Mary Bowerman

USA TODAY Network

Tilikum, the SeaWorld killer whale whose troubles are chronicled in the 2013 documentary Blackfish, is suffering from a bacterial infection in his lungs, SeaWorld said Tuesday.

The massive killer whale has become “increasingly lethargic” and veterinary teams at the park believe his health is “beginning to deteriorate." Veterinarians have been treating the infection with antibiotics, but the suspected bacteria are resistant to treatment, according to SeaWorld.

The whale, known for his collapsed dorsal fin, was linked to the death of his trainer Dawn Brancheau in 2010, as well as two other deaths. Blackfish questioned the ethics of keeping killer whales, which are highly intelligent and social animals, in captivity.

According to former trainers and experts interviewed in the film, killer whales can become depressed and aggressive toward humans and each other after being kept in small spaces for their entire lives.

Since the release of Blackfish, SeaWorld has been under intense pressure to end killer whale shows in its parks. Amid mounting public pressure the company announced in 2017 it would change the killer whale shows at the San Diego park to "focus on conservation" and highlight "more of the species' natural behaviors."

The People for Ethical Treatment of Animals (PETA) tweeted on Tuesday that SeaWorld should "move the orcas to sanctuaries, where they could enjoy a more natural life."

Throughout the backlash, SeaWorld maintains that the animals are cared for in an environment where they “are continually engaged socially, mentally and physically.”

SeaWorld veterinarians plan to continue managing Tilikum's illness, the park said in a statement.

"Like many older animals facing significant health issues, his condition may continue to fluctuate," SeaWorld said in a statement.

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