Mammal Species of the World
Stenella attenuata lives in the Atlantic, Indian, and Pacific oceans. It migrates seasonally to the Japanese coast and is the most common cetacean in the Gulf of Mexico. (Lang 1996, Nowak 1997)
Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )
Stenella attenuata graffmani – the coastal Spotted Dolphin is found only in a narrow band (<200 km wide) along the coast of Latin America, from southern Mexico to Peru (Perrin 2001; Escorza-Treviño et al. 2005). Recent genetic data suggest there may be several populations contained within this subspecies (Escorza-Treviño et al. 2005).
The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Worldwide in tropical and some subtropical waters (some extralimital records from cooler waters) (Perrin et al. 1987); mainly between 40 degrees north latitude and 40 degrees south latitude, though mainly at lower latitudes (Jefferson et al. 1993). Mundialmente en aguas tropicales, c lidas, templadas. Desde M¿xico hasta Per£ en el Atl ntico desde M¿xico hasta Venezuela.
Distribution in Egypt
S. attenuata is referred to as the pantropical spotted dolphin because its skin becomes spotted as the dolphin grows older. Its dorsal surface is dark gray but covered in paler spots, while its paler ventral surface is covered with dark spots. Another distinguishing feature is the spotted dolphin's bright, white snout. It also has melon, a fatty area located on its forehead. The inshore spotted dolphins tend to be larger in size than offshore dolphins. Males also typically have larger body sizes than females, yet females have longer rostra. The spotted dolphin has between 29 and 37 small, rounded teeth on either side of its upper and lower jaws. It has pectoral fins (on the sides), a dorsal fin (on the central back), and tail flukes. The blowhole, used for breathing and communication, is located on the top of the head. Because S. attenuata has a thin layer of blubber, it has small amounts of stored energy, so it eats high energy foods to make up for the low energy. (Bernard et al. 1989, Lang 1996, Misek et al. 1997, Myers 1997, Nowak 1997, Perrin et al. 1994)
Range mass: 60 to 165 kg.
Other Physical Features: endothermic ; bilateral symmetry
Length: 257 cm
Weight: 119000 grams
Size in North America
Range: 1.6-2.6 m males; 1.7-2.5 m females
Range: up to 119 Kg
S. attenuata lives in the tropical and subtropical areas of the ocean and seas. Although some live inshore, most members of the species live offshore, where the temperature of the deeper water remains fairly constant. The majority of this species live in between the equator and the Galapagos Islands for the same reason that they tend to live offshore. The home range is hundreds of kilometers in diameter. (Nowak 1997)
Aquatic Biomes: coastal
Habitat and Ecology
Offshore Spotted Dolphins feed largely on small epi- and mesopelagic fishes, squids, and crustaceans that associate with the deep scattering layer (Robertson and Chivers 1997). In some areas, flying fish are also important prey. The diet of the coastal form is poorly known, but is thought to consist mainly of larger fishes, perhaps mainly bottom-living species (Perrin 2001, 2002).
Habitat Type: Marine
Comments: Primarily a high-seas pelagic species found in deep water far from land; a larger form inhabits the onshore waters of Mexico and Central America (Perrin, in Wilson and Ruff 1999).
Water temperature and chemistry ranges based on 1759 samples.
Depth range (m): 0 - 60
Temperature range (°C): 13.598 - 29.446
Nitrate (umol/L): 0.036 - 10.235
Salinity (PPS): 31.742 - 36.791
Oxygen (ml/l): 4.400 - 6.082
Phosphate (umol/l): 0.058 - 0.889
Silicate (umol/l): 0.787 - 7.399
Depth range (m): 0 - 60
Temperature range (°C): 13.598 - 29.446
Nitrate (umol/L): 0.036 - 10.235
Salinity (PPS): 31.742 - 36.791
Oxygen (ml/l): 4.400 - 6.082
Phosphate (umol/l): 0.058 - 0.889
Silicate (umol/l): 0.787 - 7.399
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Makes seasonal migrations within annual home range (Perrin et al. 1987); offshore in fall and winter, onshore in spring and summer (IUCN 1991).
The spotted dolphin finds its prey, squid and small fish, near the ocean surface. These dolphins have also been known to feed on isopods and pteropods. Lactating females eat significantly more fish than pregnant or normal spotted dolphins. The lactating female's deviation from the norm is presumably because she requires more energy than normal and pregnant dolphins. More protein and also more energy is obtained from eating fish, rather than from eating the same mass of squid. In addition, fish also contain more calcium and phosphorous, which aid in lactation. Lastly, fish have lower water content, which prevents additional water loss in the lactating female since the consumed fish are hypotonic with the sea water. (Bernard 1989, Lang 1996, Nowak 1997)
Animal Foods: fish; mollusks; aquatic crustaceans
Primary Diet: carnivore (Piscivore , Molluscivore )
Comments: Recorded stomach contents include various small epipelagic and mesopelagic fishes and squids and unidentified nemertean worms and crab larvae (Perrin et al. 1987). In eastern tropical Pacific, diet dominated by squid in pregnant females, by fishes in lactating females (Bernard and Horn 1989).
10,000 to >1,000,000 individuals
Comments: Northern offshore population in the eastern tropical Pacific may have averaged 2.5 million in 1981-1986; the southern offshore stock was estimated at 250,000-500,000 in the 1980s (IUCN 1991).
In eastern tropical Pacific, commonly associates with yellowfin tuna (as do spinner dolphins and sea birds). Pod size: a few individuals to several thousand. For oceanic populations, annual home range diameter may be several km or more. (Perrin et al. 1987).
Life History and Behavior
Perception Channels: tactile ; chemical
Status: wild: 46.0 years.
Lifespan, longevity, and ageing
The mean age of sexual maturity for northern offshore female spotted dolphins is estimated to be 11.1 years, which is higher than the estimated age of 9.8 years for southern offshore females. On the other hand, males' average age of sexual maturity is 14.7 years. S. attenuata does not have any particular birthing season, although the number of births does rise in spring and autumn months. The time between births is between 26 and 36 months in the eastern Pacific and approximately 48 months near Japan. The gestation period lasts a little less than a year, and the lactation period can last for 1.5 years or longer. Females usually give birth to a single offspring (Bernard et al. 1989, Chivers et al. 1993, Nowak 1997)
Breeding interval: The time between births is between 26 and 36 months in the eastern Pacific and approximately 48 months near Japan
Breeding season: These dolphins breed year round
Average number of offspring: 1.
Range gestation period: 12 (high) months.
Average gestation period: 12 months.
Average weaning age: 18 months.
Average age at sexual or reproductive maturity (female): 9.8 to 11.1 years.
Average age at sexual or reproductive maturity (male): 14.7 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Average birth mass: 10000 g.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 3956 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 2983 days.
This lactation period is more than three times as long as other large whales. Occasionally females have been known to lactate during a new pregnancy, and some have also been known to give birth to twins, although this is rare. Mother dolphins feed near the surface so that they don't have to leave their calves. Pregnant females up to age 35 have been discovered.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); extended period of juvenile learning
Two calving peaks occur in the eastern tropical Pacific, one in spring and one in fall (Jefferson et al. 1993). Calving interval averages 2-3 years in eastern Pacific, 4-6 years in western Pacific. Males are sexually mature at average age of 15 years, females at average of 10-12 years. Old females may not reproduce. Maximum longevity may exceed 45 years (see Perrin et al. 1987).
Molecular Biology and Genetics
Barcode data: Stenella attenuata
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Stenella attenuata
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1
Because S. attenuata tend to swim with yellowfin tuna, Pacific fishermen use sightings of these dolphins to help them locate their yellowfin tuna targets. The majority of S. attenuata deaths are a consequence of yellowfin tuna fishing operations. The enormous nets used to catch these tuna can unintentionally entangle dolphins as well as fish. S. attenuata is the dolphin species that has been affected to the greatest extent by the tuna fish industry. Between 1985 and 1990, almost 130,000 were killed each year because of the tuna fish catching methods. Thanks to United States government regulations, such as requiring improvements in fishing equipment, this number has decreased substantially by 100,000 deaths per year. Some spotted dolphins are killed intentionally by Japanese fishermen. Between 500 and 2000 spotted dolphins are harvested annually in order to be eaten by the Japanese. (Bernard et al. 1989, Chives et al. 1993, Nowak 1997, Perrin et al. 1994)
IUCN Red List of Threatened Species: least concern
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1994Insufficiently Known(Groombridge 1994)
National NatureServe Conservation Status
Rounded National Status Rank: NU - Unrankable
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Worldwide range in warm oceans; population may be near 3 million in eastern tropical Pacific portion of the range; a decline has occurred in the eastern tropical Pacific as a result of mortality in the tuna fishery.
Status in Egypt
Global Short Term Trend: Relatively stable (=10% change)
Comments: Still widely distributed and abundant, but some populations have declined. Northern offshore population in the eastern tropical Pacific apparently declined by 40-60% from the early 1960s to the mid- to late 1970s; declined from about 4 million in 1975-1980 to an average of 2.5 million in 1981-1986, though fluctuations in oceanographic conditions may have confounded these results (IUCN 1991).
Spotted Dolphins are also taken incidentally in local fisheries along the Central American coast (Palacios and Gerrodette 1996).
Yang et al. (1999) also reported incidental mortality in Chinese fisheries, and Dolar 1994 found incidental spotted dolphin takes in the Philippines. An unknown but suspected large number of Pantropical Spotted Dolphins are taken by the large-mesh pelagic driftnet fishery off eastern Taiwan (J. Wang pers. comm.).
Japan takes large numbers of spotted dolphins for human consumption. The catch in 1982 was 3,799, and annual catches between 1994 and 1997 ranged from 23 to 449 (Perrin 2002). Between 1995 and 2004, the average annual catch was 129 animals (Kasuya 2007). The drive fishery for Spotted Dolphins began in 1959 and is thought to have caused a slight decline in the minimum age at attainment of sexual maturity in females (Kasuya 1985).
Pantropical Spotted Dolphins are also taken in hand-harpoon fisheries in the Philippines (Dolar et al. 1994); in Taiwan, where it is the locally preferred species of cetacean for human consumption (J. Wang pers. comm.); and regularly or opportunistically by gillnet and harpoon in India and Sri Lanka (Perrin and Hohn 1994). Drive hunts at Malaita in the Solomon Islands took several hundred or thousands of Spotted Dolphins annually in the 1960s; the hunts continue at present (Ross et al. 2003, Kahn 2006). Small numbers are taken in numerous small subsistence fisheries for dolphins and whales around the world, e.g. at St. Vincent in the Lesser Antilles (Perrin and Hohn 1994) and Lamalera in Indonesia (Kahn 2004). Most of these kills have not been adequately monitored and the effects on the subpopulations are usually not known.
Dolphins and small whales of several species, including S. attenuata, putatively interfere in hook-and-line fisheries for squid and yellowtail in the Iki Island region of Japan (Kishiro and Kasuya 1993). Bounties have been paid to fishermen for dolphins killed since 1957. During the period 1976–1982 a total of 538 Spotted Dolphins were killed. The effect of these takes on the regional population is not known (Perrin and Hohn 1994).
Degree of Threat: C : Not very threatened throughout its range, communities often provide natural resources that when exploited alter the composition and structure over the short-term, or communities are self-protecting because they are unsuitable for other uses
Comments: Some populations have declined as result of mortality associated with purse-seine tuna fishery in eastern tropical Pacific (Smith 1983, IUCN 1991); takes of 100,000s per year occurred in the 1960s and 1970s (Jefferson et al. 1993); estimated that 70,000 were killed in 1986 (IUCN 1991); annual mortality in the late 1980s was in the 10,000s (Jefferson et al. 1993). Taken also in drive fisheries in Japan and the Solomon Islands, in gillnet and harpoon fisheries in Sri Lanka, and in the Caribbean small cetacean fishery, among others (Jefferson et al. 1993).
Spotted Dolphins, as with other species impacted by the ETP tuna purse-seine fishery, are managed both nationally by the coastal countries and internationally by the IATTC. The IATTC has imposed annual stock mortality limits on each purse seine and promulgated regulations regarding the safe release of dolphins (Bayliff 2001).
As the species comprises several subspecies and regional populations, the conservation status of each of these should be assessed separately since the available estimates of abundance and removals suggest that some of them may fall into a Threatened category.
Relevance to Humans and Ecosystems
Regulations designed to lessen the number of dolphins killed by tuna fishermen have increased the cost and complexity of the fishery.
The spotted dolphin helps yellowfin tuna fishermen to locate their target. (Nowak 1997)
Comments: Some (at least several hundred) are taken directly in fisheries in various parts of the range. One of the dolphin species blamed for interference in a hook-and-line fishery of Iki Island in Japan. See IUCN (1991).
IUCN Red List Category
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 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.
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.
Three subspecies are recognised in Rice's 1998 survey of cetacean taxonomy. Two of these have not been formally named.
- S. a. subspecies A, the off-shore form found in the eastern Pacific
- S. a. subspecies B, a form found around the Hawaiian Islands
- S. a. graffmani, a coastal form found from Mexico to Peru
- S. a. attenuata.
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.
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 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 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 120 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 found across all tropical and subtropical 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.
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.
The pantropical spotted dolphin's propensity for associating with tuna, particularly in the eastern Pacific, has in recent history been a very real danger. In the 1960s and 1970s, fishermen would capture thousands of dolphin and tuna at once using purse seine nets. The dolphins all died. Over a period of about 25 years, 75% of this region's population, and over half the world's total were wiped out. The issue has received wide public attention. Many major supermarkets have found it economically expedient to use tuna suppliers whose fisherman catch tuna by more discriminatory means, and thus advertise their tuna product as dolphin-friendly. Some such products are approved by the Whale and Dolphin Conservation Trust.
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.
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 use of Order Cetartiodactyla, instead of Cetacea with Suborder Odontoceti, is favored by most evolutionary mammalogists working with molecular data  and is supported the IUCN Cetacean Specialist Group and by Taxonomy Committee  of the Society for Marine Mammalogy, the largest international association of marine mammal scientists in the world. See Cetartiodactyla and Marine mammal articles for further discussion.
- Mead, J. G.; Brownell, R. L., Jr. (2005). "Order Cetacea". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. pp. 723–743. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. (2008). Stenella attenuata. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 7 October 2008.
- Agnarsson, I.; May-Collado, LJ. (2008). "The phylogeny of Cetartiodactyla: the importance of dense taxon sampling, missing data, and the remarkable promise of cytochrome b to provide reliable species-level phylogenies". Mol Phylogenet Evol. 48 (3): 964–985. doi:10.1016/j.ympev.2008.05.046. PMID 18590827.
- Price, SA.; Bininda-Emonds, OR.; Gittleman, JL. (2005). "A complete phylogeny of the whales, dolphins and even-toed hoofed mammals – Cetartiodactyla". Biol Rev Camb Philos Soc. 80 (3): 445–473. doi:10.1017/s1464793105006743. PMID 16094808.
- Montgelard, C.; Catzeflis, FM.; Douzery, E. (1997). "Phylogenetic relationships of artiodactyls and cetaceans as deduced from the comparison of cytochrome b and 12S RNA mitochondrial sequences". Molecular Biology and Evolution 14 (5): 550–559. doi:10.1093/oxfordjournals.molbev.a025792. PMID 9159933.
- Spaulding, M.; O'Leary, MA.; Gatesy, J. (2009). "Relationships of Cetacea -Artiodactyla- Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution". PLoS ONE 4 (9): e7062. Bibcode:2009PLoSO...4.7062S. doi:10.1371/journal.pone.0007062. PMC 2740860. PMID 19774069.
- Cetacean Species and Taxonomy. iucn-csg.org
- "The Society for Marine Mammalogy's Taxonomy Committee List of Species and subspecies".
- The Illustrated Encyclopedia Of North American Mammals: A Comprehensive Guide to Mammals of North America. MobileReference. 2009. ISBN 9781605012797.
- University of California, San Diego, Scripps Institution of Oceanography (November 24, 2008). "Dolphin Population Stunted by Fishing Activities". Newswise, Inc. Retrieved September 24, 2012.
- "Appendix II" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.
- Convention on Migratory Species page on the Pantropical spotted dolphin, Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia
- Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region
- Pantropical Spotted Dolphin by William F. Perrin in Encyclopedia of Marine Mammals pp. 865–867. ISBN 978-0-12-551340-1
- Whales Dolphins and Porpoises, Mark Carwardine, Dorling Kindersley Handbooks, ISBN 0-7513-2781-6
- National Audubon Society Guide to Marine Mammals of the World, Reeves, Stewart, Clapham and Powell, ISBN 0-375-41141-0
- Variation of spotted and spinner porpoise (genus Stenella) in the Eastern Pacific and Hawaii William F. Perrin
Names and Taxonomy
Comments: Inshore and offshore stocks may warrant taxonomic separation (Douglas et al. 1984). See Perrin et al. (1987) for taxonomic revision and synonyms.