A state government report released on Friday recommends allowing SeaWorld to expand its killer whale facility at its San Diego park, outraging environmentalists who say the larger tanks could be used to breed more orcas to be kept in captivity.

The staff of the California Coastal Commission made the recommendations before the regulatory board’s 8 October meeting where it is scheduled to vote on SeaWorld’s permit request for the expansion.

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The staff recommends attaching nine conditions to the permit that include requiring SeaWorld to not house newly captured orcas at its San Diego location.

Tens of thousands of people have written to the commission in opposition to the plans, calling the expansion a marketing ploy to boost its plummeting marine theme park attendance and not address their belief that orcas should not be in captivity at all. Attendance has dropped since the release of the popular 2013 documentary Blackfish, which suggested SeaWorld’s treatment of captive orcas provokes violent behavior.

Some environmentalists fear the bigger tanks will be used by SeaWorld to breed more orcas.

“This is not limiting them in any way. In fact, this would do the opposite,” said Sara Wan, a former commissioner who now works as a consultant for the Animal Defense Legal Fund. “They could breed all the orcas they want with this facility and ship them all over the world.”

As part of its expansion, SeaWorld proposes demolishing portions of its 1995 “Shamu” killer whale facility, which included a 1.7 million gallon pool. In its place would be a 5.2 million gallon pool and a smaller 450,000 gallon pool. There would be no changes to seating at the existing stadium. SeaWorld says in its proposal that the orca population housed at the new facility would not significantly increase.

The nine conditions would not restrict the breeding program. Under the conditions, SeaWorld could not house any orcas captured in the wild after February 2014 at its San Diego location, with the exception of rescued killer whales approved by one or more government agencies for rehabilitation or deemed by one or more governmental agencies as unfit for release into the wild.

It also could not use any genetic material from wild whales caught after February 2014. The conditions would only apply to its San Diego park, since the coastal commission only has jurisdiction over that location.

SeaWorld says it would agree to those conditions and has not collected a killer whale in more than 35 years. About 80% of the killer whales in its care were born at SeaWorld parks or other zoos.

The project, called Blue World, would open in 2018 if approved. SeaWorld has also promised to fund additional research on the animals along with programs to protect ocean health and whales in the wild.

The company, based in Orlando, Florida, said the renovations had been in the works for some time and were not in response to the documentary Blackfish.

The company’s stock has fallen 50% over the past two years, and attendance at the original SeaWorld, in San Diego, has lagged behind its other theme parks. Legislators in California also proposed banning performances featuring orcas, which kept criticism of SeaWorld in the news. The company has blamed competition from other theme parks for its overall drop in attendance of about 2%.

SeaWorld says the animals are well treated and their shows help garner support for conservation and research.

The company sent the commission tens of thousands of postcards from people supporting the expansion of the killer whale environment.