SeaWorld should release its remaining orcas now it has decided to end its breeding programmes, People for the Ethical Treatment of Animals (PETA) says.
Last week, SeaWorld in the US announced that it would end all orca breeding programmes.
PETA Australia campaign coordinator Claire Fryer told Sunday Morning it was a step forward, but she would like to see the orcas released into ocean sanctuaries.
"[There] they can enjoy a more natural life outside their prison tanks."
However, SeaWorld has said the animals would likely die if they were released.
Ms Fryer said the marine parks should focus on the rescue and rehabilitation of animals, and protecting them in the wild.
Sea World in Australia was not affiliated with SeaWorld in the US, she said, and the Australian park took in about $A133 million ($NZ148m) in gate sales annually.
"Of that they spend $A1m on rescue, research and rehabilitation - that is three quarters of 1 percent."
For many decades, orcas, dolphins, seals and many other animals had suffered in confinement, she said.
"These animals don't belong in captivity, and they certainly don't belong in shows where they are performing mindless tricks for fish."
SeaWorld, which has 12 parks across the US, has faced heavy criticism over its treatment of its captive orcas, also known as killer whales.
The 2013 documentary Blackfish focused on a series of violent incidents involving an orca called Tilikum at SeaWorld.
Since the film was released, visitor numbers have fallen at SeaWorld's main theme parks and its share price has halved.
Ms Fryer said the decision to end the breeding programme was based on the fallout from the film, and was a way to improve their public image.
"But of course there are still so many animals who are being bred and enslaved in marine parks and zoos around the world," she said.
SeaWorld described the film as inaccurate, misleading and exploitative and launched a multi-million dollar marketing campaign to rebuild its reputation.
It has previously announced it will phase out live orca shows, and will also scrap plans for a $US100m project called Blue World that would have enlarged its orca habitat at San Diego.