Pantropical spotted dolphins can be identified by their long beak sharply demarcated from the melon, slender body, strongly recurved fin and spotted body. The ventral spots fuse and fade to a medium grey, and the dorsal light spots intensify, sometimes to the point of making the animal appear nearly white above. The tip of the beak is white. Details of coloration and spot intensity vary regionally. The newborn calf is unspotted. Males are on average slightly larger than females.

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 )

Red Sea.

Spreads in the tropical and warm waters around the world.

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

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.

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.

Length: 166 – 257 cm; Weight: up to 119 kg.

Length: 257 cm

Weight: 119000 grams

• Marine

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

Stenella attenuata live mainly in tropical or warm waters, and are found in both near-shore and oceanic habitats.

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).

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).

The prey of the pantropical spotted dolphin is made up primarily of small epipelagic fish, squid and crustaceans, with some take of mesopelagic animals. The gregarious pantropical spotted dolphin forms schools that can range in size from less than one hundred to thousands of individuals. Spotted dolphin females reach sexual maturity at 9 years, males at 12 years. It is thought to mate year round. Calves are born in May and September following a gestation period 11-12 months. The pantropical spotted dolphin can live for 46 years.

Average lifespan

Status: wild: 46.0 years.

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); 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).

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

Accidental?

Not Assessed (not resident).

Very rare.

United States

Rounded National Status Rank: NU - Unrankable

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.

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).

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).

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).

Comments: Inshore and offshore stocks may warrant taxonomic separation (Douglas et al. 1984). See Perrin et al. (1987) for taxonomic revision and synonyms.