You didn't mention which key you will be visiting in the spring but I would highly recommend Islamorada, the fishing capital of the world. It really doesn't matter which key its just great to go fishing. Dolphin, Sailfish, Marlin, Kingfish & Wahoo, or anchor just off the reefs for bottom huggers such as Grouper and Snapper. You may want to hire a boat & a Captain to take you where the fish are bitting or you can just rent a boat & go out on your own. They all have rentals for half or full day excursions. Most of the boats are okay but if you don't know ask some of our locals & I'm sure they will recommend a couple to ya. Or you can get the local paper & see for yourself which one fits the bill. Ask the clerk or the owner at the hotel who they might recommend, always pretty good with there recommendations. When you are dinning out look for some fishermen in the establishment & ash them, thet will know. Hope this helps & enjoy the trip & the fishing. :)