The dusky dolphin is a small, moderately robust species. The rostrum is short and clearly demarcated from the melon (forehead). The conspicuous dorsal fin is moderately falcate and pointed. The flippers are moderately curved on the leading edge, with a blunt tip.
The body coloration is complex, and is generally countershaded, dark gray to blue black above and white below. The sides are marked with blazes and patches of pale gray. In front of the dorsal fin, they bear a broad light gray thoracic patch that encompasses the face, most of the head, and flanks, tapering towards the belly. A separate crescent-shaped flank patch reaches the top of the tail stock just in front of the flukes. The front of this flank patch splits into two blazes, a shorter ventral and a longer dorsal one; this latter narrows and stretches up onto the back, almost to the blowhole. The rostrum is gray-black around the tip, tapering back to darken just the lips near the gape. The eye is set in a small patch of gray-black. A variable crescent of pale gray contrasts the trailing half of the dorsal fin with the dark-colored front half, and the flippers are pale gray, but darken around the edges. There are 27-36 teeth on each side of each jaw.
The maximum recorded length is 2.1 m. Most adults are less than 2 m long. Healthy adults weigh 70-85 kg. Length at birth has been reported to be 80-100 cm.
Can be Confused With
At sea, dusky dolphins can be distinguished from the closely related, but larger and more robust, Peale’s dolphin primarily by careful attention to color pattern components.
Dusky dolphins are widespread in the Southern Hemisphere. They occur in apparently disjunct populations in the waters off New Zealand (including the Chatham and Campbell Islands), South America (including the Falkland Islands), and southwestern Africa. This is a coastal species and is usually found over the continental shelf and slope.
Ecology and Behavior
Dusky dolphins are highly social, gregarious animals. They sometimes form impressive herds of over 1,000 individuals, but are more likely to occur in groups of 20-500. Dusky dolphins are one of the most acrobatic of dolphins, frequently leaping high out of the water, at times tumbling in the air. They readily approach vessels to engage in bowriding. Many species of cetaceans have been observed in association with dusky dolphins.
These dolphins are known to gather into large cooperative groups for feeding on schooling fish. In Peru, calving is believed to peak in September to October, while in Argentina, South Africa and New Zealand, calving appears to occur in summer months (November to February).
Feeding and Prey
Dusky dolphins take a wide variety of prey, including southern anchovy near the surface in shallower waters, as well as mid-water and benthic prey, such as squid and lanternfishes. They may also engage in nocturnal feeding, in association with the deep scattering layer.
Threats and Status
Dusky dolphins are known to be taken directly in the multi-species small cetacean fisheries of Peru, which make use of both driftnets and harpoons for capture. Although recent catches appear to have decreased, the Peruvian catch is still thought to be unsustainable. Dusky dolphins are also killed incidentally in gillnets in New Zealand, and in trawl nets in Argentina.
Dusky dolphins are currently listed as ’Data Deficient‘ (IUCN) and ’Not Listed‘ (ESA).
Brownell, Jr., R.L., and F. Cipriano. 1999. Dusky dolphin Lagenorhynchus obscurus (Gray, 1828). pp. 85-104 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Vol. 6: The second book of dolphins and the porpoises. Academic Press.
Cipriano, F.W. 1992. Behavior and occurrence patterns, feeding ecology, and life history of dusky dolphins (Lagenorhynchus obscurus) off Kaikoura, New Zealand. Ph.D., University of Arizona.
Van Waerebeek, K. 1993. External features of the dusky dolphin Lagenorhynchus obscurus (Gray, 1828) from Peruvian waters. Estudios Oceanologicos 12:37-53.
Van Waerebeek, K. and B.Würsig. 2002. Pacific white-sided dolphin and dusky dolphin Lagenorhynchus obliquidens and L. obscurus. pp. 859-861 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.
Würsig, B., F. Cipriano, E. Slooten, R. Constantine, K. Barr and S. Yin. 1997. Dusky dolphin (Lagenorhynchus obscurus) off New Zealand status of present knowledge. Reports of the International Whaling Commission 47:715-722.