An aquarium news release said Kenai had progressively deteriorating health and quality of life associated with advanced age.
At 23 years old, Kenai exceeded the known median life expectancy of sea otters by several years.
Kenai, along with another female currently living at Point Defiance Zoo and Aquarium in Tacoma, Wash., were the last two oil spill otter survivors in the United States.
"The past twenty-four hours have been very difficult for the entire Shedd family who held a special place in their hearts for Kenai," said Ken Ramirez, executive vice president of animal care and training, who assisted in the wildlife rescue efforts in 1989. "It was a difficult, yet clearly compassionate decision as her quality of life quickly deteriorated over the last several weeks."
The Exxon Valdez environmental disaster leaked 11 million gallons of oil into the Prince William Sound in Alaska, killing almost 2,000 otters immediately. Shedd took in four rescued otters, including Kenai.
Kenai contributed vital scientific data to long-term studies on sea otters exposed to oil and provided assistance for research on common health issues associated with old age, such as arthritis, cataracts and dental work.
In 2010, she had a root canal procedure performed on a cracked upper canine, an essential tooth for crunching and chewing her food. Thanks to Shedd's animal health team, she was able to continue to enjoy her seafood meals, except for capelin, for which she had a distinct distaste, the news release said.
Named after the Kenai Peninsula off the Gulf of Alaska, she took the role of a protective surrogate mother for several of Shedd's other young rescue otters including Kiana, another orphan found on an Alaska beach in 2005. Kenai also enjoyed the company of Kachemak, another aging otter, with whom she often shared a reserve pool when it wasn't occupied, the release said.
Earlier this year, Shedd helped to rescue a stranded southern sea otter pup along the California coastline. Cayucos, following the aquarium's tradition of naming rescued animals after the area that they were found, continues to grow adding on 20 pounds since arriving at the aquarium.
