Which is better for SeaWorld’s whales: glass-and-concrete enclosures or ocean sea pens?

There will be no “Free Willy” happy ending for the killer whales at SeaWorld San Diego.

Since the 2013 release of a documentary that accuses the company of neglecting and abusing its orcas, animal rights activists have demanded the San Diego theme park free its 11 killer whales.

But marine biologists – including SeaWorld critics – agree the whales probably will never be released to the open seas.

Even if the whales don’t spend the rest of their lives in the theme park, performing for capacity crowds, the closest they’d get to freedom would be retirement in ocean coves separated from open water by netting. There, they would be fed and cared for by humans for the rest of their lives.

“They are not good candidates for release to the wild, either because they were born in captivity or because they have been in captivity for a very long time,” said Naomi Rose, a marine mammal scientist for the Animal Welfare Institute.

No enclosed sea pens exist to hold all 11 whales, either as a group or individually. And the cost of building such pens could reach $5million each, with staffing costs of up to $500,000 a year for each pen, Rose said.

Although animal rights groups have pushed the idea of moving SeaWorld’s whales to sea pens, the discussion may be merely academic because SeaWorld Entertainment Inc., the parent company of the San Diego theme park, has rejected the idea of giving up its whales, saying they are safer living in the parks’ concrete and glass enclosures.

“They would not be better off in sea pens than where they are now,” said Chris Dold, the lead veterinarian for SeaWorld Entertainment. “We would not ever feel comfortable putting our whales into that setting.”

Dold and other SeaWorld supporters say sea pens could expose whales to ocean toxins, viruses and harsh weather that long-captive whales can’t withstand.

“There are so many reasons why sea pens are not a panacea,” said Kathleen Dezio, executive director of the Alliance of Marine Mammal Parks and Aquariums, an international accreditation group.

The call to release the whales has grown louder since the 2013 release of the documentary “Blackfish,” which charged SeaWorld’s parks with abusing and neglecting its killer whales.

SeaWorld Entertainment has 23 orcas in three parks across the country. (An 18-year-old orca died at SeaWorld San Antonio in December after a monthslong illness.) Miami Seaquarium has one killer whale.

Facing customer blowback from the documentary, SeaWorld San Diego proposed a $100million plan last year to double the size of its whale enclosure, under a project called Blue World. The project won the approval of the California Coastal Commission in October, but the panel added the condition that SeaWorld end its captive breeding program and halt the transfer of its whales in and out of the park.

SeaWorld has put Blue World on hold and has filed a lawsuit challenging the commission’s authority to impose the no-breeding conditions.

During the commission hearing, SeaWorld critics waved banners calling for the release of the whales. Activists said the captive whales are tortured and driven insane by their concrete enclosures, insisting that the whales would be happier in sea pens.

A petition on change.org has collected more than 220,000 signatures, calling for SeaWorld Orlando to release a whale featured in “Blackfish,” Tilikum, to a sea pen.

The most often cited example of a captive orca released to a sea pen is Keiko, the whale featured in the 1993 movie “Free Willy.”

Keiko was captured off Iceland in 1979 and trained to perform at theme parks. After years at a theme park in Mexico City, the whale was transported to a sea pen in Iceland in 1998. Experts disagree on whether the move was a success.

Caretakers say they spent up to $300,000 a month to care for and attempt to train the whale to feed itself in the wild.

During a short swim outside of the pen, accompanied by caretakers on a ship, Keiko swam away and turned up in a deep inlet in Norway where he was found cavorting with children and fishermen along the shore. The whale died a few months later of acute pneumonia.

Mark Simmons, a former SeaWorld trainer who was hired to assist with Keiko in Iceland, said the Keiko experience showed sea pens are not a safe environment.

Simmons said storms and strong currents in Iceland damaged Keiko’s sea pen, creating so much noise and vibration that it likely unsettled the whale.

Dold, SeaWorld’s chief veterinarian, said sea pens can also expose whales to viruses passed on through other fish in the pens or toxins and oil spills that wash in with the tide.

“It’s very hard to eliminate all of those threats that exist out there,” he said. “They are particularly dangerous to a precious group of killer whales born in a zoological setting such as ours.”

Animal rights activists say critics dismiss the idea because they don’t want to consider an alternative to keeping the whales captive.

“They are blindsiding it because they don’t want a solution,” said Ingrid Visser, founder of the Orca Research Trust, a New Zealand-based nonprofit dedicated to education and the research of orcas. “We can put a man on the moon, surely we can move an animal out of a concrete life.”

Howard Garrett, founder of the Washington state-based Orca Network, has an idea of what such an operation would cost.

He filed a lawsuit against Miami’s Seaquarium in hopes of getting a judge to order the release of its only orca, Lolita.

Garrett helped draft a 17-page plan that outlines how to transfer Lolita from the park to a protected cove in the San Juan Islands.

The move would require a stretcher hooked to a crane to lift the whale from its pen. Then, a truck with a specially made cradle would haul the whale to Miami-Dade International Airport, where it would be loaded onto a commercial carrier or military aircraft.

The transportation cost alone would be up to $200,000, according to Garrett’s plan, plus as much as $1.5million to care for the whale for the first year.

Seaquarium General Manager Andrew Hertz said Lolita is in good health.

“It would be reckless and cruel to treat her life as an experiment and jeopardize her health and safety in order to appease a fringe group,” he said.

Simmons, the former SeaWorld trainer, argues the money proposed for the care of whales in sea pens could be better spent saving many more endangered animals such as elephants.

“I don’t accept the premise that there is a problem,” he said. “They are in a much better environment where they are.”

Sea pen advocates counter by saying money needs to be raised to protect captive killer whales.

“It’s not an either-or proposition,” said Lori Marino, executive director of the Kimmela Center for Animal Advocacy. “I don’t think if we focus on this, we are saying, ‘To hell with everyone else.’”