A Hawaiian monk seal who lived at the Waikiki Aquarium for more than two decades has died. 

Director Andrew Rossiter said today that Nukaau was euthanized following a dramatic decline in his health. He was about 31 years old, which is about 90 in human terms, aquarium officials said. His death was peaceful and painless, said Rossiter. 

The monk seal, commonly known as Nuka, was a favorite among staff and visitors. Scientists brought him to the aquarium on July 20, 1983. At the time, a large scar was observed on his abdomen, possibly caused by a shark or from marine debris. Nuka spent more than 25 years at the aquarium where scientists cared for him.

“With his endearing charm, we’ve been privileged to have Nuka as part of the Waikiki Aquarium ohana. Unfortunately, due to a sudden and dramatic decline in his health and his quality of life, and based on veterinary advice, we felt obligated to make this difficult decision,” said Rossiter.