Sperm whales

From: Howard (howard@orcanetwork.org)
Date: Thu Jun 06 2002 - 00:07:24 EDT


I have been searching for an answer to a specific question and can't seem
to find the answer anywhere. My question is, "Why can't scientists get a
reliable population count for sperm whales or other whale species? I
appreciate your help.
Sincerely
DMGspace@aol.com

Your question has great historical import. Before the mid-70's, the only
method of counting whale populations was called the CPU or Catch per Unit
of Effort. So when the whaling ships went out to kill whales, the time and
energy they spent to hunt them was the only record of how many there were.
Of course they effectively reduced the numbers each time they went out.

Along about 1974 Dr. Mike Bigg of Canada's Pacific Biological Station in
Nanaimo, BC realized that he was seeing and photographing the same whales
year after year as he attempted to survey the orcas (killer whales) of BC
and Washington State. Though much of the established scientific community
scoffed at his amateurish efforts, he persevered and along with Ken Balcomb
on the US side accurately counted two resident populations of orcas down to
each individual, each year.

About that time Balcomb and other researchers tried to count humpback
whales in the Atlantic by photographing their flukes, which, like the
dorsal fin and saddle patch of the orcas, is different for each individual.
Thus was born the photoidentification method of population census, based on
the methodology of individual recognition, actually pioneered by Jane
Goodall in her chimp studies in the mid-60's.

Photoidentification has since proved to be immensely valuable not only for
counting individuals but for determining demographic parameters such as
birth rates, maturation rates, longevity, and eventually social system
dynamics. In 1990 the IWC published a complete description of the Southern
Resident orca community based on just 14 years of field work.

The photo-ID method is now being used around the world to survey orcas,
gray whales, blue whales, many species of dolphins, porpoises etc.,
including sperm whales.

Sperm whales, however, live out on the open ocean and move around a lot.
Some localized populations have been counted using photo-ID, but the world
population is nowhere near counted. Realistic estimates necessarily have
wide margins of error due to the paucity of data.

Now factor in the various vested interests of some of the parties who make
estimates. Whaling nations hire statistcians who are expected to make
incredibly high estimates, which justifies industrial whale-killing. Some
conservationists may tend to underestimate the size of populations in hopes
of convincing the IWC to reduce or ban whaling on those species.

A lot more could be done to refine the estimates with field studies, but it
would be expensive and many people are happy with the uncertainty. It
allows them to plug in their favorite fictional numbers.

In the end, however, we can't measure everything and we can't know
everything, so we'll just have to plod along unsure of exactly how many
sperm whales there are. I hope this helps.

Howard Garrett
Orca Network
2403 So. North Bluff Rd.
Greenbank WA 98253
(360) 678-3451
www.orcanetwork.org
howard@orcanetwork.org



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