Pantropical Spotted Dolphin - Stenella attenuata

Taxonomy & Nomenclature

Scientific Name Stenella attenuata
Author (Gray, 1846)
Taxonomic Rank Species
Taxonomic # 180430
Common Names English: Pantropical Spotted Dolphin
Spanish: Delfín moteado
Current Standing valid
Taxonomic Parents Kingdom: Animalia
  Phylum: Chordata
    Subphylum: Vertebrata
      Class: Mammalia
        Subclass: Theria
          Infraclass: Eutheria
            Order: Cetacea
              Suborder: Odontoceti
                Family: Delphinidae
                  Genus: Stenella
Taxonomic Children Subspecies: Stenella attenuata attenuata
Subspecies: Stenella attenuata graffmani
Synonyms (since 1950)
Taxonomic data is courtesy of the Integrated Taxonomic Information System (ITIS)
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Physical Description / Field Identification

Pantropical spotted dolphins (sometimes called "spotters") are slender, streamlined animals. They have a long, slender beak that is separated from the melon by a distinct crease. The dorsal fin is narrow, falcate, and usually pointed at the tip, and the flippers are slender and recurved.

Although unspotted at birth, by adulthood spotted dolphins have varying degrees of white mottling on the dark dorsal cape, which is narrow on the head and sweeps low on the flank in front of the dorsal fin. The spotting ranges from very slight (or even non-existent) in offshore animals to mottling extensive enough to obliterate the cape in coastal dolphins. The lower sides and belly of adults are gray and the lips and beak tip tend to be brilliant white. A dark gray band encircles the eye, and continues forward to the apex of the melon; there also is a dark gape-to-flipper stripe.

In at least the eastern tropical Pacific, a separate coastal form exists. It is larger and stockier, with a thicker beak and more extensive spotting than the offshore form. At birth, pantropical spotted dolphins are about 85 cm long. Adults are from 1.6-2.4 m (females) or 1.6-2.6 m (males). Animals from offshore populations can weigh up to at least 120 kg, but coastal spotted dolphins are larger. In each tooth row are 34-48 slender, sharply pointed teeth.

Can be Confused With

Pantropical spotted dolphins can be confused with several other long-beaked oceanic dolphins. Spinner dolphins can be distinguished by differences in dorsal fin shape, beak length, and color pattern. Atlantic spotted dolphins can look similar, but attention to head shape, dorsal fin shape, and color pattern details will allow correct identification. In addition to Atlantic spotted dolphins, both bottlenose and humpback dolphins can also be spotted (generally on the belly) but will be distinguishable by differences in body shape and size.

Distribution

Pantropical spotted dolphins are creatures of oceanic tropical zones, although they do occur close to shore in some areas where deep water approaches the coast. As their name implies, these animals are pantropical, found in all oceans between about 40°N and 40°S, although they are much more abundant in the lower latitude portions of their range.

In the Atlantic Ocean, pantropical spotted dolphins are found in the Gulf of Mexico, Bay of Campeche, the West Indies, along the Atlantic coast of the United States as far north as Cape Hatteras, and east to the Canary Islands.

In the eastern Pacific Ocean, pantropical spotted dolphins are found in the eastern tropical Pacific, in the Gulf of California, and along the coast of Central America and South America to Ecuador and Peru. In the western Pacific, its range includes the coast of Japan and the waters of Micronesia, Indonesia, and the Philippines.

In the Indian Ocean, pantropical spotted dolphins are found in the Bay of Bengal, the waters near India and Sri Lanka, the Gulf of Oman and Gulf of Aden, near the Seychelles Islands, and near Madagascar and the Natal Coast of South Africa.

Ecology and Behavior

These oceanic animals are among the most abundant dolphins in the eastern tropical Pacific (ETP) and are the primary species involved in the tuna/dolphin interaction there. In at least the Pacific and Indian oceans, spotted dolphins associate with yellowfin tuna, spinner dolphins, and other oceanic predators; fishermen take advantage of this association to help them locate and catch tuna more efficiently.

School sizes are generally less than 100 for the coastal form, but offshore herds may number in the thousands. These gregarious animals are fast swimmers, often engaging in acrobatics, and frequently bowriding (except on the tuna fishing grounds of the ETP, where they generally have learned to avoid boats). Although pantropical spotted dolphins breed year-round, there are two calving peaks in the ETP, one in spring and one in fall.

Feeding and Prey

Pantropical spotted dolphins feed by seizing prey and they have a broad diet, characterized by: Fish>squid>other invertebrates. They feed largely on small epi- and mesopelagic fish, squid, and crustaceans that associate with the deep scattering layer. In some areas, flying fish are also important prey.

Known prey species include:

Fish: Oxyporhamphus micropterus, Exocoetus sp., Diogenichthys sp., Lampanyctus parvicauda, Myctophum aurolaternatum, unidentified Mycotophidae, Vinciguerria sp., Bregmaceros sp., Scopelogadus bispinosus, Cubiceps carinatus, Cubiceps sp., Symbolophorus sp., Myctophum aurolaternatum, Myctophum nitidulum, Myctophum asperum, Myctophum spinosum, Lampanyctus omostigma, Lampanyctus festivus, Lampanyctes idostigma, Lampadena luminosa, Diaphus splendidus, Diaphus mollis, Hygophum proximum, Hygophum reinhardtii, Diogenichthys mexicanus, Tarletonbeania crenularis, Notoscopelus resplendens, Ceratoscopelus warmingii, Taaningichthys spp., Parvilux ingens, Benthosema panamense, Cubiceps pauciradiatus, Cubiceps baxteri, Cubiceps cf. paradoxus, Howella sp., Auxis thazard, Hyperglyphe sp., Oxyporhamphus micropterus, Bregmaceros bathymaster, Scopelarchus guentheri, Scopelosaurus cf. harryi, Stemonosudis sp., Scopelogadus bispinosus, Vinciguerria lucetia, Ichthyococcus sp., Gonostomatidae, Xenopthalmichthys spp.

Invertebrates: Onykia sp., Ommastrephidae, Abraliopsis affinis, unidentified Histioteuthidae, unidentified Chiroteuthidae, unidentified Cranchiidae, Octopoteuthis sp., Ommastrephes bartramii, Eucleoteuthis luminosa, Sthenoteuthis oualaniensis, Dosidicus gigas, Hyaloteuthis cf. pelagica, Nototodarus cf. hawaiiensis, Onychoteuthis banksi, Ancistrocheirus lesuerii, Pterygioteuthis giardi, Mastigoteuthis dentata, Leachia dislocata, Megalocranchia sp., Liocranchia reinhardti, Pholidoteuthis boschmai, Thysanoteuthis rhombus, Octopoteuthis deletron, Chtenopteryx sicula, Grimalditeuthis bonplandi, Architeuthis sp., Histioteuthis dofleini, Histioteuthis meleagroteuthis, Enoploteuthis sp., Abraliopsis sp., Argonauta sp., Tremoctopus violaceus, Japatella mollis, Decapoda, Isopoda

Threats and Status

Main threats include:

• Fisheries bycatch

• Harvest

The IUCN classifies the pantropical spotted dolphin as “lower risk/conservation dependent”, meaning there are conservation and management programs in place that address the concerns for this species at this time. The United States does not list this dolphin as threatened or endangered.

The greatest known mortality of this species has been in the eastern tropical Pacific (ETP) tuna purse seine fishery for tuna. Since the interaction was first documented in the late 1960s, millions have been killed. Current mortality in this fishery has been greatly reduced by years of modifications to the fishing practices, fleet changes, and United States and international legislation. In addition, pantropical spotted dolphins are taken incidentally in a number of other purse seine, gillnet, and trawl fisheries throughout the range. Large direct kills occur sporadically in the Japanese small cetacean drive and harpoon fisheries, and much smaller direct kills have occurred in the dolphin fisheries of the Caribbean, Sri Lanka, Philippines, Indonesia, St. Helena, and the Laccadive and Solomon Islands.

The United States National Marine Fisheries Service has estimated abundance of several stocks of this species. In 1998, the Pacific population of pantropical spotted dolphins was estimated as follows coastal stock = 108,289 (CV = 0.405), northeast offshore stock = 1,011,104 (CV = 0.264), and western/southern stock = 743,166 (CV = 0.298). The Hawaiian stock was estimated to be 2,928 (CV = 0.45) in 2000. The Gulf of Mexico population was estimated in 1995 to be 31,320 (CV = 0.20). In the Atlantic, NMFS assesses population for pantropical spotted dolphins in conjunction with Atlantic spotted dolphins (S. frontalis) due to difficulties differentiating the two at sea. The best estimate of the combined species in the western North Atlantic, from the Gulf of St. Lawrence to Florida, is 13,117 (CV = 0.56).

Links

References

Dizon, A.E., W.F. Perrin and P.A. Akin. 1994. Stocks of dolphins (Stenella spp. and Delphinus delphis) in the eastern tropical Pacific a phylogeographic classification. NOAA Technical Memorandum NMFS 119:1-20.

Gerrodette, T. 1999. Preliminary estimates of 1998 abundance of four dolphin stocks in the eastern tropical Pacific. U.S. Department of Commerce, SWFSC Administrative Report LJ-99-04.

Hansen, L.J., K.D. Mullin and C.L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico from vessel surveys. U.S. Department of Commerce, SEFSC, Contribution No. MIA-94/95-25.

Kasuya, T. 1985. Effect of exploitation on reproductive parameters of the spotted and striped dolphins off the Pacific coast of Japan. Scientific Reports of the Whales Research Institute 36:107-138.

Mobley, J.R., Jr., S.S. Spitz, K.A. Forney, R.A. Grotefendt and P.H. Forestall. 2000. Distribution and abundance of odontocete species in Hawaiian waters preliminary results of 1993-1998 aerial surveys. U.S. Department of Commerce, SWFSC Administrative Report LJ-00-14C.

Perrin, W.F. 2001. Stenella attenuata. Mammalian Species 683:1-8.

Perrin, W.F. 2002. Pantropical spotted dolphin Stenella attenuata. pp. 865-867 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.

Perrin, W.F. and A.A. Hohn. 1994. Pantropical spotted dolphin Stenella attenuata. pp. 71-98 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Volume 5: The first book of dolphins. Academic Press.

Perrin, W.F., E.D. Mitchell, J.G. Mead, D.K. Caldwell, M.C. Caldwell, P.J.H. van Bree and W.H. Dawbin. 1987. Revision of the spotted dolphins, Stenella spp. Marine Mammal Science 3:99-170.

Robertson, K.M. and S.J. Chivers. 1997. Prey occurrence in pantropical spotted dolphins, Stenella attenuata, from the eastern tropical Pacific. Fishery Bulletin 95(2):334-348.

Waring, G.T., J.M. Quintal and C.P. Fairfield. 2002. U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments – 2002. U.S. Department of Commerce, NOAA Technical Memorandum, NMFS-NE-169.

ITIS TSN180430
Status - ESA, U.S. FWS -
    -
Status - Red List, IUCN -
    LC (Global or one of the sub regions)
#records (spatial)3,940
#records (non-spatial)0
#datasets92
Year1846 - 2016
Latitude-34.65 - 40.66
Longitude-178.30 - 167.05
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