Seals, sleep

From: Dagmar Fertl (dagmar_fertl@hotmail.com)
Date: Mon Mar 27 2000 - 14:25:43 EST


Hi Dagmar and all;

My 3 year old daughter Anwyn is very curious about how seals sleep. We
found information on the internet about harbour seals subconsiously
surfacing to breathe air while sleeping. What about other species? She
is especially interested in the leopard seal as that is the species that her
toy 'Slippery' is.

Many thanks in advance for the information!

Donna Greenley and Anwyn Greenley Olsen
Peterborough, Ontario
Canada
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Hi Donna and Anwyn,

Thanks for your question. Since I study whales and dolphins, I had to look
up the answer to your question (Riedman, M. "The Pinnipeds: Seals, Sea
Lions, and Walruses").

Although harbor seals prefer to sleep on land, they often sleep in the
water. They can sleep underwater, though they then have to wake up
frequently and regularly to surface and breathe. So, this is not something
subconcious, but something they have to conciously do.

Harbor seals sleeping on the water's surface often assume a posture known as
bottling: most of the seal's body remains submerged, but the animal's face
pokes above the surface like a snorkel, allowing the animal to breathe
regularly while sleeping or resting. Elephant seals sometimes rest in the
water in a similar manner. Northern elephant seals may possibly sleep
hundreds of meter underwater. Walruses can inflate pouches in their throat
which can help them float at the water's surface as they sleep. From studies
of sleep in grey seals, we know that grey seals have REM sleep
(rapid-eye-movement; lightest stage of sleep, in which brain-wave activity
is highest and dreaming takes place) which does not occur in all animals,
and it doesn't take place when pinnipeds during underwater sleep. It does
take place when pinnipeds sleep at the surface of the water and on land.

Looking at an older reference that had some information on seals and
sleeping, I found that Galapagos sea lions may doze in the water for a few
seconds, but remain alert even then. Fur seals have been seen sleeping at
the water's surface on their back or sides. Captive sea lions and some seals
can sleep underwater.

I couldn't find any information on sleep in the leopard seal though. Leopard
seals are pretty mean seals that live in the Antarctic, and they're not very
easy to study.

Hope this helps,
Dagmar

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