They installed covers so the birds can't get them anymore. The fish have to be a certain length to stock and if they don't spread them out over the course of the summer everyone won't be able to get a piece of the pie. Doing it this way there will be fish to be caught all summer just not as many as there would have been had the birds not got into them.
I read that article a couple days ago and have forgotten what it said about the hatchery and the protective nets. I'll blame the myriad of prescription drugs I've been under the influence of for the majority of this week.
It seems that this protective measure would've been implemented at a much earlier date though. Surely the herons have found this heavenly smorgasbord before now....?