Written By Peter Gwynne
A technique that monitors whales through the sounds they emit has answered a key issue raised by the explosion of the Deepwater Horizon oil rig in the Gulf of Mexico two years ago this month.
The sound-monitoring technique revealed that sperm whales retreated
from the immediate area around the spill caused by the explosion.
"There's obvious evidence of relocation," said team member Azmy
Ackleh, professor and head of mathematics at the University of Louisiana
at Lafayette.
The discovery is important because it provides information about a
species almost hunted to extinction for its valuable oil in the 19th
century.
Sperm whales are listed as endangered under the terms of the United
States Endangered Species Act, and estimates of their population vary
between 200,000 and 1.5 million worldwide.
However, said Vassili Papastavrou, lead whale biologist for the
International Fund for Animal Welfare who did not work on the study,
"sperm whales are difficult animals to count, because they spend so much
of their lives beneath the surface. The overall population estimates
are so uncertain that it is not possible to determine trends."
The discovery of their relocation also indicates the value of
"passive" acoustic technology, which quietly listens for things instead
of actively bouncing sounds off objects to find them. This approach,
first tried in the 1980s, uses hydrophones mounted on buoys to detect
"clicks," the powerful sounds emitted by the sperm whales. The
University of Louisiana team, led by Natalia Sidorovskaia, associate
professor and chair of the physics department, has extended the
technology to localize and track sperm whales and to estimate their
populations, and to do the same for other marine mammals, including
other types of whales and dolphins.
