VANCOUVER -- The Vancouver Aquarium has launched a legal challenge over the city park board's attempt to prohibit the breeding of whales, dolphins and porpoises at the popular tourist attraction.

The aquarium's request for a judicial review, filed Wednesday, is the latest development in an ongoing and highly contentious debate in the city over the ethics of keeping cetaceans in captivity.

The board passed a motion last month that, among other things, would prohibit the breeding of cetaceans in Vancouver parks unless the animals are considered a threatened species. The board stopped short of banning captive cetaceans altogether, which some critics had hoped for.

The aquarium is located in Stanley Park, which is overseen by the board.

Aquarium president John Nightingale said the facility is asking the court to overturn the motion because, it argues in its legal challenge, the park board acted outside its jurisdiction.

"The aquarium is exercising its legal right to challenge the validity of those resolutions in court," he said. "In short, we believe that caring for animals in the aquarium should be left to the experts."

Nightingale also accused the park board of passing the motion for political reasons.

"Frankly, we resent being turned into a political football," he said.

Last month's vote followed a special meeting in which the park board heard the opinions of 133 people on whether the animals should stay in the aquarium.

Nightingale said the aquarium has never intentionally bred the cetaceans, but when possible, it keeps the animals in mixed-sex groups to simulate how they would live in nature.

He said forcing the creatures to avoid breeding could require the aquarium to segregate the creatures by sex, which would be harmful because cetaceans are highly social.

"That would be an inhumane thing to do," said Nightingale.

He said sterilizing the animals would not be an option because the procedure could be dangerous for the creatures.

"There are lots of indications you cannot use contraceptives long-term," Nightingale said.

If the park board resolution went into effect, none of the current cetacean displays would be immediately affected by the breeding ban.

The aquarium has two Pacific white-sided dolphins, two harbour porpoises and two beluga whales.

With the exception of the porpoises, all the animals are of the same sex, making it impossible for them to breed, the aquarium said. The porpoises are still juveniles and would not be able to mate for some time.

But once renovations are finished, the aquarium intends to bring back some of the five belugas it has loaned out to facilities in the United States, and it's possible they could mate, Nightingale said.

Nightingale also said the aquarium may consider artificial insemination programs to save endangered species in the future.

Aaron Jasper, the chair of the park board, said the board intends to fight the challenge.

"Their court challenge is a challenge to a municipal government to be able to write, amend and change bylaws," said Jasper. "We have been elected by Vancouver residents to maintain and to govern our parks and we intend to continue with that mandate."

He said the board's motion balances the public's desire to stop keeping cetaceans in captivity with the aquarium's goals, he said

The board does not feel its decision affects conservation, research or education, Jasper said.

Vancouver Mayor Gregor Robertson has previously said he opposes keeping the animals in captivity. His office directed calls about the issue to the park board.

Currently, the aquarium cares for rescued animals that can't care for themselves in the ocean or those that were born in captivity.

The park board motion would also create an oversight committee that would act as a watchdog over the aquarium, and would direct park board staff to work with the aquarium to find alternatives to putting cetaceans on display.