for the Indo-Pacific Humpback Dolphin or its various forms. Abundance estimates for localized populations vary from a few tens to about 2500 individuals in the Pearl River Estuary, which is an exceptionally
Pseudorca crassidens Subic Bay, W Luzon, Philippines. Photo: Norbert Probst/Imagebroker/ FLPA
PLATE 23 inches
NE Pacific resident form
NE Pacific transient form
N Atlantic form
Antarctic type A form
Antarctic type B form
Antarctic type C form
Antarctic type D form
Plate 23 Species Accounts
Genus ORCINUS Fitzinger, 1860
9. Killer Whale Orcinus orca French: Épaulard / German: Schwertwal / Spanish: Orca Other common names: Orca
Taxonomy. Delphinus orca Linnaeus, 1758, “Oceano Europæo.” Although O. orca is currently recognized as monotypic, serious taxonomic revision is required and will likely occur in the near future. Genetic, morphological, and ecological evidence indicates that there are three ecotypes (residents, transients, and offshores) in the north-eastern Pacific Ocean, which may represent separate species or subspecies. Three distinct ecotypes have also been identified in Antarctic waters (types A, B, and C) that may correspond to putative species previously proposed in the 1980s (O. nanus and O. glacialis). Recent molecular studies strongly suggest that these three ecotypes warrant species designation. A fourth type (type D) has also been newly described from New Zealand area. Monotypic. Distribution. The most widely distributed of all cetaceans, found in almost any marine environment from the Equator to both polar zones, including semi-enclosed seas such as the Mediterranean Sea, Red Sea, Persian Gulf, Gulf of California, Sea of Okhotsk, Yellow Sea, Sea of Japan, Chukchi Sea, Beaufort Sea, Gulf of Saint Lawrence, and Ross Sea. Descriptive notes. Total length up to 980 cm (males) and up to 770 cm (females); weight up to 6600 kg (males) and up to 4700 kg (females). Neonates are 210–260 cm long and weigh 160–180 kg. The Killer Whale is the largest member of Delphinidae and is one of the most distinctive and easily recognizable cetaceans. Body is robust but streamlined, with tall dorsal fin, large paddle-shaped flippers, and blunt, poorly defined beak. It is strongly sexually dimorphic in size and morphology. Females and immature individuals have falcate dorsal fins, which may have slightly rounded tips. Adult males have much taller (up to 180 cm) dorsal fins than females (up to 80 cm) that are triangular in shape and may slant slightly forward in some geographical forms, giving the appearance of backward placement. Adult males also have larger flippers than females, and fluke tips of some older males are curved downward. Lower jaw and ventral area up to urogenital region is white, with two lobes curving up onto flanks anterior to genital slit and behind dorsal fin. Undersides of flukes are also white, and there are white patches above eyes. Rest of body is black except for gray saddle patch behind dorsal fin. Some geographical forms have distinctive gray line extending from lower point of saddle patch toward head, making a curved “cape” shape. Young individuals tend to have a more muted pattern, with white areas tinged slightly yellow or orange. There are 10–14 pairs of large, conical teeth (up to 10 cm long) in each jaw, although they may be worn down and damaged in older individuals. There are three ecotypes known from north-western coasts of North America, including Alaska. Resident. The resident Killer Whale has dorsal fin with rounded tip, medium-sized oval eye patch oriented horizontally, no distinct cape pattern, and saddle patch that can be open (with black pigmentation incurring into gray saddle) or closed, with tip extending no further than middle of dorsal fin base. Transient. The transient Killer Whale is generally larger in size than the resident Killer Whale, has pointed dorsal fin tip, no dorsal cape pattern, medium-sized oval eye patch oriented horizontally, and closed saddle patch with tip that can extend as far forward as anterior edge of dorsal fin base. Offshore. The recently described offshore Killer Whale is genetically distinct from, but similar in appearance to, the resident form, although it tends to be smaller and females have rounded dorsal fin tips. Three morphologically, ecologically, and genetically distinct types have also been identified in Antarctic waters. Type A. This type of Killer Whale is circumpolar in Antarctic waters and is similar in appearance to forms in the north-eastern Pacific Ocean. Type B. This type of Killer Whale is known primarily from Antarctic and subantarctic waters and is generally smaller than the type A Killer Whale. This type possesses dorsal cape pattern, large horizontally oriented eye patch, and closed saddle patch. A build-up of diatoms on skin may give white areas a yellowish hue. Type C. This type of Killer Whale is a dwarf form, reaching average lengths 1–3 m shorter than the other types and is restricted to Antarctic waters. Like the type B Killer Whale, type C has distinct dorsal cape, generally closed saddle patch, and pale yellow patches. Eye patch, however, is small and slanted at 45° angle to horizontal body axis. A fourth type (type D) has been described very recently from a mass stranding event on New Zealand in 1955 and several sightings at sea since 2004. An extremely small eye patch characterizes this type. Habitat. Cosmopolitan in marine habitats but somewhat more abundant at higher latitudes and in near-shore waters, especially in regions of high productivity. The Killer Whale has been documented, on rare occasions, to move into river mouths. Most observations have been within 800 km of shoreline. The Killer Whale is less abundant in lower tropical latitudes and in the ice-pack zones of the high Arctic and Antarctic oceans. In the Canadian Arctic Ocean, however, the Killer Whale is becoming seasonally more abundant as pack-ice extent and duration decline with global climate change. Resident, transient, and offshore forms of Killer Whales are most well known from populations on the north-western coast of North America, including the Aleu-
tian Islands, and there is good evidence to suggest that, in that area at least, they may each warrant full species status. Resident Killer Whales are the most near-shore distributed of the three forms, given that they feed primarily on salmon migrating into freshwater areas to spawn. The type B Killer Whale is found primarily in Antarctic regions, usually among ice floes concentrated around the Antarctic Peninsula, although their distribution may extend up to the Falkland Islands and New Zealand. The type C Killer Whale appears to be restricted to Antarctic waters and prefers the pack-ice habitats in eastern Antarctica. The recently described type D Killer Whale is subantarctic and is most abundant between 40° S and 60° S. Food and Feeding. The Killer Whale is an apex predator. Globally, it is a generalist with a diverse diet. There are over 140 species of documented prey including a wide variety of small and large fish, cephalopods, marine mammals, seabirds, and marine turtles. The Killer Whale is the only cetacean species known to have populations that specialize on mammal prey. Over 50 different species of mammals have been documented as prey including cetaceans, pinnipeds, sirenians, mustelids, and occasionally even ungulates and ursids. On a local scale, populations of Killer Whales are often distinguished by dietary specializations. For example, resident Killer Whales in the north-western coast of North America feed almost exclusively on salmon (Oncorhynchus spp.) and are not known to feed on endothermic animals. They appear to prefer the largest and most fat-rich species (Chinook salmon, O. tshawytscha, and Coho salmon, O. kisutch), despite smaller species such as sockeye salmon (O. nerka) occurring in greater abundance. Transient Killer Whales in the same area, by contrast, hunt marine mammals and do not consume fish. Preferred prey include Harbor Seals (Phoca vitulina), Harbor Porpoises (Phocoena phocoena), and Dall’s Porpoises (Phocoenoides dalli), and they will also eat Steller Sea Lions (Eumetopias jubatus), California Sea Lions (Zalophus californianus), Northern Elephant Seals (Mirounga angustirostris), Pacific White-sided Dolphins (Lagenorhynchus obliquidens), and Common Minke Whales (Balaenoptera acutorostrata). Transient Killer Whales off the coast of California specialize on Gray Whales (Eschrichtius robustus) and will attack young that are accompanying their mothers northward on their first migration. Dietary preference of offshore Killer Whales is currently poorly known but appears to include more offshore fish species such as Pacific halibut (Hippoglossus stenolepis) and various carcharinid sharks. Resident, transient, and offshore killer whales, although partially sympatric in their distributions, do not appear to associate with each other and are unambiguously distinct in mtDNA and nDNA composition. Given their dietary specializations, this genetic divergence is likely the result of foraging strategies being socially passed across generations. This would have eventually given rise to divergent enough skill-sets so as to underlie mutually exclusive lifestyles, making for an intriguing and rare case where ecological divergence is likely driving incipient sympatric speciation. Populations of Killer Whales that inhabit Norwegian fjords specialize on herring (Clupea spp.) and behaviorally resemble resident Killer Whales in the north-eastern Pacific Ocean. The Antarctic type A Killer Whale specializes on the Antarctic Minke Whale (B. bonaerensis), and type B populations in the vicinity of New Zealand may specialize on sharks and other elasmobranchs. The type C Killer Whale feeds primarily on Antarctic fish species, and some populations of type D Killer Whale are thought to prefer Patagonian toothfish (Dissostichus eleginoides). In the Canadian Arctic, Killer Whales most commonly prey on the Beluga (Delphinapterus leucas), the Narwhal (Monodon monoceros), and the Bowhead Whale (Balaena mysticetus). In multiple populations, dietary specialization has led to development of unique foraging strategies. For example, Norwegian populations of Killer Whales use a strategy called “carousel feeding,” during which a school of herring is herded into a tight ball near the water’s surface. Individual whales then stun and pick at prey around edges of the ball. Killer Whales in the Strait of Gibraltar feed on Atlantic bluefin tuna (Thunnus thynnus) by chasing schools for c.30 minutes at high speed until tuna are exhausted. Transient Killer Whales usually hunt in small groups and are more acoustically quiet than resident Killer Whales, likely to keep from alerting their mammalian prey. Killing seals and sea lions usually involves repeated ramming, slapping them with flukes, or even leaping on them. After prey is stunned, it is dragged underwater and drowned. The killed animal is then shared among the group. Killer Whales may herd large groups of dolphins or porpoises into confined bays where they can be easily killed after being trapped (a strategy that is disturbingly reminiscent of human dolphin drives). Larger groups of transient Killer Whales are required to successfully attack mysticetes and the Sperm Whale (Physeter macrocephalus). The group will coordinate itself so that some individuals grasp flippers and tail flukes of prey to impede movement while others gash at the blowhole area to impair breathing. Blubber, lips, and tongue are usually the only parts of the killed whale that are consumed. Groups of type B Killer Whale in Antarctica have learned how to coordinate forceful water waves to wash over and tilt ice floes to dislodge Weddell Seals (Leptonychotes weddellii) resting on them. When this wave-washing technique fails, one or two Killer Whales may even lift the ice floe with their heads to flip it over or break it. Killer Whales off Patagonia, Argentina, have developed a strategy for hunting young Southern Elephant Seals (Mirounga leonina) and South American Sea Lions (Otaria byronia) that involves intentionally stranding themselves temporarily on the sloping beaches. Killer Whales around the Crozet Islands use a similar method, and in this region, there is compelling evidence to suggest that adults actively teach this strategy to their offspring. Breeding. Off the Pacific coast of North America, breeding peaks in October–March but may occur throughout the year. In the north-eastern Atlantic Ocean, breeding peaks between late fall and mid-winter. Most life history data are drawn from resident Killer Whales in the north-eastern Pacific Ocean and may not be typical of all populations of Killer Whales. Mating is endogamous in resident Killer Whales, occurring when males briefly leave their matrilines to mate with females from other pods within the same social clan, usually during on temporary merging of pods (superpod). Clans
FAMILY DELPHINIDAE Ocean Dolphins
PLATE 29 inches
FAMILY TRICHECHIDAE Manatees
Plate 29 Species Accounts
Genus TRICHECHUS Linnaeus, 1758
1. West Indian Manatee Trichechus manatus French: Lamantin des Antilles / German: Karibik-Seekuh / Spanish: Manatí del Caribe Other common names: American Manatee; Antillean Manatee, Caribbean Manatee (manatus); Florida Manatee,
North American Manatee (latirostris)
Taxonomy. Trichechus manatus Linnaeus, 1758, “Mari Americano.” Restricted by Thomas in 1911 to West Indies. A subspecies from the east coast of the USA, the “Baker Manatee,” bakerorum named by Domning in 2005 that lived from North Carolina to Florida became extinct in the late Pleistocene. Two extant subspecies recognized. Subspecies and Distribution. T. m. manatus Linnaeus, 1758 – Greater Antilles and Gulf and Caribbean coasts of Mexico, Central America, and N South America (S to Alagoas and Sergipe states, Brazil). T. m. latirostris Harlan, 1824 – SE USA, primarily Florida and Georgia, with seasonal movements to other states bordering the Gulf of Mexico and the Atlantic Ocean. Descriptive notes. Total length 250–390 cm; weight up to 1620 kg. External appearance of the West Indian Manatee is identical to the West African Manatee (T. senegalensis). Body shape is somewhat fusiform but bulkier and more rounded than many other species of marine mammals. Head is small, with no neck and no external ear pinnae. Paired nostrils near the end of the snout open dorsally. Eyes are small. Pronounced
expansion of upper lip region forms the oral disk, a prehensile, grasping organ. Skin is finely wrinkled and uniformly gray to brown, with variation due to organisms that live on their skin, and sparsely haired, with specialized sensory hairs that are most prominent on the dorsum. Head has denser sensory orofacial hairs around muzzle, and oral disk and lower lips have specialized brush-like bristle fields for grasping and manipulating food. Pectoral flippers have 3–4 nails that are used for bottom locomotion and food handling. West Indian Manatees are not sexually dimorphic, other than position of external genitalia close to rectum in females and closer to umbilicus in males. Habitat. A wide variety of shallow marine, estuarine, and freshwater habitats that support forage plants, but seemingly limited to regions with periodic access to freshwater sources for drinking. Depths of typical habitats are 1–10 m. The same West Indian Manatees will use habitats ranging from seagrass beds to rivers with freshwater plants and tidal creeks where the only available food is emergent vegetation at high tide. Cold-water temperatures govern seasonal limits to distribution of manatees in both North and South America, roughly corresponding to a minimum water temperature of c.20°C. The West Indian Manatee has a low rate of metabolism and high thermal conductance, rendering individuals susceptible to a cold-stress pathological syndrome. Habitat has expanded in Florida to include areas with artificial warm water sources in winter (e.g. electric power plant effluents). The West Indian Manatee does not require wilderness (some occur in urban areas), and individuals become habituated to humans where they are not hunted. Females may seek out secluded, quiet areas to give birth. Food and Feeding. The West Indian Manatee eats seagrasses, freshwater aquatic plants, mangrove leaves, and most physically accessible rooted, submerged, floating, and bank vegetation. The list of known aquatic food plants includes multiple species in four genera of seagrasses, two genera of mangroves, eleven genera of freshwater submerged plants, twelve genera of freshwater floating plants, 40 genera of emergent plants, and 39 genera of algae (probably ingested incidentally with vascular plants). There are anecdotal reports of the ingestion of various animals (mostly invertebrates).
Plate 29 Species Accounts
Two feeding modes are used: excavating when both shoots and rhizomes of seagrasses are ingested and cropping when leaves and stems of all plants are taken. Retention time for ingesta is slow at about six days. Daily quantity of food ingested is c.7% of body weight in adults, consumed in c.4–7 hours of feeding/day. Breeding. Most of the information on reproduction in the West Indian Manatee is based on studies of the “Florida Manatee” (T. m. latirostris), but other than diffuse seasonality (with minimal birthing or mating in winter), breeding is likely to be very similar in the “Antillean Manatee” (T. m. manatus). Estrous females attract groups of roving adult and subadult males in “mating herds” that persist for up to three weeks, can involve 20 or more males, and can include group movements of up to 160 km. More than one male can mate with a female in these groups, implying sperm competition. Adult females typically produce many corpora lutea/ovary/pregnancy (average 36). Some males produce sperm as early as two years old, but most males, like females, probably are not sexually mature until about five years old. The smallest length at maturity is c.250 cm in both females and males. Mature males are not always in a continuous breeding condition. Gestation is unknown precisely but is in the range of 12–14 months. A single offspring is born (twins occur in 1–4% of births). Offspring nurse for 1–2 years before they are weaned, but this varies with the individual. Adult females give birth, on average, every 2–3 years. The Florida Manatee shows diffuse seasonality in reproduction, with lowest reproductive activity in winter. Activity patterns. The West Indian Manatee shows no evidence of circadian rhythms and is active both day and night, with intermittent periods of activity and rest. Lack of strict circadian rhythms is consistent with an absence of a pineal organ near the base of the brain. This pattern changes with environmental factors; in winter, the Florida Manatee shows activity patterns that include resting at warm water springs and industrial effluents during the coldest times of day, with some remaining at these refugia and foregoing feeding for up to a week during lengthy cold periods. The West Indian Manatee also becomes more nocturnal in areas where it is hunted in daylight or where daytime boat activity is high. The Florida Manatee spends c.20–25% of the 24-hour day feeding, c.20–25% resting, c.10–15% “cavorting” (social behavior similar to the wrestling and jostling seen in mating herds but of lesser intensity), and c.30–45% of the day traveling. Movements, Home range and Social organization. Florida Manatees show sexual differences in movements and wide individual differences in migratory behavior. During warm seasons, males spend more time traveling than females and generally cover longer circuits in their travels, presumably reflecting the search for estrous females. Traveling males can be solitary or move in small groups that vary in composition. Seasonal migrations are generally southward in early winter and northward in spring, with timing triggered by changes in water temperature (with individual variability in threshold temperatures). On the Atlantic coast, four patterns of migratory behavior were seen, and movements of individual manatees were consistent from year to year. In southern Florida, some manatees did not migrate. Long distance migrants moved 575–831 km one way; medium distance migrants moved one-way distances of 150–400 km, and short distance migrants moved 50–150 km. One male was an extreme case, with repeated seasonal movements between Florida and coastal states as far north as Rhode Island (2360 km). Travel was usually direct and rapid (25–87 km/ day) between origin and destination points, with a few stopover areas in between. West Indian Manatees have high year-to-year fidelity to seasonal home ranges. Home ranges were widely overlapping at migratory endpoints. In the vicinity of Everglades National Park in south-western Florida, movements in winter were less pronounced than on the Atlantic coast. Offshore-inshore patterns of seasonal movement were more localized, with inshore areas used more heavily in winter. Manatees that fed at offshore seagrass beds in this region in summer moved inshore to sources of freshwater every 2–8 days. The Antillean Manatee in Puerto Rico also uses seagrass beds for feeding, with periodic travel to freshwater sources. Maximum linear movements were only c.50 km in this more thermally constant environment. The Florida Manatee is not territorial; they are highly tolerant of conspecifics and are often seen in groups, but the groups are very dynamic in composition. Females with their current offspring are the only stable social unit, and this stable association ends at weaning. There is good evidence that migratory patterns and seasonal home ranges are learned by offspring from mothers through tradition. Mothers and young communicate using touch and by underwater contact vocalizations that sound to the human ear like squeaks, grunts, and groans. Sounds are single-note calls with multiple harmonics and overtones that typically span 1–18 kHz and 200–300 milliseconds duration, with duration varying with context up to 900 milliseconds. These sounds have distinctive individual qualities that allow individual recognition between mothers and offspring. Manatees of all ages and both sexes use sound to communicate, with young manatees vocalizing more frequently than adults. Mostly anecdotal observation has raised the hypothesis that Florida Manatees use a form of underwater scent communication. The recent discovery of anal glands (poorly known in other aquatic mammals) in Florida Manatees lends further support to this possibility. Status and Conservation. CITES Appendix I. Classified as Vulnerable on The IUCN Red List, but each subspecies is classified as Endangered. The Antillean Manatee appears to have suffered declines in abundance throughout its distribution due to hunting, incidental killing in gill nets set for fish, and other human-related mortality factors. The West Indian Manatee is legally protected in every country or territory in which it occurs, but conservation actions and law enforcement are variable among nations. The Florida Manatee has been the subject of intensive protection, research, and con-
servation. These efforts have been very strong over the past 40 years, and the population of this subspecies has shown marked growth during this time period. Recent estimates for the Florida subspecies are at least 5000 individuals. There are no technically reliable estimates for population size of the Antillean Manatee, but limited expert opinion suggests the subspecies may have fewer individuals than the Florida subspecies. Overall genetic diversity in the West Indian Manatee is not dangerously low, but there is substantial geographic structuring, resulting in low diversity in several regions, particularly Florida. Bibliography. Bengtson (1981, 1983), Bills et al. (2013), Deutsch et al. (2003), Domning (2005), Domning & Hayek (1984), Etheridge et al. (1985), Garcia-Rodriguez et al. (1998), Hartman (1979), Hernandez et al. (1995), Hunter et al. (2010), Irvine (1983), Kendall et al. (2004), Kinnaird (1985), Larkin (2000), Larkin et al. (2007), Ledder (1986), Lefebvre et al. (2001), Marmontel (1995), Marsh et al. (2011), Marshall, Huth et al. (1998), Marshall, Kubilis et al. (2000), Marshall, Maeda et al. (2003), Moore (1951), Nourisson et al. (2011), O’Shea & Hartley (1995), O’Shea & Poché (2006), Ortiz et al. (1998), Ralph et al. (1985), Rathbun & O’Shea (1984), Rathbun, Powell & Cruz (1983), Rathbun, Reid et al. (1995), Reep, Marshall & Stoll (2002), Reep, Marshall, Stoll & Whitaker (1998), Reep, Stoll et al. (2001), Reich & Worthy (2006), Reid (2006), Reid et al. (1995), Reynolds & Rommel (1996), Reynolds et al. (2004), Stith et al. (2006), Thomas (1911), Tucker et al. (2012), Vianna et al. (2006), Whitehead (1977).
2. West African Manatee Trichechus senegalensis French: Lamantin d’Afrique / German: Westafrika-Seekuh / Spanish: Manatí de África Occidental Other common names: African Manatee
Taxonomy. Trichechus senegalensis Link, 1795, Senegal. This species is monotypic. Distribution. Coastal areas and large inland rivers of West Africa from the Senegal River at the Mauritania–Senegal border S to the Longa River in Angola. They occur as far as 2000 km from the ocean in the Inner Niger Delta of Mali, up to 75 km off the continental shore in the shallows and mangrove creeks of the Bijagos Archipelago of Guinea-Bissau, and as far E as Lake Tréné in Chad; formerly in Lake Chad itself. Descriptive notes. Total length up to 350 cm; weight 460 kg. Very little morphometric data are available for the West African Manatee, although 18 presumed adults measured in Ivory Coast averaged 260 cm in body length. The West African Manatee appears indistinguishable in external appearance from the West Indian Manatee (T. manatus). Eyes appear to bulge outward more than in the West Indian Manatee or the Amazonian Manatee (T. inunguis), but this trait has not been investigated thoroughly on an anatomical basis. Habitat. Shallow coastal waters, estuaries and lagoons; mangrove swamps; flooded agricultural fields; and rivers as far inland as depths and rapids permit. Habitats used by the West African Manatee are comparable to those of the West Indian Manatee in their breadth. The West African Manatee is euryhaline, but it is unknown if it requires periodic access to freshwater. Relationships between temperature and limits to the distribution of the West African Manatee have not been well established, but a water temperature of 18°C has been suggested to be a lower limit of tolerance. Food and Feeding. The West African Manatee eats plants from at least 38 genera, invertebrates, and fish from a diversity of aquatic habitats. Many more food plants are likely to be revealed in the diet with further study. Methods of feeding and anatomical specializations seem identical to those of the West Indian Manatee. In some areas, West African Manatees feed on cultivated grains and crops in flooded fields, and they can be regarded as agricultural pests. Feeding occurs primarily at night in areas with histories of hunting by humans. Breeding. In some areas, the West African Manatee has been reported to mate when rainy-season water levels are rising, which may result in parturition and early lactation coinciding with periods of increased aquatic plant productivity. Births of singletons (c.100 cm in length) have been reported. Anecdotal accounts of groups of up to 15 individuals suggest mating herds, as in the West Indian Manatee, but there are no published details on breeding and reproduction of the West African Manatee. Activity patterns. There is little information available for this species, but in Ivory Coast they are reported to feed for 4–6 hours daily, largely at night to avoid human hunters. Movements, Home range and Social organization. There is little information available for this species, although some studies are underway. In Ivory Coast West African Manatees can move several kilometers between resting places and nocturnal feeding sites, which can be repeatedly used on successive nights. Seasonal movements occur in response to changing water levels in wet and dry seasons. West African Manatees are largely solitary but feeding and mating aggregations can occur. The breeding system involves an estrous female followed by mating herds of males similar to those better documented for West Indian Manatees. Status and Conservation. CITES Appendix I. Classified as Vulnerable on The IUCN Red List. West African Manatees are protected by law in all nations in which they occur, but enforcement is sometimes lax, and exemptions occur for cultural purposes in some countries. The Nigerian government has allowed permits for killing of 1–2 manatees annually for a wrestling festival, and captures for symbolic uses also have been
FAMILY TRICHECHIDAE Manatees
On following pages: 3. Amazonian Manatee (Trichechus inunguis).
FAMILY DUGONGIDAE Dugong
The golden trevally (Gnathanodon speciosus), above, will often accompany a Dugong, waiting to feed on the invertebrates dug up or disturbed by an individual as it forages in the seagrass beds. Remoras (Echeneidae), below, attach themselves to Dugongs to take advantage of small prey disturbed in this way. Some remora species appear to feed on Dugong feces. The Dugong apparently gains nothing from these relationships, which are believed to be commensal rather than symbiotic. Dugongs do enjoy the services of “cleaner fish,” such as the cleaner wrasse (Labroides dimidiatus), which feed on external parasites on their skin. A variety of worm and crustacean species including barnacles have been identified living on Dugongs; some of these are also found on other large marine animals, such as green turtles (Chelonia mydas). Dugong flesh has been found in the stomachs of tiger sharks (Galeocerdo cuvier); how much is due to predation rather than scavenging is not known. Nonetheless, Dugongs may modify their behavior in response to the presence of tiger sharks. Dugongs often feed in shallower intertidal seagrass areas, but in Shark Bay in Western Australia, the Dugongs feed in deeper water when the risk from tiger sharks is high. Above: Dugong dugon Dimakya Island, north of Busuanga Island, N Palawan, Philippines. Photo: Jürgen Freund/naturepl.com
Below: Dugong dugon Red Sea, off Egypt. Photo: Yves Lefèvre/Bios
FAMILY DUGONGIDAE Dugong
The Dugong is highly dependent on seagrasses growing in shallow water and intertidal zones, but it will feed opportunistically on other marine plants (such as the algae in this photograph) when seagrasses are depleted or inaccessible because of low water temperature. In some environments, Dugongs apparently subsist largely on algae. In addition to their simple-peg like teeth, horny plates in the mouth play a significant role in masticating food. Dugongs apparently forage effectively only on relatively non-fibrous plants and have difficulty masticating some fibrous seagrass species, although they will eat such species during times of food shortage. Dugong dugon N Red Sea, off Marsa Alam, Egypt. Photo: Andrey Nekrasov/VWPics.com
Food and Feeding Dugongs are the only strictly marine herbivorous mammals. They are highly dependent on seagrasses communities growing in intertidal and shallow subtidal areas. Dugongs use two feeding modes: leaf cropping and excavating. When feeding on seagrasses with accessible rhizomes, they excavate the aboveground and belowground parts of plants by digging up the plants and leaving a serpentine feeding trail in the sediment. Although feeding trails of Dugongs have been found at depths of 33 m, most feeding takes place in shallow water. Dugongs feed on at least eight of the nine genera of seagrasses (Amphibolis, Cymodocea, Enhalus, Halodule, Halophila, Syringodium, Thalassia, and Thalassodendron) and most of the approximately 26 species that occur within their distribution. Quantitative comparisons of mouth and stomach contents of Dugong indicate that the relative importance of seagrass genera differs among locations and with changes in availabilities of seagrasses. Dugongs expand their diet opportunistically when seagrass beds are seriously depleted by natural or human-induced seagrass loss. Dugongs may also change their diet on a seasonal basis, especially when their access to some seagrass meadows is limited by water temperature. In some environments, Dugongs apparently subsist largely on algae. Dugongs also deliberately eat invertebrates such as burrowing mussels, ascidians, chaetopterid worms, and possibly sea pens, at least in winter in the subtropics. As yet, there is no scientific evidence that Dugongs deliberately feed on invertebrates in the tropics, although they certainly consume invertebrates incidentally when feeding on whole seagrass plants. Seagrass leaves tend to be richer in nitrogen than their rhizomes, which are generally richer in starch. The factors influencing selection of seagrasses by Dugongs appear complex. Dugongs tracked in winter in Hervey Bay in eastern Australia were consistently associated with seagrass patches where nitrogen concentrations were relatively high, except during the day at low tides when their choice was restricted. Dugongs then associated with seagrass patches of high biomass. As a
result of their relatively simple dentition, Dugongs seem to be able to effectively masticate only relatively non-fibrous species of food plants.
Breeding The mating behavior of Dugongs is variable. Observational accounts from various locations in Australia suggest male and female promiscuity, with single estrous females tended by roving males that coalesce into larger groups termed “mating herds.” In contrast, observations of Dugongs in Shark Bay on the west coast of Australia suggest that lek mating in which males gather to engage in competitive displays to entice visiting females may occur under some as yet poorly understood conditions. In addition, lone pairs of Dugongs have been sighted mating in parts of Asia such as Palau. The oldest recorded wild Dugong was a female from the west coast of Australia estimated to be 73 years old. Dugongs usually bear a single offspring after gestation of about 14 months. Twins are very rare. Sparse data suggest that lactation can last up to about 18 months, although young Dugongs start eating seagrasses soon after birth. There is considerable individual variation in pre-reproductive periods that range from six to 17 years and interbirth intervals that range from 2·5 to seven years, suggesting that Dugongs postpone breeding under certain conditions. Significant fluctuations have been documented in pregnancy rates, ages at first reproduction in both sexes, sizes at sexual maturity, and incidences of reproductively active males. These fluctuations apparently track major changes in the status of the Dugong’s food supply, which is subject to episodic diebacks often associated with extreme climatic events, such as floods and severe storms.
Movements, Home range and Social organization Like cetaceans, Dugongs swim by oscillations of the tail. Dugongs can travel at surprisingly fast speeds, cruising up to 10 km/h with short sprints up to about 20 km/h. Dugongs hold their flippers pressed to the body while cruising or traveling. They use their flippers independently or together for fine
distress, or male aggression and display. Adults of both sexes produce vocalizations, but exchanges of communication calls seem most common between females and their nursing offspring.