I haven't been down there much this year, but I had no trouble finding bait in the upper part of the lake. Since shad typically spawn in the upper shallow regions, maybe that's why they aren't as prevalent on the main lake.

One other possibility is that their spawning was also interrupted by constantly changing water levels and the water warming quickly. The northern Gizzard shad have developed a greater tolerance for cold water, so if numbers are down, don't expect it for long.