We have a number of heavily stocked trout fisheries which for years carried out a netting policy to keep the pike numbers down by netting the spawning areas in the spring. What happened was that they killed the larger (female) fish that were spawning and it lead to an explosion of small pike. The bigger fish definitely eat the smaller ones and keep the numbers in check. When the reservoirs stopped netting the pike (as they realised people would pay good money to fish for the pike) the first few years were hopeless for pike anglers. You could go out and catch as many sub 10lb pike as you could put up with, but over the years the average size has started to increase and the numbers of little ones decrease, ending up with a relatively balanced population (for a stocked trout fishery.

I would imagine that the opposite is also true, so if there has been a new rule, or change in angler attitude, leading to less of the larger musky being killed it is likely that there is a year class or two of fish which are reaching their growth potential and probably eating a greater proportion of the smaller musky. As the big year classes grow old and die off there will be a gradual restoration of a more usual range of sizes and numbers.