Subject: Age determination

Martine Berube (martine@newt.bio.uci.edu)
Mon, 13 Oct 1997 10:54:01 -0700

>How  do you tell a whale's age?

You know that whales are divided in two orders, the mysticetes or baleen
whales and the odontocetes or toothed whales.  The methods are different
for the two orders.
When whaling operations supplied carcasses, it was possible to determine
the age of baleen whales, for example fin whales and blue whales, by
counting the annual growth layers of the sectioned ear plugs.  Each layers
are made up of one light and one dark lamina, deposited in the horny plug
at the proximal end of the ear canal.  In some cases where it was
impossible to collect or identify the laminations of the ear plug,
alternative methods were to count the grooves and ridges of the baleen
plates or use the asparctic acid racemisation in eye lenses.  However
today, as commercial whaling came to a stop, only age-classes can be
estimated which are correlated with the length of individuals.  The
measurement of the animal can be done from vertical-aerial photographs or
by the comparison of the length of a young animal with their accompanying
adult.
For toothed whales, for example beluga or dolphin sp., the age is
determined by counting the growth layers in teeth.  This, of course
requires that the animal is captured or found dead.
Finally, in some areas, such as the Gulf of Maine, the Gulf of St.
Lawrence, etc..., biologists have been studied whales for more than a
decade.  Therefore, when a newborn calf is seen, it is photographed in
order to individually identify the animal, and followed in the next years,
hence, you know it's age.
I hope that this is of some help for you.
Sincerely,
Martine

Martine Berube
Dept. of Ecology and Evolutionary Biology
University of California
Irvine, CA, 92697-2525
PHONE:714-824-8680
FAX:714-824-2181
E-mail: martine@newt.bio.uci.edu