California has become the first state in the US to ban performances by captive killer whales. The law, which will come into effect in 2017, also prohibits breeding the animals in captivity.
The move follows mounting protests against keeping the massive mammals in restrictive pools.
SeaWorld, which has killer whales, or orcas, at its park in San Diego, ended its breeding programme in all of its American theme parks in March after an outcry over the depiction of their capture and lives in captivity revealed in the 2013 documentary Blackfish.
The documentary also recounted the death in 2010 of SeaWorld trainer Dawn Brancheau by a killer whale named Tilikum. The whale may now be dying of an incurable lung infection.
Starting from June 2017, under the new Orca Protection and Safety Act, killer whales already in captivity may remain in the state, but they can only be used for "educational presentations".
SeaWorld plans to retain its 11 orcas but will use them for "educational orca encounters" beginning in 2017 rather than doing stunts for audiences, according to a company statement. Because most of the animals were born in captivity, handlers fear they would not survive in the wild.
"Most of SeaWorld's orcas were born in a zoological setting and the environmental threats in our oceans like oil spills and pollution are huge dangers for these animals," said a company statement. "The best, and safest, future for these whales is to let them live out their lives at SeaWorld."
The new law allows the rescue of killer whales for rehabilitation or research purposes but it stipulates that they cannot be used for breeding, performance or entertainment, and encourages all to be released back into the wild if at all possible.
"As more and more members in the public in this post-Blackfish era are deciding to turn away from entertainment, the future holds a more hopeful animal-friendly entertainment outcome," Carney Anne Nasser, senior counsel for wildlife and regulatory affairs at the Animal Legal Defense Fund, told the National Geographic.
The next states that animal activists hope will consider a similar bill are Texas and Florida, which both have have marine parks with orcas.
"It's only a matter of when, not if, the use of animals in entertainment will become a relic of the past," said Nasser.