A team of experts has said dolphins should be given the same rights to life and liberty as humans because of their high levels of intelligence and self-awareness.
Scientists meeting in Canada were told the mammals deserved to be treated as non-human "persons" who were given the same ethical considerations as humans.
A small group of experts in philosophy, conservation and dolphin behaviour were canvassing support for a "Declaration of Rights for Cetaceans".
It is hoped recognising cetaceans' rights could mean an end to whaling and the captivity of dolphins and whales, or their use in entertainment.
The move is based on years of research that has shown dolphins and whales to have large, complex brains and a human-like level of self-awareness.
This has led experts to conclude that the animals are "people" in a philosophical sense, which has far-reaching implications.
Ethics expert Professor Tom White, from Loyola Marymount University , Los Angeles, author of In Defence Of Dolphins: The New Moral Frontier, said: "Dolphins are non-human persons. A person needs to be an individual. If individuals count, then the deliberate killing of individuals of this sort is ethically the equivalent of deliberately killing a human being.
"The captivity of beings of this sort, particularly in conditions that would not allow for a decent life, is ethically unacceptable; commercial whaling is ethically unacceptable.
"We're saying the science has shown that individuality, consciousness, self-awareness, is no longer a unique human property. That poses all kinds of challenges."
The declaration, originally agreed in May 2010, contains the statements "every individual cetacean has the right to life", "no cetacean should be held in captivity or servitude, be subject to cruel treatment, or be removed from their natural environment", and "no cetacean is the property of any state, corporation, human group or individual".
It adds: "The rights, freedoms and norms set forth in this declaration should be protected under international and domestic law."
The US authors brought their message to the annual meeting of the American Association for the Advancement of Science (AAAS) in Vancouver, Canada, the world's biggest science conference.