Since 2010, 630 dolphins have died in the Gulf of Mexico, according to scientist Suzanne Smith of the Audubon Aquarium of the Americas. The deaths began a few weeks before the massive BP oil spill in the area, in which some 5 million barrels of oil -- the worst spill in history -- contaminated the Gulf. Experts are trying to determine whether the oil spill or a virus is causing the dolphin deaths.

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