Dusky dolphin
The dusky dolphin is a small oceanic dolphin found in coastal waters of the Southern Hemisphere. It is most closely related to the Pacific white-sided dolphin. The dolphin's range is patchy, major populations occurring around South America, southwestern Africa, New Zealand, and several oceanic islands, with some sightings around southern Australia. It has a somewhat stocky body with a short beak and a curved dorsal fin and flippers. Like its closest relative, the dusky dolphin has a multi-coloured pigmentation of black, grey, and white.
The species prefers cool currents and inshore waters. It lives in a fission–fusion society where groups change size based on social and environmental conditions. The dolphin feeds on several fish and squid species and has flexible hunting tactics, including daytime bait ball herding and nightime feeding in deep scattering layers. Mating is polygynandrous, and several males will chase after a single female, the fittest being able to catch her and reproduce. Females raise their young in nursery groups. The dusky dolphin is known for its acrobatics, displaying leaping behaviours which vary in complexity and may or may not create splashes.
The dusky dolphin is classified as Least Concern by the IUCN Red List as many populations appear to be healthy and stable. It has been caught in gill nets and killed to be used as bait. It is a popular tourist attraction and the object of whale watching tours. Both vessels and mussel farms can interfere with the dolphin's activities.
Taxonomy
The dusky dolphin was described as Delphinus obscurus by John Edward Gray in 1828 based on stuffed skins with skulls shipped from the Cape of Good Hope to the British Museum in 1827. Gray later wrote that a similar dolphin was described as Delphinus superciliosus by French surgeons and naturalists René Lesson and Prosper Garnot in 1826 based on a specimen near Tasmania. Lesson and Garnot did not keep the specimen for their description but only an illustration of it, and later taxonomists did not consider this significant enough for a new species. Meanwhile, Charles Darwin described a "Delphinus fitzroyi" from a specimen harpooned off Argentina in 1838, which was later identified as this species, and thus become a junior synonym. The dusky dolphin was placed in the genus Lagenorhynchus by the American biologist Frederick W. True in 1889. Lagenorhynchus consists of the Greek lagenos and rhynchos ; obscurus is Latin for "dark".The genus Lagenorhynchus included the dusky dolphin, Pacific white-sided dolphin, Atlantic white-sided dolphin, white-beaked dolphin, hourglass dolphin, and Peale's dolphin, though genetic evidence indicates that this grouping is not a natural taxon. A 2019 study proposed moving four species to the resurrected genus Sagmatias. A 2025 phylogenomic study found that Sagmatias as defined by the 2019 study is also not monophyletic and instead suggested that the dusky and Pacific white-sided dolphin be classified under a new genus, Aethalodelphis, which is Greek for "sooty or dusky dolphin". This is considered valid by the Society for Marine Mammalogy as of 2025.
The dusky dolphin is most closely related to the Pacific white-sided dolphin, and these two sister species diverged around two million years ago. Dusky dolphin populations may have originated somewhere in the South Pacific or southern Indian Ocean and dispersed to their current range following the spread of favoured food like anchovies. Possible hybrids of dusky dolphins with other species have been suggested based on observations and photographic evidence, including with a common dolphin and a southern right whale dolphin.
The following cladogram is based on a phylogenomic study by Galatius and colleagues :
Subspecies
Three dusky dolphin subspecies are recognised by the SMM:- The African dusky dolphin
- Fitzroy's dolphin
- The Peruvian/Chilean dusky dolphin
Description
The dusky dolphin is a small cetacean; specimens from New Zealand have been recorded at in length and in weight for females and in length and in weight for males. Peruvian dolphins may be larger, but this is based on small sample sizes; a female was measured at and a male was measured at. Newborns have an average length of and a weight of off Peru.The species has a somewhat stocky build, with a short, pointed beak, curved dorsal fin and flippers, and between 108 and 144 small, conical teeth. It has a distinctive colouration that resembles the Pacific white-sided dolphin, with a dark-grey or black upper side, orbital region, and beak; a light-grey face, chest area, and flank patch; and a white underside. The flank patch has an extension or blaze that reaches over the back and towards the blowhole. The dorsal fin is darker in front and lightens towards the back; the flippers are light-grey with darker edges. The dusky dolphin differs from the Pacific white-sided dolphin in having a more slender skull and a shorter blaze.
Distribution
The dusky dolphin has a discontiguous range in the Southern Hemisphere; including the coasts of western and southeastern South America, southwestern Africa, New Zealand, and some oceanic islands in the south Atlantic and Indian Ocean. It has also been sighted off southern Australia.Dusky dolphins can be found throughout New Zealand waters and are most common along the eastern coasts, between East Cape on the North Island and Timaru/Oamaru on the South Island. They are sighted year-round in the stable, cold waters off the coast of the northern Canterbury Region. Off South America, they range from southern Peru to Cape Horn in the Pacific and then up to around 36°S in the Atlantic, along with the Falkland Islands, where they are thought to be less abundant. Off Africa, the dusky dolphin ranges from Lobito Bay, Angola, in the north to False Bay, South Africa, in the south. Within Australian waters, dusky dolphins have been recorded off Kangaroo Island, eastern Tasmania, and in the Bass Strait, although they are uncommon and may be transients from New Zealand. Dusky dolphins are also found around the islands of Tristan da Cunha, Prince Edward, Crozet, Île Amsterdam, and Île Saint-Paul.
Ecology and behaviour
Dusky dolphins live mostly in coastal waters within the continental shelf and prefer cool, upwelling waters, as well as cold currents. Dolphins off Argentina and New Zealand move to and from shore between day and night and between seasons. Seasonal migrations have been recorded between Kaikōura and Admiralty Bay, New Zealand. Around Kaikōura, the majority of individuals have only been seen once in the area over a 30-year period, suggesting high levels of immigration and emigration. Dusky dolphins were recorded swimming up to and diving up to.Most studies of foraging and social behaviour in the species have been conducted at Kaikōura, Admiralty Bay, and San Jorge Gulf, Argentina. Dusky dolphins live in a fission–fusion society and individuals move in and out of groups depending on social and environmental conditions. At Kaikōura, group sizes can reach 1,000 dolphins, while in Admiralty Bay, they peak at around 50 dolphins. Groups form for different activities, including foraging, resting, travelling, and socialising. At Kaikōura, groups are larger when resting and smaller when foraging, but the reverse is true at San Jorge Gulf. At Admiralty Bay, foraging leads to larger aggregations; resting does not appear to correlate with group size. Most associations between individuals are weak but long-term bonds do occur.
Dusky dolphins can be found in mixed groups with other cetacean species, including common dolphins, southern right whales, Risso's dolphins, southern right whale dolphins, and pilot whales. Off Argentina, they have been found around bottlenose dolphins, but seem to ignore them. Dusky dolphins also feed with non-cetacean species such as South American sea lions, kelp gulls, cormorants, terns, shearwaters, petrels, albatrosses, and Magellanic penguins off Argentina, and Australasian gannets, shearwaters, terns, gulls, spotted shags, New Zealand fur seals, spiny dogfish, and common threshers off New Zealand.
Vocalisations and echolocation
Like other oceanic dolphins, dusky dolphins produce three basic types of sounds: echolocative click trains, burst pulses and tonal whistles. Their echolocation signals are quick and broadband, much like in other whistle-producing species, and have two peaks: between 40 and 50 kHz at low frequency and between 80 and 110 kHz at high frequency. Burst pulses are similar to echolocation signals but the pauses between clicks are shorter, at 0.5–10 milliseconds. Off New Zealand and Argentina, they often consist of 2–14 clicks in succession and appear to be important for communication. Whistling is more common when dusky dolphins mingle with other dolphin species such as common dolphins.Foraging
Dusky dolphins mainly feed on fish and squid. Fish species eaten include anchovies, lantern fish, pilchards, sculpins, hakes, horse mackerel, hoki, and red cod; the squids they prey on include those of the genera Nototodarus, Todarodes, and Loligo. Dusky dolphins are generally coordinated hunters, and their flexible foraging strategies can change depending on the environment. In the Kaikōura Canyon, where deep oceanic waters meet the coast, they forage at night in deep scattering layers. Dolphins travel to the hunting site individually and form groups when in the layer. The number of individuals in these groups ranges up to five members and decreases to single dolphins as the layer descends down the water column.In San Jorge Gulf, between October and January, and Admiralty Bay, between August and November, dusky dolphins herd schools of fish into bait balls during the day. They use the water surface as a barrier for the fish as they circle around them. and may also scare them with sound or by flashing their white bellies. The larger the group, the more effective dolphins are in herding the school. These hunts may also involve other species, including other dolphins, seabirds, sharks, and pinnipeds. Common dolphins seem to participate in herding with dusky dolphins. By contrast, pinnipeds, sharks, and other predatory fish take food without helping in the hunt, and foraging by diving birds like gannets can make herding more strenuous for dolphins. From May to October in San Jorge Gulf and between May and July at Admiralty Bay, dusky dolphins hunt deeper below the surface.