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.