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Winter
Wildlife
(part 2 of 4)
Thursday February 8th 2001
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Unlike
other seals, Weddell seals do not migrate north during winter.
Instead they live on top of or underneath the thick sea ice
near the coast. For the Weddell seals in winter the sea ice
forms a barrier between the food in the ocean below and the
fresh air above so the most important things for them are
the breathing and haulout holes. To make breathing holes they
have to exploit weak points in the sea ice called tide cracks
where the sea ice sheets meet. Once they have created a hole,
they have to stop the holes from freezing over so they use
their teeth to grind away at the ice. After years of grinding
away at the ice the seals wear out their teeth and are unable
to feed. On a number of occasions we found a breathing hole
that was open and being used. I thought it was an enthralling
sight to see a Weddell with it's nose and face just above
the water taking in deep breaths of air, holding it for a
few seconds and then blowing out the stale air life a sneeze
After about 5 minutes of very deep breathing the seal dived
back down for another dive lasting 20 minutes or more.
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A
Weddell seal in a breathing hole taking in fresh air.. |
When
the Weddell seals are not feeding that usually find a hole large
enough for them to "haulout" onto the sea ice where they
spend long hours on sleeping. Haulout holes are also where most
of the scats are found along with seal imprints in the snow which
allow us to determine the sex of the seal by the location of the
urine stain. During Rhonda's seal surveys if we saw a haulout hole
we stopped the quad and counted the numbers and sexes of the seal
imprints along with the numbers of scats. This information was written
down along with the GPS location of the hole. Seal scats were also
collected for latter analysis back at Mawson.
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Rhonda
put each scat into a fine mesh bag and washed it in a washing
machine so that the fish ear bones and, squid beaks and other
undigested remains could be separated and counted to determine
what the seals were feeding on. If you were lucky enough to
visit Rhonda on one of her washing days you would discover
that seal poo stinks when it is wet, compared to when it is
a frozen odourless mass on the sea ice!
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A
clear male Weddell seal imprint on ice at Macey |
In
between collecting scats and surveying haulout holes, Patrick chose
a suitable location to drill a hole in the sea ice and drop down
a hydrophone. The hydrophone was connected to a DAT tape recorder
which was able to record the sounds under the ice for around 2 hours.
Sound travels a long distance underwater and the sounds of people
walking or vehicles travelling on the surface were easily heard.
So after Patrick had started recording we quickly drove off to make
sure our sounds did not interfere with the recording. Back at Mawson,
Patrick went back through his tapes and analysed the seal calls.
Underwater, Weddell seals have a very large vocabulary and after
a number of months of recordings Patrick had separated out about
80 different types of calls!
Weddell
seals and Emperor penguins around a haulout hole in the sea ice
near Macey Island.
Email
continues in part 3
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