As it hit a whale and the animal submerged, the harpoon's rope snagged the Greenpeace boat, tossing Canadian activist "Texas Joe" Constantine into the water. Speaking of the incident, which occurred on Saturday, Mr Constantine said: "We were out defending the whales. We had been out there for about an hour.
"I was driving our boat and we were in a good position and the whaler fired its harpoon," he went on. "All of a sudden the harpoon line came down on us, trapping us between the whale and the catcher.
"The line came tight at that point and threw me from the boat into the water," Mr Constantine said. "It was a few minutes before I was picked out of the water."
Last week, a whaling factory ship and a Greenpeace vessel collided. Each side blamed the other. Greenpeace spokesman Steve Shallhorn said a Japanese harpoon came within three feet of their inflatable craft. The Institute of Cetacean Research in Tokyo accused Greenpeace of taking increasing risks.
"The fact that one of the activists fell in the sea is entirely their fault," said institute director general Hiroshi Hatanaka.