(CNN) - After the El Niño storms of 1997, animal experts decided that an orphaned sea otter pup they had found could not survive on his own in the wild.
Instead, that adorable pup named Charlie arrived at the Aquarium of the Pacific, a waterfront aquarium in Long Beach, California, that was set to open to the public the next year.
There, Charlie thrived. The scruffy mammal participated in a number of scientific studies over his 22 years, and eventually became the oldest southern sea otter at any zoo or aquarium. He was even featured in a section on senior animals in the 2018 "Guinness Book of World Records: Wild Things," the aquarium said.
On Monday, the aquarium announced that he had died.
"It is with a heavy heart that we share the news that our sea otter Charlie passed away this morning," the Aquarium of the Pacific said over a black and white photo of Charlie.
At 22, Charlie lived beyond his expected years. Generally, male southern sea otters in the wild live for 10 to 14 years, and those in a zoo or aquarium environment can live up to 20 years, the aquarium said.
California's southern sea otters were listed as threatened under the Endangered Species Act in 1977. They are among the smallest of marine mammals and therefore among the cutest, and Charlie was a spunky animal ambassador at the aquarium.
"Known for his intelligence and easy-going disposition, Charlie could often be seen sucking his paw while relaxing on exhibit," the aquarium said.
But Charlie was both brains and beauty, and the aquarium highlighted his significant contributions to scientific research.
For one, he was the first otter in the world to give a voluntary blood sample without sedation.
In addition, from 2011 to 2013 he participated in a study at the University of California, Santa Cruz's Long Marine Lab, of how sea otters perceive sound, the aquarium said, which could inform government decisions on ocean noise.
"Charlie was selected for the study in part because of the behavioral training he had received at the Aquarium. To participate, Charlie learned to enter a specialized acoustic testing environment, listen for sound signals, and respond to the researchers, notifying them whether or not he had heard the sound by touching his nose to a target or remaining still," the aquarium said.
It's been a tough few months for the aquarium's sea otter fans. In January, Charlie's longtime zoo-mate Brook, a 21-year-old sea otter, died after being diagnosed with congestive heart failure. She had been the oldest female southern sea otter at any zoo or aquarium.
The two were original animals at the Aquarium of the Pacific, and the aquarium posted a Throwback Thursday video last summer of the significant otters when it first opened in 1998.
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