The whale named Kavna died Monday afternoon after showing "inconsistent behavior" during the past few weeks, the aquarium said in a release. Blood tests and other veterinary examinations were inconclusive, the facility said.
Spokeswoman Charlene Chiang said most beluga whales in the wild have a lifespan of about 30 years, so to live an estimated 46 years in captivity was a "long and healthy life," the Vancouver Sun reported.
A 2-day necropsy process began Tuesday to assess factors in the whale's death, the report said.
The whale came to the aquarium from a facility in Churchill, Manitoba, in 1976. A year later, Kavna had a calf that died of an infection at the age of four months.
The aquarium has two other female beluga whales, a mother and calf.
Puzzle-maker slips 'Murdoch Is Evil' into Rupert Murdoch's Sunday Telegraph
Exploding whale video goes viral on Internet