Ribbon seals are among the most striking and easily recognizable seals in the world. They can be identified by the distinctive light-colored bands or “ribbons” that encircle their neck, each foreflipper, and hips. Adult males are the most striking, having a dark brown to black pelage with white ribbons, while adult females range from silvery-grey to dark brown with paler ribbons. Juvenile ribbon seals are typically a light brown dorsally, light grey ventrally, and have indistinct ribbons that usually develop after two to three years as the seals mature. Ribbon seals molt their coat of hair annually, beginning in May and finishing in July, with younger individuals molting earliest. Ribbon seal pups are born with a wooly white lanugo coat that is molted after four to five weeks. At birth, ribbon seal pups are approximately 86 cm long and weigh about 10 kg, while adults can attain lengths of about 1.5 – 1.8 m and weights of about 90 – 148 kg.
Ribbon seals primarily inhabit the North Pacific Ocean, including the Bering and Okhotsk Seas, and adjacent parts of the Arctic Ocean, including the Chukchi Sea, eastern Siberian Sea, and western Beaufort Sea. Ribbon seals are considered relatively solitary, spending most of their time in the open ocean and forming loose aggregations in the pack ice during spring to give birth, nurse pups, and molt. They are very rarely seen on shorefast ice or land. This species seems to prefer moderately thick, “clean” ice floes found in the inner zone of the ice front. From late-March to early-May, ribbon seals in the Bering Sea range from the Pribilof Islands to Gulf of Anadyr, roughly along the continental shelf break, being more abundant in the northwestern ice front. As the ice recedes during May to mid-July, the seals move farther to the north where they haul out on the receding ice edge and remnant ice, occasionally in dense groups. After the ice has melted, most ribbon seals probably either migrate with the receding sea ice through the Bering Straight into the Chukchi Sea or remain pelagic in the Bering Sea during the rest of the year.
Ribbon seal mothers give birth to their pups far offshore in the pack ice during April to early-May. The pups double their weight during nursing and are weaned after three to four weeks. Mating likely occurs shortly after weaning, though little is known of the breeding system. Ribbon seals are known to eat a variety of fishes, cephalopods, and crustaceans; however, information about their feeding habits is limited and mostly restricted to the spring when ribbon seals are typically feeding less, as evidenced by their decreased weight and blubber thickness. Although there is little direct evidence of predation, potential predators of ribbon seals include polar bears, killer whales, sharks, and walruses. Ribbon seals are relatively unwary while hauled out and can be approached closely by boat. This behavior suggests that ribbon seals probably do not experience much predation by polar bears, but may also make them especially susceptible to hunting by man. Siberia and Alaska Natives have hunted the ribbon seal for many generations for subsistence, and the current annual take by Alaska Natives is estimated to be less than 200 seals per year. Commercial harvests of ribbon seals were conducted by Soviet sealers in the 1960s to 1980s, during which time the Bering Sea population is thought to have declined from 80,000 or 90,000 animals to 60,000. Surveys during the early and mid-1970s put the worldwide population estimate of ribbon seals between 200,000 and 240,000, with estimates ranging between 60,000 and 100,000 in the Bering Sea (Shustov, 1972; Burns, 1981). A more recent and reliable abundance estimate is not currently available.
The MML’s Polar Ecosystems Program is actively studying and monitoring ribbon seals to support a more reliable assessment of their status. Studies include surveys of abundance and distribution; satellite telemetry of movements, foraging, and haul-out behavior; sampling of tissues for evaluation of population structure and health; and collection of feces for investigation of diet.