The first beluga whale born at the Georgia Aquarium died Wednesday, less than a week after her birth, the Atlanta attraction said.
The 82-pound beluga was underweight and had been in critical condition since her birth Friday and had been under 24-hour care from aquarium workers. The workers had reported the whale was improving steadily before her death.
"This was a very sudden loss," said William Hurley, the aquarium's chief animal officer. "Her blood indicators suggested her little body was working the way it was supposed to. The level of how critical she was improved every day."
The aquarium is performing a necropsy to determine cause of death.
The birth was challenging and the calf, which was unnamed, had difficulty swimming and rising to the surface of the water to breathe, aquarium officials said.
First-time pregnancies in belugas and other types of marine mammals are often unsuccessful both in captivity and in the wild.
Hurley said Maris, the calf's mother, is being monitored by aquarium staff and is doing "wonderfully." She was the first mammal to conceive at the aquarium since the attraction opened in 2005, the world's largest aquarium.
The pair was not on public display but visitors to the aquarium could see Maris' bulging belly over the last 15 months.
Maris got pregnant naturally _ not through insemination _ which is rare for belugas in captivity. Any future pregnancies will likely be more successful, Hurley said.
The number of successful births has increased in the last decade as aquariums and other facilities learn more about whale pregnancies, Hurley said.
Aquarium trainers worked with Maris to help her learn how to feed and care for the baby. They plopped divers in the cold-water tank at 3 a.m. to help get her accustomed to visitors in the middle of the night in case she went into labor after hours.
They also trained her to present her mammary glands to different objects so she was more likely to nurse the baby.
Hurley said Maris was displaying all the right maternal signs but the calf was too weak to respond much.
Just seven North American facilities house belugas, and just a handful are born each year.
"While we recognize that death is part of the natural cycle of life, this remains a difficult loss for the entire aquarium team," said David Kimmel, president & chief operating officer of the aquarium.