Then the Japanese should close, board and seize the Sea Shepherd and any other ships used by that group.
I still remember when the French botched the sinking of the RAINBOW WARRIOR years ago.
The bombs planted were supposed to go off at sea, they went off in the harbor.
http://en.wikipedia.org/wiki/Sinking_of_the_Rainbow_Warrior
A 3" naval gun will serve nicely from a standoff distance of a few miles. Then the Japs won't have to handle the dirty hippies!