There are many redfish, locally called red drum, in that area. If the tails were a pale blue, that's probably what it was. If the tails were pale green or rather transparent, however, it might have been striped bass. Without more description, it's hard to tell, but if I were to guess, I'd choose redfish. One way to find out: Throw a fly at them. If they are drum, you'll find out quickly enough because they will take a fly when they are acting this way.