Specimen of the Week 323: The harp seal
By Nadine Gabriel, on 29 December 2017
It’s Nadine Gabriel with a Christmas dose of Specimen of the Week! As it’s only a few days after Christmas, I decided to choose a somewhat festive specimen for this week’s blog, so here’s an animal from (near) the North Pole – the harp seal!
Ice-lover from Greenland
The harp seal’s scientific name (Pagophilus groenlandicus) means “ice-lover from Greenland”. Despite their icy name, they actually spend most of their time underwater and are able to hold their breath for 15 minutes while diving to a depth of up to 270 m. To help them survive in their freezing habitat, harp seals have a thick layer of insulating blubber which also acts as a source of energy when food is scarce. Their brown fat (a type of fat that can burn energy) warms their blood, and their flippers also help with heat regulation. Their range covers the North Atlantic and Arctic Oceans. There are nine million harp seals (as of 2014) split across three populations, making them the most abundant pinniped in the northern hemisphere. The largest population is off the coast of Canada with 7.5 million individuals, the West Ice population near Greenland has 627,000 individuals and the White Sea population near Russia has 1.4 million.
A short, fluffy childhood
Harp seals give birth to one pup between late February and April. Delayed implantation allows mothers to synchronise their births. The embryo is able to remain in the womb for up to three months before implanting itself on the uterus wall and developing further. Baby harp seals weigh 11 kg and are 80-85 cm long with yellowish-white fur for camouflage. They are nursed for 12 days with milk that contains 65% fat; for comparison, blue top cow’s milk contains just over 3% fat. This energy-rich milk allows them to gain about 2.2 kg a day.
After 12 days, the mother abandons her pup and will sometimes mate again. Since baby harp seals are not able to swim and hunt for food straight away, they live a sedentary life for 7-8 weeks. During this period, they lose about 50% of their body weight and they moult their baby fur (here’s a partially moulted individual). Because they spend so much time resting in one place, they often melt the ice underneath them and this forms a little “ice cradle”.
Harp seals go through another moult when they are 13-17 months old and this reveals the grey adult coat. This coat has black spots and a horseshoe-shaped pattern along the back; this pattern is less pronounced in females. Adult males are 171-190 cm long with an average weight of 135 kg while females are 168-183 cm long and weigh on average 120 kg. Every year in the spring, tens of thousands of harp seals gather on the ice during the annual moult. After this, they can migrate up to 4000 km to summer feeding grounds in pods numbering dozens to hundreds. They live a long life and some individuals have been known to reach 30 years old.
Nadine Gabriel is the Museum Intern at the Grant Museum of Zoology
Hammill M. O., Stenson G. B., Mosnier A. and Doniol-Valcroze T., 2014. Abundance Estimates of Northwest Atlantic Harp Seals and Management Advice for 2014. Canadian Science Advisory Secretariat Research, Document 2014/022