The Harp Seal, Pagophilus groenlandicus, is a marine mammal inhabiting the Arctic region. This species navigates the cold northern waters. Its unique characteristics, from physical appearance to migratory behaviors and reproductive patterns, allow it to thrive in this extreme environment. This article explores its distinct features.
Distinctive Features and Adaptations
Harp Seals exhibit physical traits that change throughout their lives. Newborn pups are known as “whitecoats” due to their fluffy, pure white fur. This thick coat helps absorb sunlight and trap heat, providing insulation. After two to three weeks, pups molt, shedding their white fur to reveal a silvery-gray coat with irregular dark spots as they learn to swim.
Adult Harp Seals are silver-gray with a distinct black mask on their face and a curved, harp-shaped black patch on their back. This harp pattern is more defined in males, while females may have lighter coats with scattered dark spots. Adults measure 1.7 to 2.0 meters (5.6 to 6.6 feet) in length and weigh between 115 to 140 kilograms (254 to 309 pounds).
These seals possess adaptations for cold, icy environments. A thick layer of blubber provides insulation and serves as an energy reserve, allowing them to fast for extended periods. Their circulatory system can also control blood flow to their extremities to minimize heat loss. Their large, dark eyes are well-suited for low-light conditions and underwater vision, aiding in navigation and prey detection.
Habitat and Migration
Harp Seals inhabit the cold waters of the North Atlantic and Arctic Oceans. They are widely distributed across continental shelf regions, preferring ice floes for breeding and molting. There are three distinct populations, identified by their pupping sites: the Northwest Atlantic, the Greenland Sea, and the Barents Sea/White Sea.
Harp Seals are highly migratory, undertaking seasonal journeys. The Northwest Atlantic population, for instance, spends summers in the Canadian Arctic and Greenland, then migrates south to the Gulf of St. Lawrence or off southern Labrador and northern Newfoundland in the fall. These annual migrations can cover distances of over 2,500 kilometers (1,550 miles) one way. Their movements are linked to the distribution of their prey.
Diet and Foraging
Harp Seals have a varied carnivorous diet that changes with age, season, and location. Their primary food sources include fish species such as capelin, Arctic cod, polar cod, herring, and redfish. They also consume crustaceans, including shrimp, prawns, amphipods, and euphausiids (krill). They focus on smaller fish and invertebrates.
Harp Seals are skilled underwater hunters, capable of diving to depths. They dive to depths of 100 meters (330 feet) while foraging, with some recorded dives reaching over 500 meters (1,600 feet). They can remain submerged for 15 to 20 minutes. Their excellent eyesight and sensitive whiskers help them detect prey by sensing subtle vibrations in the water. Small fish are swallowed whole underwater, while larger catches may be brought to the surface before consumption.
Reproduction and Pup Development
Harp Seals gather in large breeding colonies on pack ice, often containing thousands of individuals, during their breeding season from late February to March. Females give birth to a single pup, with twins being rare. Newborn pups, known as “whitecoats,” weigh 10-11 kilograms (22-24 pounds) and are 80-85 centimeters (31-33 inches) long. They are born without a thick blubber layer, relying on their dense white fur for insulation.
The nursing period is short, lasting about 10 to 12 days. During this time, the mother does not feed, losing up to 3 kilograms (6.6 pounds) per day. Harp Seal milk is rich in fat, initially containing about 25% fat and increasing to 40% by weaning. This high-fat milk allows pups to gain weight rapidly, over 2.2 kilograms (4.9 pounds) per day, developing a thick blubber layer. Pups can gain up to 20 kilograms over the nursing period, reaching an average weight of 34-36 kilograms (75-79 pounds) at weaning.
After weaning, the mother leaves the pup to mate again, often with multiple partners, usually in the water. The weaned pups, sometimes called “ragged-jackets” as they molt their white fur, remain on the ice without feeding for several weeks, relying on their acquired blubber reserves. During this period, they can lose up to half of their body weight before hunger motivates them to forage independently.
Conservation and Challenges
The Harp Seal is classified as “Least Concern” by the IUCN, indicating a healthy and abundant global population. For instance, the Northwest Atlantic population was estimated at 7.4 million animals in 2019. Despite this status, the species faces ongoing challenges that require monitoring.
Climate change poses a threat, primarily due to its impact on sea ice. Harp Seals depend on stable ice platforms for birth, nursing, and molting. Reduced ice extent and thickness can lead to increased pup mortality from drowning, being crushed by unstable ice, or abandonment on shore. Poor ice conditions have resulted in significant increases in pup mortality in some years.
Commercial hunting, where permitted and regulated, is a challenge, although its impact has decreased in recent years. Harp Seals can be affected by fisheries through bycatch in fishing gear, with an estimated 17,000 individuals from the Northwest Atlantic population killed in gillnets in Newfoundland annually. Overfishing of their prey species and ocean pollution, including chemical contaminants, also concern their long-term well-being.