Odobenus rosmarus, Linnaeus, 1758

Russell A. Mittermeier & Don E. Wilson, 2014, Odobenidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 118-119 : 118-119

Walrus

Odobenus rosmarus

French: Morse / German: \Walross / Spanish: Morsa

Other common names: Atlantic Walrus (rosmarus); Laptev Walrus (Laptev Sea population); Pacific Walrus (divergens)

Taxonomy. Phoca rosmarus Linnaeus, 1758 ,

“intra Zonam arcticam Europe, Asie, America.”

The “Laptev Walrus” (laptevi) described by K. K. Chapskii in 1940 in the Laptev Sea is not recognized here as distinct subspecies. Mitochondrial sequence data presented by C. Lindqvist and her colleagues in 2009 suggested that the population in the Laptev Sea was the westernmost population of the “Pacific Walrus” (dwvergens) and not a distinct subspecies. Twosubspecies recognized.

Subspecies and Distribution.

O.r.rosmarusLinnaeus,1758—NCanada(HudsonBay)toWGreenlandanddiscon-tinuouslyfromEGreenlandtoSvalbardandNRussia(FranzJosefLandandKaraSea);occasionallyreportedinIcelandandstragglersinWEuropeStotheBayofBiscay.

O. r. divergens Illiger, 1815 — Laptev Sea off N Russia, Bering and Chukchi seas in N Russia and Alaska; vagrant individuals reported S to New England, USA.

Descriptive notes. Total length 250-350 cm, averaging 315 cm (males) and ¢.260 cm (females); weight 800-1800 kg, averaging 1500 kg (males) and c.1000 kg (females). Newborns are ¢.10 cm in total length and weigh ¢.85 kg. Walruses have relatively small heads, broadly flattened muzzles with thick short bristly whiskers, and robust torsos. Adult male and female Walruses are recognizable by their long external tusks (modified upper canine teeth). These canine teeth start developing early in life and can grow to 100 cm long and weight 5 kg. Tusks function as weapons, particularly for males during the breeding season; both sexes use them for support when foraging on the seafloor and as picks to anchor themselves to edges ofice floes and assist in pulling themselves out of the water. Post-canine teeth are very small pegs and appear to be largely non-functional. Chest and neck of adult males are massive and covered with wart-like nodules and tubercles. Skin is very thick, up to 6 cm on the chest of males. Both sexes have sparse pelage of brown to cinnamon hair and thick fat layers. Skin color varies from pale gray or even white to pink or reddish brown or gray, depending on whether blood is being restricted from flowing to the skin (light tones) to conserve heat (vasoconstriction) or specifically directed to the skin (dark tones) to dissipate heat (vasodilatation). The Pacific Walrus in the Arctic region of the North Pacific Ocean is more numerous, weighs more, and has longer upper canines and broader snout than the “Atlantic Walrus” (O. » rosmarus).

Habitat. Open pack ice of Arctic regions of the northern Pacific and Atlantic oceans in winter. In some areas, Walruses remain with the sea ice as it recedes in summer, although they can also be found ashore on islands and mainland coast in the Bering Sea, eastern Canada, and west-central Greenland.

Food and Feeding. Walruses mainly eat benthic invertebrates that they locate with their sensitive vibrissae on their upper lips on the muddy seafloor. Food items are extracted with powerful suction created by their tongues and mouth. They can supplement this diet with slow moving fish, worms, molting crabs, and shrimps. The most important prey of Atlantic Walruses near Svalbard, Norway, are the blunt gaper clam (Mya truncata) and various medium-sized sea snails in the genus Buccinum. Pacific Walruses in the Bering and Chukchi seas eat a variety of bivalves, gastropods, and polychaete worms. Occasionally, Walruses hunt and eat Northern Fur Seals (Callorhinus ursinus), Bearded Seals (Erignathus barbatus), Ringed Seals (Pusa hispida), and Spotted Seals (Phoca largha). They also scavenge cetacean carcasses by sucking out blubber and inner organs. Foraging dives are to depths of 200-500 m or more and last up to c¢.40 minutes.

Breeding. 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. Nevertheless, there are scant details on most aspects of breeding behavior of Walruses because their breeding season is in December—-March generally in areas with considerable cover of sea ice that are difficult to access and not often visited by researchers. It has been suggested that their breeding system might resemble a “lek system” whereby males use vocal and visual displays while in the water to attract females in areas where they are more densely distributed relative to suitable sea-ice conditions and food availability. Mating is thought to occur in the water. After impregnation, the egg develops briefly and then is dormant for ¢.5-6 months before the embryo attaches to the uterine wall and resumes development (i.e. delayed implantation). Single neonates are born from mid-April to mid-June, with a peak in May. Offspring nurse for 2-2-5 years. In some populations, birth interval may be as along as three years. Most young are weaned by c.3 years old when juvenile males tend to join male groups. Females can be sexually mature at c.8 years old, and many give birth for the first time when they are ten years old. Males mature a few years later, and although they are capable of mating at ten years of age, few evidently do until they are c.15 years old.

Activity patterns. Adult males shed and replace their hair in June-August, and adult females shed over a longer period in summer when they can spend time ashore on islands or mainland coasts, or hauled-out on stable ice. Males emit stereotypic, pulsed sounds underwater during the breeding season, which presumably function to attract females and in courtship. Male Atlantic Walruses near Svalbard moved into areas of very high ice cover (more than 90%) in winter, deep into the ice pack and up to 600 km from ice-free water. They spent relatively little time diving to the seafloor, presumably to feed. Activity budgets from data loggers showed that 44% oftheir time was spent under the water, 39% at the water’s surface, and 17% on land. Data loggers suggested that only 40% of the time that these males spent submerged involved foraging.

Movements, Home range and Social organization. In most areas, Walruses appear to move north as sea ice recedes in spring and summer and then south as it forms and thickens. Little is known about social organization of Walruses, although they appear to be mostly solitary or as females with suckling young. Exceptions occur in spring and summerin ice-free areas where mostly males aggregate in large dense numbers ashore on islands and mainland beaches. Walruses are generally gregariousin sea-ice habitats near good feeding areas and at mainland and island haul-out sites in summer. Nevertheless, they are not particularly social, and females with offspring generally occur in only very small groups of several dozen, loosely spaced or alone. Social hierarchies develop among males during the breeding season when they compete for access to estrous females.

Status and Conservation. CITES Appendix III (Canada population only). Classified as Data Deficient on The IUCN Red List. Walruses have long been hunted by Arctic human cultures for their tusk ivory to make tools, weapons, and crafts; their thick skins to make kayak coverings and clothing; their meat for food; and their oil rich fat for food and cooking. They were hunted commercially for more than 300 years by Norwegians, Russians, and British for skins, ivory, blubber to render to oil, and meat; they might have been exterminated in some areas. Russian commercial harvests in the Bering Sea killed up to 8000 Pacific Walruses each year between 1930 and 1960. Subsistence hunting continues in most areas of the Arctic although commercial hunting was banned by Canada in 1931 and the USA in the early 1940s; Russia continued harvests through the 1980s. Poaching, mostly for ivory, continues in many areas. The estimate of the global population of Walruses in the early 1980s was ¢.280,000 individuals, with 90% living in the Pacific sector of the Arctic and 4000-5000 individuals in the Laptev Sea region. Nevertheless, unregulated harvests for ivory since then have evidently reduced the population, perhaps substantially. Overall population estimates in the late 1990s suggested only ¢.200,000 Walruses throughoutits distribution. There has been very slow recovery of populations of Pacific Walruses and very little apparent recovery of populations of Atlantic Walruses.

Bibliography. Allen (1880), Berta (2009a, 2009b), Boessenecker & Churchill (2013), Born (1984), Born et al. (2001), Chapskii (1940), Charrier et al. (2010), Cronin et al. (1994), Dyke et al. (1999), Fay (1960, 1981, 1982, 1985), Harington (2008), Horikawa (1994), Kastelein (2009), Lindqvist et al. (2009), Lowry & Fay (1984), Lowry et al. (2008), Lydersen & Kovacs (2013), Miller (1975, 1976, 1982, 1985), Miller & Boness (1983), Oliver et al. (1983), Ray & Watkins (1975), Reeves (1978), Reeves & Stewart (2003), Reeves, Stewart, Clapham & Powell (2002), Reeves, Stewart & Leatherwood (1992), Repenning (1976), Repenning & Tedford (1977), Salter (1979), Sheffield & Grebmeier (2009).

Figures

Subspecies and Distribution. O.r.rosmarusLinnaeus,1758—NCanada(HudsonBay)toWGreenlandanddiscon-tinuouslyfromEGreenlandtoSvalbardandNRussia(FranzJosefLandandKaraSea);occasionallyreportedinIcelandandstragglersinWEuropeStotheBayofBiscay. O. r. divergens Illiger, 1815 — Laptev Sea off N Russia, Bering and Chukchi seas in N Russia and Alaska; vagrant individuals reported S to New England, USA.