His health failing, Shedd Aquarium officials this week euthanized Otis, one of their California sea lions.
"We are very saddened by this difficult but necessary decision due to the deterioration of Otis’ quality of life," said Ken Ramirez, executive vice president of animal care and training, in a written statement.
Otis, 13, had a rapid decline in health caused by complications related to a progressive advancement of urogenital cancer, the Shedd said.
A necropsy performed Thursday evening yielded preliminary findings consistent with the diagnosis, officials said.
Otis was one of two animals who came to Shedd in the spring of 2009 from State of Washington wildlife officials. The others, Biff and Tyler, are said to be in good health. The animals were brought to Chicago as part of a government effort to relocate or remove dozens of sea lions from the Bonneville Dam area that were jeopardizing endangered fish stocks in Washington's Columbia River.
"Through our animal care expertise we were able to provide Otis with a second chance, while also giving the marine mammal community the opportunity to learn vital information that will help us better understand sea lions in the wild," said Ramirez.
Shedd Aquarium officials said ongoing studies indicate the wild and rescued California sea lions are dying from metastatic cancer, suggesting the disease may be related to contaminants in the ocean and their effects on the health of its inhabitants.
Veterinarians plan to archive tissue samples taken from the necropsy that may help further research studies.