Animal rights activists from People for the Ethical Treatment of Animals (Peta) have voiced support for marine biologists and philosophers who want a bill of rights for whales, dolphins and porpoises.

Proponents of the bill insist that the creatures, who make up the cetacean order of marine mammals, possess such high intelligence that they warrant a universal bill of rights.

Spanish laws already grant some great apes the right to life and freedom animal rights and the group wants the pricinciple extended.

A Peta UK spokesperson said: "In 2008 the Spanish government passed legislation to give some great apes, including chimps, bonobos, apes, and orangutans rights under Spanish law, such as the right to life and freedom.

"It's time that we afforded cetaceans the same kind of protection. We have long known that dolphins are smart, work co-operatively, engage in complex relationships and swim up to 100 miles every day.

"In nature, orcas live their entire lives with their families or pods, close-knit communities.

"We can no longer in good conscience continue to rip these social, emotional, and intelligent animals from their ocean homes and keep them enslaved in small, barren, concrete tanks in dolphinariums."

Experts gathered at the Association for the Advancement of Science meeting in Vancouver to discuss the proposal for a Declaration of Rights for Cetaceans, which would give them the same ethical considerations as humans.

Dr Lori Marino, a professor of neuroscience and behavioural biology at Emory University in Atlanta, Georgia, is behind the proposal.

She said: "We went from seeing the dolphin or whale brain as being a giant amorphous blob that doesn't carry a lot of intelligence and complexity to being an enormous brain with a complexity that rivals our own.

"It's different in the way it's put together, but in terms of the level of complexity it is very similar to the human brain."

Peta has also argued that people need to rethink the way they view intelligent life as society evolves.

Its spokesperson said: "History has shown that as society evolves, the law evolves with it. Animals are no longer regarded as 'things' to dominate, but as breathing, feeling beings.

"Just as we look back with horror at a time when we enslaved people and viewed some as property less deserving of protection and consideration, we will look back on our treatment of animals with shame."

Peta recently tried to sue SeaWorld on behalf of their "enslaved" orca whales.