Bluefin tuna certainly faces severe existential threats. That much is no longer in doubt. Sure, Pacific bluefins are not officially endangered -- but Southern and Atlantic ones are. Indeed, bluefin experts are quickly shifting their conversation away from the question of whether or not the species are endangered to the more difficult one of what to do in light of the fact that they are.
That means different things to different people.
If a recent report in Fast Company is to be believed, Mitsubushi executives had a plan to seize on the impending collapse of tuna stocks for their own profit. They were buying up tons of tuna and putting the meat in deep freeze, at -60 degrees celsius, in hopes of jacking up the price after bluefins went extinct. Sounds pretty nefarious, and potentially effective. But the plan was apparently foiled by the earthquake. Mitsubushi's refrigerators lost power after Japan was hit by a huge tsunami, ruining the tuna steaks and dashing the company's hopes of cornering the tuna market.
Overall, Fast Company called the loss a gain for bluefin tuna's chances of survival, because a major buyer will have less incentive to buy meat in excess of demand. But if it was a gain, it was a far less significant one than the news that a fish farm had successfully bred bluefin in captivity after years of trying. The success was modest, but Umami fish, the company that spawned the tuna, in a Croatian farm, hopes it will be able to use its technique to develop full-fledged sustainable bluefin tuna farms. Farmed isn't quite as good as wild -- but it's also better than dead.
UPDATE: Commenter SimonBao makes the excellent point that the best way to avert collapse of tuna stocks would be a massive international halt on bluefin tuna fishing. He's right. The issue with a ban is one of political viability. On several occasions, nations have proposed bans on bluefin tuna fishing; the Obama Administration have even voiced its support of a ban on Atlantic bluefin fishing. But decisive action has stalled every time a proposal has come up. Moreover, Japanese fishermen and sushi eaters have demonstrated their willingness to flout international fishing restrictions before -- and they have said that they will not comply with a ban on bluefin tuna fishing.