The way I see it, yeah it's a drop in the ocean, but these individual sites will act as "seeds", safe havens for wildlife that, from there, can spread out far and wide. Like these fish, they don't stay there, they go far and wide and become part of a much bigger ecosystem. Part of the reason why these restoration projects are important is because at the time, people weren't aware (or didn't care) of the scale or impact their efforts in hunting beavers had. I'm sure the individual hunters also figured their hunting was a drop in the ocean.