by: Suzanne Yin and Bernd Würsig
The genus comes from the Greek word lagenos for bottle or flask, and rhynchos meaning nose or snout; obscurus comes from a Latin word meaning 'dark, indistinct'.
Dusky dolphins have a complex body coloration pattern. Laterally, the body can be separated into four areas: spinal field, flank patch, thoracic patch and white abdominal field. The body is counter-shaded, with bluish black dorsal surface, snout and tail and a white belly and throat underneath. Blazes of gray run along the flanks.
Duskies have a short stubby beak, much different from the prominent beaks of the stenellid species. The tall and slightly hooked dorsal fin is darkly colored on the leading edge but fades to lighter gray towards the trailing edge. Flippers are pale gray in front but darken in color along the trailing edge.
The body shape is small and moderately chunky. Maximum reported length for African specimens is 1.93 m for females and 1.81 m for males. Adult weights range from 40 to 80 kg, though birth weight is not known for the African population. Reported birth length ranges from 55 to 70 cm in other areas. African specimens tend to be larger than specimens from New Zealand, but smaller than those from Peru. The largest measured female from New Zealand is 1.78 m in length while the largest female specimen from Peru is 1.93 m. Males are slightly smaller, but heavier.
In Africa, duskies are only found on the west coast, from South Africa north to Angola. This meso-pelagic species can be found in coastal or continental shelf areas associated with cool currents of the Southern Hemisphere. Other disjunct populations of duskies can be found around New Zealand, both the east and west coasts of South America, especially off Peru and Argentina, and around several oceanic islands including Tristan de Cunha and Amsterdam Islands.
Dusky dolphins are one of, if not the most, acrobatic of dolphins. Spectacular leaps, somersaults and side slaps are common, and are often repeated many times in succession by an individual animal. Duskies also readily approach boats to bowride. These dolphins can be found in groups of over 1500 animals, though group sizes of 6-300 are more common. Duskies feed on organisms associated with the Deep Scattering Layer, mainly squid and in deep waters, fishes and lanternfishes, though diet differs in different regions. Cooperative foraging on southern anchovy has been reported off Argentina and on yellow-eyed mullet off New Zealand. There, several dolphins work together to keep a school of fish in a tight ball at the surface, where members of a group can take turns feeding. Feeding bouts where this balling technique has been observed last longer than bouts where individuals feed separately. Many different species of cetaceans have been seen in association with duskies, including sperm whales, bottlenose, common and southern right whale dolphins. The oldest known dusky dolphin was from New Zealand and is estimated by dentinal or tooth growth layers to be between 35-36 years old, relatively old for a moderately sized dolphin.
Dusky dolphins have been captured for public display in South Africa and New Zealand. In fact, between 1961 and 1981, 37 dusky dolphins have bee captured for this purpose, some remaining in public display facilities in South Africa. In the past, these dolphins have also been harpooned as well as caught and killed in nets for human consumption along Cape Peninsula, South Africa. Other individuals have been incidentally killed in South African purse seines; also a significant problem in areas of South America and New Zealand. Probably the most serious threat to this species comes from the fisheries off Peru and Chile, where thousands of dusky dolphins have been killed for crab bait and human consumption. One year, the annual catch from just one Peruvian port totaled more than 700 dusky dolphins. Since 1997, this dolphin "fishery" is reported to have been discontinued or at least strongly curtailed.
In New Zealand, commercially-permitted operators can take hundreds of paying customers per week to swim with free-ranging dusky dolphins off Kaikoura, South Island. Though obviously less of a severe problem than the one faced by duskies in Peru, more work is necessary to determine the potential short and long-term impact these tourist industries may be having on the dolphins.
Insufficiently known.
Brownell, R. L. Jr. and F. Cipriano. Dusky dolphin Lagenorhynchus obscurus (Gray, 1828). Ridgway, S. H. and R. Harrison (Ed.). Handbook of Marine Mammals, Vol. 6. Handbook of Marine Mammals. Academic Press, Ltd.: London, England, UK. In press.
Jefferson, T.A., Leatherwood, S. and M.A. Webber. 1994. FAO Species Identification Guide, Marine Mammals of the World. FAO of the United Nations, Rome.
Leatherwood, S. and R.R. Reeves. 1983. The Sierra Club Handbook of Whales and Dolphins. Sierra Club Books, San Francisco.
Van Waerebeek, K. and A. J. Read. 1990. Catch of small cetaceans at Pucusana Port, central Peru, during 1987. Biological Conservation. 51: 15-22.
Würsig, B., Cipriano, F., Slooten, E., Constantine, R., Barr, K., and S. Yin. 1997. Dusky dolphins (Lagenorhynchus obscurus) off New Zealand: Status of Present Knowledge. Reports of the International Whaling Commission, 47: 715-722.
Würsig and Würsig. 1980. Behavior and ecology of the dusky dolphin, Lagenorhynchus obscurus, in the south Atlantic. Fishery Bulletin. 77: 871-890.
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