A veterinarian says three-year-old Tiqa likely had pneumonia, and officials agree the break-in occurred so close to the death it appears to be a coincidence.
Standing near the pool where only two belugas remained on Friday, aquarium general manager Clint Wright said Tiqa had a mild illness for about 10 days, wasn't eating and appeared to have an infection.
"She had been on antibiotics for most of the week," he said, adding the whale seemed to sicken quickly on Thursday and died early Friday morning.
Later in the day, vet Martin Haulena reported that preliminary results of a necropsy indicate pneumonia, although its underlying cause is not yet known.
Vancouver police Const. Jana McGuinness said the intruder didn't get into the pool and it would be very speculative to make the link between the death and the break-in.
"We need to let the science come back and the investigation continue to provide those answers," she told reporters Friday.
Officials said the perimeter alarm did not go off, indicating someone had breached security. A staff member who had been watching the sick whale saw the man, yelled and he quickly escaped by scaling the wall.
Aquarium CEO John Nightingale said the aquarium will take police up on an offer to review the aquarium's security.
Nightingale said Tiqa is the third beluga calf to die there since 2005 and staff need to determine why the whales are dying.
He said the loss is "infuriating" and "staggering" for the aquarium.
Nightingale said they would make all the information around the deaths public and he said he's hoping some expert somewhere might be able to offer clues.
"I don't care if it's a dentist in Topeka, Kansas, or a doctor in Hamilton, Ont., or a scientist in Japan who spots something we don't, we want their perspective and that information (to try) to help us understand what has happened."
Nightingale couldn't say if there was any connection between the three dead calves.
Tiqa was born at the aquarium in June 2008. Wright said she was still occasionally nursing on both adult females at the aquarium and the weaning period can be a tenuous time for the health of the calf.
In 2005, a three-year-old whale named Tuvaq died at the aquarium.
And last June, a one-year-old calf died from an apparent infection, and an examination later found a pocket in the whale's larynx contained two stones and a penny.
Little is known about belugas in the wild or the survival of calves, but Wright said if they're similar to killer whales, about 50 per cent of the calves would die before they reach adulthood.
The aquarium stopped displaying killer whales in 2001 after one of its two orcas died. The remaining female was shipped to a U.S. marine park.
Nightingale said aquarium staff came to the realization they couldn't provide the facilities the orcas needed. But belugas are much more suitable for Vancouver's aquarium, he said.
"If the killer whale is the Ferrari of the whale world, the beluga is the 1955 Volkswagen bus. They are a putter-around whale. They're pretty ideally suited to living in an aquarium."
Nightingale said among the more than 600 marine parks in the world, the Vancouver aquarium is widely regarded as giving some of the best care to its animals.
Haulena is now researching whether a metabolic disorder was underlying the pneumonia and is still awaiting the results of more tests.
Nightingale said aquarium staff and volunteers are distraught.
"Some of these staff spend more time with the animals here at the aquarium than they do at home with their kids. The relationships aren't taken lightly at all."
The aquarium is undergoing a renovation, so the male belugas have been moved to marine parks in the United States, along with a couple of females and their calves.
Nightingale said the aquarium plans to continue its breeding program once the renovation expansion is complete and the males and females are reunited.