Gregor Robertson has joined a mounting chorus calling for the Vancouver Aquarium to stop holding whales and dolphins in captivity.

The Vancouver mayor lauded the aquarium for its conservation work and ocean research Wednesday but said he wants to see the holding of cetaceans phased out.

“I’m hopeful that the Aquarium and the park board can work collaboratively and come to an agreement on how to achieve this,” Robertson said in an email statement.

Robertson added he doesn’t support a petition calling for a referendum on the issue because it falls under the park board’s authority.

The aquarium shot back with a defense of its practices, arguing its beluga whales and dolphins receive “exceptional care” from its team of scientists, curators, trainers and veterinarian.

“Dolphins and belugas at Vancouver Aquarium play a direct and vital role in engaging people in key ocean issues,” it said in a statement.

“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 hasn’t participated in capturing wild dolphins or whales since 1996, when the practice was banned in a park bylaw.

All of the animals obtained since have been rescued or adopted from other aquariums.

“The aquarium is the only facility in Canada that can rescue, rehabilitate and provide a long-term home to marine animals that are deemed non-releasable by appropriate government authorities,” it said.

The referendum petition has already been signed by more than 12,000 people, including Vancouver park board members Sarah Blyth and Constance Barnes.

“The more you learn, you just feel sad. Look in the window there and you just feel [whales and dolphins] should be in the wild,” said Blyth.

Blyth said since the documentary Blackfish premiered, she’s been getting more emails from concerned residents. She believes the key issue is keeping the aquarium a vibrant destination without captive whales and dolphins.

The aquarium is in the process of finishing the first phase of an almost $100 million expansion. The renovations include larger whale and dolphin tanks. With the expansion came a renewed lease with the park board until 2029.