- Maris, 21, showed no signs of illness before her death
- "This is a case of sudden, acute animal death," chief vet says
Atlanta (CNN)A beloved female beluga whale has died suddenly at the Georgia Aquarium in Atlanta.
Maris, 21, showed no signs of illness before her death Thursday, the aquarium said in a statement.
She ate and interacted normally with Grayson and Qinu, the other two beluga whales at the aquarium.
"This is a case of sudden, acute animal death," said Dr. Gregory Bossart, chief vet at the Georgia Aquarium.
An autopsy is underway.
Fisheries experts at the National Oceanic and Atmospheric Administration estimate that beluga whales often live to be 35 to 50 years of age in the wild.
Maris lived at the aquarium for 10 years, and had a calf this year that died in June shortly after birth.
PETA: 'Killed by captivity'
The rights group People for the Ethical Treatment of Animals said Maris died because she was a captive animal.
"Maris was denied her freedom her entire life. She was transferred from one facility to another, and her babies died, one after the other," PETA senior vice president Lisa Lange said in a statement Friday. "Whether or not she had a physical ailment that went unnoticed, she was killed by captivity, plain and simple."
The Georgia Aquarium says the study of belugas in human care helps researchers expand their knowledge of belugas in the wild, in areas such as rising ocean temperatures, diseases and how underwater sounds affect the animals.
"The data can be combined and applied to help conserve and protect wild belugas from threats in their natural habitats," its website says.
Maris came to Atlanta from the New York Aquarium, where she was born.