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Family: Delphinidae
Genus: Lagenorhynchus
Species: L. obscurus (Gray, 1828)
Taxonomic Notes: Some populations displaying slight color variations are occasionally referred to as Lagenorhynchus fitzroyi and called Fitzroy’s dolphin, although this is not officially recognized.
Despite the fact that the populations are widely separated, the dusky dolphin’s color pattern bears striking resemblance to that of the Pacific white-sided dolphin. Some researchers have attempted to bunch all Lagenorhynchus found in the Pacific Ocean, Peale’s and dusky dolphins, into one species, Lagenorhynchus obliquidens. This has met with a great deal of resistance, for although they look remarkably alike, they are apparently different in ways other than color and minor physical disparities.
Dusky dolphins are extremely inquisitive animals which seem to enjoy the company of ships in their waters.
Physical Description: The dusky dolphin’s physique is very similar to that of Peale’s dolphin and the Pacific white-sided dolphin. A prominent ridge runs from the dorsal fin to the flukes.
Color: Blue and white. A beautiful turquoise dorsal region runs from a small but discernible beak to and including the flukes and drops longitudinally across the upper flanks. The ventral region is white with a thin light stripe extending from the lower peduncle area across the upper flanks to dissolve near the blowhole. A bold white stripe runs from the ventral area into the blue region, then to just under the dorsal fin where it tapers out sharply. The leading edges of the flippers fade from blue to white on their posterior edges. In most, the eyes and tips of the jaw are dark.
Fins and Flukes: A large falcate dorsal fin is well developed. The flippers are well spread and nearly pointed at the tips. The flukes are small and pointed at their tips, with a median notch.
Length and Weight: The average length is 4.5 ft (1.4 m), weight about 300 lb (136 kg). The largest recorded animal was 6.75 ft (2 m). Males are slightly larger than females.
Teeth: There are 24 to 36 small, conical teeth in each side of the upper and lower jaws.
Feeding: They are known to feed on squid and small fish such as anchovies.
Breathing and Diving: The behavior of Argentine animals is markedly different during evening and daylight hours. Slow, lethargic swimming and breathing are typical during evening; daytime patterns show much more activity, no doubt because the animals are feeding.
Mating and Breeding: The gestation period is 9 to 11 months. Calves of New Zealand herds reportedly are born in midwinter; in Argentina birthing takes place in the summer months. Lactation lasts about 18 months. Calving intervals are 2 to 3 years.
Herding: Normally 5 to 30, but herds of up to several hundred are quite common. It has been suggested that herds form on an age-group basis.
Distribution: Apparent circumpolar distribution in cool temperate inshore waters off South America, South Africa, Kerguelen Island, Campbell Island, southern Australia and New Zealand.
Migration: Australian and New Zealand animals appear to migrate to northern New Zealand in April to mate and calve, and return to extreme southern waters in October and November. South African populations migrate progressively as far north as Walvis Bay, returning to the Southern Hemisphere in October and November.
