http://news.nationalgeographic.com/May 1, 2006—Hundreds of dead dolphins mysteriously washed ashore Friday on a beach popular with tourists on the Tanzanian island of Zanzibar (map).
As shown in this photograph taken Saturday, the water along a two-and-a-half-mile (four-kilometer) stretch of coast on the East African island turned reddish with the blood of the dead bottlenose dolphins.
Villagers and fishermen said they buried the remains of 400 animals.
Scientists don't know what killed the bottlenose dolphins, which usually live in deep offshore waters.
"It is quite strange for so many animals to strand," said Douglas Nowacek, an oceanographer at Florida State University in Tallahassee, who has studied dolphin deaths. "These animals are normally quite able to cope with stressors."
Local residents speculated that low tide combined with heavy rains and wind might have disoriented the marine mammals.
An early examination showed the animals' stomachs were empty. They either had not eaten for a long time or had recently vomited. Further tests will look for traces of poisonous substances, such as "red tide" algae.
Experts will also examine the dolphins' heads to assess whether the animals might have been affected by military sonar. A U.S. Navy task force routinely patrols along the East African coast as part of counterterrorism operations.
Loud blasts of sonar may disorient or scare marine mammals, many scientists believe, causing the animals to surface too quickly and suffer the equivalent of what divers call the bends, or decompression sickness.
"Naval sonar has been associated with toothed whale deaths, and the most well documented case was the mass stranding of beaked whales in the Bahamas in 2000," Nowacek said. "To my knowledge, though, sonar activity has not been associated with such a large number of deaths" as this one.
—Stefan Lovgren
