Science of the Seasons: Bearded seals buoy the Arctic food chain

By Dr. David Wartinbee, for the Redoubt Reporter

Bearded seals are about four times the size of a ringed seal and can weigh up to 900 pounds. They are named for the abundant, thick, bristlelike whiskers on their muzzle. Like ringed seals, they are intimately tied to sea ice in the Arctic Ocean and are considered one of the ice seals.

During the winter months, bearded seals maintain numerous breathing holes in the Arctic Ocean ice. They also maintain larger openings where they can haul out to rest on the ice after foraging. This resting time is when they are most susceptible to hungry polar bears or hungry humans.

In April, the females give birth to a single pup on the ice. The young seal has the thick lanugo fur to keep it warm until it builds up a layer of blubber from its mother’s fat-rich milk. Unlike the ringed seal, bearded seals do not dig out a protective lair for their young; they just lie out there on the ice and snow.

Bearded seal pups have to nurse heavily because the mother will only nurse them for about 18 days. During this active feeding, pups can gain up to one quarter of their birth weight every day. Not surprising, the mother is losing an equal amount of body fat as her body sacrifices its fat stores to make the 50 percent fat-content milk for the pup.

Less than three weeks after birth, the pup is weaned and is ready to start foraging for itself. Because of the rich milk diet, bearded seal pups are able to swim under the ice to avoid predation fairly quickly after being born.

Their diet consists of a variety of invertebrates, like various crabs and bivalve mollusks. Their thick whiskers are thought to be used for finding clams just below the ocean floor substrate. They are also known to take a variety of fish, such as sculpins and cod.

Because bearded seals are much larger than ringed seals, they are more sought after by human subsistence hunters and polar bears. Polar bears and humans primarily hunt them when they are resting on top of the pack ice. However, bearded seals are also preyed upon by killer whales when they are in more open waters.

The meat from bearded seals, like virtually all seals, is unmistakably dark in color. This color comes from the abundance of myoglobin in the individual skeletal muscle cells. Myoglobin is a compound that holds extra oxygen within muscle cells and essentially enables muscles to function for longer periods of time without receiving oxygen from the lungs.

The oxygen is used for the most efficient extraction of energy from energy-rich molecules, like sugars or lipids. This is a valuable commodity for animals that can spend a half hour or longer under water.

Another interesting characteristic of seals is their dentation. They have front incisors (cutting) teeth, as well as canines. The rest of their teeth are sharp, pointed and somewhat arrowhead shaped. They do not have grinding molars nor bicuspid teeth other predators often use for cutting through tough tissues. Because of this dental arrangement, they are good at catching and holding on to fish or invertebrates, but not chewing the catch afterward. Thus, seals are forced to swallow their prey whole or in large chunks.

Next time we’ll look at walruses.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus.

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