The community started celebrating Snooty's birthday when he turned 20 in 1968, and it has been an annual event ever since. "I-and our staff, volunteers and board members-considered him a star".
Snooty was found in an underwater area only used to access plumbing for the exhibit life support system.
Normally the access panel is bolted shut but it was knocked loose which explains how Snooty was able to swim in, Besio said.
No other details were given about the cause of death, but the museum said they were devastated and that the circumstances are being investigated.
But the museum said there was no sign of any problems with the manatee's 230,000-litre pool the day before his death.
Snooty was described as am intelligent, social manatee, who had the staff of the South Florida Museum under his flipper.
The museum says around a million people saw him in his lifetime.
By the time staffers found Snooty, he was dead.
The museum said that Snooty's habitat undergoes a "daily visual inspection" and that there were "no indications" on Saturday that there was "anything amiss".
Besio said the museum will be conducting a full investigation into the circumstances surrounding the death.
Thousands of people regularly attended Snooty's birthday parties, and he served as the official mascot of Manatee County.
His birth was one of the first recorded of a manatee, making him the oldest one in captivity, and likely in the world.
After the discovery of the body on Sunday morning, the aquarium was closed for the day and staff helped to share the news with visitors at the front door. He moved to Bradenton in 1949.
Most wild manatees die before the age of 10, and can be victims of alage blooms, fishing debris and boat strikes.
There are now three manatees in the rehab program, Rodgers said.
In 68 years, the museum has not had any manatee injuries.
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