Mystic — A beluga whale that arrived at the Mystic Aquarium in May on a controversial transport from Canada has died.

Known as Havoc when he arrived with four female belugas from Marineland in Niagara Falls, Canada, the approximately 6-year-old whale was brought in as part of a non-invasive research program at the aquarium meant to help with wild beluga conservation efforts.

Mystic Aquarium in a statement said he died Friday about 6:30 a.m. He was being treated for gastric ulcers developed before arriving and had been showing signs of improvement throughout his acclimation period, according to the aquarium.

Aquarium spokesman Dan Pasquera said the exact cause of death is unknown. The whale is being examined at the University of Connecticut biopathology laboratory with the aquarium's medical team assisting. The results of the necropsy are expected soon, according to Pasquera.

"We will also continue to carefully monitor the other beluga whales, who are healthy and behaving normally," the aquarium said in its statement. "The information we have indicates that this is an isolated situation and that none of the other whales have had their health impacted."

Mystic Aquarium had been involved in a yearslong process of moving the whales to its Arctic Coast habitat to join the three resident belugas: Juno, an 18-year-old male; Natasha, a 41-year-old female; and Kela, a 40-year-old female.

The decision to transport the whales to Mystic from Canada was a controversial one, with many animal rights groups speaking out against the move. The Canadian government had to approve an export permit that allowed the transport to move forward.

The arduous transfer of the whales by flatbed truck and jet from Niagara Falls to Mystic took more than 10 hours.

Marine animal advocates argued the transport would endanger the whales and violate the intent of a 2019 Canadian law aimed at phasing out the captivity of whales, dolphins and other cetaceans. It also restricts their import and export but the minister of fisheries and oceans can approve permits for research purposes if it is in the best interests of the cetacean. The law is designed to eventually end the captivity of cetaceans in Canada by banning their breeding.

The import permit from the U.S. National Marine Fisheries Service prohibits the animals from being bred for at least five years or included in public performances.

Naomi Rose, a marine biologist with the U.S.-based Animal Welfare Institute, had raised questions throughout the permitting process about the health of the Marineland animals and their suitability for transport.

In a phone interview Friday, she said three of the whales deemed too sick for the trip were replaced with three different belugas from the facility through an amendment to the permit application. She said "it makes no sense" that the aquarium would pick one sick whale to take the place of another sick whale.

"When they chose to replace three whales for illnesses, why did they choose a whale who had a condition that killed him three months after his transport?" she asked.

She also wondered what good it did the aquarium to announce on its social media accounts Friday that the beluga whale had a condition before it arrived in the United States.

"Maybe they said it was a preexisting condition because they wanted to say that this was something that happened at Marineland, not at Mystic," she said. "But then they never should have imported him."

Pasquera, the aquarium spokesman, said those involved with the transfer — including the authorizing agencies on both sides of the border — were aware of the whale's preexisting condition. He said it was also well known that Marineland had "challenges" in caring for its animals.

Media reports state Marineland has been the subject of complaints and investigations, and numerous orcas have died there.

"We secured the best possible future for them by bringing them here," Pasquera said. "Obviously releasing them was not going to be an option. They were born in captivity at Marineland, so bringing them here was the best scenario, and that was something that was verified and agreed upon by various parties on both sides of the border and agencies and veterinary experts and beluga whale research experts."

He said the whale was monitored very closely by veterinary attendants before, during and after the transport: "The situation with the condition was under control, he was stable, and he was stable throughout the transport."

Pasquera said indications once the beluga got settled at the aquarium were that his specific gastrointestinal condition was improving.

"In terms of what ultimately caused this whale to die, we just simply don't have enough information at this time," he said. "We really don't know."

He said Rose doesn't know, either.

"She simply does not have the information and details that we have, and Marineland has, about these whales to speculate one way or the other on that," he said.

There are grief counselors available for members of the Mystic Aquarium community mourning the loss of the beluga whale, according to Pasquera. He noted the whale had been receiving round-the-clock health monitoring, which gave his medical team a lot of time to get attached to the whale.

"We just ask that people respect the fact that we're grieving and not speculate at the things they don't have knowledge of," he said.

e.regan@theday.com