The principle criterion for dolphin habitat is food. They eat fish, squid and crustaceans. Dolphins choose their habitats based on stable food supply, not the particular species that they feed upon. They hunt in small groups called pods, families of seven on average. Several pods will organize into a herd if a local threat requires greater numbers for security. Dolphins hunt individual prey, and they socially organize hunts that exploit large schools of prey animals.
Dolphins are divided into onshore and offshore species, or shallow-water and deepwater species. Deep-water species predominate where shallow water produces little food. Deep-water dolphins are more apt to remain in the same region, where prey species tend to remain stable throughout the year. Shallow-water dolphins are more likely to follow seasonal migrations of prey fish and to adjust their locations based on water temperature.
Unlike prey animals bound to habitats by instinct, the highly intelligent dolphin can think creatively and solve problems. In this respect, the dolphin resembles humans: It can adapt to dramatic changes in habitat by changing survival strategies without waiting for evolution to select a more survivable behavior.
Dolphins can selectively share habitats with humans. If an area's human population proves hostile, the dolphins can migrate away. If the humans are amicable, the dolphins can remain, and even cooperate with them in the acquisition of food.
Pacific dolphins inhabit the regions from Japan to Australia, and from Chile to California. Atlantic dolphins inhabit the coastal waters from South Africa to Norway, and from Patagonia to Nova Scotia. Indian Ocean dolphins occupy the waters from Indonesia to southern Africa, including the Red Sea. Dolphins also inhabit the Mediterranean Sea and the Black Sea. The most abundant dolphin populations in the United States extend from Cape Cod down along the Atlantic Coast and along the entire Gulf of Mexico.