Dr Post at the U of C has done these kind of studies on virgin(fishless) lakes in the Merritt BC region.
It doesn't take long for trout to remove most of the largest prey items like big sedges, the largest scuds, diving beetle larva etc. Fish grow incredibly fast when all the bugs are available. Once the bugs are gone, the growth rate rapidly decreases. More trout, the bigger the impact.
The same thing happened in Sparrow's Egg lake in Kananaskis. The pre-fish bug populations were incredible. Today it is a shadow of what it once was, and the trout growth rates have declined accordingly. You can go to Marl lake behind Elkwood campground and see for yourself the amazing invertebrate populations in the water where there are no trout. The 2 lakes are in the same neighborhood.
In a perfect world, a big lake study to find suitable stocking densities would be nice. The cost and labor required ensure it will never happen in Alberta. The government can't even bother to do some science on the so-called blue ribbon Bow River....even back when the government was flush with money.
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