RIBBON SEAL

 

The ribbon seal (Histriophoca fasciata) is a medium-sized pinniped from the true seal family (Phocidae). A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white strips and two white circles against dark brown or black fur.

It is the only living species in the genus Histriophoca, although a possible fossil species, H. alekseevi, has been described from the Miocene of Moldova.

Distinctive characteristics

Ribbon seals have the most striking color pattern found on any seal. Adults of both sexes have pale bands of variable width that encircle each fore flipper, the neck and nape, and the hip area. The bands have sharply defined edges and vary greatly in width. On some animals, the bands are so wide that they merge. Band color ranges from a shade just paler than the surrounding dark pelage to white. Adult males are black to brownish black, while females are light to dark brown. The bands are less distinct on females and subadults. Juveniles are plain looking until they are about two years old and lack the dramatic markings that will characterize them as adults. They are gray to light brown after molting the woolly whitish lanugo or birth coat at an age of about five weeks.

Ribbon seals are more slender than other Bering Sea ice seals. The head is small, relatively wide, and flat topped. The forehead is small in profile. The close-set eyes appear large. The muzzle is short, blunt, and slightly tapering. The nostrils are also small and terminal, forming a “V” pattern that converges at the bottom. The vibrissae are light-coloured, beaded, and fairly prominent. There are long, hooked claws on all digits of the fore flippers. The ends of the fore flippers are weakly pointed with a somewhat longer first or outer digit and successively shorter digits 2-5.

Dental formula    I 3/2, C 1/1, PC 5/5.

Size

Adult ribbon seals reach a maximum length of about 1.8 m and weights of 90-148 kg. Pups are approximately 86 cm long and 10.5 kg at birth.

Life Span    Both male and female live up to 20- 30 years.

Gestation Period    304-334 days.

Can be confused with

Four other phocids: ringed, harbor, spotted, and bearded seals share the range of the ribbon seal. Look for details of pelage markings and coloration, particularly the presence of markings (other than the four obvious wide pale bands on adult-sized seals) such as spots, blotches, or large numbers of rings, all of which are absent in ribbon seals. This also includes the smaller plain gray juvenile stage. Also, note overall size, relative size of the head and muzzle, foreflipper shape (squared off at the end in the bearded seal), and mystacial vibrissae density. The bearded seal has a much greater density of downward curving vibrissae than the ribbon seal, and all other northern phocids.

Distribution

Ribbon seal distribution most closely matches that of the spotted seal. They occur in the Seas of Okhotsk and Japan, the western North Pacific, and from the Bering Sea northward through the Chukchi Sea east to the western Beaufort and west to about 180° longitude.

Three separate populations of ribbon seals have been proposed and include the southern and northern Sea of Okhotsk, and the Bering Sea breeding groups. Ribbon seals inhabit the southern edge of the pack ice from winter to early summer. Most are thought to be pelagic in the Bering Sea during the summer. Records from the North Pacific south of the Aleutians suggest a possibly wider range during the summer when ribbon seals are not associated with sea ice. A stranding from central California is evidence of occasional distant wanderings.

Ecology and behavior

Ribbon seals are solitary for much of their lives. Pups are born on ice floes from early April to early May. Broken pack ice is preferred over solid ice sheets and highly concentrated pack ice, as ribbon seals can only open and maintain access holes in ice up to approximately 15 cm thick. Males are generally nowhere to be seen during the nursing period. Ribbon seals are able to move rapidly on ice, using slashing side-to-side motions. They also extend their necks to peer at sources of disturbance, but are fairly approachable by boat. They are rarely encountered, because of the remote and inhospitable nature of their polar habitat.

Predation

A common Predator of ribbon seals is humans (Homo sapiens). From 1956 to 1992 hunting of several species of seals that lived on ice was a popular sport. This drastically decreased population size of ribbon seals. Human still hunt ribbon seals but it is not a common as it once was. Polar bears (Ursus Maritimus), Walruses (odobenus rosmarus), killer whales (Orcinus Orca), and pacific Sleeper Sharks (Somniosus Pacificus) also prey on ribbon seals. Ribbon seals have been found in their stomach contents.

Feeding and prey

Diet varies by area and age of the seal. Ribbon seals in the Okhotsk and Bering seas are known to take 35 different species of fish and invertebrates. Young ribbon seals feed on euphausiids after weaning and until about age one when they switch to feed predominantly on shrimp for a year. As two-year-olds they take up the adult diet, which includes a variety of fishes, squids, and octopuses. Russian scientists have determined that ribbon seals in the Sea of Okhotsk have a diet that is 65% Pollock, while those in the Bering Sea consume about the same percentage of squid and octopuses.

Exploitation

Ribbon seals, Histriophoca fasciata, like other Arctic seals, are at-risk of climate change due to global warming, which may impact the distribution of polar ice. Although little is known about this species, it is thought that, like other seals, they may be affected by commercial fishing and disturbance from oil and gas exploration as well.

Because of their pelagic habitat, fewer than 100 ribbon seals are taken by subsistence hunters in Alaska each year. Between 1950-1980, these seals were hunted in Russia for their pelts, oil, and meat in the Okhotsk and Bering Seas, however they are no longer hunted commercially. There is a small by catch of ribbon seals in north Pacific trawl fisheries.

Threats and status

Commercial hunting was carried out in the Sea of Okhotsk and Bering Sea from the middle to the late 20th century. Subsistence hunting by Alaskan Natives occurs at low levels in the United States. Global warming, accumulation of contaminants, entanglements in commercial fisheries and depletion of prey species such as pollock in commercial fisheries are all on-going threats and concerns.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN status      

Data deficient (Data in adequate to determine a threat category).