SAN DIEGO — An effort to free whales from SeaWorld by claiming they were enslaved made a splash in the news but flopped in court Wednesday.

A federal judge in San Diego dismissed an unprecedented lawsuit seeking to grant constitutional protection against slavery to a group of orcas that perform at SeaWorld parks, saying the 13th amendment applies only to humans.

U.S. District Judge Jeffrey Miller stopped the case from proceeding two days after he became the first judge in U.S. history to listen to arguments in court over the possibility of granting constitutional rights for members of an animal species.

"As `slavery' and `involuntary servitude' are uniquely human activities, as those terms have been historically and contemporaneously applied, there is simply no basis to construe the Thirteenth Amendment as applying to non-humans," Miller wrote in his ruling.

People for the Ethical Treatment of Animals filed the lawsuit in October and named five whales as plaintiffs. PETA says the wild-captured orcas are enslaved by SeaWorld because they are held in concrete tanks against their will and forced to perform in shows at its parks in San Diego and Orlando, Fla.

SeaWorld called the lawsuit baseless and a waste of the court's time and money.

"We cannot hope that this is PETA's last publicity stunt but we can now refocus our energy in more positive and constructive ways: delivering high quality education experiences to our guests and providing the highest possible standard of care to our animals," spokesman Dave Koontz wrote in a statement.

Legal experts say it opened an interesting debate about the expansion of animal rights.

PETA attorney Jeffrey Kerr says his organization does not plan to give up the fight to protect the orcas, but he did not specify the next action.

PETA is known for its provocative anti-fur and pro-vegan campaigns to engage the court of public opinion.

"Today's decision does not change the fact that the orcas who once lived naturally wild and free, are today kept as slaves by SeaWorld," Kerr said in a statement. "PETA will regroup and determine how to continue to work for the legal protection they deserve."

SeaWorld denies any mistreatment of the animals and says its parks have raised awareness that has helped conservation efforts. It also says it has rescued orcas injured in the wild.