Later in the summer, after roughly the middle of May, the mullet thin out and many tarpon fishermen switch to crabs. A 100-pound tarpon will eagerly slurp down a small crab the size of a silver dollar, so don't let a bait-and-tackle shop try to sell you crabs the size of Frisbees - you don't need them, and they won't work as well. Mullet can be cast-netted, or you can sometimes buy them from a bait truck at marinas, but that's not always reliable. You're much more likely to find crabs on a consistent basis, and they work great. You will also pick up an occasional permit when using crabs for bait, a decidedly wonderful bonus.
I deploy two baits behind the skiff, one fished about 30 feet back in the current, with the second fished about twice that far back. I also like to have an angler pitch a free-floating bait forward and off to the side, letting that bait drift back with the current. Leave the two rods fished behind the boat in rod holders. The combination of circle hooks and the hook-set provided by "Rodney" seldom misses, with the fish hooked perfectly in the corner of the mouth virtually every time.
As an alternative, you can also cast artificials off to the side. I like bouncing a white jig along the bottom, with a long grub tail attached. You can also dredge with a fly rod spooled with a sinking line.
When you hook a fish, get on top of them quickly to maintain control of the fish. The waters surrounding the Keys passes aren't deep, so the tarpon can't drop off into a deep hole like they sometimes do in places like Boca Grande. Still, these are large, strong fish, and it takes some power to bring them to the leader and release them.
Bear in mind that Florida law views bringing tarpon into the boat for a photograph as "possession," meaning you need a tarpon kill-tag to do so. Leave them in the water alongside the boat for a quick photo instead. Using careful release methods will help ensure the continuation of this ancient fish migration for future generations.