Lagenorhynchus cruciger
hourglass dolphin

Hourglass dolphins, Lagenorhynchus cruciger, are a truly pelagic species of dolphin. They are found throughout the southern oceans of the world and are circumpolar in their distribution. They range between 43 degrees south (S) and 67 degrees S and are most often associated near the Antarctic convergence. The farthest northern sighting of this species was off of the coast of Chile, 33 degrees 40' S (Goodall, 1997; Leatherwood and Reeves, 1983)

Widely distributed throughout their range, L. cruciger is rarely seen near shore and prefers the colder waters of the open ocean. Surface water temperatures range between -0.3 degrees Centigrade (C) and 7.0 degrees C with 71% of the sightings occurring between 0.1 degrees C and 0.3 degrees C. The warmest recorded surface temperature associated with this species was 13.4 degrees C (Brownell Jr. and Donahue, 1999; Goodall, et al., 1997; Klinowska, 1991)

Hourglass dolphins are small, robust, dolphins with a unique black and white color pattern. Pigmentation patterns vary greatly among L. cruciger individuals, but the sexes are monomorphic.

Hour glass dolphins have highly recurved, falcate dorsal fins with highly keeled tailstocks. The color pigmentation resembles that of an hourglass pattern for which the species gets its common name. It was first described by Qouy and Gaimard in 1824 and was called “cross bearer”.

These dolphins have homodont dentition with 53-69 conical-shaped teeth. The dental formula is 26-34 teeth in the upper jaw with 27-35 teeth in the lower jaw.

The dorsal side is all black with the white flank patches extending up to the keel of the tailstock. The sides are mostly black, marked with two variable white patches. The first (thoracic) patch begins behind the rostrum, extending above the eye and ends mid flank just before the dorsal fin. The rear (flank) patch starts behind the dorsal fin and extends to the tailstock. The two patches may or may not connect below the dorsal fin. The ventrum is mostly white from the rostrum to the tail flukes, which are black. The beak and eyes are outlined with black pigmentation.

The maximum length for L. cruciger is not known, as there are only nine records for this species. The average length of five females was 157.1 cm; 174.5 cm for three males and a third specimen of unknown gender was 155 cm. This measurement was taken from the snout to the tail fluke notch. These records would suggest that males are larger, however not enough data have been recorded to make such an assessment.

The weights of three specimens were recorded. One male weighed 94.0kg and two females weighed 73.5kg and 88.2kg. These data are also consistent with the notion that males of the species are larger than females, but with a sample of so few individuals, no generalizations can be drawn.

These dolphins can easily be distinguished south of the Antarctic convergence. They are the only small dolphin species with a dorsal fin found below this point. Above the convergence they may be confused with dusky dolphins, L. obscurus, and Peale's dolphins, L. australis (Goodall, 1997; Goodall, et al., 1997; Leatherwood and Reeves, 1983)

The mating behavior of these animals is not known.

There are very limited data on reproduction for this species. One female that was 183 cm in length was nearing sexual maturity. Two males that measured 174 cm and 187 cm in length were sexually mature. The age of these animals was not known.

There is some information on reproduction in other memebers of the genus Lagenorhynchus. Study of L. obscurus females killed in Peruvian fisheries indicates that the gestation period is about 12.9 months, and that most births occur late in the Southern Hemisphere winter (August-October). A lactation period of 12 months and an interbirth interval of 28.6 months are also recorded. In L. acutus, nursing last for about 18 months, and young become independant around the age of two years. There is generally only one offspring per pregnancy, but one female of this genus was recorded as having two embryos. Young are 90 to 125 cm in length at birth. (Goodall, et al., 1997; Nowak, 1999)

Females nurse their young, who are able to swim along with their mothers from birth. In other memebers of the genus for which data have been collected, lactation can last from 12-18 months. Other information on parental care is lacking for these animals. (Nowak, 1999)

The lifespan of L. cruciger is not known, however it may be similar to other species within its genus. The Atlantic white-sided dolphin, L. acutus, can live 27 years and the Pacific white-sided dolphin, L. obliquidens, can live up to 46 years in the wild. (Goodall, et al., 1997; Nowak, 1999)

Hourglass dolphins are social animals and travel in small groups. Social group size varies from one to 100 individuals, with an average group size of seven. It is not known if these groups are made up of related individuals, mixed sexes, or random dolphins. In 223 observed social groups, with a total of 1,634 individuals, only three calves were observed. The low cow-calf ratio may be a result of ship avoidance by cows with calves, or may result from a winter birthing season, when little research is done and few observations are made.

There may be seasonal migrations that follow cold-water currents such as the West Wind Drift. In the summer months L. cruciger is more often found in cooler southern waters. The species is found further north during the winter months.

Hourglass dolphins are attracted to large boats and ships and will often change their course of travel to intercept them. They enjoy riding in the bow waves and wakes created by the ships.

In addition to traveling with conspecifics, these dolphins often associate with other species of cetaceans. In one study, hourglass dolphins were encountered 17% of the time traveling with Fin Whales, Balaenoptera physalus; Sei whales, B. borealis; Minke whales, B. acutorostrata; Arnoux’s Beaked Whale, Berardius arnuxii; Southern bottlenose whales, Hyperoodon planifrons; long-finned pilot whales, Globicephala melaena, killer whales and southern right whale dolphins, Lissodelphis peronii. There is one account of L. cruciger swimming near southern right whales, Eubalaena australis.

L. cruciger is often seen playing around the larger rorqual whales. Hourglass dolphins commonly ride in the bow waves of these larger animals, jumping out of the water. Whalers used these playing behaviors to locate Fin Whales in their search efforts. (Brownell Jr. and Donahue, 1999; Goodall, 1997; Klinowska, 1991; Leatherwood and Reeves, 1983)

The home range of these animals is not known.

There are no recorded data on communication for this species. However, it is likely that like all odontocetes that have been studied, they communicate with high frequency sounds. They are likely to have some tactile and visual communication as well. (Leatherwood and Reeves, 1983)

Hourglass Dolphins feed primarily on fish, squid (Onychoteuthidae and Enoploteuthidae), and crustaceans. Squid beaks from these families were found in the stomach of one specimen, and the remains of Krefftichtys andersonii, a mesopelagic lantern fish were found in another. They are often seen feeding in large congregations near the surface, which attract albatross, petrels and other sea birds. Researchers will often focus in on these large aggregations of birds to locate L. cruciger. (Brownell Jr. and Donahue, 1999; Goodall, 1997)

There is no documentation of predation on these dolphins, however, they are likely preyed upon by killer whales, Orcinus orca. Like many aquatic animals, these dolphins are countershaded. Countershading is widely thought to be an antipredator adaptation, as a light underbelly is difficult to see from below, and a darker dorsal surface is less readily detected from above. (Brownell Jr. and Donahue, 1999)

The niche of hourglass dolphins is not known. They are social animals and will often travel and feed with other whales and dolphins. Based upon their diet, L. cruciger are most likely secondary or tertiary level consumers. They therefore may play some role in regulating prey populations. (Goodall, 1997)

Hourglass dolphins are not commercially harvested, but some are taken annually along with Dusky Dolphins, to be used as crab bait by local fishermen in Chile. Increasing ecotourism in the Antarctic also allows for further observations of this species. (Goodall, 1997; Nowak, 1999)

There is no known negative impact of this species on humans.

Currently L. cruciger is not listed as threatened or endangered; rough population estimates for the species are greater than 140,000. They are not exploited commercially and attempts to bring them into captivity have never been made. This is most likely due to the distribution of the species and the remoteness of the species' range. A few specimens were collected during commercial whaling operations for scientific research. Accidental by-catches from commercial fisheries are limited. Only four dolphins have been reported as having been caught in fish nets, and an additional three specimens were found stranded with severe net scars on their bodies. (Brownell Jr. and Donahue, 1999; Goodall, et al., 1997; Klinowska, 1991)

Due to its pelagic habits and its distribution in the southern oceans, not much is known about the life history of L. cruciger. To date little research has been done on this species. The measurements used in this account are from a small sample size. Future research will undoubtedly shed some light into the habits and life history of this mysterious dolphin. (Goodall, 1997)