This may seem like a stupid question, but: "How do they intend to
identify one from another?"

Aren't the hatchery fish just released, by the thousands, into the
streams? Years ago, when I helped out in a salmon enhancement program
in BC, I just remember trucking buckets of the fish to the creeks to be
released. There was no identification of any sort. But that was long
ago, and technology may have enabled ID'ing.

Cheers
WR