The Atlantic spotted dolphin (''Stenella frontalis'') is a

dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...

found in warm temperate and tropical waters of the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. Older members of the species have a very distinctive spotted coloration all over their bodies.

Taxonomy

The Atlantic spotted dolphin was first described by Cuvier in 1828. Considerable variation in the physical form of individuals occurs in the species, and specialists have long been uncertain as to the correct taxonomic classification. Currently, just one species is recognised, but a large, particularly spotty variant commonly found near

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

quite possibly may be classified as a formal subspecies or indeed a species in its own right. Atlantic spotted dolphins in the

Bahamas The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the ar ...

have been observed mating with

bottlenose dolphins Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the comm ...

. Rich LeDuc has published data that suggest the Atlantic spotted dolphin may be more closely related to the bottlenose dolphins (genus ''Tursiops'') than to other members of the genus ''Stenella''. More recent studies in the 2020's indicate that this is a consequence of

reticulate evolution Reticulate evolution, or network evolution is the origination of a lineage through the partial merging of two ancestor lineages, leading to relationships better described by a phylogenetic network than a bifurcating tree. Reticulate patterns ca ...

(such as past hybridization between ''Stenella'' (spotted dolphins) and ancestral ''Tursiops'' (bottlenose dolphins)) and

incomplete lineage sorting Incomplete lineage sorting, also termed hemiplasy, deep coalescence, retention of ancestral polymorphism, or trans-species polymorphism, describes a phenomenon in population genetics when ancestral gene copies fail to coalesce (looking backwards i ...

, and thus support ''T''. ''truncatus'' and ''T. aduncus'' belonging to the same genus. This likely explains why Atlantic spotted dolphins can mate with both species of bottlenose dolphins.

Description

The coloring of the Atlantic spotted dolphin varies enormously as it grows, and is usually classified into age-dependent phases known as two-tone, speckled, mottled, and fused. Calves are a fairly uniform gray-white, with one or no spots. When they are weaned, speckling occurs, typically between 3 and 4 years and lasting for an average of 5 years. A juvenile is considered mottled when it develops merging gray and white spots on the dorsal surface and black spots on the ventral surface. This usually happens between age 8 or 9. A fused pattern is reached when dark and white spots are on both the ventral and dorsal sides. As the animal matures, the spots become denser and spread until the body appears black with white spots at full maturation. In comparison to other dolphin species, the Atlantic spotted dolphin is medium-sized. Newborn calves are about long, while adults can reach a length of and a weight of in males, and and in females. Compared to the much smaller pantropical spotted dolphin, the Atlantic spotted dolphin is more robust. It shares its habitat with the pantropical spotted dolphin and the bottlenose dolphin. The species exhibits a range of about ten different vocalizations, including whistles, buzzes, squawks and barks, each corresponding with different behaviors.

Behavior

Atlantic spotted dolphins are extremely gregarious animals, which gather in complex social groups of 5-15, often in mixed groups with common bottlenose dolphins. They are fast swimmers and known for their bow-riding and long, shallow leaping behaviors. Their mating system consists of one male mating with several females, and the pod is highly protective over pregnant females. The dolphin’s gestational period is ~11 months, and the mother cares for its calf for up to 5 years, with the help of the rest of her group. These animals are cooperative hunters that hunt in groups at night. They strategically encircle their prey, which consists mostly of small fish, benthic invertebrates, and cephalopods such as squid. They can dive to depths of up to and can stay beneath the surface for up to 10 minutes at a time.

Population and distribution

The species is endemic to the temperate and tropical areas of the Atlantic Ocean. It has been widely observed in the western end of the Gulf Stream, between Florida and

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. Off the

, tourism industries to swim with dolphins are available. It is also present in the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...

. More infrequent sightings have been made further east, off the

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and Canary Islands. Northerly sightings have been made as far north as

Cape Cod Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer mont ...

across to the southwestern tip of Spain. They are certainly present further south, too, as far as Rio Grande do Sul in Brazil and across to west

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, but their distribution is poorly understood in these areas. About 20 years ago, only about 80 dolphins were in the Bahamas. Now, almost 200 dolphins are found there. On account of their similar appearance to other dolphins in their range, it is difficult to be sure of the Atlantic spotted dolphin's population. A conservative estimate is around 100,000 individuals.

Human interaction

Some Atlantic spotted dolphins, particularly some of those are around the Bahamas, have become habituated to human contact. In these areas, cruises to watch and even swim with the dolphins are common. They are usually not held in captivity. Atlantic spotted dolphins are an occasional target of

harpoon A harpoon is a long spear-like instrument and tool used in fishing, whaling, sealing, and other marine hunting to catch and injure large fish or marine mammals such as seals and whales. It accomplishes this task by impaling the target animal ...

fishermen, and every year some creatures are trapped and killed in gill nets, but these activities are not currently believed to be threatening the survival of the species. This species lives in the mesopelagic layer of the ocean. These dolphins are not threatened by extinction, however, commercial trade may affect their evolution and sustainability. Sometimes they are killed by harpoons off St. Vincent.

Conservation

The Atlantic spotted dolphin is included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia. They are also marked as Least Concern of the Conservation Action Plan for the World's Cetaceans.

References

*''Whales Dolphins and Porpoises'', Mark Carwardine, Dorling Kindersley Handbooks, *''National Audubon Society Guide to Marine Mammals of the World'', Reeves, Stewart, Clapham and Powell, and there is no characteristics for survival. * Perrin, William F. (2002).
Stenella frontalis
. ''Mammalian Species'' (702):1–6.

External links

Whale and Dolphin Conservation Society
{{Taxonbar, from=Q247990 Atlantic spotted dolphin Cetaceans of the Atlantic Ocean Fauna of the Mediterranean Sea Fauna of the Caribbean Mammals of the Dominican Republic Marine fauna of Africa Marine fauna of Europe Marine fauna of North America Marine fauna of South America Biota of the Gulf of Mexico Atlantic spotted dolphin Atlantic spotted dolphin