GATT Consistency of a Commercial Fishing Ban

For you law professors out there searching for a good exam question, take a look at this fact pattern from an Economist article:

IN PALAU, the traditional prescription for an ailing reef is a fishing ban called a bul. Local chiefs may declare a bul to rest a busy fishing spot or protect endangered sea turtles. Now Palau’s president has a more drastic plan. He proposes a complete ban on commercial fishing—a bul to turn the 600,000 square kilometres (232,00 square miles) of Palau’s Exclusive Economic Zone (EEZ) into a marine reserve the size of Ukraine. Locals could still fish close to shore, but not for export.

The ban would last until world leaders implement programmes “to reverse the devastation to our oceans and seas”, Palau’s president, Tommy Remengesau, recently told the United Nations. Environmentalists have rallied to his cause. ...

So it all sounds pretty clear so far: an almost total ban on fishing, with exceptions for local fishers but no export permitted. In terms of GATT obligations, it's pretty clear there is an export restriction, and thus a GATT Article XI violation.  For one thing, local fishers are not allowed to export.  In addition, is the ban on commercial fishing an export restriction, maybe on a de facto basis?

Though small, its waters are full of bigeye and yellowfin tuna. Japanese and Taiwanese boats pay to fish there, helping Palau earn $5m in revenue from fishing taxes and licensing fees in 2013.

I'm guessing those Japanese and Taiwanese fishers are selling for export.Then you get into Article XX.  Surely this measure "relates to the conservation of exhaustible natural resources" under Article XX(g), right?  Probably, but there's this:

Palau’s bet, however, is that its fish are worth more in the water than out. Mr Remengesau doubts that small islands will ever capture more than “a drop” of a tuna fishery worth billions but dominated by foreign fleets. Ecotourism, meanwhile, accounts for about half of Palau’s GDP.

Palau’s leaders hope that a national marine reserve will lure enough tourists to offset lost fishing revenue. ...

However, even if Palau's plan is, in a sense, all about money, I'm not sure how that undermines the conservation effect.

Then you've got the Article XX chapeau to deal with.  What about those exceptions for local fishers?  Are they "arbritary" or "unjustifiable"?

Anyway, there's a lot more to say, but I'll leave it up to others to fill in the details.  (It's also worth noting that Palau is not a WTO Member, and is one of the few nations not to have applied).