The harp seal (Pagophilus groenlandicus) is a medium-sized pinniped navigating the icy waters of the North Atlantic and Arctic Oceans. They do have fur, but the coat changes dramatically throughout their lives, transitioning from a thick, woolly layer in pups to a sleek, specialized adult coat.
The Adult Harp Seal Coat
The mature harp seal develops a short, dense coat well-suited for its aquatic life. This pelage consists of stiff guard hairs that lie flat against the skin, helping to streamline the seal’s body for efficient swimming. The adult fur provides minimal insulation when the seal is immersed in frigid ocean water. Its primary function is hydrodynamic, reducing drag, and offering a small barrier against the cold when the seal is hauled out on the ice.
The adult coat’s coloration transitions significantly as the animal ages. It is silver-gray, often appearing steel-blue when wet, which offers camouflage against the icy backdrop of their habitat. The most recognizable characteristic is the dark, curved patch that develops on the back, resembling a harp or saddle, which gives the species its common name. This pattern is typically more defined in males, while some females may retain a spotted appearance.
The Distinctive Fur of the Newborn Pup
Harp seal pups are born with a thick, long, woolly white coat called lanugo, which leads to them being referred to as “whitecoats.” This dense, white fur is highly insulating in the air, trapping heat and absorbing sunlight to keep the pup warm on the ice. The initial coat is also effective camouflage, allowing the pup to blend seamlessly with the snow and ice floes.
The lanugo is not suitable for swimming because it quickly loses its insulating properties when wetted. The pup must shed this coat completely before it can become fully independent and enter the water for extended periods. This molting process begins around two to three weeks of age, often coinciding with the end of the intense nursing period. Once the lanugo is shed, the pup enters the “beater” stage, characterized by a silver-gray coat with dark spots.
Insulation: The Role of Blubber and Fur
While harp seals possess fur, the main mechanism for regulating their body temperature in the Arctic environment is a thick layer of subcutaneous fat known as blubber. This blubber layer is a dense, energy-rich tissue that provides thermal insulation, maintaining the seal’s core temperature even in near-freezing water. Blubber’s effectiveness is not compromised when the seal is submerged, making it the primary insulator during their frequent dives.
The adult fur plays a secondary role in insulation, largely losing its ability to trap air and heat when compressed and wet in the water. True seals, or phocids like the harp seal, rely heavily on blubber, unlike fur seals and sea lions which use dense underfur as a major insulator. The pup’s initial lanugo is insulating in air, but the rapid development of a thick blubber layer from the mother’s high-fat milk prepares the young seal for survival after it molts.