Welcome to the forum... Sounds like you have lucked into a nicely balanced pond. For its size, it's impressive it is producing so many quality fish. You didn't mention any fertilization so it would appear your pond is naturally quite fertile.
Yes, CC(channel cats) do feed on crappie just like they will feed on just about any other fish they can get in their mouths. Particularly the larger cats will be predacious on any fish. I suspect the number of crappie being eaten by your catfish is rather low though. It is the bass in your pond that are eating the vast majority of your crappie.
If you're looking to help your crappie along, I would focus on two things. One, keep every single crappie you catch! You will never catch them all and the ones remaining will have less competition and will grow faster. It is a very rare pond where you can grow quality crappies for an extended period. Perhaps the fact that you have such a well spread out size range of bass is helping to control your crappie population. The second thing I'd focus on is working to keep the bass size structure well spread out. Having mediium and large sized bass in the pond will help the bass control the crappies. In many ponds where the bass max out at 14" or so because of stunting, the crappies are able to grow just large enough that most bass cannot feed on them and then they stunt. Whereas in your pond, with bass pushing 28", crappies are being eaten even at 10" plus.
Take some pictures and share them with us... We love to see pond pictures and the fish caught out of them!
