The Department of Land and Natural Resources today reopened Mahaiula Beach at Kekaha Kai State Park on the Big Island after a Hawaii Fire Department helicopter flyover this morning did not sight any sharks in waters off the park. Yesterday the park remained closed when a number of reef sharks were spotted in offshore waters during a morning flyover.  On Tuesday, a Kailua-Kona man was bitten by a shark while swimming at about 1 p.m. He was taken to the hospital in serious condition.