Scientists are studying the remains of some of the 400 dolphins that washed up dead on a beach popular with tourists on the northern coast of Zanzibar.
Among other possibilities, marine biologists were examining whether U.S. Navy sonar threw the animals off course.
Villagers and fishermen on Saturday buried the remains of the roughly 400 bottlenose dolphins, which normally live in deep offshore waters but washed up Friday along a 2.5 mile stretch of coast in Tanzania's Indian Ocean archipelago.
Before burial, residents had cut open the animals' bellies to take their livers, which they use to make waterproofing material for boats.
The animals may have been disturbed by some unknown factor, or poisoned, before they became stranded in shallow waters and died, said Narriman Jiddawi, a marine biologist at the Institute of Marine Science of the University of Dar es Salaam.
Experts planned to examine the dolphins' heads to assess whether they had been affected by military sonar.
Some scientists surmise that loud bursts of sonar, which can be heard for miles in the water, may disorient or scare marine mammals, causing them to surface too quickly and suffer the equivalent of what divers call the bends — when sudden decompression forms nitrogen bubbles in tissue.
U.S. rules out role
A U.S. Navy task force patrols the coast of East Africa in counterterrorism operations. A Navy spokesman ruled out the possibility Navy sonar might have disoriented the dolphins and led to their deaths. He said there were no U.S. Navy vessels within 580 miles of the location in the 48 hours before it happened.
"In the U.S. alone, a person is 10 times more likely to be struck by lightning than for sonar to cause a marine mammal stranding," Lt. William Marks said.
The most conclusive link between the use of military sonar and injury to marine mammals was observed from the stranding of whales in 2000 in the Bahamas. The U.S. Navy later acknowledged that sonar likely contributed to the stranding of the extremely shy species.
And U.S. scientists on Thursday said Navy sonar may have caused a group of whales to strand themselves in Hawaii in 2004.
Experts are also investigating the possibility that sonar from U.S. submarines could have been responsible for an incident in Marathon, Fla., where 68 deep-water dolphins stranded themselves in March 2005.
In Zanzibar, a preliminary examination of their dolphins' stomach contents failed to show the presence of squid beaks or other remains of animals hunted by dolphins.
Their general condition, however, appeared to show that they had eaten recently, since their ribs were not clearly visible under the skin, she said.
Although Jiddawi said Friday that poisoning had been ruled out, experts were preparing to further examine the dolphins' stomachs for traces of poisonous substances such as toxic "red tides" of algae.
Zanzibar's resorts attract many visitors who come to watch and swim with wild humpback dolphins, which generally swim closer to shore than the Indo-Pacific bottlenose.
The humpbacks, bottlenose, and spinner dolphins are the most common species in Zanzibar's coastal waters.