Authorities announced that a dolphin died on the beach of the Navy's San Nicolas Island late January during the Navy sonar training exercises but it wasn’t clear if that was the cause of its death.

At the time of the female northern right whale dolphin death, the Navy's Third Fleet in San Diego was training in the sonar use.

Even so, Lt. Mark Walton, a spokesman for the Third Fleet, said that “"there is no evidence that any type of naval activities caused or contributed to this dolphin's death,” the Associated Press reports.

After a necropsy which was performed at the Santa Barbara Museum of Natural History, the researchers found blood and fluid in its ears but couldn’t determine the exact cause of death.

Teri Rowles, a veterinarian with the National Oceanic and Atmospheric Administration and head of the nation's Marine Mammal Health and Stranding Response Program said: "At this point, we cannot rule in or rule out sonar or any other kind of intense noise."

The dolphin’s head will be examined by a team of expert radiologists through the magnetic resonance images and federal pathologists will analyze its tissues to see if there are gas or fat bubbles, signs that indicate damages made by sonar, Los Angeles Times informs.

Such symptoms were found in 10 beaked whales which washed ashore in 2002 on the Canary Islands and in 2000 in Bahamas when exercises using sonar were carried out.

The Navy makes an appeal to the ruling made by a Los Angels federal judge last month about the using of sonar. The ruling says that the Navy must limit the use of mid-frequency sonar within 12 miles of Southern California, which would greatly reduce the negative impact on marine life (whales and dolphins). It is meant to avoid the use of mid-frequency sonar within the migrating corridor the various marine mammals use in their journey.

The judge ordered the sonar to be shut down when the mammals are within 2,200 yards and the waters to be scouted one hour before the exercise, in order to identify the possible presence of marine mammals.

By March 3 the U.S. 9th Circuit Court of Appeals is expected to rule on the Navy’s appeal, while the next trainings of the Navy is scheduled to begin mid-March.