Card Sharks, Pool Sharks, and Loan Sharks all have nasty bites. Lucky for you there aren't a lot of them on the island.
The main thing to remember is not to feed them unless you have chain mail on. And don't carry food down the streets of San Pedro - since their sense of smell can pick up the scent of chicken/beans and rice up to a mile away.
The River Shark
ps. Don't fall out of a fishing boat while sharks are in the area - it's just good commom sense! Trust Me!