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Rather than building enormous tanks, we could use parts of the big one we already have - the oceans.

The problem is, what carrot and/or stick do you use to get sovereign nations to agree to a plan to leave enormous fisheries untapped?

[Willie Green]

Rather than building enormous tanks, we could use parts of the big one we already have - the oceans.
The problem is, what carrot and/or stick do you use to get sovereign nations to agree to a plan to leave enormous fisheries untapped?

That's no problem. It's exactly why I proposed building the big tanks just like the freshwater hatcheries.
IMHO, all you've suggested is "don't build the hatcheries" then wondered how it's gonna work.

If you ever try to prune a tree, be mighty careful which side of the limb you're sitting on before you start to saw.