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Sperm
whales have been present off Eden and Merimbula now for
several weeks. Large matriarchal pods are not unusual
off the east coast of Australia and there are regular
sightings off other parts of the coast as far north as
Sydney. The animation below is a small (160Kb) animated
GIF which shows the location of encounters between 23
April and 2 May 2005.
In
late April, a warm core eddy appeared off the New South
Wales coast and water can be seen spiralling in an
anti-clockwise rotation, taking surface water offshore
around Green Cape, on the south-east corner of
Australia. This appears to have promoted some upwelling
(colder green water) which may explain why many
cetaceans including killer whales, Risso's dolphins,
pilot whales and sperm whales have recently put in an
appearance close off the coast here. These currents have
presumably supported a bloom in the prey of these
species, particularly squid.
The
movement of sperm whales over this period is in a
generally southern direction and appears to be guided in
part by the southern edge of the warm water front which
almost reached Green Cape by the beginning of May.
Click on the image above to view the animated
GIF (160Kb). The maps are adapted from CSIRO data
at: http://www.marine.csiro.au/remotesensing/oceancurrents/
The maps at http://www.marine.csiro.au/remotesensing/oceancurrents/Syd-Hob/
appear to show another very strong warm core front just
north of Sydney. Sperm whales are probably to be found
in many of these stronger fronts but we don't normally
see them due to the fact that this activity is well
offshore.
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