Published: May 04, 2010 10:05 PM EDT

GULFPORT, Miss. (AP) - Wildlife officials are saying that at least 35 endangered sea turtles have washed up on Gulf coast beaches, but it's not clear what's killing them.

Moby Solangi, director of the Institute for Marine Mammal Studies in Gulfport, Miss., said Tuesday necropsies had been completed on the turtles and found no oil.

Experts are still warning the turtles may have eaten fish contaminated by the oil spill in the Gulf of Mexico. Some wildlife officials say the turtles may have been killed by aggressive shrimpers trying to haul in catches before the oil potentially contaminates their fishing grounds.

The Washington, D.C.-based conservation group Oceana says officials need to determine what is killing the turtles quickly.