A scuba diver missing from the Florida Keys since Tuesday has been identified as a well-known Canadian underwater filmmaker and conservationist. Rob Stewart, 37, was diving with a small group on the wreck of the Queen of Nassau near Alligator Reef off Lower Matecumbe Key in about 225 feet of water, his sister Alexandra Stewart said by phone from Toronto on Wednesday morning. He was filming an installment of his Sharkwater documentary series, she said. Stewart and another diver were using closed-circulation rebreathing dive equipment instead of conventional scuba tanks, which are open-air circulation, according to an email from the...