It died at a research aquarium where it received round-the-clock care by a team of marine mammal experts.

Officials at the Alaska SeaLife Center said that despite everyone’s best efforts, the whale died early Monday morning after it became evident Sunday that the young whale’s condition was declining. A full necropsy was to be performed later Monday.

“We are deeply saddened by the loss of this beluga calf,” Tara Riemer Jones, the Seward center’s president and CEO, said in a statement.

Jones praised the care provided by marine mammal specialist from across the country. She said their knowledge allowed the center to provide the best care possible.

“There is more we will continue to learn about beluga whales as a result of this loss that will ultimately benefit beluga whales in the marine mammal community and in the wild,” she said.

The whale is believed to be the first baby beluga to be rescued in the United States since the Marine Mammal Protection Act of 1972.

The calf was found June 18 near South Naknek. Officials believe a storm likely separated the calf from its mother.

The calf was flown 90 minutes to Seward. In the plane, it was placed on an air mattress and positioned so its weight wouldn’t put pressure on vital organs. It was constantly covered with wet towels.

Last week, center officials expressed guarded optimism about the calf’s rehabilitation. It was swimming on its own. It was learning to take food from a bottle, which officials said had been challenging. However, it was still in critical care.

The beluga was 5 feet (1.5 meters) long and weighed 115 pounds (52 kilograms), up 5 pounds (2.3 kilograms) since its arrival.

Survival odds for an animal this age coming into a stranding program are low, Brett Long, the husbandry director at the center, said at the time.

“We take it a day at a time,” he said, adding that the beluga was “maintaining its weight, and we’re seeing slow, incremental weight gain.”  The biggest worry was the calf’s immune system, which was insufficiently developed because it did not receive any of its mother’s milk.