I was under the impression that most fish is caught semi-locally - i.e., fish caught near Japan tends to be eaten in Japan.

I do know that much of the bluefin tuna consumed in Japan comes from the Mediterranean or other international waters - bluefin migrate across oceans. And they are woefully overfished, with the WWF and the French government saying that the bluefin will be extinct by 2013 at current rates. Japan has consistently fought listing the bluefin as an endangered species.