The film chronicles the controversial Sea Shepherd Antarctic Campaign against a Japanese whaling fleet. The volunteer crew spends most of their time twiddling their thumbs, swimming, falling over board and basically not doing anything to stop the hunting of whales.
When they do manage to find whaling ships they use a variety of tactics to stop the whalers mostly by being annoying - but their ships are too slow so that Japanese ships can easily outrun them.
Activists Paul Watson and Alex Cornelissen are ultimately only mosquitoes trying to annoy the proverbial bear that is the Japanese whaling fleet. If they were absolutely serious about stopping whalers they wouldn't be using two slow and cumbersome ships - they would be using an aircraft carrier and fighter jets (something like the 800 NAS Sea Harrier FRS1) to just plain attack and sink whaling ships.
Sea Shepherd and their ilk seem to be more about getting media attention than actually doing anything concrete to stop whaling permanently. Yes, okay, they're attacking whaling ships by ramming them, etc. But if they had a submarine with torpedoes they could be outright sinking the whaling ships instead of merely damaging them.
Now you might think "Hey, isn't that going overboard?"
No, I don't think it is. Whaling has been going on for almost 2 centuries now and despite international bans whalers continue to ignore the laws - and they wouldn't have to sink "all" of the whaling ships to cause them to give up on whaling. Just sink two or three and they should find it difficult to get people to sign up to be crew on a whaling ship. A steady stream of sunken whaling ships should send a clear message to other whalers that its time to start obeying the law.