What would be a situation where an animal (specifically a dolphin, I'm trying to get all the nuances of the captivity debate) has been successfully rehabilitated but can't go back to the wild?
I asked someone who works with stranded marine mammals because I wanted to make sure that I didn’t get it wrong (and because it’s hard to find official documents regarding it that aren’t low-resolution scans). Their input is in quotes, my commentary is not.
First off, it’s important to note that the rehabilitators don’t get to decide if the animal is unreleasable - all stranded marine mammals are under the jurisdiction of the National Marine Fisheries Service, a subset of National Oceanic and Atmospheric Association. They also are the ones who enforce the Marine Mammal Protection Act, which is the federal law (supposedly) prevents people from approaching, touching, swimming with and/or generally bothering marine mammals. So no matter where in the country an animal is, or what facility it is cared for at, the scientists with NMFS make the call about if it is releasable.
Factors that can make an animal unreleasable include age, injuries or physical conditions that prevent everyday function, chronic but manageable conditions, re-stranding, or human intervention/interference.
Age: “A cetacean determined to be under two years of age that strands without its mother (or the mother subsequently dies in rehab) will almost never be considered for release because they are still dependent calves.”
Most dolphins have a really strong bond with their mothers for a least the first two years of life, and still aren’t “adults” for another number of years. Unassisted babies in social species don’t survive in the wild very well, no matter what taxa.
Injury or Impairment: “Animals with significant hearing loss, blindness, injuries that prevent or greatly impede locomotion, or animals found to be suffering from chronic but medically manageable conditions will not be released.”
Some good examples in captivity currently are a rough-toothed dolphin with severe scoliosis, a number of deaf conspecifics, and Winter, the famous bottlenose dolphin who has a custom tail prosthetic to help her compensate for an injury sustained as a calf.
Restranding: If an animal can’t survive well enough to need to be rescued more than once, it’s probably not going to get released another time.
Human involvement: “Places like Panama City Beach have a huge issue with people feeding dolphins and petting them from boats. Some of these “beggar dolphins” are known and recognizable. If one of these animals got hit by a boat and had to be brought in and it was a known and identifiable beggar dolphin, I don’t think he or she would go back out. Other dolphins in the area imitate their behavior and add to the danger.”
These are all assessed independently and in combination with each other, so a single issue may not be the sole reason for an animal being deemed unreleasable. For instance:
“Panama, an old female dolphin who lived with Winter at Clearwater Marine Aquarium, stranded in Panama City Beach very underweight and ill. She was later found to be deaf, but she was also a suspected beggar dolphin and that alone may have been enough to have her declared non-releasable even if she wasn’t deaf. She may actually have been begging because she was deaf.”