Common Bottlenose Dolphin

Tursiops truncates

What fun it is to look out to sea and notice dolphins! They lift our spirits and bring a smile to our faces. If you see a large dolphin just off-shore it is probably a common bottlenose dolphin. At Piedras Blancas bottlenose dolphins are frequently observed just outside the surf line. In some areas they have been seen riding the waves, body surfing!

Bottlenose dolphins are seen in marine theme parks, trained to do a variety of behaviors on demand. Many people know of them from the Flipper television series. When most people hear the word “dolphin” they think of the bottlenose dolphin. They are probably the best known cetacean in the world.

Color: They have a dark gray or gray-brown cape on their backs with a paler gray on the sides and flanks. The color fades to white or pink on the belly. Flippers and flukes are dark to medium gray. A muted gray stripe runs from the eye to flipper. The calves are darker than the adults. Scars and scratches, called tooth rakes, are often seen – caused by other dolphins.

Shape: The common bottlenose has a wide head with a short stubby beak. A groove runs between the forehead and the snout. Given the shape of their mouth, they appear to have a permanent smile on their faces. They have long, pointed flippers and a moderately tall, curved (falcate) dorsal fin located about midway down the back. The flukes are curved and deeply notched. An offshore variety tends to be darker with smaller flippers.

Weight and length: The coastal variety averages around 420-570 pounds. The larger offshore type may weigh as much as 1000 pounds. Males are slightly larger than females. The coastal variety averages 8-9 feet in length while the offshore may grow to 12 feet long.

Feeding: Dolphins use echolocation to find food. Intense bursts of high-frequency sound are produced in the forehead and transmitted through a fatty structure called the melon. Traveling through the water, these clicks reflect off objects and the returning echoes give the animal information about the size and location of the prey. In other words, echolocation helps them “see” using sound.  Some of the sounds may be loud enough to stun the prey.  Bottlenose dolphins eat various fish, squid, shrimp and crab. They have sharp conical shaped teeth used to seize the prey which is swallowed whole and head first so the spines don’t catch on their throats. An adult may eat 15-30 pounds a day.

Breathing and diving: Dolphins have a single blowhole (nostril) at the top of their head. They breathe very quickly, beginning exhalation just before reaching the surface. After inhaling they relax the muscular flap that closes the blowhole. They usually breathe 2-3 times a minute. Most dives are in water that is 10-150 feet deep but they can dive deeper than that, to below 1000 feet deep.  

Migration: They exhibit a variety of migration patterns, from year-round home ranges to long range movements, with every variation in between. The coastal variety appears to have more limited home ranges; the offshore type is less restricted in their movements. 

Movement/behavior: Dolphins propel themselves forward using up-and-down movements of their flukes. Flippers are used for stabilization. They are often seen leaping out of the water or breaching and they like to ride the bow waves of boats or large whales. They engage in body surfing and sometimes approach humans in the water. They normally swim at 3-7 mph but they can reach 18-22 for short bursts.

Bottlenose dolphins do well in captivity and are the most common cetacean seen in marine theme parks. They can be trained to perform complex tasks. They spend about 1/3 of their time sleeping, resting one hemisphere of the brain at a time. Because 5 of the 7 neck vertebrae are not fused they have great flexibility in the neck.

A group size of 2-15 is typical for bottlenose dolphins found near shore, but groups of hundreds may be seen offshore. Pods are usually open associations, with individuals leaving or joining.  Mothers and calves tend to stay in groups. Sub-adult males group together and adult males travel as individuals or in pairs or trios. Some female groups stay together for years, visited briefly by adult males. Some males have been documented forming bonds that last 20 years or more. At times pods join together to form large herds.

Dolphins engage in a lot of interacting. Although many behaviors are friendly (touching, caressing, chasing) some behaviors are aggressive, earning them the nickname “the bad boy dolphin). They have been known to kill other dolphins in their pods.  A dominance hierarchy (pecking order) is established by biting, jaw clapping, and tail smacking. They rake one another with their teeth leaving parallel scratches on the skin. Bubble clouds are a sign of aggression.

Sounds: Dolphins make a variety of noises. Clicking noises are produced during echolocation, thought to help them find food, navigate, and detect predators. They produce a wide variety of whistles, including individual “signature whistles” that uniquely identify each animal. Most male calves develop a signature whistle similar to their mothers but the female calves do not.  Whistles come from deep in the larynx and sometimes communicate alarm or sexual excitement. They also produced pulse bursts (squawks) associated with social interaction. Although it isn’t believed they possess true language they can produce sounds similar to human words, leading some biologists to suggest dolphins may be capable of learning to communicate with people.

Reproduction: Females are sexually mature at about 5-13 years of age. Males are sexually mature around 9-14 years of age. Females reach sexual and physical maturity before males. The females usually initiate courtship and mating. Gestation is about 12 months. The breeding season varies with locale. Along Southern California most calves are born in the fall. Females have a calf every 3-6 years.

Calves: Born either head-first or tail-first, calves can swim and breathe minutes after birth. They are weaned at 18-20 months old but they may stay with their mothers several years after that. “Babysitting” has been observed, in which other adults stay with a calf while the mother forages. Calves are about 2 feet long at birth

Longevity: Female common bottlenose dolphins can live to be 50 years old. Males may reach 40-45 years of age. Growth layers in their teeth are used to determine age.
           
Predators: Some shark species prey on bottlenose dolphins, especially on the calves. Rarely there are attacks by orcas. Bottlenose dolphins have been hunted by man for meat, leather, oil, fertilizer, and animal food.

Distribution: Bottlenose dolphins are found in temperate and tropical waters worldwide. It may be the most adaptable cetacean. In addition to being found along continents and islands, some reside in bays and estuaries. Some populations are centered far offshore. The only areas they seem to avoid are the high latitudes. They are mainly found in water with a surface temperature of 50-90 degrees F.

Status: Common bottlenose dolphins are considered abundant and widely distributed. In the United States they are protected by the Marine Mammal Protection Act. They are plentiful in some areas but in others, like the Black Sea, their numbers are depleted because of hunting.

Because bottlenose dolphins are attracted to human activities, like fishing, they are sometimes shot as a nuisance. An estimated 4.8 million died accidentally trapped in tuna nets during the years 1959-1972. Due to pressure from consumers and animal rights activists some canneries refuse tuna from fleets that do not protect dolphins.

Other threats include pollution and habitat destruction. Concern has also been expressed about the treatment of dolphins in public aquariums and “swim with the dolphins” programs.