The Dry Valleys have
a number of odd phenomena, one of which is the occasional mummified
seal many miles from the sea. Crabeater and Weddell
seals have been found up to 40 miles from the sea and at altitudes
of up to 5000 feet. These corpses have been carbon dated and
found to often be hundreds of years old and up to 2600 years
old.
They often appear to be much
younger than this having died relatively recently. The cold
drying winds desiccate the carcass quickly and lead to mummification,
a lack of carrion feeders and decay mean that there is only
the wind blown dust and sand to make the carcass break down
along with the effects of freeze thaw and the summer sun. The
newer ones (a mere hundred years or so old) are very well preserved,
but as they age they start to disintegrate until only scattered
and slowly eroding bones are left.
There are places where there
are several of these carcasses are found in the same position
giving the impression that they arrived together, though closer
investigation has shown that they have simply been funnelled
by the landscape to the same position and in fact differ in
date of arrival and death by decades.
No-one is exactly sure
how or why these seals end up in the middle of the Dry Valleys
in such horribly inhospitable conditions and after what must
have been such a dreadful journey to get there, but there are
some indications.
Most of the seals examined are
juveniles, less than a year old, it is thought that they simply
take the wrong direction on the annual seasonal migration north
as the winter arrives and start to head inland instead. Some
of them are heading for the glaciers and it may be that once
lost, they see the ice and start to head that way.
The story told by the carcasses
is quite sad, there is often minimal blubber left, suggesting
it has been used up on the extended trek. Some of the seals
have injuries and significant blood loss where they are found
indicating bleeding immediately prior to death (possibly from
cuts from rocks?). The seals have stomachs that are totally
empty of food as might be expected, but some have appreciable
amounts of sand, gravel and small stones from the immediate
environment, much more so than seals that have access to the
sea implying that they are attempting to eat what is available
to them. Ultimately they seem to starve to death, though some
are found at the bases of small cliffs having fallen off and
others have much blood-sodden sand nearby and injuries that
would fit with this.
There have been a much smaller
number of penguin carcasses found in similar circumstances,
this may be because penguins are less likely to get lost, because
as they can walk rather than crawl across the terrain more easily,
perhaps they can find their way back to the sea more easily
or that as they are considerably smaller than the seals, perhaps
their carcasses break up more quickly.
Thankfully, this seems to be
a fairly rare occurrence with a study showing that one seal
every 4-8 years enters the valley system and dies - link below.
More information (external site)
An older Dry Valley mummified seal in an
advanced state of disintegration
Photograph by: Kristan Hutchison National
Science Foundation
Picture courtesy of Mike Usher
- Mike went on a Ross Sea expedition on board the Kapitan Khlebnikov
in 2005.
You can purchase a selection of Mike's pictures
here
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