(Gray, 1828) - Dusky dolphin
Distinctive Characteristics
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 grey to black above and white below. The sides are marked with blazes and patches of pale grey. In front of the dorsal fin, they bear a broad light grey 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 2 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 grey-black around the tip, tapering back to darken just the lips near the gape. The eye is set in a small patch of grey-black. A variable crescent of pale grey contrasts the trailing half of the dorsal fin with the dark coloured front half, and the flippers are pale grey, but darken around the edges.
There are 27 to 36 small, pointed teeth on each side of each jaw.
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 differences in colour pattern.
Size
The maximum recorded length is 2.1 m. Most adults are less than 2 m long. Healthy adults weigh 40 to 80 kg. Length at birth has been reported to be 55 to 70 cm.
Geographical Distribution
Dusky dolphins are widespread in the Southern Hemisphere. They occur in apparently disjunct populations in the waters off New Zealand, South America, and southern Africa. This is a coastal species and is usually found over the continental shelf and slope.
Biology and Behaviour
Dusky dolphins are highly social, gregarious animals. They sometimes form impressive herds of over 1000 individuals, but are more likely to occur in groups of 20 to 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.
In New Zealand and Argentina, calving is believed to peak in summer (November to February).
Dusky dolphins take a wide variety of prey, including southern anchovy and mid-water and benthic prey, such as squid and lanternfishes. They may also engage in nocturnal feeding. Cooperative feeding is practiced commonly in some areas.
Exploitation
In New Zealand, some dusky dolphins are entangled in gill nets. Incidental mortality at one fishing port is estimated to be 100 to 200 animals per year. The situation in Peru is of greater concern. It has been calculated that the fishing industry from just one port kills more than 700 dusky dolphins each year. These dolphins are sold for food, so they are taken incidentally and as deliberate targets. Dusky dolphins are assumed to be relatively abundant throughout their range. However, very few surveys have been conducted and no population estimates are available.
IUCN Status
Insufficiently known.