Chris and Melanie from Ohio caught plenty of blackfin tuna on a Florida Keys fishing charter off Marathon, 14 blackfin tuna and 2 skip jacks to be exact. We had a couple of large sharks on as well. Blackfin tuna are the smallest species of tuna, typically ranging between 15 to 35 pounds. Grilled blackfin tuna steaks with a little lime and seasoning rub makes a delicious meal. Book your next Florida Keys fishing trip with Captain Doug and let him show you a good time.