Paul Watson told Australia's ABC radio his flak jacket had stopped a bullet and two of his crew members aboard the Sea Shepherd group's "Steve Irwin" ship had been injured by flash grenades thrown from the Japanese whaling ship "Nisshin Maru," The Times of London reported.
"What hit me was a bullet -- it wasn't a flash grenade. We pulled it out of the vest," Watson told the broadcaster. "If I wasn't wearing the vest, it would have been pretty serious."
Japanese authorities said no gun shots had been fired by the whaling crew but rather sound-emitting "warning balls" at the Sea Shepherd ship after activists threw bottles of rotten butter at their ship.
The Japanese whaling fleet has a declared aim of killing 935 minke whales and 50 endangered fin whales as part of its annual "scientific" harvest and is being dogged by environmentalists, the newspaper said.