Investigators will look at whether some shrimp boats taking part in an emergency shrimping season ahead of the Gulf oil spill removed devices from their nets that are intended to allow turtles to escape, said Sheryan Epperly, sea turtle team leader for the National Marine Fisheries Service.

Wildlife officials say at least 35 endangered sea turtles have washed up on Gulf coast beaches, but it's not clear what's killing them. Necropsies have shown no signs of oil.

The Washington, D.C.-based conservation group Oceana has said officials need to determine what is killing the turtles quickly. Some experts have speculated the turtles may have eaten fish contaminated by the oil spill.