Summary of common dolphin
Relation to humans
Conservation and management
Scientific name: Delphinus delphis
Danish: Almindelig delfin
English: Common dolphin
The maximum lifespan for common dolphins (for both sexes) is estimated at 30 years.
Adults reach between 150 and 220 cm in length and can weigh up to 235 kg.
Females give birth to a calf every one to four years after a gestation period of 10 to 11.7 months.
Common dolphins are found worldwide in warm-temperate and tropical waters, generally between 60°N and 50°S. Their distribution varies depending on the season and sea-surface temperatures.
Common dolphins are among the most abundant cetaceans worldwide. They have a lean body with a relatively long, delimited beak and high, moderately curved dorsal fin. A criss-cross colour pattern extends across their whole body, crossing mid-body underneath the dorsal fin. This pattern results in a four-part pattern of dark grey to black coloration on the upper side of the body, a white underside, a pale yellow patch on the anterior and grey posterior patch (Perrin, 2018).
The criss-cross pattern on the common dolphin’s sides distinguishes them from similarly shaped dolphins such as the spinner and striped dolphin as well as the similarly coloured (but with narrow stripes) Atlantic white-sided dolphin (Carwardine 2020).
Common dolphins are known for bow riding the waves created by boats and even large cetaceans.
Common dolphins belong to the Delphinidae family and Delphinus genus. The genus used to consist of two species (short-beaked and long-beaked common dolphins, D. delphis and D. capensis respectively), but more recent research questions this split and since 2016 the common dolphin has been considered a single species (Natoli et al., 2008; Perrin, 2018; Pinela et al., 2011). Currently, four subspecies are recognised: the short-beaked common dolphin (Delphinus delphis delphis), the Eastern North Pacific long-beaked common dolphin (D. d. bairdii), the Indo-Pacific common dolphin (D. d. tropicalis) and the Black Sea common dolphin (D. d. ponticus).
Life History and Ecology
Adults reach lengths between 150-225 cm for both sexes and can weigh up to 235kg (Perrin 2018). The maximum estimated age is 30 years (in the western North Atlantic). Sexual maturity varies with regions, but is estimated at 3 years for the Black Sea population, 7-12 years in the eastern Pacific and Western Atlantic for males. Females are thought to reach sexual maturity between 2-4 years in the Black Sea region and 6-8 years in the eastern Pacific and western Atlantic region (Perrin 2018).
Females are estimated to be pregnant for 10-11.7 months (Danil & Chivers, 2007; Murphy et al., 2006; Perrin & Reilly, n.d.) before giving birth to a calve between 80 and 93 cm in length. The calving interval varies per region from about 1 year in the Black Sea region to about 4 years in the eastern Atlantic. The mating system between common dolphins seems to be promiscuous (dependent on sperm competition) (Carwardine 2020).
Common dolphins are a very social species. Schools of great variety (10 up to 10,000) have been recorded, often split in smaller subunits of 20-30 individuals (Evans 1994; Carwardine 2020). Group composition and sizes likely vary seasonally, but mixed groups of males and females with sub-adults and calves are common (Carwardine 2020). Genetic analyses suggest that the members of a school are not necessarily closely related, and there may be group segregations depending on age and sex (Viricel et al., 2008).
Common dolphins are regularly seen in association with other species such as pilot whales (Globicephala spp.), striped dolphins (Stenella coeruleoalba), several oceanic dolphins (Lagenorhynchus spp.) and Risso’s dolphins (Grampus griseus) (Frantzis & Herzing, 2002; Evans 1994). They have also been observed ‘bow riding’ on the waves created by mysticete whales (Perrin 2018).
As a highly vocal species, the common dolphin repertoire includes clicks, whistles, burst pulse calls to buzzes (Carwardine 2020). Their clicks are very short, high-frequency sounds (23 to over 100 kHz) used in echolocation to sense their environment and locate prey. Burst pulses are a series of rapidly produced clicks (up to 10 times faster than echolocation clicking) and are used in communication. Buzzes (a rapid succession of clicks that seem to be a continuous sound to the human ear) and whistles (most commonly simple up- and downsweeps between 3 kHz and 24 kHz) are also used to communicate. Like many other delphinid species, common dolphins produce unique so-called ‘signature whistles’ that last between 1-4 seconds and serve as a name tag for each dolphin.
Listen to common dolphin sounds (© NEFSC-NOAA) here:
Swimming and Diving Behaviour
Like many dolphin species, common dolphins are known for their aerial behaviour. They are often seen leaping out of the water to perform acrobatics and somersaults, slapping the water surface with their flippers or lobtailing. The leaps can reach heights of up to 6-7m. A common aerial display is called a ‘pitch-pole’ in which the dolphin aims to produce the largest splash after jumping straight up from the surface. Common dolphins are fast swimmers, with speeds reaching up to 40km/h when porpoising (Carwardine 2020).
Dives up to 280m have been recorded for as much as 8 minutes, though most foraging dives are much shallower and remain around 50m of depth that last between 10 seconds and 3 minutes (Perrin, 2018; Carwardine 2020).
Food and Feeding
The diet of common dolphins varies as much as the range of habitats they reside in, and varies with season and region (Ambrose et al., 2013; Evans 1994). At greater depths, common dolphins prey on squids and small fish such as scombroids and clupeoids, but they also hunt for schooling fish (such as herring, mackerel or smelt) and crustaceans (such as pelagic red crabs and krill) at shallower depths (Perrin 2018; Carwardine 2020). In some regions, common dolphins tend to feed during the night as their prey that usually occurs in deeper ocean layers migrated towards the surface in the dark (Carwardine 2020).
Natural predators of common dolphins include killer whales and sharks (Biton Porsmoguer et al., 2015), and they may also be attacked by pilot whales and pygmy killer whales (Carwardine 2020).
Common dolphins are found in tropical to temperate waters globally, with a preferred sea surface temperature of 10-28°C extending from about 40°N in the North Pacific and 60°N in the North Atlantic to 50°S. Likely due to the water preference, they may at times be found outside the normal distribution range when following warm-water currents (Carwardine 2020). In some regions, populations are distinct to the extent of being considered sub-species (for instance Black Sea population).
Within their range, they can be found anywhere between near-shore waters to several thousand kilometres offshore, although most common dolphin populations show a preference for areas with seamounts that are known for their strong upwelling (Amaral et al., 2012; Bearzi et al., 2003; Perrin, 2018).
The common dolphin is considered abundant with numbers estimated around at least 4-5 million individuals, although recent estimates are needed. European offshore waters (between 53° and 57°N) are thought to comprise 273,000 of these dolphins, with 63,000 occurring in the European continental shelf waters, up to 20,000 in South Africa, 19,000 in the western Mediterranean and some tens of thousands in the Black Sea (Carwardine 2020).
Common dolphins were hunted historically by several countries until at least the 1990s, with over 1.5 million individuals taken between 1931 and 1966 in the Black Sea prior to a ban of commercial hunting of small cetacean species (Carwardine 2020). Today, direct take is still practiced in some areas including Japan, Taiwan, Venezuela, Peru and Mexico for consumption as well as other usage (Carwardine 2020).
Trawl, gillnet and purse-seine fisheries are threats to common dolphins globally, although the precise impact of bycatch on the populations is not certain (Murphy et al., 2006; Thompson et al., 2013; IUCN 2016; Perrin et al., 1994). One study investigating the impact of by-catch did however estimate a reduction in population size of 20% from the current size in 2012 for the North Atlantic region and a likely extinction in the next 100 years (Mannocci et al., 2012).
Aside from by-catch of common dolphins, over-fishing of prey species is an additional threat to common dolphins (Carwardine 2020).
Noise and Disturbance
Man-made noise is known to be a threat to most cetaceans, including common dolphins. Military activity involving sonar can be dangerous to marine mammals and is a possible cause for a mass stranding of common dolphins that occurred in the UK in 2008 (Jepson et al., 2013). Underwater explosions from construction or other sources is another known threat to this species (Danil & St. Leger, 2011).
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