Hourglass Dolphin

The hourglass dolphin is colored black on top and white on the belly, with white patches on the sides and sometimes variations of dark grey. For this reason, it was colloquially known by whalers as a "sea cow" (although it does not belong to the taxonomic order Sirenia) or "sea skunk". Each flank has a white patch at the front, above the beak, eye and flipper, and a second patch at the rear. These two patches are connected by a thin white strip, creating, loosely speaking, an hourglass shape; hence the common name of the dolphin. The markings can vary between individuals. The scientific name cruciger means "cross-carrier" and refers to the area of black coloration, which, viewed from above, vaguely resembles a Maltese cross or cross pattée.

The range is circumpolar from close to the Antarctic pack ice to about 45°S. The northernmost confirmed sightings are 36°S in the South Atlantic Ocean and 33°S near Valparaíso, Chile, in the Pacific. The overall circumpolar distribution is about 45°S to 67°S, with few sightings made near islands and the majority in the Southern ocean. Sightings have been made most commonly from the south of New Zealand, around the South Shetland Islands and off Tierra del Fuego, Argentina.

Hourglass dolphins are often seen in smaller groups up to 10–15 individuals, though groups of up to 100 have been observed.

They share feeding grounds with other cetaceans such as pilot whales, minke whales and southern right whale dolphins and are regularly seen with fin whales. Hourglass dolphins frequently bow-ride waves from ships and baleen whales. There has been observations of hourglass dolphins with southern bottlenose whales, orcas, and Arnoux's beaked whales.

Examinations of the stomach contents of the few specimens indicate they eat mantis shrimp, polychaete worms, and various (unrecorded) species of squid and small fish.

The hourglass dolphin life-span is estimated to be similar to that of Atlantic white-sided dolphin and Pacific white-sided dolphin, around 27-46 years.

Sighting surveys were conducted in 1976–77 and 1987–88. Abundance was estimated to be 144,300 individuals, based on line transect sightings in January 1977 and January 1988 in northern Antarctic waters. While the population of the hourglass dolphins has slightly declined since 1988, they are not considered endangered.

The hourglass dolphin is covered by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU). They are also listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). Although they have not been studied extensively, there are no known major threats to hourglass dolphins, and the species is listed as Least Concern on the IUCN Red List.