I saw that Bill asked me to chime in with a couple of questions above.
You guys ask the toughest questions!! Man, this is a tough crowd. :-)
I don't know of specific information to the detailed level that Bill requested. There have been a lot of crappie food habits studies, in a lot of places.
My general overview is this. Both crappie species will feed on fish prey when it is abundant and of the proper size. So, in southern reservoirs, they feed on age-0 gizzard shad when the shad are sufficiently small. I don't think there is any doubt that, given a chance, crappies prefer fish prey.
Having said that, however, there are many times and places when crappies feed much more on invertebrates (zooplankton and aquatic insects) than on fish.
Here's my "pet" belief on crappies in small impoundments (I'll define that as up to 100 acres). I think that if you are going to try crappie management (and based on comments in this and other threads, don't do this lightly!), blacks are superior to whites. I base this on some food habits work we did on Kansas ponds back in the 80s.
In one pond with black crappies up to 12 inches in length, we did monthly food habits on the crappies. The pond only contained largemouth bass, black crappie, and a low abundance of green sunfish. In 11 months of open water sampling (we had ice one month), we found a grand total of 1 small green sunfish in black crappie stomachs, for crappies of all sizes. The crappies were eating zooplankton and insects. How in the world is this possible? Well, I always explain it to my students this way. Let's assume we actually know that this pond could support a maximum of 50 pounds per acre of black crappies. In this case, the largemouth bass kept the crappies in check, and perhaps there was only 25 pounds per acre of crappies out there. Thus, they had plenty of food per individual, and even though I'd consider an invertebrate diet to be inferior to a fish diet, they had enough food to grow fast and reach 12 inches in 5 years. These were plump, healthy crappies.
Now, we also worked on another KS pond that had white crappies, largemouth bass, and green sunfish. The bass were crowded, thin, and few exceeded 12 inches. They cropped the white crappies pretty well. Despite that, the pond produced 9-10 inch white crappies, but that was about it. My pet belief is that white crappies rely a lot more on fish as food than do black crappies. 9-10 inch white crappies aren't necessarily bad, and certainly are better than stunted 6-8 inch white crappies. However, it's just a so-so fish in my book. I’d much rather catch those 12 inch black crappies in the other pond!
Dave
