(CNN) -- Coast Guard personnel in the air and on the water were unable to locate a pod of 24 short-finned pilot whales that had been stranded in shallow water.
Their disappearance could mean they safely swam back into deeper waters, saving their lives. Or, they might remain stranded and hidden.
"It's encouraging that they can't be found," said Blair Mase, a marine mammal scientist with the National Oceanic and Atmospheric Administration. "But we just don't know."
Experts have been monitoring the pilot whales this week after a mass stranding saw 11 of the mammals die.
Although the group of 24 wasn't spotted, officials did find nine other pilot whales that they remain concerned about.
Two whales were spotted inshore near Plover Key. It was not immediately known whether this pair was alive, in danger or dead, Mase said.
Seven other whales were spotted swimming in an area with water 12 to 14 feet deep, she said.
Mass strandings by pilot whales are not altogether uncommon in Florida. In 2012, nearly two dozen pilot whales stranded and beached themselves. In 2011, 23 pilot whales stranded and beached themselves.