Dolphins typically live from about 17 to about 25 years, with no significant difference between dolphins in captivity and those in the wild. Dolphins can live to about 50 years old, and scientists have not figured out why they usually do not even when provided with veterinary care and protection from predators.
Dolphins both in captivity and in the wild develop many of the same ailments that humans and other animals do, such as cancer, heart disease and respiratory problems. They succumb to viruses, as well as fungal and bacterial infections. Parasites such as roundworms, tapeworms, flukes and lice cause problems for dolphins. Wild dolphins can be attacked by sharks and stingrays. They also are prey for orcas, or killer whales, even though the orca is a member of the dolphin family.
Humans cause a large number of dolphin deaths in the wild. Many thousands of marine animals are accidentally caught and drowned in fishing nets each year. Dolphin hunting occurs in nations such as Japan, Peru and Taiwan. Humans have also disrupted dolphin habitat with boat traffic and pollution, resulting in dolphins eating refuse such as plastic bags and cigarette butts, absorbing carcinogens and being killed by boat propellers. Dolphins become overly accustomed to boats, increasing the chances they can be injured or killed by one.
A major problem for dolphins in the wild is humans feeding them, although this is illegal in many countries, including the United States. People feed dolphins food that is not healthy or natural for them, such as hot dogs and doughnuts. They also feed dolphins fish that are not fresh. In addition, when people feed fish to dolphins, these intelligent animals learn to become scavengers instead of hunters, following fishing boats and pulling fish off lines, sometimes consuming the fishing lines and hooks as well. Feeding wild dolphins in the United States is a prohibited behaviour. Some areas of dolphin habitat are notorious for this problem, particularly southern Florida, and officials say this is mainly due to lack of education among tourists.
National Marine Fisheries Service marine biologist Thevor Spradlin used an animal called Dolphin 56 as an example of problem feeding behaviour. This dolphin spent 20 years in specific areas in Florida and developed a habit of begging from boaters. Then he began travelling up the coast, apparently for further opportunities, and was observed as far north as New York.
Dolphins are not always gentle as people tend to think they are. For instance, in 1999 a dolphin bit a 14-year-old girl near Sarasota who had reached out to pet the animal. The dolphin probably had expected food.
Some environmental and animal rights groups are pressing for the elimination of dolphin captivity programs. They see the lack of extended longevity among captive dolphins as evidence that this type of life is stressful. They theorise that captive dolphins should live longer because they are free from predators, have veterinary care to prevent and eliminate disease and parasites, and are given plenty of healthy food. The activists say dolphins should be swimming for miles every day the way they do in the wild, interacting with other dolphin pods and foraging for food.