A Hawaii marine park's purchase of Kina, a 40-year-old false killer whale long used in echolocation research, has reignited a debate about captive marine mammals and the places that care for them.

Most of the world's captive cetaceans – dolphins, whales, and porpoises – are now born in marine-park breeding programs, though some are still taken from the wild. Since they're so expensive to care for, even marine mammals used solely for research, like Kina, often end up at attractions like Oahu's Sea Life Park.

Animal-rights activists are calling for the creation of ocean-based refuges, where they say captive marine animals could retire and live a life closer to nature. At least two groups already are working to create such sanctuaries, but experts question whether they can stay afloat.

A closer look at the discussion:

How do marine mammals end up in captivity?

In the past, many were captured from the wild, taken from their family pods and put in marine parks.

In Japan, fishermen would round up scores of dolphins and whales in coves, killing most but selecting some for sale to parks. That fishery has been widely criticized, and most marine parks no longer take its animals.

Kina is believed to be the last living captive animal in the United States taken from a Japanese dolphin drive.

Today, most marine mammals in parks are born in captive breeding programs that originated when wild animals were taken from the ocean.

Parks and aquariums have long moved animals among different facilities to ensure genetic diversity but can now mail sperm from their animals to other parks to ensure a healthy population.

What types of sites hold these animals?

Most research labs around the world that keep marine mammals solely for science have closed because of funding problems, said Paul Nachtigall, founder of the University of Hawaii's Marine Mammal Research Program.

His sea pens where Kina lived at the university were among them. It cost nearly $1 million a year to keep three animals at the lab.

Scientists agree most captive whales wouldn't survive if released into the wild.

Keiko, the orca that starred as Willy in the 1993 blockbuster "Free Willy," is an example of the difficulty involved in releasing captive animals. In the film, a boy helps set the captive whale free. But in real life, Keiko was rescued after the movie because of an outcry over his conditions at a Mexico park. The whale eventually was released into the wild but died a short time later.

What are ocean sanctuaries?

Animal-rights activists are proposing establishing refuges for retiring show animals by netting off large areas of coastal ocean.

The sanctuaries would be much larger and deeper than tanks and pools at family attractions, though the animals would still require constant care. Advocates say the refuges would employ trained staff similar to those at marine parks.

Are any in the works?

Yes. A group called The Whale Sanctuary Project is raising money and hopes to open a sea sanctuary in the coming years.

Project organizers started with about 100 possible sanctuary sites and have narrowed that to 20 locations in British Columbia, Nova Scotia, and Washington state. They will begin pursuing permits for two or three promising locations next year, President Lori Marino said.

The refuge will publish observational data on its whales and dolphins but will not allow in-depth, invasive research on them, Ms. Marino said.

Meanwhile, the National Aquarium in Baltimore last year announced it will retire its dolphins into a "pioneering" ocean pen by 2020.

People for the Ethical Treatment of Animals welcomed the news, and the CEO of the Humane Society of the United States blogged that the head of the aquarium "has done something terribly important."

"There's no model anywhere that we're aware of for this," aquarium CEO John Racanelli told The Associated Press in an interview ahead of the announcement. "We're pioneering here, and we know it's neither the easiest nor the cheapest option."

Would these facilities work?

Mr. Nachtigall says sanctuaries are a great idea, but he worries they'll face the same money problems his research program experienced.

The animals need quality food, veterinary care, and stimulation, which requires a large staff and expensive infrastructure.

"If you're going to care for the animals the best way you can, you have to have the funding to do it," he said. "The best way to bring in funding consistently is to have a paying public."

Marino believes a shift in thinking – and funding – could be the answer. She says her project, which was incorporated last year, has raised about $1 million of the $20 million needed to get off the ground. Continued funding of about $2 million per year would come from donors and public education programs.

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If marine parks collaborated with sanctuary creators, she says, more dolphins and whales could be swimming in the ocean. "I think there are people in the captivity community that want to see this happen."

This story was reported by The Associated Press.