The tally of dead sea turtles found since the Deepwater Horizon disaster hit 417 today. But just nine of those found so far have had visible signs of oil, and experts have emphasized that time-consuming analyses will be needed to determine whether the turtles died from oil exposure.
Now the first of those results on 67 turtles that washed up on gulf beaches soon after 30 April, when authorities began collecting dead turtles, the Los Angeles Times reports:
Barbara Schroeder, sea turtle coordinator for the National Marine Fisheries Service, said authorities had examined 67 turtle carcasses, 40 of them intact enough to conduct a full initial necropsy. Of those, 21 "showed various degrees of aspiration of black sediment into the respiratory system," she said.
"There was no gross evidence of any significant infectious or underlying disease process as a cause of the strandings," she said. "Drowning and asphyxia from sediment aspiration are primary considerations for the immediate cause of death for almost all animals for which complete examination was possible."
According to the Times, some scientists speculate that the turtles likely drowned in trawl nets, as they were found soon after the opening of shrimping season.
Shrimp-trawler nets have long been a cause of accidental sea turtle drownings, but in recent years trawlers have installed escape hatches in their nets to allow turtles to escape. Scientists worry that the oil spill may have caused many fishermen to close the devices to catch as many shrimp as possible.
Other experts warned that oil has not been ruled out as a "contributing factor," according to the Times. Turtles normally strand in summer on the Gulf Coast as they return to beaches to nest—the sick and the weak don't make it back out to sea. Flukes of nature can also be to blame—sudden drops in water temperature, for instance, paralyze turtles, who can't regulate their body temperature quickly enough.