Whales and dolphins can no longer be bred or kept in captivity under new legislation that was passed in the House of Commons Monday.

The legislation, dubbed the “Free Willy” bill by its proponents, marks a new era in animal-rights law. For the first time, Canadians can be found guilty for possession of marine mammals – not just for poor treatment.

Barbara Cartwright, the CEO of Humane Canada, an animal-welfare group, said the bill is a watershed moment for Canadians, who she said are visiting institutions that host captive whales and dolphins far less than in the past.

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“This legislation heralds a change in how Canadians are thinking,” Ms. Cartwright said.

The bill began its journey through the legislative process in 2015, when then-Liberal senator Wilfred Moore, the original sponsor, presented it as a private member’s bill in the Senate.

Mr. Moore said the bill was a result of encouragement from his son after the two watched Blackfish, a documentary about captive killer whales.

“[My son] said, ‘Dad, can you do something about that?’ And I thought ‘Well, I can try,’ ” Mr. Moore said.

The bill includes a grandfather clause that will allow marine institutions to keep mammals that were born or conceived before the legislation was passed. Currently, Marineland in Niagara Falls, Ont., and the Vancouver Aquarium are the only institutions in Canada that host cetaceans, the scientific term for whales, dolphins and porpoises.

The bill also prohibits the import and export of marine mammals in Canada, except for scientific research or for the “best interest” of the mammal.

Marineland said in a statement Monday that the bill affirms that having cetaceans living at Marineland doesn’t amount to cruelty.

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Marineland also said the legislation amends the Criminal Code to include exemptions, which clarifies its role as a caretaker for the cetaceans currently residing at the facility.

The Vancouver Aquarium last year announced its commitment to divesting itself of its marine mammals.

At a press conference after the bill’s passing, Camille Labchuk, executive director of Animal Justice, an advocacy organization for animal protection, said there needs to be a discussion about what “best interest” means. Ms. Labchuk also said that Marineland and the Vancouver Aquarium must seek additional permits for any mammals that haven’t been shipped already, despite pre-existing permits.

Ms. Cartwright said she hopes any cetaceans that remain in captivity under the grandfather clause are eventually sent to sanctuaries.

The bill has already passed the Senate and is awaiting royal assent before it becomes law.

Three other pieces of legislation currently before Parliament deal with the treatment of animals; they deal with banning shark fin imports; sexual assault and all forms of animal fighting; and cosmetic testing on animals.

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“It’s certainly an exciting time and these bills have important measures that are going to put Canada into a leadership position when it comes to animal-welfare legislation,” Ms. Cartwright said.