I have a pond of about two acres that was renovated about 4 years ago. In it we added YP, RE, HSB, SMB, BG, a few channel cats, some shiners and some rosy reds. All we ever catch is blue gills, most of them pretty good size.
The only one of the others species we have ever caught was a shiner.
Is there a trap we could use to see what else is in there since they don't seem to want to be caught with a hook? If so, what style?

You can build one of these traps for less than $10

http://www.memphisnet.net/product/2382/traps-fish-minnow

To accommodate different sizes of fish just change baits and increase the inlet size

Fyke nets work really well.