Scientists don't have any answers yet as they struggle to find out why hundreds of dead dolphins washed up on a tourist beach in Tanzania.
But some marine biologists are pointing to the use of sonar by the U.S. Navy as a factor in the deaths.
Some scientists have suggested that loud bursts of sonar may disorient or frighten ocean animals and cause them to rise to the surface too quickly, an event which can give them the equivalent of the bends, which leads to the formation of nitrogen bubbles in tissue. It's a painful and sometimes deadly experience.
There is a U.S. Navy task force that operates off of the coast of East Africa as part of counterterrorism operations, but the Americans have refused comment on the dolphin deaths.
In 2000, the Americans acknowledged that sonar likely contributed to the stranding of whales in the Bahamas.
The more than 400 bottlenose dolphins that washed up along a three-kilometre stretch of Zanzibar beach had not eaten for some time.
Researchers will also examine dolphin remains to see if the creatures had been affected by a toxin such as the deadly red tide.
However, it's the navy's use of sonar that is gathering attention from researchers.
Bottlenose dolphins normally live in deep waters offshore, so something happened to drive them close to shore, where they became stranded and died.
Area fishermen said Saturday they were surprised by the discovery of the dead dolphins.
"These animals must have been disoriented and ended up in shallow waters, where they died," said Abdallah Haji, a 43-year-old fisherman.
"We have never seen this type of dolphin in our area."