As millions of Americans head to the beach for the Fourth of July weekend, shark experts say there’s little reason to stay out of the water — though people need to stay alert. Marine biologist Mike Heithaus, Ph.D., of Florida International University told Fox News Digital that shark bites remain extremely uncommon, even during the busy summer beach season. “Shark attacks are still extremely rare,” Heithaus said. JULY 4 TRAVEL EXPECTED TO HIT RECORD HIGHS DESPITE HIGH COSTS “People should always…