Tarpon are enormous fish.  50 to 60 pound tarpon are considered small and fish over 100 pounds are fairly common.  Even though tarpon will eat large bait fish, whole crabs and a variety of other bigger baits, they will also take a small fly.  Fly fishermen typically target tarpon in shallow water, however, you can usually find some very big tarpon in some of these shallow backwater areas.  There are several flies that do a good job of imitating what they eat and these flies can be very effective.