common dolphin Common dolphins (Delphinus delphis) are the most abundant cetacean (whale, dolphin and porpoise) in the world, with a global population of about six million. Despite its name it is not regarded as the archetypal dolphin. That distinction goes to bottlenose dolphin due to its popular appearances in aquariums and the media. However, common dolphins, rather than bottlenose dolphins, are the dolphin species most often depicted in Ancient Greek and Roman art most notably in a mural painted by the ancient-Egyptian-era Greek Minoan civilization. [Source: Wikipedia]
Common dolphins are currently the only member of the genus Delphinus. The common dolphin belongs to the subfamily Delphininae, making this dolphin closely related to the three different species of bottlenose dolphins, humpback dolphins, striped dolphins, spinner dolphins, clymene dolphin, spotted dolphins, fraser's dolphin and the tucuxi and guiana dolphin.
Common dolphins were originally categorized into two different species (now thought to be ecotypes), the short-beaked common dolphin and the long-beaked common dolphin. However, recent evidence has shown that many populations of long-beaked common dolphins around the world are not closely related to one another and are often derived from a short-beaked ancestor and do not always share common derived characteristics. For this reason, they are no longer considered different species. Some sources — such as the NOAA wbesites — still consider them separate species though
Websites and Resources: Britain-based Whale and Dolphin Conservation Society uk.whales.org ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Short-Beaked Common Dolphin
Short-beaked common dolphins (Scientific name: Delphinus delphis) are one of the most abundant and familiar dolphins in the world. This highly social and energetic species is widely distributed, preferring warm tropical to cool temperate waters that are primarily oceanic and offshore. Short-beaked common dolphins are often found in association with underwater ridges, seamounts, and continental shelves where upwelling (a process in which deep, cold, nutrient-rich water rises toward the surface) occurs and prey is abundant. [Source: NOAA]
Short-beaked common dolphins are closely related to — and easily confused with — long-beaked common dolphins. The two species differ slightly in size, appearance, and habitat preference. Short-beaked common dolphins prefer warm tropical to cool temperate waters that are primarily oceanic and offshore. They can be found along the continental slope in waters 650 to 6,500 feet deep. Their lifespan is estimated to be 35 to 40 years.
In the western North Atlantic, short-beaked common dolphins are often associated with the Gulf Stream current. Short-beaked common dolphins also prefer waters altered by underwater geologic features such as underwater ridges and sea mounts where upwelling occurs, increasing nutrient concentrations and supporting higher productivity. The abundance and distribution of short-beaked common dolphins vary based on interannual changes, oceanographic conditions, and seasons. They can be found on the continental shelf or farther offshore. On the U.S. west coast, these dolphins are primarily associated with the California Current and are abundant off California year-round from near shore to about 300 miles offshore. On the U.S. east coast, they are more common north of Cape Hatteras, North Carolina. However, from summer through autumn, large aggregations of dolphins can be found near Georges Bank (extending from Cape Cod, Massachusetts, to Nova Scotia, Canada), Newfoundland, and the Scotian Shelf. Other distinct populations can be found off of northern Europe, Newfoundland, Africa, Japan, southern Australia, and New Zealand, and in the Black Sea, the Mediterranean Sea, and the southwestern Pacific. [Source: NOAA]
Short-Beaked Common Dolphin Physical Characteristics
Short-beaked common dolphins are relatively small, measuring under 1.8 meters (6 feet) long and weighing about 77 kilograms (170 pounds). As adults, males are slightly larger than females. They have a rounded forehead (known as a melon), a moderately long rostrum, and 40 to 57 pairs of small sharp teeth in each jaw. Their body is sleek with a relatively tall, triangular dorsal fin in the middle of their back. [Source: NOAA]
Short-beaked common dolphins can be identified by their distinctive color pattern, which is often referred to as an ‘hourglass.’ A dark gray cape extends along the back from the head to just below the dorsal fin where a "V" is visible on either side of the body, creating a hourglass. Forward of the dorsal fin, behind the head, is a yellow/tan panel that contrasts with their dark back, and the side of the body behind the dorsal fin is light gray. A narrow dark stripe extends from the lower jaw to the flipper, and there is a complex facial color pattern that includes a dark stripe from the rostrum, or “beak,” to the flipper. The eye is not typically within the stripe, but the eye stands out due to a patch of dark pigment around the eye.
The color patterns of young and juvenile short-beaked common dolphins are somewhat more muted and pale than older, adult dolphins. Considerable variation in color patterns are evident within populations but more markedly different coloration patterns are evident in some distant geographic areas.
Short-Beaked Common Dolphin Behavior, Diet and Reproduction
Short-beaked dolphins are usually found in large social groups averaging hundreds of individuals and are occasionally seen in larger herds — known as mega-pods — consisting of thousands of animals (up to at least 10,000). These large schools are thought to consist of sub-groups of 20 to 30 individuals that are possibly related or separated by age and/or sex.
Short-beaked common dolphins are often active at the surface. These highly social, energetic dolphins commonly leap out of the water at high speeds, turn end-over-end, and somersault. They will also swim alongside ships and even large whales for long periods of time. They usually rest during the day and feed at night. They can dive to approximately 1,000 feet but typically dive to about 100 feet to feed on schooling fish and cephalopods (such as, squid) that migrate towards the surface at night. Short-beaked common dolphins associate with schools of tuna and seabird feeding flocks, especially in the eastern tropical Pacific Ocean. They have also been observed in schools with spinner dolphins and striped dolphins.
On average, males become sexually mature at 10 years and females at 8 years although individuals may become sexually mature between 5 and 12 years. Off the California coast, calving takes place during winter after a a 10- to 11-month gestation period, whereas calving takes place year-round in the eastern tropical Pacific. Every 2 to 3 years, adult females give birth to a single calf that is about 2.5 to 3 feet long. Calves begin to wean after about 1 year, but remain dependent for another year or more.
Long-Beaked Common Dolphins
Long-beaked common dolphins (Scientific name: Delphinus capensis) can be found in large social groups in the Atlantic, Indian, and Pacific Oceans. This highly social and energetic species prefers shallow, tropical, subtropical, and warmer temperate waters closer to the coast and on the continental shelf. They have an estimated lifespan of approximately 40 years. [Source: NOAA]
Long-beaked common dolphins are closely related to — and easily confused with — short-beaked common dolphins. They differ slightly in size, appearance and habitat preference. Long-beaked common dolphins are less abundant but often bigger than their short-beaked relatives. Long-beaked common dolphins generally prefer shallow, tropical, subtropical, and warmer temperate waters within 15 nautical miles of the coast and on the continental shelf.
There are discrete populations with limited distribution along coastlines in the Atlantic, Indian, and Pacific Oceans. In U.S. waters, this species is only found along the west coast, and their distribution extends from Baja California, Mexico, northward to central California. Other, discrete populations can be found off the coasts of South America (Peru, Chile, Venezuela, Brazil, and Argentina), West Africa, South Africa, Madagascar, the Arabian Peninsula, India, Indonesia, China, Korea, and southern Japan. The distribution and population center of this species may change with varying oceanographic conditions.
Long-Beaked Common Dolphin Physical Characteristics
Long-beaked common dolphins are small but, measuring 1.8 to 2.6 meters (6 to 8.5 feet) long and weighing between 75 and 225 kilograms (160 and 500 pounds). Males are around 5 percent larger than females. They have a recognizable dolphin shape with a rounded forehead (known as a melon), a moderately long rostrum, and 47 to 58 pairs of small sharp teeth in each jaw, more than any other dolphin species. Their bodies are sleek and have a relatively tall, triangular dorsal fin in the middle of the back. [Source: NOAA]
Long-beaked common dolphins can be identified by their distinctive color pattern. They have an hourglass pattern created by a dark back, a dull yellow/tan panel on the side in front of the dorsal fin and a lighter gray panel extending along the side from the dorsal fin to their tail stock.
The color patterns of young and juvenile long-beaked common dolphins are generally more muted than in adults. A broad dark stripe extends from the lower jaw to the flipper and the dark cape on their back typically includes the eye. Distinguishing between long-beaked common dolphins and short-beaked common dolphins is most difficult among young dolphins.
Long-Beaked Common Dolphin Behavior, Diet and Reproduction
Long-beaked common dolphins are usually found in large social groups averaging from 100 to 500 animals, and they are occasionally seen in larger herds of thousands of individuals. These large schools are thought to consist of smaller sub-groups of 10 to 30 potentially related individuals or individuals of similar age and sex. [Source: NOAA]
Long-beaked common dolphins are often active at the surface and display various behaviors. These highly social, energetic dolphins are commonly seen swimming rapidly and leaping out of the water at high speeds. They will also swim near the front of ships and ride the pressure waves (or bow-riding) for long periods of time.
Long-beaked common dolphins feed on small schooling fish (such as, anchovies, hake, pilchards, and sardines), krill, and cephalopods (such as, squid). Dolphin groups may work together to herd schools of prey. Their diving behavior is thought to be like that of short-beaked common dolphins.
Long-beaked common dolphins become sexually mature at about 10 years. Calving takes place primarily in spring after a 10- to 11-month gestation period. Every 2 to 3 years, females give birth to a single calf that is about 3 feet long.
Threats to Short-Beaked Common Dolphin
Short-beaked common dolphins are not endangered or threatened. Overall, they are abundant worldwide, except for a few specific populations. The Convention on International Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled:. They are protected by the Marine Mammal Protection Act (MMPA) like all marine mammals. [Source: NOAA]
One of the main threats to short-beaked common dolphins is getting caught in fishing gear. They can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines. Many fisheries in the Atlantic Ocean capture short-beaked common dolphins as bycatch, and they have the highest mortality rate of all cetaceans impacted by the drift gillnet fishery operating off the coast of California.
Russia, Japan, and nations bordering the Black Sea and Mediterranean Sea hunt short-beaked common dolphins for their meat and oil.
Threats to Long-Beaked Common Dolphin
Although they are less abundant than short-beaked common dolphins, long-beaked common dolphins are not considered threatened or endangered. The eastern North Pacific long-beaked common dolphin, the only population found in the United States, is not endangered or threatened. CITES places them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled: Like all marine mammals, they are protected under the MMPA. [Source: NOAA]
One of the main threats to long-beaked common dolphins is entanglement in fishing gear. They can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines. Small numbers of long-beaked common dolphins have been killed for food and bait in the Caribbean, Peru, West Africa, and other offshore islands.
Long-beaked common dolphins are particularly susceptible to domoic acid poisoning, which is a neuro-toxin produced by algae. When harmful algal blooms (HABs) occur, sardines and anchovies eat the harmful algae, and they are eaten by long-beaked common dolphins. This bioaccumulation of toxic algae can cause seizures and sometimes death in these dolphins and other marine mammals who consume affected prey. [Source: NOAA]
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated June 2023