The Vancouver Aquarium is currently undergoing a $100-million expansion project, which will include bigger whale and dolphin tanks once completed.

But earlier this week, Vancouver Mayor Gregor Robertson put his weight behind a growing movement calling on the Vancouver Aquarium to stop holding whales and dolphins in captivity.

“My personal view is I’d like to see a phasing-out,” Robertson told CTV Vancouver. “But it isn’t up to me, it’s up to the park board and the aquarium to work that out.”

Vancouver Board of Parks and Recreation member Constance Barnes echoed Robertson’s statement, saying keeping the animals in captivity is “not acceptable.”

“It’s not right to have these amazingly beautiful beasts caged up,” she told CTV Vancouver.

The Vancouver Aquarium responded to Mayor Robertson’s remarks on Wednesday, saying that dolphins and belugas at the aquarium “play a direct and vital role in engaging people in key ocean issues.”

“In addition, with the rapid environmental changes in the Arctic where belugas live, continued research, much of which must be done in marine science centres like the Vancouver Aquarium, is critical to their future,” the aquarium added.

The aquarium, which no longer holds orcas, has two dolphins and two beluga whales, but says it hasn’t captured wild dolphins or whales since 1996. Instead, it rescues or adopts from other aquariums.

Vancouver Board of Parks and Recreation commissioners will be facing mounting pressure to confront the Vancouver Aquarium, however, as a petition calling for a referendum on the issue of keeping whales and dolphins in captivity has already been signed by more than 12,000 people.

The mayor said he didn’t add his support to the referendum since it falls under the park board’s authority.

The issue of whales and dolphins in captivity has been fueled by the hard-hitting 2013 documentary “Blackfish,” which sparked public outcry against the use of orcas for entertainment.

The documentary prompted California lawmakers to propose a bill that would end killer whale shows. Aquariums such as SeaWorld, however, argued against the legislation, saying it was based on misinformation. The bill is currently on hold.

The issue of holding cetaceans in captivity will likely be considered by Vancouverites this November when electors head to the polls, as Robertson seeks a third term in office.

With files from CTV Vancouver’s Melanie Nagy