Harp seals gather together at their breeding grounds in the winter. At the breeding grounds, there may be up to 2,000 seals per square kilometer. The mating system of harp seals is much disputed and they been described as monogamous, polygynous, and polyandrous. To attract females, some male seals blow bubbles and make noises beneath the ice near where females have made entry holes into the water. Males also may chase females or making pawing gestures towards them. To compete for females, male harp seals may splash and bite other males. Research has suggested that female harp seals may also choose their mates based upon the size of their baculum. ("Harp Seals", 2004; "Pagophilus groenlandicus", 2008; Jefferson, Leatherwood, and Webber, 1994; Kovacs, 1995; Kovacs, 2008; MarineBio.org, 2009; Miller and Burton, 2000; Novak, 1999)
Both male and female harp seals reach sexual maturity at around 5.5 years old, though they both don’t tend to copulate regularly until a few years later. The average reproducing age for females is 10 years old. Males don't successfully compete for breeding opportunities until they are 8 years old. Harp seals remain sexually active for the rest of their lives. ("Harp Seals", 2004; "Pagophilus groenlandicus", 2008; Kovacs, 1995; Kovacs, 2008; MarineBio.org, 2009; Novak, 1999)
Harp seals breed 10 to 12 days following the birth of their pups. Females enter estrus and breed near the end of lactation. The gestation period is divided into four months of delayed implantation and 7.5 months of active gestation. Birthing of harp seal pups occurs from late February to April. Females give birth on the ice near open water. Harp seals birth one pup at a time, they are nursed and cared for by their mother for 10 to 12 days. The mother’s milk is 48% fat and the pups gain an average of 33 kg while they nurse. Once the pup is weaned it is abandoned by its mother and remains alone on the ice as it waits for its silver-gray pelage to grow in so it can go into the water. While the pup waits, it loses up to 50% of its body fat. Pup mortality is 20 to 30%. ("Harp Seals", 2004; "Pagophilus groenlandicus", 2008; Jefferson, Leatherwood, and Webber, 1994; Kovacs, 1995; Kovacs, 2008; MarineBio.org, 2009; Novak, 1999; Schliemann, 1990)
Female harp seals are the sole providers of care to their pup. Mothers nurse their pups for 10 to 12 days. While the pup is still nursing, the mother is very active and leaves the pup alone for extended periods of time. Pups remain near the area where the mother enters the water. Once the pup is weaned, it is left alone on the ice while it sheds its white coat and develops a silver-gray pelage. After about four weeks the pup will become fully independent and forage for its own food. ("Harp Seals", 2004; "Pagophilus groenlandicus", 2008; Jefferson, Leatherwood, and Webber, 1994; Kovacs, 1995; Kovacs, 2008; MarineBio.org, 2009; Novak, 1999; Schliemann, 1990)
- Jefferson, T., S. Leatherwood, M. Webber. 1994. Marine Mammals of the World. Rome: United Nations Environment Program and Food and Agriculture Organization of the United Nations.
- Kovacs, K. 1995. Harp and hooded seals - a case study in the determinants of mating systems in pinnipeds. International Symposium on the Biology of Marine Mammals in the North East Atlantic, Developments in Marine Biology 4: 329-335.
- Novak, R. 1999. Pagophilus groenlandicus. Pp. 887-888 in Walker’s Mammals of the World, Vol. Volume II, Sixth Edition. Baltimore: The Johns Hopkins University Press.