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Delphinus delphisshort-beaked saddleback dolphin

By Maria Alspaugh

Geographic Range

Common dolphins can be found throughout the Atlantic and Pacific Oceans. They are abundant in the Mediterranean Sea, as well as in the Black Sea, the Gulf of Mexico, and the Red Sea. At times, these dolphins follow the Gulf Stream up to Norwegian waters. In addition, scattered populations have been found in the Indian Ocean and waters near Japan. They seldom venture into the Arctic.

(Baker, 1987; http://whales.ot.com/).

Habitat

Common dolphins are fond of coastal waters, but are also found well out to sea. Generally, they prefer surface temperatures greater than 10 degrees Celsius. These dolphins normally travel at 5 to 7 miles per hour (although they are known to reach speeds of 29 miles per hour when pursuing food), and can move up to 150 to 200 miles in a 48 hour period. When swimming, schools follow and dive over prominent features of the ocean bottom. Also, herd movements correlate with the seasonal shifts in population of certain fish.

(Alpers, 1961; Baker, 1987; Schevill, 1974; http://whales.ot.com/).

Physical Description

The common dolphin is one of the smallest dolphins. Overall length can vary from 5 feet to a maximum of 8 feet. Females are slightly smaller than males. The common dolphin has a dorsal fin that is almost triangular, in addition to small flippers and flukes. The beak is sharply divided from the lower forehead by a deep groove. The beak is elongated and pointed more than any other species of the same genus. The jaws on each side of the beak are lined with 20 or more small, sharp, recurved teeth, perfect for catching slippery fish. Common dolphins are a colorful dolphin species. The back is either black or dark brown, and they have a white or cream-colored underside. A dark streak stretches from the the lower jaw to the flipper. The flippers and flukes are the same color as the back, black or dark brown, and the eyes are encirled with black markings that extend to the beak. The most distinctive feature is a crisscross pattern which runs across the dolphin's side. It resembles an hourglass and divides the top and bottom colors. This band is a buffy tan in front and gray towards the tail. This characteristic has given this species the nickname "crisscross dolphin".

(Allen, 1979; Baker, 1987; Flower, 1866).

  • Range mass
    100 to 136 kg
    220.26 to 299.56 lb

Reproduction

Common dolphins are viviparous, as are all mammals except monotremes. Females normally give birth to one baby at a time, but have been found to carry twins or triplets. Gestation usually lasts 10 to 12 months. When the calf is born (tail first) it is 3 feet long and usually weighs 25 to 35 pounds.

Common dolphins reach sexual maturity after 12 to 15 years. Courtship occurs in the spring and fall. Males and females court by stroking each other with their flippers, by vigorously rubbing their bodies together, and by swimming along side each other. The male often rushes towards the female as if he is about to bump into her before moving away. The female often swims away from the male's pursuits. After this playful courtship, these dolphins mate in the belly-to-belly position. The male enters the female with his hidden penis and gives a short series of pelvic thrusts. Females have also been observed thrusting. Other sexual activity includes beak-genital propulsion.

Common dolphins have an estimated life span of 35 to 40 years.

(Alpers, 1961; Baker, 1979; Cousteau, 1988; McIntyre, 1974; http://whales.ot.com/).

  • Range number of offspring
    1 to 3
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    10 to 12 months
  • Range age at sexual or reproductive maturity (female)
    12 to 15 years
  • Range age at sexual or reproductive maturity (male)
    12 to 15 years

Babies immediately become a part of the family group. The calf stays close to its mother and never wanders more than a few feet away. The calf feeds on milk from the teats of its mother. Unlike human babies, however, dolphins do not have the lips needed to suck the teats. Also they could not breathe under water if they were able to suck. To solve these problems, the mother squirts milk into her offspring's mouth by contracting muscles. The young dolphin then goes up to the surface to breathe and then comes down for more. Dolphin milk has 6 times more protein and is much more fattening than human milk. It allows the baby dolphin to increase its weight 2 to 3 times faster than a human baby does during the first six months. Suckling goes on for about a year and a half. After six months, the baby occasionally takes solid food.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female
  • post-independence association with parents
  • extended period of juvenile learning

Lifespan/Longevity

Behavior

Dolphins are very social organisms. Common dolphins are seldom alone. They travel together, they eat together, they even breathe together! The whole school can all be in the air at one time. Schools can contain as many as 1000 to 100,000 individuals. Common dolphins are the most abundant and wide spread species of dolphins.

In higher latitudes, when the first storms of fall move over the waters, females and their young assemble into large companies to face the vigors of winter. They depend on their large numbers to find food and on their speed and caution for protection. Males live apart from these large herds of females. Although they remain in the same area, they stay a considerable distance away until the warmer spring season approaches. Further separation of the sexes occurs in nursery schools of pregnant and nursing females.

Dolphins are playful creatures. The common dolphin is no exception. They are both active and boisterous. They do various flips and somersaults. They leap with their whole bodies out of the water. Smaller dolphins sometimes leap vertically. Common dolphins play with one another in a somewhat rough fashion, rushing towards one another. The favorite activity of the common dolphin, however, is bow-riding. They ride off ships and the pressure waves created by whales. They may stay with the vessel, jumping and playing, for a period of up to several hours.

Common dolphins are also a very affectionate species. They care for their sick by using their fins to keep the ailing dolphin afloat so it may breathe. Moreover, they make friends with the members of their groups and show obvious emotions towards them. In captivity, two males who were separated became very excited when reunited. Also when members of the group are separated or die, dolphins exhibit emotions of sadness and seem to be pining away for their playmates.

Within the groups, adults act as teachers to the young. Younger dolphins are disciplined when proper manners are not performed. In addition, mothers in the groups share responsibilities in taking care of the young. They take turns watching over those that are too active.

Common dolphins, as with other cetaceans, are a very vocal species. They communicate with each other using two voices--one being for navigation and location and the other being for social communication. The voice can be described as whistle-like pulse sounds. Variations in loudness, speed, and pitch convey different messages. In captivity, attempts to teach dolphins to speak are made. Common dolphins, however, are not easily trained despite their friendliness. In captivity, common dolphins are very uncharacteristically shy. Voices can also be used as aids in "sight." Sound is the primary sense. Vision is often difficult, espcially in dark and murky waters.

Common dolphins have very few enemies. Those they do have to worry about are sharks and killer whales.

(Allen, 1979; Alpers, 1961; Cousteau, 1988; McIntyre, 1974; http://whales.ot.com/).

Communication and Perception

Food Habits

Delphinus delphis feed on small fish as well as squid and octopus. Small fish include young herring, pilchard, anchovies, nocturnal hake, sardines, small bonito, as well as sauries. Individual dolphins eat up to 18 to 20 pounds of fish per day. Groups of common dolphins all feed at the same time during the night or day. They are sometimes joined by bands of bottlenose or white-sided dolphins. These feeding forays can last up to an hour. During these, each dolphin rushes to the center of the school the group has been pursuing and tries to seize as many fish as possible, which it swallows whole. Common dolphins have also been known to dive below schools and drive them to the surface. They push their prey completely out of the water and catch them in midair.

(Allen, 1979; Alpers, 1961; Baker, 1987; http://whales.ot.com/).

  • Animal Foods
  • fish
  • mollusks

Economic Importance for Humans: Positive

Common dolphins are a very helpful and friendly species. They have been known to rescue humans. They also provide entertainment for sailors as they play along the sides of their ships. Furthermore, fisherman use common dolphins in trying to locate fish. In some cultures, such as on the Polynesian Gilbert Islands, dolphins are also eaten as food.

(Alpers, 1961).

Economic Importance for Humans: Negative

Common dolphins feed on fish. This can be a problem for those trying to catch the fish on which these dolphins are preying. In fact, the United Nations reported that dolphins along the California coast eat an average of 300,000 tons of anchovies each year, whereas commercial fisherman take in only 110,000 tons. Because of this, many angry fisherman who catch these enemies in their nets often kill them.

(Allen, 1979; http://whales.ot.com/).

Conservation Status

Common dolphins face many obstacles at the hands of human beings. They face exploitation by man, entanglements in fishing nets, hunting, as well as other human disturbances. These, however, can be avoided if the dolphin is lucky. Unfortunately, common dolphins, as well as other aquatic life, cannot avoid the pollution that is overtaking their habitats. Many laws have been enacted to protect the dolphins and other marine life.

(Alpers, 1961; http://whales.ot.com/).

Other Comments

Strandings are not common among this species. This is perhaps because many herds remain mostly further out to sea.

Common dolphins do not sleep with both eyes closed. The dolphin closes one eye for 5 to 10 minutes and then the other eye. In a 24 hour period each separate eye is closed for an average of 3 to 4 hours.

Common dolphins are mammals. Therefore, unlike fish they cannot breathe underwater via gills. Dolphins have a blowhole on top of their heads and to breathe they must jump out of the water. They surface several times a minute to breathe.

Lastly, dolphins are intelligent organisms. Their intelligence lies somewhere between that of dogs and chimpanzees. They have success in problem solving. Common dolphins have the capacity for sustaining interests and fears. They have moods as well as emotions which can both last for long periods of time.

(Allen, 1979; Cousteau, 1988; McIntyre, 1974; http://whales.ot.com/).

Contributors

Maria Alspaugh (author), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

piscivore

an animal that mainly eats fish

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Allen, Thomas B., ed. 1979. Wild Animals of North America. National Geographic Society, Washington D. C.

Alpers, Antony. 1961. Dolphins: The Myth and the Mammal. Houghton Mifflin Co., Boston.

Baker, Mary L. 1987. Whales, Dolphins, and Porpoises of the World. Doubleday & Co., Inc., New York.

Cousteau, Jacques. 1988. Whales. Harry N. Abrams, Inc., New York.

Flower, William Henry, ed. 1866. Recent Memoirs on the Cetacea. Robert Hardwicke, London.

McIntyre, Joan. 1974. Mind in the Waters. Charles Scribner's Sons, New York.

Shevill, William, ed. 1974. The Whale Problem: A Status Report. Harvard University Press, Cambridge.

Whales Songs. http://whales.ot.com/

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