You do not need a big enormous boat to do whaling, that is a common misconception. More often than not, you drag the whale back to shore while it
Also, responsible whaling is possible. Yes, in the early years there were over fishing on some species, but sustainable hunting was never an issue until modern times - for any kind of hunting and fishing.
I'm no expert on whaling, especially not when it comes to non-Norwegian whalers, but the Norwegian side I know quite well. And if anyone claims this is not sustainable, they need a dictionary. Of course, I cannot speak for the Japanese side of things, but I have an impression that they are not too far away from this reality either even though the industry is bigger.
Also, tuna fishing has only one thing in common with whaling: Sea Shepherd. It is not a part of the whaling discussion and there is nothing else linking these cases.
Eating that delicious piece of whale steak that has been grilled just a few seconds on each side, with a hint of salt and pepper, is something I do with a clean conscience.
And to me, Sea Shepherd has lost most of it's credibility equal to Greenpeace, but I assume they need to be picky about their cases in order to secure funding. Picking the great big battles that matter will annoy too many of the people they need in order to have funds for their work. I find them irrelevant when it comes to contributing to a sustainable use of our resources.