Last week the National Aquarium in Baltimore, Maryland, announced that it may retire its eight bottlenose dolphins. The animals would be moved to a seaside sanctuary—the first one for dolphins in the United States.

Although it's not clear where the sanctuary would be or how it would be created, the idea has met with enthusiasm from conservationists and the public.

The announcement also puts the aquarium at the forefront of a debate about keeping dolphins and whales in captivity—a discussion that gained momentum last year following the release of the documentary film Blackfish, about an orca that kills its trainer at SeaWorld.

Times have changed, and our understanding of the needs of the animals in our care has changed. A