Gizzard Shad vs. Crappie on SI

Fellow Crappie Anglers,

We fished Lake Roosevelt here in AZ last weekend and my fishing buddies and I were having trouble figuring out what we were seeing on the graph. Lake Roosevelt has been a good to great Crappie lake for sometime now. With in the past few years Gizzard Shad (GS) started showing up and now there is a rather large population of them. My question is for those that have GS in their lakes, how do you determine if you are seeing schools GS or schools of Crappie on your normal haunts? They are about the same size and look the same on the SI. Any help would be greatly appreciated. One thing we did notice is that it looked like the GS were suspended more horizontally and the Crappie were stacked vertically The boat/graphs were not mine so I don't have pics to share.

Drop a jigging spoon down there in the school. After 10 minutes you will usually snag one of the shad, or get a bunch of "bites" (just the jig bumping into the shad) and no successful hookups. I got fed up trying to figure out what was showing up on my depthfinder too, the jigging spoon was initially dropped to see if the school was striped bass, but it taught me another trick instead.