Greg LeNoir said he took his 14-pound rat terrier Jake for a daily swim at a marina Friday.
The five-foot shark suddenly surfaced and grabbed nearly the entire dog in its mouth.
LeNoir said he yelled, then balled up his fists and dove headfirst into the water. He hit the shark in the back and the creature finally let go of the dog.
Man and dog made it safely back to shore. The dog suffered bite wounds but was not critically injured.