Big Jake I send you an email. Make sure to not get gizzard in the net unless you want them. Kinda hard to tell a small gizzard from a small threadfin, know your stuff. I suggest catching them in the spring usually two species are separate then. Like mentioned fertility is key. Also getting them near spawnining size and time.
I however think cover has little to do with shad "an open water fish" in their survivial. If established they will add lots of weight on your bass like David said, but don't get fooled bass harvest is still critical.
