SeaWorld, the US theme park operator, said on Thursday that it has decided to end its killer whale breeding program. This means the current killer whales at the theme park would be the last generation. SeaWorld, which operates 12 theme parks across the US, has been facing severe criticisms for its alleged mistreatment of the killer whales, also known as orcas.

Animal activists have urged the company to release the killer whales into the wild, but SeaWorld claimed that the orcas are likely to die in that condition.

“For as long as they live, the orcas at SeaWorld will stay in our parks,” Joel Manby, president and CEO of SeaWorld, wrote in an op-ed article in the Los Angeles Times. “Most of our orcas were born at SeaWorld, and those that were born in the wild have been in our parks for the majority of their lives,” he wrote. “If we release them into the ocean, they will likely die.”

Manby added that the park hasn’t collected a killer whale from the wild in four decades and the current generation would be the last in the care of the theme parks.

The company has previously announced that it will be ending its live orca shows soon. The company also said on Thursday that it will drop its plan for a US$100 million (AU$132 million) called “Blue World.” The project would have expanded its orca habitat at the theme park in San Diego.

“SeaWorld has been listening and we’re changing,” the company said in a statement, as quoted by NBC News. “Society is changing and we’re changing with it. SeaWorld is finding new ways to continue to deliver on our purpose to inspire all our guests to take action to protect wild animals and wild places.”

Animal rights group People for the Ethical Treatment of Animals said that the Thursday’s announcement was a “payoff” of its campaigns against SeaWorld’s policies.