Hourglass Dolphin, Lagenorhynchus cruciger
The hourglass dolphin (Lagenorhynchus cruciger) is a rare species that can be found in Antarctic and subAntarctic waters. Most sightings of this species have been made in the southern waters near the Shetland Islands, off the coast of Tierra del Fuego, Argentina, and in the southern waters near New Zealand. It is thought that this dolphin does not congregate in large numbers in any area of its circumpolar range.
Qouy and Galmard first recognized the hourglass dolphin as a new species in 1824, by studying a drawing made in 1820 in the South Pacific. This species is the only cetacean that has been accepted as a distinct species by the sole means of sighting accounts.
Even after decades of whaling that occurred in the Southern Ocean, only three individuals have been captured. By 2010, that number rose to only six captures and fourteen visual studies. Experts studying four stranded individuals in isolated areas also gathered information about this species. This dolphin is classified within the Lagenorhynchus genus, but recent genetic studies have shown that it may be more closely related to species classified within the Cephalorhynchus genus.
The hourglass dolphin can reach an average body length of 5.9 feet with a weight between 200 and 260 pounds. It is though that females are slightly larger than males, but there have not been enough studies on this species to confirm a sexual dimorphism. This species is black and white in color, with some individuals appearing to have dark or light gray colors intermixed. Because of this, it is locally known as the sea cow. Two white patches appear in each side of this dolphin, which are separated by a black patch in between. This distinct coloring is where the species gained its common name.
Its scientific name, cruciger, is also derived from its coloration, being taken from the Latin term meaning cross-carrier. If viewed from above, this coloration resembles a cross pattée or Maltese cross. This species is so distinct within its range that it is easily identifiable when compared to other species of dolphin in the same area.
The hourglass dolphin is a social species that gathers in small groups between five and ten individuals, although one study conducted by the International Whaling Commission recorded a group of sixty individuals. This dolphin shares a feeding range with many other species including the southern right whale dolphin, minke whales, and pilot whales. This species is often associated with fin whales, so whalers once used it as a “look out” to locate their target. A study conducted on the stomach contents of one individual found that the species most likely eats a variety of small fish and squid.
The total population if the hourglass dolphin is estimated to be more than 140,000 individuals. It is protected by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU) and appears on the IUCN Red List with a conservation status of “Least Concern.”
Image Caption: Hourglass Dolphins in Drake Passage. Credit: Lomvi2/Wikipedia (CC BY-SA 3.0)