They're prolific spawners...whats the problem? They're a good food source for predators, and in a lake that large, they're a vital part of the food chain.
They feed on the same micro organisms as "good fish" fry do. Balanced, they are great for a fishery- every lake down south has them. The problem is up here most of our predators dont get big enough and the population density of the big predators are so low that the shad take over. Lots of lakes have been ruined for panfish because of shad, the bass, walleye, and musky love them.
As for fishing with shad below you, I always have a jigging or rippin rap with me.. Snag a couple of them and they take off quick.