Sperm whales showed good sense after the Deepwater Horizon oil spill, acoustic surveys show. They left.

Sperm whales showed good sense after the Deepwater Horizon oil spill, acoustic surveys show. They left.

THE GIST

An acoustic survey shows there was a drop in the numbers of sperm whales near the Deepwater Horizon site after the spill.

The drop may only mean the whales left the polluted, noisy disaster site for more comfortable locales.

The acoustic study is one of a growing number that are cheaper and safer than visual ship and aerial surveys.

A lucky placement of acoustic survey equipment has allowed scientists to get some rare insight into what sperm whales did in response to the Deepwater Horizon oil spill. The bottom line: they left town.

An acoustic site just nine miles from the spill and 1,000 meters (0.6 miles) down has nine years of data on local sperm whales. That, along with other acoustic archives of sperm whale calls from around the Gulf of Mexico and a rapid response grant from the National Science Foundation given to gather more acoustic data right after the spill, has allowed scientists to draw some preliminary conclusions about sperm whales' reactions to the spill.

For years before the oil spill, the listening post nearest the now destroyed BP oil rig had detected a fairly steady rate of about five sperm whales nearby. After the spill that number had dropped to two.

"What is important for us is not the absolute number but the change," said Sidorovskaia. That's because, like all surveys, the acoustics give only an estimate of how many whales are out there. "So it's the trend that's important."

The good news is that at another listening site, 25 kilometers (15.5 miles) away, the average number of sperm whales appears to not have changed.

The decrease in whales detected near the spill versus no change further away suggests the whales near the site left. Perhaps the presence of the oil, along with the noise of the Deepwater Horizons disaster, the emergency drilling and other ships coming and going spurred the sperm whales nearer the disaster site to hightail it for more comfortable, peaceful waters.

"It makes sense for the animals to just move away," Sidorovskaia told Discovery News. "They probably just migrated."

Only one sperm whale had been reported found dead in the Gulf, and it had not been linked to the oil spill, she said.

"It was somewhat of a relief," said Sidorovskaia. "We were very relieved to see that they are still there."

That relief comes also from the fact that the EARS data is backed by all those years of baseline data of whales in the vicinity -- a scarce commodity in an incident like this one. In fact, said Sidorovskaia, her team is the only one with baseline data in this area, which makes a good case for the need for more such surveys in other part of the oceans.

There is a growing number of acoustic surveys of marine mammals and even other marine organisms underway, said marine scientist Dave Mellinger of Oregon State University. The reason is simple: acoustic surveys are cheaper and can gather more data more easily and safely than the more traditional visual ship and aerial surveys, he said.

"Some species are very hard to see," said Mellinger. But they are pretty readily heard and identified by their telltale vocalizations. The trick is to develop algorithms that allow computers to search the endless hours of recordings to find the animals calls, which can then be interpreted by humans.

Then there is the matter of safety, Mellinger said. Almost everyone in the marine animal survey field knows someone who has died from a plane crash while doing their job. That danger disappears with the automated listening posts at sea.

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