|Harp Seal, Pagophilus groenlandicusCommon Names: harp seal, Greenland seal, saddleback
General Description The harp seal, one of the ‘earless’ or ‘fur’ seals (family Phocidae), is a solitary streamlined aquatic mammal. The bones of its limbs are short and withdrawn into the body, making the flippers a power source close to the body. These flippers have fur on all surfaces, unlike other pinnipeds. Another reason that the saddleback is a good swimmer is because of its blubber. The blubber is thickest in the dorsal area. It starts to thin out in the neck and foreflipper regions. The harp seal can grow to be an average length of 1.7 meters and 130 kg, although it can reach 2 meters and 160 kg. There are distinctions in the colour pattern at different ages and between the sexes. Adult males have light grey fur with a horse-shoe or ‘harp’ shaped band of black fur over its back and along its sides. His head is also covered in black fur. The slightly smaller female is a paler grey. The dorsal and lateral black band is also lighter, if not fragmented. The pup is born with yellowish fur, which will change to a silky white coat within the first couple of days of its life. After about 1-1½ weeks, the pup will moult and be a silvery grey with irregular dark or black spots. Harp seals (no matter their age) moult every year around April-May. They have an acute sense of vision, as well as an acute sense of hearing, especially under water. Their average body temperature is approximately 36ºC.
Geographical Distribution and Habitat Requirements This species can be found in arctic and sub-arctic waters. It is distributed into three main population stocks: 1) the northwest Atlantic population, which breeds in the Gulf of St.-Lawrence, 2) the east Greenland population, which breeds on Jan Mayen Island (north of Iceland), and 3) the Barents Sea population, which breeds in the White Sea. In autumn, most seals migrate south to breed and moult. In the summer, they will return north with the receding ice pack. This migration can be as far as 8000km. In New Brunswick, harp seals are usually sighted along the northern coastal areas in the Gulf of St.-Lawrence. Although, multiple sightings have been made in the Bay of Fundy (specifically, St.Andrews). Wandering and stray seals would account for the latter sightings. Pagophilus groenlandicus live along the open sea on rough ice approximately 25cm thick (this is where they mate). Many seals will share one breathing hole, which is 60-90cm in diameter. This hole is used for obtaining air between dives (which can go as far as 275 meters down). It has been recorded that during the breeding season, up to 40 individuals will share an opening in the ice.
General Biology The adult harp seal eats capelin, arctic cod, and sculpin. When the seal migrates south, the diet changes to Atlantic cod and herring, redfish, shrimp and other invertebrates. These fish make up the majority of the food ingested, but the harp seal diet consists of over 160 different species. They eat an equivalent of 1-5% of their body weight in food each day. The young seals (under one year of age) feed on smaller prey, mainly euphasiids. During the first two weeks of a pup’s life, it will feed on its mother’s milk, which consists of 11% protein and 43% fat (this is ten times fatter than cow milk). After this initial 2-2½ weeks, the mother will leave the pup to fend for itself. At this point, having gained approximately 2.5kg/day (mostly in blubber), the pup will be able to swim and catch its own food.
These solitary aquatic animals will group up during migration. Once they reach their breeding destination, males will fight for females, using their teeth and flippers. Once the mating event has occured, the couple will remain monogomous for the rest of the breeding season. 90% of the pregnancies are successful leading to a gestation period of 11 months, not including the 3-4½ months where the fertilized ovum remains dormant (delayed implantation). After this time, usually sometime between January and April, one pup will be born. At this time, females will lactate for about 12 days. 20-30% of these pups will die within their first year due to predators like the polar bear, killer whale and shark, or simply due to hunting, starvation or freezing. If they survive past this initial year, females will reach sexual maturity at 5-6 years old, and males, 7-8 years old. Most will live to be 35 to 42 years old. The mortality rate of adults is approximately 8%.
Another interesting fact about the harp seal is that even though its swimming in ice water, it’s metabolic rate does not increase. As the ambient temperature decreases, so does the size of the arterioles of the skin. So the skin temperature drops to slightly above the water temperature, which prevents freezing. Heat is therefore trapped within the body and core temperature can remain constant.
Conservation The harp seal has no particular status at present, but concerns about the rate of population decline are starting to increase. The two main threats to the seal population are: 1) over exploitation of its food stock (capelin, cod and herring), and 2) over exploitation of the actual seal stock. It is killed for its fur, oil and leather, as well as for food by the natives. ‘Whitecoats’ (pups younger than 2-3 weeks) are hunted for their silky white fur. It was not until recently, in 1987, that Canada put a ban on such hunting for commercial purposes, but other countries continue to kill the pups (although, only during a restricted time frame). One conservation group claims that approximately 20 000 pups are killed illegally each year in Canada alone. It is thought that the size of the seal population today is declining at the same rate as it was in the 1950-1970’s, at which point the harp seal population deceased by 50%.