Workers in the Gulf of Mexico, struggling to bring the massive BP oil spill under control, found themselves with yet another issue to deal with: What is killing the sea turtles in the spill zone?
It's not the spilled oil, said officials. At least 35 dead turtles have been found washed up on shore, an unusual number. But necropsies found they were clean of the toxic brown crude that has been spewing from the floor of the Gulf since April 20, when the Deepwater Horizon drilling rig exploded and burned, 50 miles off the Louisiana coast. Eleven oil workers were presumed killed, and an estimated 5,000 barrels of oil per day have been leaking from the wrecked wellhead since.
"We are seeing turtles and marine mammals, including dolphins and whales, in and outside the oil," said Sheryan Epperly of the National Marine Fisheries Service, which has been surveying the area by helicopter.
So why are they washing up on shore dead? Federal fisheries officials said they are investigating whether shrimpers, heading out early as part of an emergency shrimping season, are to blame.
Epperly said investigators are looking into whether shrimpers are removing "Turtle Excluder Devices" -- TEDs for short -- from the trawling nets they lower into the water to catch shrimp. A TED is a kind of grid that filters turtles from the smaller shimp gathered up by a net, allowing the turtles to escape.
Shrimpers in the Gulf are required to have TEDs in their nets, but some shrimp escape through them, and investigators say anxious shrimpers may be trying to catch all they can before more fishing areas are declared off limits because of the oil spill.
Louie Miller of the Sierra Club had his doubts: "I discount that theory heavily. I think shrimpers are in enough trouble as it is. I point the finger at BP at this point until they are proven innocent."
Miller was suspicious of the chemical dispersants being used to break up the slick.
"What concerns us is that there's a lot of talk from BP that these chemicals are under proprietary protection, so therefore we can't get the information," he said. "That's totally unacceptable to this situation."
Most of the turtles found so far are Kemp's Ridleys, which are an endangered species. The only place in the world where Kemp's Ridley turtles nest is the western Gulf of Mexico. They are currently in peak nesting season, and their foraging grounds are located in the spill area.
Cleanup crews have used any techniques they could to corral the leaking oil. Floating booms are deployed to surround the slick, which mostly floats on the surface, but they are ineffective in rough seas. Controlled burns of some floating oil resumed this week.
BP has been pinning hopes on a large metal "dome" -- actually box-shaped -- to be lowered over the wellhead to trap the leaking oil so that it can be pumped to the surface and collected by a drill ship.
Even hair, donated by barber shops and salons and stuffed in panty hose, has turned out to be useful for sopping up oil.
Gulf Oil Spill: Protecting Wildlife
Chemical dispersants, pumped into the water or sprayed on the surface of the Gulf slick, have been used to break up the oil. But late Wednesday BP said it would stop using dispersants underwater until tests can be done to make sure there are no major environmental consequences.
Dispersants have been used for years, but BP took the unprecedented step of pumping them directly down to the vicinity of the leaking wellhead, 5,000 feet below the surface of the water.
"When the dispersant and the oil mix, it just breaks the oil into smaller molecules, and the oil just breaks into smaller droplets," said Bob Fryar, a senior executive of BP. "At that time the ocean just takes over and it just degrades naturally."
Fryar, at BP in Houston, played down the risks, saying oil leaks into the Gulf of Mexico all the time.
"You know, actually, you typically have small oil seeps that come up from the ground already," he said. "There's probably one to two thousand barrels a day oil seep that's taking place in various places, and the earth just naturally takes care of that."
Biologists have been worried about other wildlife -- birds, fish and dolphins -- that could be in danger if the winds change and the oil spreads beyond the current slick area near the mouth of the Mississippi River.
Oil breaks down many animals' natural protection. A bird's feathers are naturally coated as insulation against the elements; a dolphin's eyes have an outer layer that shields them from toxins.
"An animal out there doesn't know that this is crude oil and it's toxic," said Moby Solangi, president of the Institute for Marine Mammal Studies in Gulfport, Miss. "All it knows is that this is something to play with."
Ayana Harry reported from Gulfport, Mississippi and Ned Potter wrote from New York. Additional reporting by Clayton Sandell in Houston.