Wasn't able to find much on walleye but two more articles of interest. All disturbing articles about the problems over population is causing the Susquehanna.
https://www.ydr.com/in-depth/news/20...ve/5853999002/
Second article is walleye specific:
https://www.outdoornews.com/2009/02/...uehanna-river/
I realize it's an older article but might still be relevant. Found it interesting as well where they indicate they stopped stocking walleye fry in three rivers, Susquehanna, Lehigh and Allegheny. Have to question at minimum what impact that's causing the fishery.
Many things impact the overall balance in these systems. Pollution is at the top of that list. Shad have apparently declined significantly in the Susquehanna, lose a part of the food chain and the entire balance in the system is altered. Juvenile shad are a major source of forage in rivers that support a shad fishery, if it declines a major source of forage base goes with it. Maybe even the decline in the smallmouth population has had an impact on walleye fishing since I'm sure walleyes feed on juvenile smallmouth as well.
I'm just not convinced flatheads are impacting indigenous species to any degree which would be reason for concern. Pollution, destruction of habitat, water quality, climate change etc. I believe are having significantly greater impacts on these systems. Unfortunately people point fingers in directions that fit their agendas and narratives. Science helps us see through those illusions and science is saying in this particular case the Susquehanna River has more than it's share of man made problems.