The only evidence of fry releases that worked (i.e., provided better returns than leaving the fish in the water) that I've seen was purely anecdotal, and when genetic testing was done, turned out to be completely wrong.

The workers dumped in a ton of fry during times of good marine conditions, and a ton of fish returned...they very wrongly assumed it was an excellent return of their fry plants, and harvested accordingly.

Turns out later that the fry returned no fish, and that the high returns were the progeny of the wild fish that weren't mined, but were left in the river to spawn. When the poorer marine conditions returned the "great returns" from the fry plants stopped, too...because they never actually existed.

Hatch boxes have proven repeatedly to be only minutely better...except, of course, for Gary's Cedar Creek coho...and, yes, I'm kidding.

Fish on...

Todd