Not sure if there are already one of these, but.. yeah..
Primarily, the built-in tracker in lacking in telling you what kind of rare fish you've caught where.
Unless you have a good memory, or written down, you're gonna end up fishing in types of water in a region you've already completed, because you still need 1 rare fish in that region, but no way of telling what kind of water you need to fish to catch that last fish.