How to

31 May 2016

How They Keep Warm: Harp Seals

It’s one thing to keep warm out in the icy winds of the Arctic Circle, but what about when you have
to take care of that, and figure out a way of withstanding hours spent beneath the surface of the
water, where it is, if anything, even colder. This is the challenge faced by harp seals, a species which
lives almost exclusively in the arctic.
Nearly every species of seal needs to be adapted for cold water, but harp seals have a fair harsher
deal on this front than any other kind, to say nothing of all the predators they have to contend with.
Like all other seals, they are coated with a thick layer of blubber which helps them to retain thermal
energy, but there’s more. The younger seals have a layer of white, water repellent fur which is shed
when they reach adolescence, very gradually, enabling them to acclimatise to the coldness of the
water as they grow. 

In adulthood, seals will moult layers of skin away in order to maintain a resistant layer. They come
onto the land to do this, and make sure to stay out of the sea until their new skin has fully grown in.
This is the really amazing part, though: harp seals can actually reduce their heart rate by 90% when
submerged, reducing blood flow to the outer extremities and thereby reducing heat loss. Only their
vital organs and nervous system are left with a normal blood supply, yet they can function perfectly
this way, and even hunt. 
Their flippers are also designed to conserve heat when they’re on land, as well as propelling them
through the water at speed. In order to better see their prey, harp seals have a filmy layer over their
eyes to protect them from the harsh arctic water. Their diet consists largely of fish, which they scare
out from the ice by blowing bubbles, but they can also eat krill by filter feeding through gritted teeth.
They are remarkably fast swimmers, due to the way they conserve energy and the streamlined
nature of their bodies (unlike most mammals, they keep their landing gear stowed, so to speak).

Callum Davies

Callum is a film school graduate who is now making a name for himself as a journalist and content writer. His vices include flat whites and 90s hip-hop.