Sea lions are often seen floating with one or more flippers extended
out of the water. They do this to regulate their body temperature.
The sun warms the blood in their dry flippers and the heat is then
transferred to the rest of the body. To cool down, they dip their
flipper into the water and then raise it back up into the air, a
behavior that results in lowering the blood temperature through evaporative cooling.
A California sea lion under water
(courtesy of Dan Costa, UCSC)
Sea lions are adapted for movement on land as well as in the water.
Wing-like front flippers have bone structure similar to that in
our arms and hands. They swim by making long simultaneous sweeps
with their front flippers, "flying" though the water.
When on land, they are able to rotate their hind flippers underneath their body and use all four flippers
to walk. Sea lions are fast swimmers and can swim in burst speeds
up to 25-30 knots (30mph), but generally cruise at about 5-15 knots
(11mph). Sea lions gain speed by porpoising,
leaping clear of the water and then gliding near the water's surface
to minimize resistance.
Sea lions have been recorded diving to a maximum depth of 125
feet (375m) and can be underwater for an average of 2-8 minutes,
diving with at least partially inflated lungs. Sea lions are able
to dive so deep and stay under water so long because they have a
high tolerance for carbon dioxide and the oxygen in their body is
shunted (diverted) to the heart and central nervous system rather
than on non-vital organs.