Charlie, a southern sea otter, lived a long life—so old that was he was recognized last year by the Guinness Book of World Records.

The Aquarium of the Pacific was mourning his death on Monday at the age of 22.

Staff at the aquarium had been monitoring Charlie, who had recently been showing signs of his age—yet was still active and alert, the aquarium said in a statement.

He was the oldest living southern sea otter at any zoo or aquarium. Male southern sea otters typically live 10 to 14 years, and females live 12-18 years, but can live up to 20 years or more in a zoo or aquarium, the local aquarium said.

Charlie arrived at the Aquarium of the Pacific in 1998 before the facility opened to the public. He had been orphaned during El Niño storms in 1997, and was found stranded in Northern California, according to the statement.

“After going through a rehabilitation program, otter experts determined it was not possible to release him back into the wild, as he had not learned survival skills from his mother as sea otter pups typically do,” the aquarium said.

“Charlie was beloved by the Aquarium’s staff, members, and the public for his kind nature and intelligence,” the statement said. “He was the first otter in the world to give a voluntary blood sample, which aided in his annual physicals and medical exams.”

Charlie’s fans and supporters can pay tribute to him at the Aquarium from 9 a.m. to 4 p.m. Sunday, April 28. Visitors will be able to fill out a card in Charlie’s memory that will hang from the railing at the Sea Otter Habitat all day (Aquarium admission is required).

Donations to the aquarium can also be made in Charlie’s name.