Eric-
I don’t want to speak for the IDNR folks on this at all, but I’ll give you my impression of what I think their reasoning might be. Keep in mind that I may not have all of the details straight here.

The problem with shad presence is that the fishery is already out of balance, so worrying about that is a moot point. The normal progression of a gizzard shad infestation is that the fishery will decline regardless of any known management steps available. All of the options then are related to what managers can do with what is left.

As I understand the current thinking, for the short term the abundance of young shad makes good feed for the bass. The bass will suffer later from a loss of recruitment, as the young bass have increasing difficulty surviving to adulthood.

So, while the bass population is still making good use of the shad, it is seen as desirable allow them to do so to the largest degree possible. This consideration is prompted in part because bass are a preferred sport fishing species, and giving them the priority is seen as a way to get the most out of the fishery, for the time being.

Introducing another large predator now would not prevent the inevitable decline due to the shad infestation, but would have the effect of competing with the adult bass. Later, when the bass population begins to decline as the adults die out and the young are not surviving to replace them, it might be decided to introduce another species. If that happens, it would still not be an effort to save the fishery, but to salvage as much use of it for anglers as possible.

Eventually the only way to fix the problem is to kill it out and start over. And then we will have to realize that some well-meaning soul that thinks they know something we all don’t, will try to help out the bass again by bringing back shad. In modern fisheries management, that too seems to be a known factor that can be predicted.