Even weeks after about 600 bluenose dolphins were washed ashore at Zanzibar's Nungwi beach, a popular tourist destination, scientists are still clueless. Experts say the dolphins might have been hurt by oil pollution, poisonous seaweed or simply a fast-receding tide, reports Reuters. Others hint that sonar from us submarines might be the cause since similar cases had occurred earlier. A us Navy task force patrols the East Africa coast as part of counter-terrorism operations. The deaths have injured Zanzibar's tourism industry.