The pantropical spotted dolphin (Stenella attenuata) is a species of dolphin found in all the world's temperate and tropical oceans.
:S. a. attenuata or the offshore pantropical spotted dolphin, found worldwide in tropical waters
:S. a. graffmani or the 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.
thumb|Dolphin skipping on its tail over the water
Description
thumb|left|Pantropical spotted dolphins porpoising
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 This species has a long, thin beak and a falcate dorsal fin, which is the thinnest among dolphins.
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.
<!--According to a study reported in the October, 2008 issue of Marine Ecology Progress Series, n-->Negative impacts from fishing activities remain, despite broad "dolphin-safe" practices. Instead of reducing numbers through direct mortalities, fishing activities have disrupted the reproductive output of the northeastern pantropical spotted dolphin. The fishing had a negative impact on calf survival rates and/or birth rates. This could be caused when fishing operations separate mothers from their suckling calves, interfere with the conception or gestation of calves, or a combination of the two.
Major threats
The eastern Pacific populations of pantropical spotted dolphins are divided into 3 units – coastal and 2 offshore populations, northeastern and western-southern. Just under 5 million dolphins were killed between 1959 and 1972. 3 million of these were from the northeastern offshore population unit. Since that time, this subpopulation has been the slowest to recover, if it is truly recovering at all. Natural mortalities are occurring as well, but they are difficult to estimate.
The major threat to Stenella attenuata is individuals killed as by-catch in fisheries.
Conservation actions
The eastern tropical Pacific and Southeast Asian populations of the pantropical spotted dolphin are listed in Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As the pantropical spotted dolphin can be divided into three subspecies, studies of these distinct populations would be needed to assess conservation efforts.
In addition, the pantropical spotted dolphin is covered by the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU) and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU). The U.S. Marine Mammal Protection Act was established in 1972. U.S. Fishing vessels have since reduced dolphin by-catch deaths by 95%. The U.S. Marine Mammal Protection Act lists the northeastern and coastal stocks as "Depleted."
Dolphin deaths have greatly decreased since the establishment of the Inter-American Tropical Tuna Commission (IATTC). The Commission set mortality limits on the international fleet. In 2005, only 373 spotted dolphin deaths were observed.
Dolphin populations are able to grow at 4% per year, but the pantropical spotted dolphin populations did not improve or worsen between 1979 and 2000. The population has not recovered, even though 30 years of management has been in effect.
Although the US and international fishing agencies have reduced dolphin bycatch significantly, the northeastern subpopulation is not showing strong signs of recovery.