SeaWorld is coming under renewed criticism after the death last week of an 18-year-old orca whale named Unna at its San Antonio theme park. Unna had undergone several months of treatment for a fungal infection.

Unna is the third whale to have died at SeaWorld San Antonio since mid-2015. A beluga whale named Stella died in November of gastrointestinal complications and a premature beluga calf died in July.

Dr. Naomi Rose, marine mammal scientist at the Animal Welfare Institute, said Unna's death at a relatively young age is cause for concern.

"Unna was only 18 years old and that is young; there's just no way around it," she said. "In the wild, reproductively mature female orcas have a very low mortality rate."

She added, "[SeaWorld] shouldn't be losing their young adult females. It's not a sign of good husbandry, good caretaking."

An investigation conducted by the San Antonio Express-News found that, prior to Unna's death, 14 animals died at SeaWorld San Antonio since 1991. The oldest whale was 26 years old, with the majority under twenty.

In the wild, though, the lifespan of whales is typically 50-100 years, depending on the species, according to the National Oceanic and Atmospheric Administration. But the median lifespan of orcas in US parks is just 12 years, according to research published in the journal _Marine Mammal Science _in April.

SeaWorld San Antonio did not respond to requests for comment.

In a press statement, the company, which operates SeaWorld facilities in Orlando, San Antonio, and San Diego, said Unna had undergone several months of treatment for a Candida infection, which can occur in all sorts of animals.

"Candida, and fungal infections in general, are found in wild cetaceans," it said. "Fungal infections can be found, and can be the cause of death, in both wild cetaceans and those in zoological facilities."

Rose said SeaWorld's statement was misleading. While Candida is found in wild cetaceans, an order of mammals that includes whales, dolphins, and porpoises, it is not commonly found in orcas.

"As far as I'm aware, in the literature, fungal infections are common in some cetaceous species, like bottlenose dolphins, but in orcas, they are not," she said.

SeaWorld said in its statement that it will conduct a necropsy in order to determine the ultimate cause of the animal's death. But Rose believes it's likely Candidiasis, a systemic infection that occurs when an individual infected with Candida is stressed or its immune system becomes compromised. But even the presence of Candida, she added, highlights the general conditions of orcas in captivity.

"There is no literature showing that Candida is found commonly in wild orcas," she added. "In captivity, however, it's very common."

The most frequent cause of captive-orca deaths is pneumonia, according to the Marine Mammal Inventory, a government database. All organizations that hold marine mammals in captivity, including for public display, must submit necropsies to the database, under the 1972 US Marine Mammal Protection Act.

SeaWorld has faced persistent criticism of its captive whale program, particularly since the 2013 documentary _Blackfish _first brought major attention to conditions within its parks. The film suggested that brutal treatment of orcas by SeaWorld trainers caused them to lash out — and in some cases kill.

In August of last year, SeaWorld announced it would build new, larger environments for its orcas and fund animal research and conservation efforts.

SeaWorld came under fire this past July when the animal welfare rights organization People for the Ethical Treatment of Animals (PETA) accused SeaWorld of infiltrating its ranks with the cooperation of Pasadena police. PETA has since filed a lawsuit against the law enforcement agency for not releasing documents that the organization believes would demonstrate police collusion in corporate espionage.

And, in October, California banned SeaWorld's San Diego park from breeding orcas in captivity. A month later, the company announced that it would discontinue its killer whale shows at the park.

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