Mercury levels in whales caught in Japan's coastal waters increase the further south the creatures are caught, with one specimen from Okinawa's Nago registering a mercury density more than 57 times the nation's provisional safety limit, according to a group of experts.
Group member Tetsuya Endo, a lecturer at the Health Sciences University of Hokkaido, said that mercury dissolved in seawater may have accumulated in fish and other whale prey along the Black Current, which flows north toward Japan's Pacific coast from east of the Philippines.
The mercury may stem from industrial pollution in Japan and Southeast Asia, as well as from natural sources such as undersea volcanic activity, Endo said.