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 purse seines. In the 1980s, the rise of "dolphin-friendly" tuna capture methods saved millions of the species in the eastern Pacific Ocean and it is now one of the most abundant dolphin species in the world.
Taxonomy
The species was first described by John Gray 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.
Two subspecies of the pantropical spotted dolphin are recognized: S. a. attenuata or offshore pantropical spotted dolphin, found worldwide in tropical waters S. a. graffmani or coastal pantropical spotted dolphin, found in coastal waters in the eastern tropical Pacific
Another unnamed subspecies, which inhabits inland Hawaiian waters, was recognized in Rice (1998)'s overview of marine mammal taxonomy.
Description
The pantropical spotted 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).
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.
The pantropical spotted dolphin is a fairly slender, streamlined animal, with a dark cape and light spots on its body that increase in number and size as it gets older. This species has a long, thin beak and a falcate dorsal fin, which is the thinnest among dolphins. 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 number of spots. The flanks are separated into three distinct bands of color — 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 tail stock matches the color of the middle band.
The vocal repertoire of the pantropical spotted dolphin has not been clearly documented. There is no published information about the acoustic signals from South Atlantic Ocean populations of the mammal.
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.
In the eastern Pacific, the dolphin is often found swimming with yellowfin tuna (hence the problem with dolphin deaths caused by tuna fishing). However, they do not feed on that fish. In fact, the two species have similar diets of small epipelagic fish. In other areas, the species may also feed on squid and crustaceans.
Birth length is 80–90 cm. Adults are about 2.5 m long and weigh 110 to 140 kg. Sexual maturity is reached at 10 years in females and 12 years in males. The average lifespan is around 40 years.
Population and distribution
The pantropical spotted dolphin, as its name implies, is widely distributed around tropical and marine waters from 40°N and 40°S and is one of the most common dolphin species in the Atlantic and Indian oceans.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.
The pantropical spotted dolphin is the most common cetacean species observed within the Agoa Sanctuary, located in the Lesser Antilles in the eastern Caribbean. Because it is common within the sanctuary it is considered a resident species; however, no research has been carried out to estimate its population status and movement patterns between islands.
Centres of highest population density are the shallow warmest waters (water temperature in excess of 25 °C). They also tend to concentrate where a high temperature gradient is found.
Appearances of vagrancy in the Levantine Basin of the Mediterranean Sea through Suez Canal is expected.