A three-year-old beluga that died early Friday morning was killed by pneumonia, according to the preliminary results of a necropsy.

Tiqa, born June 10, 2008, passed away at the Vancouver Aquarium around 5:45 a.m. Friday. A preliminary necropsy performed later in the day gave the apparent cause of death as pneumonia, but veterinarians have not yet identified any underlying disorders.

Dr. Martin Haulena is now awaiting results of histopathology, microbiology and toxicology tests to confirm the cause of death.

Police are also investigating a break-in reported at 4:30 a.m. in the beluga habitat, but say there is no evidence suggesting that it is connected to the death.

A staff member who was monitoring the sick animal called 911 after seeing a man standing inside the whale's enclosure. They were able to scare him off after just a few moments.

Investigators are looking for a dark-skinned man, estimated to be about 5-10 tall, who was wearing a long-sleeved white shirt and light coloured jeans.

Aquarium President John Nightingale says that the facility has dealt with police incidents over the years, but added that, "it's been years since anything like this has happened."

Clint Wright, the aquarium's senior vice president, said that Tiqa had been mildly sick for about 10 days, but its blood appeared to be normal. The young beluga took a turn for the worse on Thursday, when staff noticed a "dramatic change" in the blood samples.

Wright says he was called back into the aquarium at 4:30 a.m. as the whale's health began a step decline. Tiqa died just a little more than an hour later.

"We don't know what happened at this point -- we're assuming some kind of infection," Wright said.

The death is taking a heavy toll on those who worked with Tiqa every day.

"You can imagine the impact of a death like this on our staff and volunteers," Nightingale said.

"Some of these people spend more time with these animals than they do with their own families at homes."

Three calves dead in 10 years at Aquarium

Tiqa was the first-ever calf in Canada to be born to an aquarium-born beluga.

This is the second whale death at the facility is just over a year, and the third death of a beluga calf in 10 years.

Nightingale says he is concerned about that record.

"I'm less happy about that than all of you are," he said. "We simply have to get to the bottom of what's going on."

He says that aquarium staff will "leave no stone unturned" as they search for the cause of the deaths.

But he stressed that there is, "absolutely no assurance that there is any direct connection between the deaths of these three calves."

Nala, a calf who was born to much fanfare, died in June 2010 of a bizarre infection when debris became stuck in her voice box.

Staff revealed that Nala had a pocket beneath her larynx, or voice box, which contained a penny and two small stones.

It is believed the penny may have been dropped in the pool by a visitor, despite signs asking patrons to keep foreign objects away.

The death prompted animal groups to reiterate their calls for the aquarium to stop keeping whales in captivity.