Whale sharks, the huge fish that feed by vacuuming the sea surface, have been seen in heavy oil a few miles from BP’s spewing well in the Gulf of Mexico, a scientist says.

The University of Southern Mississippi researcher who’s studied their migratory habits in the Gulf says the question now is how many are dying in the oil.

“Taking mouthfuls of thick oil is not conducive to them surviving,” said Eric Hoffmayer of the USM Gulf Coast Research Lab.

Oil could clog the cartilage filter pads that direct food to their throats, and could coat their gills.

Hoffmayer said three of the sharks, the world’s largest fish, were spotted within four miles of the spill site on Monday. They migrate north in late spring from waters near Yucatan to feed off the mouth of the Mississippi River. The Deepwater Horizon site is about 40 miles southeast of the river.

“That basically confirms our worst fear: these animals do not know to stay away from the oil,” Hoffmayer said.

They’re easy to recognize, up to about 40 feet long and black with rows of white spots.

There won’t be any way to tell how many die. Sharks don’t float.

“If they do die from the oil, they’re going to sink to the bottom,” Hoffmayer said.

News of whale sharks in the oil came less than a week after a huge group was spotted elsewhere off the Louisiana coast where oil had not yet been found.

One aerial photograph showed about 90, Hoffmayer said. “It blew my mind. There were probably more than a hundred sharks.”

The group seen June 22 was about 70 miles southwest of Port Fourchon, and about 60 miles from the western edge of the spill as shown on a federal map, he said.

Hoffmayer didn’t know whether the three seen Monday were from that group.

“It’s hard to say. These animals can travel like 100 kilometers in a day,” he said.

However, Hoffmayer said, “I’ve got a feeling that until whatever the food source they found disappears, they’re not going to want to go.”

Nobody knows just how many whale sharks exist. They’re on the World Conservation Union’s “red list” of threatened species.

Hoffmayer said the animals can dive a mile deep, and could escape any effort to herd them away from the oil.

Last week’s spotting came as part of a two-day excursion organized by the director of a documentary being filmed about marine biologist Sylvia Earle, creator of the Mission Blue Foundation.

Hoffmayer said four of the sharks were tagged.