Hi,
Having now seen all of Rohan's images, I am confident that the animal seen at
Ashmore Reef is not a fin whale but a Bryde's Whale. This is really interesting
because the characteristics match Omura's Whale, which is a fairly recently
described subspecies of Bryde's and to the best of my knowledge, not previously
reported from Australian waters. It is however, reportedly from the east Indian
Ocean.
Rohan's photos are here: http://www.pbase.com/wildlifeimages/fin_whale
Note particularly the last three images, which are definite fin whales. This
image http://thump01.pbase.com/t1/73/838473/4/108103428.1lDzT4Kg.jpg is
particularly notable. This is a classic dorsal fin shape for Fin Whale. See the
way it is big, thick-based, and triangular. It almost seems to fall off the
back of the animal as it rolls. The sheer girth of the dorsal fin base can also
be seen in the pictures of animals logging in the Antarctic (second last
image), as well as the huge distance between splash guards and dorsal.
Now back to the animal from the northwest shelf. Note, when we talk about
Omura's, we're talking about a type of Bryde's Whale. Taxonomy on Bryde's is
incomplete and Omura's was only described in 2003. Since getting accurate adult
lengths depends on whaling or stranding, we don't really know. So I would not
put great stock in any absolute indications of size in any books. It is likely
that they vary somewhere around the length of a Bryde's Whale. Estimates from
the time apparently varied from 15-20m, based on the length of the vessel.
Shirihai and Jarrett say that Omura's is smaller than Bryde's, however I have
other books that disagree. Since length is very difficult to estimate at sea -
when you can only see small parts of an animal - there is every likelihood this
whale was small enough to be at the large-end of Bryde's for size.
Second, the lack of rostral ridges. This is also down as a feature for Omura's
whale, as is the white lower jaw, visible here:
http://ic2.pbase.com/t5/73/838473/4/119350416.luhnQCnw.jpg
This simply doesn't look like a fin whale. The dorsal is small, thin and like
an isoceles triangle with a slight curl at the top. In fin whale it would be
big, thick and tipped backwards off the body.
http://www.pbase.com/wildlifeimages/image/119350415
The base colour is wrong. Fin whales are an amazing steely-grey colour. This
animal is cloaked in mottling, which is also very Bryde's whale. The
splashguards are too small http://www.pbase.com/wildlifeimages/image/119350416
and the rostrum is not long and flat-enough.
There is a page with a description on fin whale here:
http://oceans.wildiaries.com/species/20199. Brett Jarrett's image also
indicates the sheer size and length of features on this animal.
Here's info on Bryde's for comparison:
http://oceans.wildiaries.com/species/20197
That all said, this is a very exciting discovery. Omura's whale has, to the
best of my knowledge, not been confirmed in Australia before.
Regards,
Simon.
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