A young beluga whale at the Vancouver Aquarium died Monday night after its airway became blocked, officials say.

The aquarium's veterinarian, Martin Haulena, said the female calf, named Nala, died at about 10:15 p.m. PT, and a full necropsy was performed overnight.

During the necropsy, staff discovered a pocket that had formed inside the whale's airway. The pocket had swollen up because of debris that had become trapped inside. Several small pebbles and a penny were found in the pocket.

Five belugas have been born in captivity at the aquarium, and three of them have died before their third birthdays, but this is the first time staff have seen this type of problem, said Haulena.

A beluga calf, named Nala, swims with its mother shortly after it was born at the Vancouver Aquarium on June 7, 2009. Nala died Monday after its airway became blocked. (Darryl Dyck/The Canadian Press)

"It's such a bizarre situation. I wouldn't normally look for this," said Haulena. "I just honestly would not have thought of this before."

Nala was born in June 2009 to Aurora, a 20-year-old beluga grandmother at the aquarium.

"Vancouver Aquarium staff — particularly its animal care team — and volunteers were deeply saddened by this loss," said a notice released by the aquarium.

"Nala was an energetic and curious calf who enjoyed socializing with the belugas in the aquarium family, including playmate Tiqa - the aquarium's oldest calf - mom Aurora, and Qila," the statement said.

Aurora's first calf, Qila, was born in 1995. She was the first calf to be conceived and born in a Canadian aquarium. Aurora's second calf, Tuvaq, was born in 2002 but died suddenly in 2005. Qila gave birth to her own calf, Tiqa, in 2008.