I made the assumption he was referring to the major creek arms. The major migration routes. I will also add that it is much tougher to find crappie out of the major creek arms if they are not out near the channels.Bluegill and Redear beds,much easier to find in the smaller " creek arm coves" then crappie. At least that has been my experience. Might fish several coves which do not have named creeks but have the natural drainages or " dry creeks" as they are sometimes referred to when it was still dry land ,and find bluegill or other species but not crappie. The crappie do have a propensity to use arms that had creeks that held water or were actually running the majority of the time. So typically if your not in one of the largest or "major" creek arms check the the arms that have the smaller creeks that have or had flow when it is wet enough.

It is sort of like envisioning it before it was a Lake. If you would walk through the woods, where could you fish before it was flooded? On natural lakes and non flood control impoundments I catch a lot of fish in coves that have only drainages or non named creeks. The reservoirs where an actual large river was impounded have more of a tendency for the fish to use the old river and creeks sort of like a tree and its branches. The trunk,the main branches,then the smaller branches.