I don't know. First i would have to know for sure that predators are the cause of my reduced turkey numbers. That's one of the big questions I have about the research you're quoting. It's very difficult to isolate a single cause for observations made in wild, natural populations, which makes it very difficult to arrive at a precise conclusion to a study. That's a big part of why the results of a given study or series of study's don't guarantee similar results elsewhere.
I wonder how many times this study was replicated with no clear conclusion or with a different conclusion? We're those trials published?
I dont think any of them claimed that predation was the cause of decline, and its almost never THE CAUSE. Its almost always a symptom. Rarely (and by rarely I mean Im not sure its ever happened) is anything other than habitat or weather or introduction of a non native species the cause of population declines. Possibly disease in rare cases. Excess predation is caused by habitat issues. Loss, fragmentation, manipulation, encroachment, quality, etc. Predators simply dont destroy a population in good habitat, and they dont go from being just fine with predators to steep decline with the same predators present in good habitat. They have adapted over thousands of years to evade those predators.
So to your point, I know there have been predator control studies on declining populations and none that I know of deemed predator control effective to reverse the trend.
Id be interested to know if MDC is trapping the grouse areas?
Plus, what good is another hatched nest if the poults all get picked off in poor habitat by species that you cant control? Or if they survive and the hens have no access to high quality nesting areas? Then what? Or if the raccoon you trapped would have been dinner for the owl or bobcat or coyote that raided the nest and killed the hen?