Gabriela Cowperthwaite was a mom who took her twin sons to SeaWorld before the death of a killer whale trainer prompted her to make her 2013 documentary "Blackfish."

She never expected it to help persuade the US theme park operator to stop breeding killer whales and end its signature "Shamu" whale entertainment shows.

"I think 'Blackfish' struck a nerve," the Los Angeles-based director said on Thursday. "I originally came into the film trying to explore the trainer relationship and experience. I thought of myself as a story teller that would pull back the curtain on some things, but I didn't think the documentary would effect change."

Animal activists and others were quick on Thursday to give credit to "Blackfish" for what Cowperthwaite called a "giant step" by SeaWorld both in halting its orca breeding program and investing $50 million to advocate for an end to commercial whaling and seal hunting.

"Huge respect to @blackfishmovie for putting orca captivity at @SeaWorld on the agenda" Greenpeace UK Oceans said on Twitter.

Melissa Silverstein, founder of the website "Women and Hollywood," said SeaWorld's action shows the impact of film.

"If you think a movie can't make a difference, see @blackfishmovie," Silverstein said on Twitter. "Congrats on getting @SeaWorld to change its policies towards Orcas."

"Blackfish" has taken only a meagre $2 million at the North American box office, but after screenings on CNN, on demand digital services and in schools, it has been seen by more than 60 million people, Cowperthwaite said.

Cowperthwaite interviewed former SeaWorld trainers and whale experts to paint a moving portrait of the Orlando theme park's orca Tilikum, who killed trainer Dawn Brancheau in 2010, and how he was captured in the wild in 1983 at the age of two.

The Hollywood Reporter described "Blackfish" as a "damning indictment of the SeaWorld theme park franchise."

By the end of 2013, Willie Nelson, Heart and Bare Naked Ladies were withdrawing from music events organised by SeaWorld and Joan Jett and others were asking SeaWorld to stop blasting their music during its "Shamu" whale shows. Attendance at SeaWorld parks dropped and the company's shares fell by about 11 percent in the past year.

Cowperthwaite, who has visited dozens of schools in the past three years, said perhaps children had the biggest influence in changing minds at SeaWorld.

"I think they have been the ones to guide their parents on where to go for vacations. They're the ones who say, 'We can't go there anymore,'" she said.

SeaWorld has been critical of the movie over the years and made no mention of it on Thursday. However, Seaworld Entertainment Inc (SEAS.N) Chief Executive Officer Joel Manby acknowledged in an op-ed in the Los Angeles Times that "a growing number of people don't think orcas belong in human care."