I have watched the "Whale Wars" show, and have seen their disruptive attempts, evolve into more bold and violent attacks on ships.
Maritime law, is old and pretty specific, Also noticed the "whaler's footage" showed the "stealth" boat in gear, wake behind transom, deliberately cutting in front of the whaling ship, which doesn't turn really well in tight spaces.
They got what they deserved. Regardless of what you "feel" about whaling, these idiots cut in front of a whaling ship, and got rammed.
In the old days, ships had cannons, or small deck guns, rifles for sure, and would just consider it act of piracy. Seems the Shonen Maru, acted like any good Capt. would.
Let the tree huggers go to Oregon and stand in the middle of the mountain roads the logging trucks roll down, and see what happens...