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Pantropical Spotted Dolphin

The Pantropical Spotted Dolphin (Stenella attenuata) is a species of dolphin found in all the world’s temperate and tropical oceans. The species was beginning to come under threat due to the killing of millions of individuals in tuna. The 1980s saw the rise of “dolphin-friendly tuna [capturing methods]” in order to save millions of the species in the eastern Pacific Ocean.

Taxonomy

John Gray first identified the species in 1846. Gray’s initial analysis included the Atlantic Spotted Dolphin in this species. They are now regarded as separate. Both the genus and specific names come from Latin words meaning thin or thinning.

There are three subspecies recognized in Rice’s 1998 survey of cetacea taxonomy. Two of these have not been formally named

  • S. a. subspecies A, the offshore form found in the eastern Pacific
  • S. a. subspecies B, a form found around the Hawaiian Islands.
  • S. a. graffmani, coastal form found from Mexico to Peru

Physical description

The Pantropical Striped Dolphin varies significantly in size and coloration throughout its range. The most significant division is between coastal and pelagic varieties. The coastal form is larger and more spotted. (These two forms have been divided into subspecies only in eastern Pacific populations “” see taxonomy above).

Spots are key defining characteristics in adults, though immature individuals are generally uniformly colored and susceptible to confusion with the Bottlenose Dolphin. Populations around the Gulf of Mexico may be relatively spot-free even in adulthood. In the Atlantic, confusion is possible with the Atlantic Spotted Dolphin.

Broadly speaking the Dolphin has a long thin beak. The upper and lower jaws are darkly colored but are separated by thin white “lips”. The chin, throat and belly are white to pale grey with a limited amount of spots. The flanks are separated into three distinct bands of colour “” the lightest at the bottom, followed by a thin grey strip in the middle of the flank and a dark grey back. The tall concave dorsal fin is similarly colored. The thick tailstock matches the colour of the middle band.

The Pantropical Spotted Dolphin is very active and is prone to making large splashy leaps from the sea. It is a common breacher and will often clear the water for a second or more. Bow-riding and other play with boats is common.

Birth length is 2.5 to 3 ft (80-90 cm). Adults are about 8 ft (2.5 m) long and weigh 265 pounds (120 kg). Lifespan is approximately 40 years.

Population and distribution

The Pantropical Spotted Dolphin, as its very name proclaims, is found across all tropical and sub-tropical waters around the world “” roughly speaking all oceans and seas between 40° N and 40° S. The total world population is in excess of three million “” the second most abundant cetacean after the Bottlenose Dolphin “” of which two million are found in the eastern Pacific. However this represents a decrease from at least 7 million since the 1950s.

Centers of highest population density are the shallow warmest waters (water temperature in excess of 77 °F 25 °C). There is also a tendency for groups to concentrate where there is a high temperature gradient.

Pantropical Spotted Dolphin


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