Longevity & Causes of Death
- Most bottlenose dolphins probably live 20 years or less. This estimate is based on census data from the bottlenose dolphin population off the coast of Sarasota, Florida. The Sarasota Dolphin Research Project (SDRP) is the longest-running study of wild dolphins in the world.
A bottlenose dolphin's average life span is probably 20 years or less. Studies
have shown that dolphins can live into their 40s. This appears to be
a maximum age, comparable to a human living to be about 100.
- SDRP studies have shown that some dolphins live into their 40s; a few females have even lived past 50. This appears to be a maximum age, comparable to a human living to be about 100. Only 1% to 2% of dolphins reach that age.
- Current scientific data show that bottlenose dolphins in Alliance of Marine Mammal Parks and Aquariums (AMMPA) member facilities, such as SeaWorld, live longer than their counterparts in the wild.
- In a facility that is a member of the AMMPA, a one-year old bottlenose dolphin is expected to live an average of more than 25 years.
- As a dolphin ages, it periodically produces growth layer groups (GLGs) of dental material. Age can be estimated by examining a sliced section of a tooth and counting these layers.
- Researchers studying bottlenose dolphin survivorship in the Indian River Lagoon System on Florida's east shore used teeth from stranded animals for age estimation. The researchers decalcified and stained 2-mm (0.8 in.) tooth sections then examined GLGs, which represent annual layers. They placed dolphins into age classes by rounding to the last fully formed GLG.
Age can be estimated by examining a sliced section of a tooth
and counting the growth layer groups of dental material.
Disease & Parasitism
- As in any animal population, a variety of diseases and parasites can be responsible for dolphin deaths.
In 1987 and 1988, more than 740 dead bottlenose dolphins washed ashore on the east coast of the United States. Scientists originally believed that the dolphin deaths were triggered by a naturally occurring "red tide" toxin (originating in small marine organisms called dinoflagellates) combined with bacterial and viral infections. Further analysis concluded that, while exposure to brevetoxin may have made the dolphins more vulnerable to infection, morbillivirus caused the deaths. Morbillivirus is a deadly disease that rapidly affects many animals in the same area at the same time.
- Dolphins may suffer from viral, bacterial, and fungal infections. In addition, they may develop stomach ulcers, skin diseases, tumors, heart disease, urogenital disorders, and respiratory disorders.
- Parasites that typically affect dolphins include tapeworms, flukes, and roundworms.
- Natural predators include certain large shark species such as tiger sharks (Galeocerdo cuvier), dusky sharks (Carcharhinus obscurus), bull sharks (Carcharhinus leucas), and great white sharks (Carcharhinus carcharias). It's not uncommon to see dolphins with shark bite scars.
Dolphins sometimes fall prey to large species of sharks.
- Killer whales (Orcinus orca) may occasionally prey on bottlenose dolphins, but documented cases are rare.
- While stingrays are not dolphin predators, some dolphin deaths have been attributed to trauma, infection, and poisoning from stingray wounds.
- Dolphins, particularly coastal animals, are affected by heavy boat traffic, habitat destruction, and pollution. Industrial and agricultural pollutants in coastal habitats have resulted in high levels of toxins in the water and high concentrations of toxins in dolphin tissues.
- In a study of South African dolphins, researchers found that first-born calves acquired 80% of their mother's accumulated toxins.
- Accumulation of toxins in body tissues, even at low levels, may make dolphins more vulnerable to disease or even death.
- In the past, bottlenose dolphins have been taken directly for meat, leather, oil, and meal (for fertilizer and animal feed). Hunting still occurs in various parts of the world including Peru, Sri Lanka, Taiwan, and Japan.
- Fisheries interactions.
- In the course of fishing operations, gear and nets can accidentally entangle and injure or drown dolphins. Dolphins that are injured or killed and discarded in the course of fishing operations are called bycatch. Experts have concluded that it's likely hundreds of thousands of marine mammals are killed as bycatch each year. The incidental capture of whales and dolphins in fishing gear is one of the most significant threats to some bottlenose dolphin populations. In the United States, when data indicate that the bycatch of a species exceeds its sustainable removal threshold, experts must develop and implement a plan for reducing bycatch. As a result, the bycatch of whales has declined since 1995.
- In some areas, prey populations become overfished, leading to depleted populations of dolphins. In the Mediterranean and Black Seas, for example, prey depletion by commercial fisheries caused significant drops in populations of bottlenose dolphins.
- When catches decline, fishermen sometimes believe that local populations of toothed whales are the cause. In some areas, fishermen organize dolphin kills in an effort to control their populations. In some places, they may offer bounties for dead animals. Probably the largest and best-known of these kills was the drive-fishery on Iki Island, Japan. Over the course of ten years, thousands of toothed whales, including bottlenose dolphins, were killed. The Iki Island kills ended in 1986.
- United States federal laws do not permit people to feed and swim with dolphins or other marine mammals in the wild. These actions are considered "harassment." When people try to get close to wild marine mammals, they put the animals and themselves at risk. Feeding and swimming with marine mammals in the wild is harmful to animals and sometimes dangerous to people.
- When people feed marine mammals in the wild, the animals may become less able or willing to search for food on their own.
- The U.S. National Marine Fisheries Service (NMFS) has serious concerns about the quality of fish being fed to wild marine mammals and has received complaints that animals are being fed harmful items such as sandwiches, cookies, candy, and chips. Fish that has not been inspected for freshness can cause illness in the animals fed. There also is strong evidence that feeding marine mammals in the wild can lead to their learning to steal fish off fishing lines. Animals that have stranded on the beach have been found with hooks and fishing lines in their stomachs.
- Reports of injuries to people by marine mammals habituated to being fed in the wild are increasing. Unsuspecting individuals have been bitten, and swimmers have been rammed and pulled under water by wild dolphins that have been taught to expect food from humans.
- Feeding, swimming with animals, or intruding on wild environments also can have a negative influence on many other normal marine mammal behaviors. People are disturbing dolphin resting areas. Scientists believe that the long-term effects of such activities may include the disruption of normal resting patterns, mother-calf nursing and bonding behaviors, and social interactions between animals.
- Marinelife parks, aquariums, and zoos offer many animal interaction programs that are carefully controlled, monitored by knowledgeable staff, and approved by the government, and are safe, positive experiences for both human and animal participants.
- According to the results of a 2005 public opinion poll conducted by Harris Interactive®, 91% of respondents agree that interacting with dolphins offers people a deeper understanding and appreciation of them.
- Because most people will not engage in behavior that they know will hurt animals, NMFS, the Alliance of Marine Mammal Parks and Aquariums, and SeaWorld are educating people of the harm caused by disturbing marine mammals or their habitats in the wild. The Alliance of Marine Mammal Parks and Aquariums is an international association of more than 36 marinelife parks, aquariums, zoos, scientific research facilities, and professional organizations that are dedicated to the conservation of marine mammals and their environments through public display, education, and research.