Ribbon Seal

While sailing in Arctic waters, if you spot a dark brown pinniped with white bands around its neck, flippers, and hips, you can be sure it is a ribbon seal. Unlike other seals, they glide across the ice on their front flippers, moving their heads and hips in a snake-like motion.

They belong to the true seal family Phocidae and are the only species of the genus Histriophoca. Compared to two other species of the same family, they are medium-sized, noticeably larger than ringed seals but smaller than bearded seals.

Description

Size: Length: 165 cm to 175 cm (65 inches to 69 inches)

Weight: 70 kg to 95 kg (154 lbs to 209 lbs)

Body and Coloration:

Like all pinnipeds, Ribbon seals have a cylindrical body, a long neck, and a slender trunk. They get their name from the four white bands resembling ribbons that create a striking black-and-white pattern against the dark base. One band is around the neck, another around each fore-flipper, and one around the lower back before the hind-flippers. Though all ribbon seals have this general pattern, the precise shade and location of the bands may vary among individuals. The dark brown to black bands in males are more prominent than in females, which usually have a silvery gray base color.

Newborn ribbon seal pups have a white wooly coat that, after molting, changes to blue-gray on their backs and silver on the underside. Over the next three years, portions of the skin become darker and brighter with every molt, and only at the age of four does the striped pattern become noticeable. 

These seals have short snouts, deep internal nares, round front-facing orbits, large auditory bullae, and 34 weakly-rooted teeth. Unlike other phocids, they have widely spaced, curved dentition and smaller canines.

Distribution

They are native to the Arctic region, spreading across the northern Pacific Ocean and the southern Arctic Ocean. In the U.S. waters, they reside in the ice front of the Bering and Okhotsk Seas and seasonally in the Chukchi Sea, the western Beaufort Sea, and the northern Sea of Japan. The southernmost limit of their range extends to the Aleutian Peninsula, a series of volcanic islands to the west of the Alaskan Peninsula. 

So far, there are three recorded instances of ribbon seals accidentally reaching as far south as British Columbia, Long Beach, and Washington.

Habitat

These marine mammals inhabit deep waters with ice sheets, so breaking holes into them for aeration is relatively easy. Regions with broken ice chunks provide a constant supply of circulating water, facilitating a continuous influx of prey. They prefer staying near their food sources rather than foraging long distances to procure their feed.

Diet

Ribbon seals are carnivores, specifically piscivores, feeding exclusively on aquatic fish and invertebrates. The juveniles feed primarily on shrimps, crabs, and other crustaceans, while the adults prefer fishes like pollocks, cods, capelins, and eelpouts, and cephalopods like squids and octopuses. On average, they can consume about 7.7 kg of food per day. 

Behavior

• They are relatively solitary compared to other seals, aggregating only during spring to molt, give birth, and nurse their pups.
• These seals move across the ice in a ‘serpentine’ motion, a pattern different from the caterpillar-like movement of most seals. They alternate their fore-flipper strokes to propel themselves forward while moving their head and hips sideways.
• They leave their pups alone for extended periods, unlike most true seals. A probable reason for such behavior could be the relative absence of large predators. Since the young are reared on thinning ice, the shaky substrate keeps the predators from attacking them.
• When hauled out, they are mostly indifferent to their surroundings, letting humans approach their habitats easily. When captured in nets, they often feign death.
• Due to their poor vision on land, they scan for their predators for a prolonged period compared to other pinnipeds. However, their vision is relatively better underwater.

Lifespan

They have an average lifespan of around 20 to 30 years in the wild; however, their life span in captivity is still unknown.

Reproduction and Life Cycle

Like all true seals, ribbon seals have a polygynous mating system where a single male mates with multiple females. The males reach reproductive maturity at about 3 to 6 years, while the females mature by five years.

Breeding occurs annually, along with molting, usually around May to June, when the sea ice has already thawed in spring. Around this time, the males vocalize or phonate, using their air sacs to attract mates and defend their breeding territories. The couples mate and give birth to their young on chunks of sea ice detached from the land (ice rookeries).

After fertilization, the embryo takes 2 to 4 months to implant, providing the female access to maximum ice thickness during parturition. The gestation period for pregnant females is approximately 11 months, followed by the birth of a single pup, or rarely two puppies, measuring 73 to 98 cm in length (29 to 38 inches) and weighing 6 to 10 kilograms (13 to 22 lbs). The pups born have a white furry coat or ‘lanugo,’ which they shed about a month later.

The mother provides milk enriched with proteins and lipids that help the pup grow in size. When lactating, the mother does not forage for food but depends on her body’s fat storage for nutrition. The pups are nursed for about 4 to 6 weeks, after which they are weaned. They are not ready to venture through the icy waters until their lanugo is completely shed and the layer of blubber is fully formed.

Predators

Their natural predators include orca (killer) whales, walruses, Pacific sleepers, great white sharks, and polar bears. However, their greatest enemy is humans. Between the 1950s and 1990s, hunting ribbon seals was a popular sport. Despite strict regulation in countries like the United States, they are still poached for the commercial value of their skin.

Adaptations

• The thick layer of fatty blubber under their skin helps insulate the body against extreme cold conditions. 
• They possess a large inflatable air sac connected to the trachea and extending over the ribs. This structure adds to their buoyancy and helps produce underwater vocalizations for attracting mates and defending their breeding territory.
• Their long vibrissae or whiskers around the snout are sensitive to vibration and thus help locate prey underwater. They also have highly developed auditory bullae, which allow them to hear at different frequencies through a system similar to echolocating for navigation and hunting.

Conservation Status

Based on the assessment of The IUCN Red List of Threatened Species in 2015, ribbon seals are listed as Least Concern. 

Between 1961 and 1967, about 13,000 ribbon seals were commercially harvested in Russia, causing a significant decline in their numbers. However, the annual harvest was reduced to 3000 seals in 1969, recovering the population to pre-exploitation levels. Currently, scientists estimate the presence of at least 200,000 to 300,000 seals in the wild.

Ribbon seals are also sensitive to global warming. With the increasing temperature, the melting of polar ice could adversely affect their abundance. In some cases, offshore oil drilling and gas exploration activities release toxic chemicals into the ocean, which may further decline the ribbon seal population.