ZANZIBAR, Tanzania – Scientists tried to discover Saturday why hundreds of dolphins 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 were burying the remains of the roughly 400 bottlenose dolphins, which normally live in deep offshore waters but washed up Friday along a 2½-mile stretch of coast in Tanzania's Indian Ocean archipelago.
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.
A U.S. Navy task force patrols the coast of East Africa as part of counterterrorism operations. A Navy official was not immediately available for comment, but the service rarely speaks about the location of submarines at sea.
A preliminary examination of their dolphins' stomach contents failed to show the presence of squid beaks or other remains of animals hunted by dolphins.
That was an indication that the dolphins either had not eaten for a long time or had vomited, Jiddawi said.
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.
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.
"These animals must have been disoriented and ended up in shallow waters, where they died," Abdallah Haji, a 43-year-old fisherman, said Saturday as he helped bury the dolphins near the bloodied beach.
Residents had cut open the animals' bellies to take their livers, which they use to make waterproofing material for boats.
"We have never seen this type of dolphin in our area," said Haji, who said he has fished in Zanzibar's waters for more than two decades.