Worldwide, 32 species of seal have
survived the twists and turns of evolution to the present
day. They share a common genetic record that suggests
they have lived in our seas for about 27 million years, being
descended from a land-based carnivore, similar to a giant
Only two species of seal live on the Welsh coasts – the grey seal
and the common seal. You can tell them apart by their size,
head shape and colour.
Nearly 40% (about 125,000) of the world population of grey seals
is found in the British Isles, with a relatively stable population
of about 6,000 in Wales. Grey seals can be huge, with males
growing to over 2 metres in length and weighing up to 330kg. They
have large Roman noses - in fact, their scientific name -
Halichoerus grypus - actually means 'sea-pig with a hooked
nose'. They are usually dark grey or brown, often with
blotches. The pups have soft white fur.
The common seal is quite rare in Wales. These animals
are smaller than the grey seal and have more rounded dog-like
faces. Their colour varies from pale to dark grey, often with dark
spots or rings.
On land, seals may look awkward and clumsy, but they are
extremely agile and graceful underwater, where a duvet of blubber
about 5 centimetres thick (in a healthy seal) keeps them
warm. Their body temperature is almost the same as that of a
Being mammals, seals need to hold their breath underwater, but
rather than descending with lungs full of air as human divers do,
seals expel air before they submerge.
Their blood stores more oxygen than human blood which reduces
buoyancy and the risk of the bends (a common problem for human
divers, where nitrogen bubbles form in the blood as pressure falls
This oxygen store in the blood allows them to make foraging
dives of up to about 8 minutes. At rest, including while
asleep, they may remain submerged for up to 13 minutes.
Many seals regularly dive to 50 metres but may dive to much
Another helpful adaptation to underwater life is the seal's
ability to regulate its heartbeat in a process called
bradycardia. While at the surface, a seal's
heart may beat at a rate of about 120 beats per minute as they
rapidly expel the waste products of respiration (carbon dioxide)
and take in more oxygen. Underwater, the seal's heartbeat
drops to about 40 beats per minute, which allows them to maximise
the time spent under the surface catching fish.