(Zimmerman, 1783) - Ribbon seal
Distinctive Characteristics
Ribbon seals are more slender than other Bering Sea ice seals. The head is small, relatively wide, flat, and somewhat cat-like. The forehead is small in profile. The close-set eyes appear large, and the muzzle is short, blunt, and tapers slightly. 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, thin, hooked claws on all digits of the foreflippers. The ends of the foreflippers are weakly pointed to somewhat squared off, with only slightly different digit lengths.
Ribbon seals have an exceptionally striking colour pattern. Newborns have a shaggy, woolly, whitish lanugo that is shed at about 5 weeks. Youngsters are fairly plain-looking, without a hint of the bold pattern of adults. Subadults are blue-black above, including the crown and tops of the foreflippers, fading to silver-grey on the flanks and undersides. The face is pale and the end of the muzzle, lower jaw, and chin are dark. In adults of both sexes, pale bands of variable width encircle each foreflipper and shoulder, the neck, and the lower back, flank, and abdomen. The bands vary greatly in width (on some animals they are so wide that they merge). Band colour ranges from a shade just paler than the surrounding dark pelage to off-white. The freshly moulted base colour in adult males is reddish brown to black Adult females are much paler, tan to light brown, rendering the bands less distinct.
The dental formula is I 3/2, C 1/1, PC 5/5.
Can be confused with
Four other phocids: ringed, harbour, Larga, 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 4 obvious wide pale bands) such as spots, blotches, or large numbers of rings. Also, note overall size, relative size of the head and muzzle, and girth-to-length ratio.
Size
Adult ribbon seals reach a maximum length of about 1.8 m and weights of 90 to 148 kg. Pups are approximately 86 cm long and 10.5 kg at birth.
Geographical Distribution
Ribbon seal distribution closely matches that of Larga seals. The former are widespread in the seas adjacent to the western and central North Pacific Ocean. They occur in the Sea of Okhotsk and Sea of Japan, and from the Bering Sea northward to the western Beaufort and eastern Chukchi seas. 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.
Biology and Behaviour
Ribbon seals are solitary for much of their lives. Pups are born on ice floes from early April to early May. 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.
Little is known of the diet of ribbon seals, except that types of prey vary by area, and probably season. Several species of fishes and crustaceans are consumed.
Exploitation
Only very small numbers of ribbon seals have ever been taken in commercial or subsistence harvests, the latter carried out by native peoples since prehistoric times.
IUCN Status
Insufficiently known.