Overfishing and dwindling fish populations are pretty established facts.

What does that have to do with the number?

I get that you wanted the original poster to realize that a big number doesn't necessarily mean anything. But we already know it's not sustainable.

You can either point at the number and say "Look at this number! Can't you just tell that it isn't sustainable?" or you can say "It doesn't matter what the number is, we know it's not sustainable for other reasons."

But neither of those is a support for the other. If you start with the assumption that the number is unsustainable, you're not doing anything when you look at the number.