* Tests performed on seven dolphins, 106 sea turtles

* None showed visible signs of oil contamination

* All being treated as suspected spill casualties

PORT FOURCHON, La., May 13 (Reuters) - Scientists are examining samples from seven dolphins and over 100 sea turtles found dead along the U.S. Gulf Coast in the past two weeks to see if they were victims of the giant oil spill in the region, wildlife officials said on Thursday.

All of the deaths are being investigated as suspected casualties of the oil gushing unchecked since April 20 from a ruptured wellhead on the floor of the Gulf off Louisiana because of their proximity in time and space to the spill.

But none of the dolphins or turtles examined showed any obvious visible signs of oil contamination. Necropsies -- the animal equivalent of autopsies -- are being performed and analyzed to determine if oil ingestion caused the deaths.

The investigations of most of the animals are still pending, and none has yet confirmed oil as a cause of death.

The information about dolphin and sea turtle mortality and the investigation into the cause of those deaths came from two sources close to the Gulf’s wildlife spill-response teams who spoke to Reuters on condition of anonymity.

The seven dolphins and 106 sea turtles were found along the coast of Louisiana, Mississippi and Alabama over the past two weeks, the sources said.

One heavily decayed dolphin carcass was seen on the beach at the very tip of Port Fourchon in southeastern Louisiana. Gooey, rust-colored globs believed to be oil debris began washing ashore on that beach on Wednesday night.

A few deaths were ruled out as spill-related because they occurred before the spill or were animals that were known to have been sick or injured beforehand, the sources said.

TOO SOON FOR CONCLUSIONS

Wildlife officials have expressed particular concern for the well-being of sea turtles in the Gulf following the spill because all five species that inhabit the region are endangered, and it is their spring nesting season.

But experts say large numbers of sea turtle deaths this time of year is not uncommon.

On a conference call with reporters on Wednesday, officials of the U.S. National Oceanic and Atmospheric Administration said it was still too early to draw firm conclusions from the latest wildlife casualties in the Gulf.

“We don’t have definitive information for most of the ... (animals) that have been found,” said Jane Lubchenco, Undersecretary of Commerce for Oceans and Atmosphere.

Impacts on bird life has been relatively light to date, according to wildlife specialists.

“So far, relatively few birds have been brought in with oil on their feathers,” said David Ringer of the National Audubon Society, who put the number at between 12 and 20.

“The birds that have been brought in are birds that catch fish in open waters” and would have come in contact with oil there, he said.