Mystic ― Mystic Aquarium on Friday announced the death of one of its most famous residents, Astro, a male Steller sea lion.

A 2010 children’s book, called “Astro the Steller Sea Lion” by Jeanne Walker Harvey, told the story of Astro’s life and adventures, from his initial rescue in 2006 through finding his permanent residence at the aquarium in 2008.

Astro, 17, was humanely euthanized Thursday after several age-related conditions, including arthritis, worsened this week, and he stopped eating and began struggling to swim, according to aquarium officials.

“As we mourn the loss of Astro, we want to extend our deepest gratitude to the animal care team who devotedly tended to him with love and dedication. We also thank our visitors and supporters for your affection and admiration of Astro these past 16 years,” the aquarium said in a statement released on its social media channels Friday afternoon.

Though female Steller sea lions can reach the age of 30, their male counterparts have a far shorter life expectancy of up to 18 years.

Astro was originally found in June 2006 on an island off the northern California coast. He was just a few days old with his umbilical cord still attached.

Members of the Marine Mammal Center of Sausalito tried three times to release Astro back into the ocean, but each time he swam back ashore, crossing miles of open ocean to return to the center. It is thought he never bonded with his mother, and the first mammals he had contact with were humans.

On his third trip ashore, he gained fame after climbing rocks up to the Marin Country Day School in California, where he joined students participating in a walkathon. He completed three-quarters of a lap with them.

The National Marine Fisheries Service determined he could not be released back into the wild, and he arrived at the aquarium in February 2008.

“Astro's larger-than-life, lovable personality made him a favorite among both visitors and our team here at Mystic Aquarium. His loss is deeply felt by many, near and far.” the aquarium’s statement read. “His presence brought joy and wonder to all who had the privilege of witnessing his spirited character.”

The statement concluded, “In this challenging time, we ask for your understanding and compassion. Let us honor Astro's memory by celebrating the joy he brought into our lives and his impact on raising awareness for the conservation of his endangered species. Rest in peace, Astro.”

Steller sea lions have been on the endangered species list since 1997 and are found along the northern Pacific Rim and along the Pacific northwest coast from California to Alaska. Females can grow to 9.5 feet in length and 700 pounds while males can grow to 11 feet long and 2,400 pounds.

Mystic Aquarium currently has three other Steller sea lions, Eden, Perl and Sitka, and is one of only four facilities in the United States able to care for the animals.