Not so quick. The fish are renewable. The proportionate allotment is an unknown quantity. We can neither know what the total fish population during the course of this man's lifetime would be, nor does the unit time portion (how many fish per day/week/month/year) remain constant over time. The population of Montana as well as the population of fish will change through time.
But then I don't think I ever said I had a problem with regulatory policies that contribute to a steady state of renewable critter populations either.
He has taken the fish he was charged with poaching at a fixed point in time. He wasn't charged with all the potential fish that he may or may not poach. Also, I calculate that I'm entitled to at least an acre or two of public land.