Funny, for a fish population that's "so depleted", why is it that a federal agency - the EPA - that hasn't been shy about putting a species on the Endangered Species List whenever it could be used to advance the cause of turning America into a Luddite society before, has balked at listing this species? Even the vaunted UN and CITES has rejected every proposal to list the species as endangered, with the accused "worst offenders" (European nations) full-out abstaining from the vote entirely. You would think that if the species were as depleted as the Sierra Club (source of the "unbiased data" you're citing) claims it is, the most leftist governing bodies in existence - the Obama Regime and the UN - would have no compunction about forcing sushi eaters to make sacrifices, "for the children"...
It's not the EPA that does that, it's the Fish & Wildlife Service for most domestic noncommercial species, and National Marine Fisheries Service for commercially-fished ocean fish species.
However, you may remember why American Samoa was exempted from the large minimum wage hike when San Fran Nan was Speaker... That same connection would probably have a lot to do with any action on bluefin or any other tuna species, even if she's just the Minority Leader rather than Speaker now.
