Hourglass dolphin (Cephalorhynchus cruciger)

In brief

The hourglass dolphin is the only small delphinid regularly encountered south of the Antarctic Convergence. It is recognised by its black coloration marked with two white patches joined in the shape of an hourglass, and by its tall, recurved dorsal fin, often glimpsed just above the waves as it comes to ride the bow wave of a ship. Listed as Least Concern by the IUCN, it nonetheless remains one of the least studied dolphins on the planet.

Identification

Small and stocky, the hourglass dolphin measures 1.6 to 1.9 m for a mass, in the few animals weighed, of between 73 and 94 kg. The body is muscular, the beak very short and barely set off from the melon, and the tail stock strongly keeled. The dorsal fin, tall and falcate, is an excellent criterion: its curvature increases with age and becomes distinctly hooked in old individuals, to the point that some animals carry an almost sickle-shaped fin. The flippers are slender and pointed. The dentition comprises 26 to 34 conical teeth in the upper jaw and 27 to 35 in the lower, that is about 53 to 69 teeth in all.

The colour pattern is the diagnostic character par excellence. The back, head, upper flanks, flippers and tail flukes are deep black, the belly white. Each flank bears two white areas: an anterior area that takes in the eye region and rises above the flipper, and a posterior area set behind the dorsal fin, the two joined by a narrow white band running beneath the fin. Seen in profile, the whole draws an hourglass, hence the vernacular name most used today. Seen from above, by contrast, the black of the back suggests a Maltese cross, which earned the species its epithet cruciger, from the Latin crux (cross) and gero (to bear). The pattern varies appreciably from one individual to another, the median band being either broad or reduced to a thin thread.

Within its range, confusion is unlikely. The southern right whale dolphin (Lissodelphis peronii), also black and white and present in the same waters, is told apart at once by the complete absence of a dorsal fin. Commerson’s dolphin (Cephalorhynchus commersonii), found around the Kerguelen Islands, is smaller, largely white on the forward part of the body and markedly more coastal. The spectacled porpoise (Phocoena dioptrica) shares the subantarctic waters but has an entirely black back with no lateral pattern, and an unobtrusive behaviour, without breaching or bow-riding. Lastly, Peale’s dolphin (Cephalorhynchus australis), confined to the approaches of Patagonia and the Falkland Islands, has a grey face and a quite different lateral pattern.

Taxonomy

The species belongs to the family Delphinidae and to the subfamily Lissodelphininae, which brings together the southern dolphins of the Cephalorhynchus-Lissodelphis group. It was described in 1824 by the French naturalists Jean René Constant Quoy and Joseph Paul Gaimard under the name Delphinus cruciger, from sightings at sea and a drawing made in the South Pacific in 1820: it is one of the very few cetaceans to have been accepted as a valid species on the sole basis of visual records, with no specimen collected.

Its generic placement was long unstable. Classed for more than a century in the genus Lagenorhynchus, it was removed from it when molecular analyses showed that genus to be polyphyletic: the revision by Vollmer and co-workers (2019) transferred it to the resurrected genus Sagmatias. The phylogenomic, morphological and acoustic data brought together by Galatius and co-workers (2025) then established that the hourglass dolphin and Peale’s dolphin are closer to Cephalorhynchus than to the dusky and Pacific white-sided dolphins. The valid name accepted today by the Taxonomy Committee of the Society for Marine Mammalogy, as by the IUCN Red List, is therefore Cephalorhynchus cruciger, with Lagenorhynchus cruciger and Sagmatias cruciger as synonyms. The echolocation signals, of the narrow-band high-frequency sonar type, support this affinity with Cephalorhynchus.

Distribution and habitat

The hourglass dolphin has a circumpolar distribution in the Southern Ocean. It occupies the band lying approximately between 45° S and 67-68° S, from the sea-ice edge in the south to the subantarctic waters in the north, where it regularly moves up to about 45° S. A few more northerly sightings reach 36° S in the South Atlantic and 33° S off Valparaíso, Chile, aided by the cold Humboldt Current. The southernmost sightings come from around 68° S in the South Pacific. It is the only small delphinid encountered on a regular basis south of the Antarctic Convergence.

It is a resolutely offshore species, associated with deep water. Shipboard surveys conducted in the southern Drake Passage, near the South Shetland Islands, show that sightings concentrate in deep pelagic waters along the southern boundary of the Antarctic Circumpolar Current; other work, on the Patagonian Shelf and in the Atlantic sector of the Southern Ocean, links them to the proximity of oceanographic fronts and of areas of high productivity. The species tolerates surface temperatures generally between 0.6 and 13 °C, with a mean of about 4.8 °C, and has been recorded down to −0.3 °C.

It is absent from metropolitan French waters: neither the Mediterranean, nor the Bay of Biscay, nor the English Channel hosts it, its distribution being strictly austral. It is, on the other hand, genuinely present in French overseas waters: the IUCN lists the French Southern and Antarctic Lands, Kerguelen and Crozet, among the territories where the species is resident, and the regional Red List treats it as a regular breeding species of the French Southern Lands. In Adélie Land it is recorded only occasionally. It also occurs off Argentina, Chile, the Falkland Islands, South Georgia, South Africa (Marion and Prince Edward Islands), Australia and New Zealand.

Biology and ecology

The hourglass dolphin lives in small groups: school size most often ranges from 1 to 12 individuals, the mean standing at around seven animals, but gatherings reaching a hundred individuals have been reported, probably linked to local prey abundance. It is a fast and energetic swimmer, which “low-leaps” in the manner of porpoises and often shows no more than a fin and a burst of spray. It has a reputation for coming of its own accord to ride the bow wave of ships, but also the bow wave of large whales. It is frequently seen in the company of fin whales, common minke whales, pilot whales and southern right whale dolphins; associations with southern bottlenose whales, Arnoux’s beaked whales and killer whales have also been reported.

Diet is known only from the examination of a handful of stomachs, five specimens in all, which contained small fish, among them myctophids, squid and crustaceans. The animals are regularly seen feeding beneath concentrations of seabirds and within plankton swarms, which suggests opportunistic predation on prey concentrated by fronts and upwellings. Like all odontocetes, the species hunts by echolocation: recordings made in the Drake Passage reveal narrow-band high-frequency clicks whose mean peak frequency reaches 126 kHz (3 dB bandwidth of 8 kHz, mean source level of 197 dB), very similar to those of dolphins of the genus Cephalorhynchus.

Reproduction remains largely an unknown. No certain observation of a newborn has been published, and neither the size, nor the coloration, nor the diet of the young is described. The values sometimes quoted, a gestation of about 12.9 months and births from the end of the austral winter into spring, are extrapolated from close relatives and do not rest on data specific to the hourglass dolphin. Sexual maturity in males appears to be reached at around 1.74 to 1.87 m. Longevity is not documented; it is estimated, by comparison with related delphinids, at between 27 and 46 years. The small number of specimens measured does not allow sexual dimorphism to be quantified precisely, even if the males examined prove on average slightly larger than the females. The killer whale is the presumed natural predator, but no attack has been formally documented.

Status and conservation

The IUCN reassessed the species on 18 March 2018 and kept it as Least Concern (LC), the status it already held in 2008 and, under an earlier wording, in 1996; it was still classed as “Insufficiently Known” in 1994. The justification is straightforward: the hourglass dolphin is widely distributed and abundant in the Southern Ocean, and no past, current or foreseeable threat has been identified. The population trend is nonetheless described as unknown, which reflects a gap in knowledge rather than a demonstrated stability: the only abundance estimate available goes back to the sighting surveys conducted from 1976-1977 to 1987-1988, which gave 144,300 individuals (coefficient of variation of 17%) south of the Antarctic Convergence. No more recent census has updated it.

The species has never been the object of commercial hunting, and the known bycatch in fishing gear remains exceptional, limited to a few isolated cases, the remoteness of its habitat keeping it largely out of reach of coastal pressures. The main concerns bear, over the longer term, on the effects of climate change on Southern Ocean ecosystems, on the development of the krill fishery and on diffuse pollution. The hourglass dolphin is listed in Appendix II of CITES.

In France, the species is protected by national regulations, which prohibit in particular its destruction, its intentional capture and its disturbance, under criminal penalties that can reach three years’ imprisonment and a fine of 150,000 euros. The regional Red List of the vertebrates of the TAAF classes it as Data Deficient (DD) in the French Southern Lands, for want of dedicated monitoring in the exclusive economic zones of Crozet and Kerguelen. The research priorities identified by the IUCN are explicit on this point: estimate the population size, refine the distribution and put monitoring of trends in place.

Watching this species

The hourglass dolphin cannot be watched from the shore: it means going to sea. The Drake Passage, between Cape Horn and the Antarctic Peninsula, is by far the best sector, to the point that most documented encounters come from expedition vessels and scientific cruises making that crossing. The approaches to the South Shetland Islands, the waters of South Georgia, southern New Zealand and the vicinity of Tierra del Fuego also produce regular sightings. In the French sector, oceanographic cruises and the supply rotations to Crozet and Kerguelen offer opportunities for an encounter, but no structured monitoring is devoted to them.

The best season is the austral summer, from November to March, when the southernmost waters, as far as the ice edge, become accessible and vessels frequent the area. Detection is often a matter of judgement: in a rough sea, what is picked up first is white spray and a tall, hooked black fin, rather than the silhouette itself. A pair of marine binoculars and a sheltered observation post are indispensable.

The ethics are simple here, since it is the animal that comes to the boat: the hourglass dolphin joins the bow of its own accord to surf there. Good practice therefore consists in holding course and speed steady, never diverting or accelerating to intercept a group, not splitting up a school, and not approaching animals feeding beneath birds. Dated, georeferenced sightings, passed on to naturalist databases, are of real value for a species whose fine-scale distribution remains poorly understood.

Frequently asked questions

Why is it called the “hourglass dolphin”?

Because of its coloration. Each flank bears two white patches, one in front of and the other behind the dorsal fin, joined by a fine white band: seen in profile, the whole draws an hourglass. Seen from above, by contrast, the black of the back suggests a Maltese cross, which explains the scientific epithet cruciger, “cross-bearer”, and the alternative French names dauphin crucigère and dauphin porte-croix.

Is the hourglass dolphin still called Lagenorhynchus cruciger?

That name remains very widespread in the literature, but it is no longer the valid name. After the break-up of the genus Lagenorhynchus, the species was first placed in Sagmatias in 2019, then transferred to the genus Cephalorhynchus following the phylogenomic work of 2025. The combination accepted today by the IUCN Red List and by the Taxonomy Committee of the Society for Marine Mammalogy is Cephalorhynchus cruciger.

Can this species be encountered in France?

Not in metropolitan France: the hourglass dolphin is strictly austral and has never been recorded in the Mediterranean, in the Bay of Biscay or in the English Channel. It is, on the other hand, present in the French waters of the Southern Ocean, around the Crozet and Kerguelen archipelagos, where it is regarded as a regular breeder, and only occasionally in Adélie Land.

How many hourglass dolphins are left?

The only estimate available dates from the sighting surveys conducted between 1976-1977 and 1987-1988: about 144,300 individuals south of the Antarctic Convergence, with a coefficient of variation of 17%. No more recent census has been published, so that the current population trend is officially described as unknown by the IUCN.

Which species might it be confused with?

Chiefly with the southern right whale dolphin, black and white and present in the same waters, but wholly lacking a dorsal fin, an immediate criterion. Around the Kerguelen Islands, Commerson’s dolphin, smaller and largely white on the forward part of the body, keeps mainly to coastal waters. The spectacled porpoise, for its part, has no lateral pattern and never rides a bow wave.

How are its sounds recognised underwater?

The hourglass dolphin produces narrow-band high-frequency echolocation clicks. Recordings made in the Drake Passage place their mean peak frequency at 126 kHz, with a 3 dB bandwidth of 8 kHz and a mean source level of 197 dB. This type of signal, well outside the range of human hearing, is characteristic of dolphins of the genus Cephalorhynchus and supports the recent assignment of the species to that group.

Why is it so poorly known when it is not rare?

Because it lives offshore, in an oceanic zone that is hard to reach and little travelled. Strandings are exceptional, and the stomach contents of only five animals have been analysed. No newborn has been formally observed, and longevity, like reproductive biology, remains estimated by analogy. The sequencing of a high-quality reference genome, obtained in 2025 from an animal stranded in New Zealand, is one of the recent advances on this species.

Sources

• https://www.iucnredlist.org/species/11144/50361701
• https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/
• https://ofb.gouv.fr/especes/lagenorhynque-sablier-lagenorhynchus-cruciger
• https://uicn.fr/wp-content/uploads/2015/03/Tableaux_Liste_rouge_Vertebres_des_Taaf.pdf
• https://en.wikipedia.org/wiki/Hourglass_dolphin
• https://fr.wikipedia.org/wiki/Dauphin_sablier
• https://animaldiversity.org/accounts/Lagenorhynchus_cruciger/
• https://www.marinebio.org/species/hourglass-dolphins/lagenorhynchus-cruciger/
• https://pmc.ncbi.nlm.nih.gov/articles/PMC12060246/
• https://www.sciencedirect.com/science/article/pii/S1055790325000168
• https://onlinelibrary.wiley.com/doi/10.1111/j.1748-7692.2009.00307.x
• https://pubmed.ncbi.nlm.nih.gov/19275335/

Species account compiled from authoritative scientific sources (IUCN, NOAA Fisheries, specialist literature) and reviewed for factual accuracy.