Necropsies conducted on 10 of 38 sea turtles found stranded on Gulf Coast beaches since April 30 showed no evidence of oil, externally or internally, federal wildlife investigators said Wednesday.

All of the recovered sea turtles were dead except one, which died shortly afterward, said Barbara Schroeder, the National Oceanic and Atmospheric Administration’s national sea turtle coordinator. “Based on careful examination, NOAA scientists do not believe that these turtle strandings are related to the oil spill,” she said.

The turtles were sent to the Institute for Marine Mammal Studies in Gulfport, Miss. to determine whether their deaths were linked to oil, or some other cause. At least 15 more necropsies of dead sea turtles are scheduled over the next few days.

Sea turtle strandings in Gulf of Mexico are common. However, NOAA scientists said the stranding numbers are higher than normal this year and are working to understand why.

Sheryan Epperly, sea turtle team leader for the National Marine Fisheries Service told the Associated Press that federal investigators will look into whether shrimp boats removed mandated devices, known as turtle excluder devices, or TEDs, that help turtles avoid being trapped in nets.

''The agency has been trying to collect information on not just the trawling fisheries but any other fishing that may have been going on in the area,'' Epperly said. ''If the turtle excluder device is not properly used, then that likely could lead to the deaths of any turtles that get caught in the nets.''

In the meantime, overflights of the oil spill area on Tuesday discovered 30 to 50 sea turtles swimming in or near the oil spill, about 30 to 50 miles off shore. NOAA is developing a plan to deal with large numbers of oiled sea turtles.

Doug Inkley, a senior scientist with the National Wildlife Federation said that even though tests have shown that turtles haven’t been killed by the oil, it doesn’t negate the long-term effects of the spill.

Greenpeace, meanwhile, reported sighting other marine life swimming in the plume of oil that has been spreading in the Gulf of Mexico since April 22. Greenpeace conservation specialist Rick Steiner reported:

“During a plane trip today, I was able to see an extensive area of the spill near the Louisiana shore as well as inside and right off shore of the barrier islands, and washing over and around the submerged Little Gosier Island and Grand Gosier island. We saw countless sharks visible below the surface, swimming beneath the oil, as well as hundreds of stingrays, and a porpoise surfacing through the slick. Some of the oil is now within 2-3 miles of the end of the [Mississippi] river."

--Louis Sahagun and Nicole Santa Cruz

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Gulf oil spill: No evidence of oil in dead turtles

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