Health and physical condition 2. Use of sonar 3. Ability to catch fish 4. But not all of them. Some dolphins have been in captivity too long and have forgotten or lost the skills needed to survive in what was once their home.
Habitat dictates behavior.
For them, it's too late. Some years ago, for instance, I had occasion to study a dolphin in Nassau who had been in captivity for a long time and was now quite mad. On one side of the wooden gate was the area where he was protected, admired and watched with fascination, sometimes by hundreds of people. He was fed all he wanted to eat and was clearly master of his world. On the other was the sea, his natural home.