HORN ISLAND, Miss. (AP) - Federal wildlife officials are treating the deaths of six dolphins on the Gulf Coast as oil-related even though other factors may be to blame.

Blair Mase (MACE') of the National Marine Fisheries Service said Tuesday that the carcasses have all been found in Louisiana, Mississippi and Alabama since May 2.

Samples have been sent for testing to see whether a massive oil spill in the Gulf of Mexico helped kill the dolphins. Mase and animal rescue coordinator Michele Kelley in Louisiana said none of the carcasses has obvious signs of oil.

Mase also said it's common for dead dolphins to wash up this time of year when they are in shallow waters to calve. The Associated Press found dolphins swimming and playing in oily waters off Louisiana last week.