The Coast Guard's Close said that because Schuyler was the only passenger found with the boat, rescuers would tailor their search to stop looking for the vessel and begin looking for individuals.
Close said Monday he was "not going to speculate on any survivability at this point."
Schuyler, he said, was first noticed by a spotter aboard the Coast Guard vessel Tornado, which then called for a helicopter to rescue the man.
The Coast Guard searched about 16,000 square miles west of Clearwater Pass but were hampered by rough seas and weather.
The men were aboard a 21-foot Everglades-manufactured boat, the Coast Guard said. The boats are built with compressed foam encased in Fiberglass, which makes them difficult to sink.
The men left the Seminole Boat Ramp in Clearwater Pass at 6:30 a.m. Saturday, according to the Coast Guard in St. Petersburg. They were expected to return that night but never did.
The Associated Press and ABC News' Scott Mayerowitz contributed to this report.