Shares in the amusement park SeaWorld fell 33% after a 6-7% decline in the company’s revenues was forecast – with falling attendances driven in part by the negative publicity surrounding the documentary film Blackfish.

The film follows Tilikum, an orca kept in captivity by the amusement park’s Florida outpost, who would perform in acrobatic displays for visitors. He became involved in the deaths of three people, with the documentary suggesting that this violence was driven by the conditions of his captivity, including incidents of harassment by fellow orcas. The film also claims that orcas’ lifespan is shortened by being kept in captivity.

Blackfish became extremely popular, getting 21m viewers in the US alone when it aired on CNN. It prompted protests at SeaWorld following its release, at both its Florida and San Diego parks, and various music artists who were set to play at SeaWorld cancelled, including Willie Nelson and Trisha Yearwood.

The director of Blackfish, Gabriela Cowperthwaite, backed a recent motion by a member of California’s state assembly to outlaw orca performance. In April the vote was delayed so that a period of review, potentially lasting as long as 18 months, can get under way. James Atchison, SeaWorld chief executive and president, acknowledged the impact of the bill on the company’s bottom line: “In California, our challenge is related more to the media attention from the legislative initiative. That was probably our biggest headwind in California.”

Expected revenues of $445m for the second quarter of the year were not met, only reaching $405m. “Until today’s report we were willing to . . . take SeaWorld’s word that there was no discernible impact,” said Tim Nollen of investment firm Macquarie. “This report was notably worse than previous reports.”

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Following a strong IPO last year which raised over $700m, just before the film’s wider release, some of SeaWorld’s shareholders subsequently offloaded their shares. Its chairman sold over a million dollars’ worth, and owners Blackstone Group sold its majority stake, going from 63% to just 25% ownership.

According to Louie Psihoyos, who directed dolphin documentary The Cove, Blackfish also impacted upon Finding Dory, the forthcoming sequel to Finding Nemo. Psihoyos said that the film’s directors met with Cowperthwaite, and subsequently reworked a SeaWorld-esque park that features in the film.

Orca trainers however have come out fighting against the film, with former trainer Mark Simmons calling it a “crusade against SeaWorld and zoological care in general... engineered by a perfect marriage between sensational animal rights organizations and disgruntled ex-SeaWorld employees.” Even the family of Dawn Brancheau, one of Tilikum’s victims, distanced themselves from the film, saying: “Dawn would not have remained a trainer at SeaWorld for 15 years if she felt that the whales were not well cared for.”