Maybe mojo rig can chime in, but best I was able to determine only 20-35 % of our walleye are natural spawn in Bull Shoals. Plenty hatch, but Green Sunfish and Longear Sunfish feast on the just hatched fish because of the lack of vegetation for the fry to hide amongst. They do better on high water years, but without the stockings numbers of fish would plummet.
I'm not sure if this is a better argument to release the fish you catch or keep them anyway. I do know that I'm more likely to release the accidental crappie than I am the accidental walleye. One walleye of 22 inches can feed my wife and I a delicious meal. One 12 inch crappie is a good start.