We work to ensure that the Pacific walrus in Alaska continues to be a healthy, functioning component of the Bering and Chukchi Seas ecosystems. Management responsibilities include:
- international cooperation with Russia on walrus management issues,
- conducting population surveys, monitoring and modeling populations,
- monitoring harvest by Alaska Natives,
- developing habitat protection measures such as regulations to minimize incidental take for industrial operations in walrus habitat, and
- collaborative management and research programs at the local, state, national, and international levels.
The Marine Mammals Management office takes an ecosystem approach to walrus management, carried out through the cooperative efforts of many partners. Some of these are the National Wildlife Refuges, the Eskimo Walrus Commission, Alaska Department of Fish and Game, National Marine Fisheries Service, Bureau of Ocean Energy Management, Alaska SeaLife Center, World Wildlife Fund, Wildlife Conservation Society, and the University of Alaska.
Walrus are an Important Subsistence Resource
Pacific walruses are an important subsistence and cultural resource to many Alaska and Russian Native cultures. Walruses make up an important part of the diet of many coastal Alaska Natives. Tusks, bones, and hides are used to make authentic Native Alaskan handicrafts, as well as many of the items necessary to continue a subsistence lifestyle. For example, walrus hides are occasionally used for covers for wooden boat frames and tusks were traditionally used for harpoon points, fish hooks, and knives.
The Marine Mammals Management office works closely with Tribal governments and Alaska Native Organizations such as the Eskimo Walrus and Qayassiq Walrus Commissions to co-manage the Pacific walrus population and ensure that it remains a functioning component of the arctic ecosystem and a sustainable subsistence resource.
Walruses belong to the family Odobenidae - a group of marine carnivores that was composed of many species in the late Miocene and early Pliocene periods. Today, the family Odobenidae is represented by a single species Odobenus rosmarus of which two subspecies are recognized: the Atlantic walrus (O. r. rosmarus) and the Pacific walrus (O. r. divergens). The two subspecies occur in geographically isolated populations. Several populations of Atlantic walrus occur in Canada, Greenland, Scandinavia, and eastern Russia while the Pacific walrus is represented by a single stock of animals which inhabits the Bering and Chukchi seas.
Pacific walruses are one of the largest pinnipeds. The head in both sexes is characterized by a pair of enlarged upper canine teeth that project downward as tusks, small eyes, a lack of external ears, dorsally situated nostrils, and a square-shaped snout with hundreds of stiff whiskers. The head and body are covered with short, tawny hair but the flippers are bare. Walruses are dark when they are young and become progressively lighter with age. Immersion in cold water causes a restriction of blood flow to the skin and a pale, almost white appearance. When warming out of the water ("hauled out"), the skin again becomes perfused with blood and a pink to red color results.
Distribution and Migration
The Pacific walrus mainly inhabits the shallow continental shelf waters of the Bering and Chukchi seas. Several hundred can also be found in the Laptev Sea. The distribution of Pacific walruses varies markedly with the seasons. Almost the entire population occupies the pack ice in the Bering Sea in the winter months. Through the winter they generally congregate in three areas, immediately southwest of St. Lawrence Island, south of Nunivak Island, and in the Gulf of Anadyr in Russia. As the Bering Sea pack ice begins to break up and melt in spring walruses begin to move northward and their distribution becomes less clumped. By late April walruses can be found from Bristol Bay northward to the Bering Strait. During the summer months, as the pack ice continues to recede northward, most of the population migrates into the Chukchi Sea. The largest concentrations are found near the coasts between 700 N latitude and Pt. Barrow in the east, and between the Bering Strait and Wrangel Island in the west. Concentrations, mainly of males, are also found on and near terrestrial haulouts in the Bering Sea in Bristol Bay and the northern Gulf of Anadyr throughout the summer. In October the pack ice begins to develop in the Chukchi Sea, and large herds begin to move southward. Many come ashore on haulouts on the Russian side of the Bering Strait region. Depending on ice conditions, those haulout sites continue to be occupied through November and into December, but with the continuing development of ice, most walruses move south of St. Lawrence Island and the Chukchi Peninsula by early to mid-December.
Food and Habitat Requirements
Although capable of diving deeper, Pacific walruses for the most part are found in waters 300 ft. deep or less, possibly because of higher productivity of their benthic foods in the shallower water. Feeding areas typically are composed of sediments of soft, fine sands; compacted sediments apparently inhibit foraging. In some instances, walruses forage among rocky substrates. They use their sensitive whiskers (known as vibrissae) to locate prey items in the sediments of the sea floor. With head down and vibrissae in contact with the bottom, the walrus proceeds forward, propelling itself with their hind flippers. Then they use their nose, jets of water and suction to dislodge their prey from the sediments.
Clams are their most common food, however other invertebrates such snails, sea cucumbers, crabs, and segmented worms are frequently found in their stomachs. Prey are manipulated by the lips and grasped with the aid of roughly textured gums, rather than by the teeth. The soft parts of mollusks are removed from the shells by suction and the shells are then spit out. Occasionally, small mollusks less than 30 mm in diameter are swallowed whole, shell and all, but from the larger mollusks only the siphon or foot ordinarily is ingested. Invertebrates without shells are swallowed whole without chewing. Walruses occasionally consume fish. They are frequently reported to prey on small seals such as ringed and ribbon seals. The incidence of seal eating may vary with location and population status. The frequency of walrus stomachs containing seals generally is less than 10% but seems to have increased in recent years.
Ice floes are used for resting and giving birth, and walruses require pack ice that will support their weight and allow ready access to the water in which they feed. While walruses can break (with their heads) ice up to 8 inches thick, they require ice thicknesses of about 24 inches or more to support their weight. Ice that rises too high out of the water, such as multi-year floes, cannot be used by walruses. Generally walruses occupy first-year ice with natural openings such as leads and polynyas (persistently open water within the ice pack) and are not found in areas of extensive, solid ice. Thus, their concentrations in winter are along the edge of the ice pack or the edges of polynyas. In summer those associating with ice are found along the southern margin of the Chukchi Sea pack ice, moving farther into the pack in stormy seas. Floe size and topography appear to be important in the selection of ice haulout sites as well as proximity to prey.
Isolated sites such as islands, points, spits, and headlands are occupied most frequently. A wide variety of substrates apparently are suitable, but protection from strong winds and surf seems also to be important. Social factors, learned behavior, and proximity to prey probably influence the location of haulout sites but little is known about such factors.
In Alaska, major terrestrial haulouts are found in Bristol Bay at Cape Seniavin, Round Island, Cape Pierce, and Cape Newenham. Consistent seasonal occupation of specific haulouts by some individuals suggests at least some degree of site fidelity. Limited data from tagging and radio-tracking studies suggest that site fidelity may be interrupted by human disturbances. In response to recent declines in sea ice in late-summer in the Chukchi Sea over the last several years, new haulouts have formed along the Chukchi coast in August and September. Several sites along the Russian coast are also used and walruses that summer in Alaskan waters have consistently used a barrier Island just north of Point Lay for the last several years. Disturbances at these haulouts that are dominated by females and young animals can result in mortalities as smaller animals are trampled as the herd stampedes into the water.
Growth and Reproduction
At birth calves of both sexes weigh anywhere from 100 to 150 lbs and are approximately 4.5 feet in length. After the first few years of life, the growth rate of females declines rapidly until a maximum body size is reached by approximately 10 years of age. Adult females are generally smaller than males, with an average weight of about 1900 lbs and an average length of approximately 9 feet. Although females reach sexual maturity at approximately 4-5 years of age they do not reach their full reproductive potential until they are nine or ten years old.
Male walrus tend to grow faster and larger than females. After a secondary acceleration of growth, males reach a full adult body size at 15-16 years of age. The head of the male is larger and more block shaped; and the tusks are stouter, straighter, and more elliptical in cross section than those of females. The tusks are used in intra-specific threat displays and fighting that is most severe in the case of breeding males. Raised nodules on the skin of the neck and shoulders develop only in sexually mature males. Adult males average over 2,700 lbs in weight and 10.5 feet in length. Males tend to become fertile at 5-7 years of age but are likely unable to compete for mates until they reach full physical maturity at approximately 15 years of age.
Pacific walrus breed in the winter between December and March. After fertilization the ovum becomes a blastocyst and remains in a state of suspended development for 3-4 months. Implantation occurs in June or July and the fetus resumes development for approximately eleven months. Calves are usually born in late April or May.
The walrus has the lowest reproductive rate of any pinniped species. The delay in implantation of the embryo, and 11 month gestation period, results in a reproductive cycle of more than one year. A successful pregnancy lasts through the next breeding season which results in an interval between successive births to 2 years. Most pinnipeds mate within days or weeks of parturition. In contrast, walruses give birth several months after the breeding season and do not have a postpartum estrus. Furthermore, fertility appears to be reduced in the breeding season following the birth of a calf. The factors affecting the resumption of estrous cycles in walruses are unknown; however in some mammals estrus is suppressed during lactation by elevated levels of the pituitary hormone prolactin which is produced and maintained in response to the suckling stimulus. Walruses nurse calves for more than a year and ovulation may be suppressed until the calf is weaned. Thus, females in good condition and at prime breeding ages may only produce a calf every 3 years.
In compensation for their low reproductive rate, walruses have relatively low rates of natural mortality. Walrus calves accompany their mother from birth and are not weaned for 2 years or more. The prolonged lactation period allows walrus calves to achieve an advanced developmental state prior to weaning, which ultimately leaves them well equipped to forage and escape predators.
The size of the Pacific walrus population is unknown. The actual size of the pre-exploitation population is unknown, but has been estimated to have been between 200,000-250,000 animals. Cooperative aerial surveys by the U.S. and the former Soviet Union (now Russia) were initiated in 1975. The 1975 survey estimated the population size at 221,360. A second joint census, conducted in 1980, estimated population size at 246,360. Surveys conducted in 1985 and 1990 produced estimates of 234,020 and 201,039, respectively. Cooperative aerial surveys were suspended in 1995 due to budget limitations and unresolved methodological problems. After much deliberation and testing, another aerial survey was conducted in 2006 incorporating advanced thermal imaging and telemetry technologies, resulting in an estimate of 129,000 animals with a confidence interval of 55,000-550,000. The estimates generated from these aerial surveys should be viewed as conservative minimum population estimates that are not useful for detecting population trends.
In 2012 a new approach to population estimation using the genetic fingerprint of individual walruses within a mark-recapture framework began testing. Two aspects of the approach were successfully assessed in 2013; the genetic identification of individuals and the ability to collect an adequate sample. Testing will continue through 2015 at which point the success of the method will be evaluated.
Sensory Perception and Disturbance
The eyes are small and vision is not well developed in walruses. Tactile perception via the vibrissae is well developed and important in feeding. As in other pinnipeds, walrus have good directional hearing capability underwater. Sensitivity to airborne sounds is lower than to underwater sounds, but the degree of sensitivity loss is not clear.
Walruses often flee haulouts en masse in response to the sight, sound, and especially odors from humans and machines. The significance of such disturbance to individuals and to populations is not well known, due to great variation in the observed responses to disturbance and a lack of relevant data.
Walruses depend on hauling out to complete their molt and grow new hair, to whelp, to nurse young, and just to rest. At those times even temporary displacement from haulout areas may be detrimental to the population. There is some evidence of haulouts being completely abandoned as a result of prolonged disturbance but those cases must be assessed carefully because evidence also exists for changes in walrus distribution for reasons not fully understood.
Females with young are the most responsive to disturbances and the separation of females from their dependent young can be a serious problem. Orphaned calves, especially in the first year of nursing, probably starve. In the first few days of the calf's life, the mother vigorously maintains contact with the calf. However, as the calf grows older that behavior wanes increasing the potential for separation during disturbance.
Even temporary separations can be lethal, in that polar bears prey upon calves and take advantage of even brief separations from the normally attentive cow. Calves especially are vulnerable to disturbance on terrestrial haulouts. Large numbers of calves have been trampled to death during stampedes caused by human and natural disturbances at terrestrial haulouts. The potential for mortalities during stampedes appears to be less in the case of animals on the ice, as groups are generally smaller and can easily reach the water.
Walruses are preyed upon by polar bears, killer whales, and man. The magnitude of natural mortality is unknown but is assumed to be low, given the population's low productivity. Eskimo hunters from St. Lawrence Island have described walruses becoming emaciated after becoming entrapped in heavy ice. It is probable that in some instances those walruses starve to death but no documentation of such events exists. Rock slides are a hazard to walruses on terrestrial haulouts and occasionally result in mortality. They have also tumbled down steep slopes and fallen off cliffs at some haulouts.
Serious injury and death can result from intra-specific interactions, mainly involving strikes with tusks and trampling. Skin lacerations and subcutaneous hemorrhages resulting from tusk strikes are common in both sexes and all age-classes. The most serious wounds are observed on males during the breeding season when they wound each other during vigorous fights in the water. Trampling can result in abortion, injury, and death during stampedes at crowded haulouts and has been observed at Wrangel Island in the Chukchi Sea, the Punuk Islands in the Bering Sea, and Icy Cape on the Alaskan coast.
Last updated: September 2015