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Gregory R. Mann, Ph.D. {ret.}

Pantropical Spotted Dolphin

“Stenella attenuata”

The most distinctive feature of the Pantropical Spotted Dolphin is as its name suggests, the spots that speckled the body of adults. Newborn calves are non-spotted but by adulthood, a varying amount of light spots cover the upper surface and dark spots cover the dolphin’s underside. Underneath this spotting, the slender, stream-lined body is grey with a darker grey cape extending back from the head and sweeping low underneath the dorsal fin. The dorsal fin is narrow & sickle-shaped. The long, thin beak of the Pantropical Spotted Dolphin is separated from the melon by a distinct crease. In most adults, the tip of the beak is white. Males are slightly larger than females. The gregarious Pantropical Spotted Dolphin forms pods that can range in size from less than 100 to a 1,000+ individuals; although it has been observed that these impressively large pods are less common in the eastern tropical Pacific Ocean than they once were as exploitation takes its toll. The Pantropical Spotted Dolphin is well-known for its tendency to associate with schools of Tuna in the region. While this may be due to an overlap in diet, other reasons for this association have also been suggested such as increased protection from predators as there is safety in numbers.

The Pantropical Spotted Dolphin is a fast swimmer that often engages in a range of aerial acrobatics and will frequently ride the bow waves of boats, except for in tuna fishing grounds where it has learned to avoid vessels. Juveniles in particular are known to make astoundingly high vertical leaps out of the water. The Pantropical Spotted Dolphin feeds mainly at night on small fish, squid & crustaceans that rise to near the surface at dusk, with flying fish forming a major part of the diet in some regions. In turn, they becomes prey for the Killer Whale and a number of sharks. While the breeding system of this species is not known, it is possible that it may be promiscuous like that of the closely related Spinner Dolphin. Every 2-3 years, mature female Pantropical Spotted Dolphins give birth to a calf after a gestation period of around 11 months. The calf is nursed for between 1-2 years. Females reach sexual maturity at 9 to 11 years, while males become sexually mature between the ages of 12 and 15 years.

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