From the Internet (Some of the following anyway, some comes from catching a boatload of each species

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Sharpnose Shark seldom gets to 48", frequently caught in the 36" range, known in NC waters in early September as a prelude to Drum fishing to come. It can bite you. Good with Children. Has white spots on back and sides.
Versus:
Blacktip Shark can approach 6',
most common Shark taken in Florida waters, will feed on Sharpnose Sharks as mentioned by Geo, if a decent size one bites you, you will be on the way to the emergency room. No white spots on back and side.