In a few places, I carried a bang stick while diving, but never used it. In SoFl, we sometimes saw bullsharks while "divebombing" deep wrecks, but they went away if we turned off the HID lights and got off the scooter triggers.I'd carry some half a sticks of dynamite with short waterproof fuses for those sharks or have a real boat.
Wonder if that 'bloke' had a stringer of fish hanging overboard. Bulls have been humanized to hang around under boats and docks to steal fisherman's catches.
Many shark bites in FL are from spinner sharks where people swim in the ocean near fishing piers.
In SC, I was spearfishing with a friend and we each got 2 nice groupers. Unfortunately we stayed a little too long and had to do 25 minutes of deco, as we didn't bring oxygen. At 20 ft, I didn't like the look of a barracuda that was watching and I put my stringer on a bag. It was successfully retrieved by the boat crew. My buddy chose to hold onto his, and the 'cuda came in closer and closer and eventually went after his stringer. He poked the barracuda with his speargun and let his stringer go, and the barracuda got his fish.
When you enter their world, you have to respect wildlife.