The Atlantic spotted dolphin (Stenella Frontalis), is a marine mammal within the family of oceanic dolphins, part of the order of cetaceans. The Atlantic spotted dolphin is an acrobatic species, frequently riding the bow waves of boats , leaping out of the water, and playing at every opportunity . It is also capable of diving to up to 60 metres, remaining underwater for up to six minutes . It is known to be preyed on by sharks, but Killer whales and other small-toothed whales may also be predators of this dolphin .
All dolphins, including Stenella frontalis, are highly intelligent and social animals. They live in close-knit groups termed pods, that involve complex social organization with individual recognition and bonding. Pods range in size from a few dolphins to several thousand in offshore regions. Generally pods consist of less than 50 individuals. Atlantic spotted dolphins often school with other species, such as Spinner dolphins. The pods of Stenella frontalis vary in make-up. Segregation by age, sex, and reproductive status has been observed.
|Stenella frontalis Atlantic spotted dolfin in south of Pico island, Azores. Source: Andre Duarte Vieira|
Kingdom: Animalia (Animals)
Atlantic spotted dolphin
As the common name Atlantic spotted dolphin suggests, Stenella frontalis, has a spotted color pattern on its body. These spots are not present at birth, and generally do not appear until the onset of weaning. The first spots to appear on the calves are dark spots on the animal's ventral surface. As the dolphin approaches puberty, the ventral spots increase in number and size and pale dorsal spots appear as well. The number of spots continues to increase with age, similar to the development of spotting in Stenella attenuata. There is a large amount of variation in the adult color pattern, between populations and between individuals. At times some individuals become so heavily spotted that they appear white from a distance. Spotting seems to decrease with the distance from the continental shores of North America. In the Azores some specimens have had few or no ventral spots, but well developed dorsal spotting.
The beak of Stenella frontalis is long and narrow, a typical feature of all Stenella dolphins. Stenella frontalis has a robust head and body, that make it larger in size, but not length, than S. attenuata. Proportionately larger flippers, flukes and dorsal fins are also characteristic of Stenella frontalis. The average adult body length of the Atlantic spotted dolphin is 166-229 centimeters. The adult Stenella frontalis females tend to be slightly larger than the males, and an average adult body mass is approximately 90 kilograms.
The skull of the Atlantic spotted dolphin varies in size with individuals and with geographical region. Skull size is generally correlated with body size. Stenella frontalis has small conical teeth, 3-5mm in diameter. In each rostral row there are 32-42 teeth, and 30-40 teeth in each mandibular row. Stenella frontalis have on average a distally broader rostrum and fewer but larger teeth than S. attenuata. At times differentiating between these two spotted dolphins is difficult, especially in areas where they converge geographically.
Mature female Atlantic spotted dolphins give birth every one to five years, with the average interval between births being three years. The young is nursed for up to five years, and females become sexually mature at an estimated eight to fifteen years of age .
Females are generally sexually mature at nine years. Males do not reach sexual maturity until their 12th year. There is evidence of year round mating, and gestation is between 11 and 12 months long. Calves are normally born in May and September. There have been some observations of pods segregated by reproductive status as well as sex and age.
Stenella frontalis. Source: Arcipelago Toscano This social marine mammal forms groups consisting of up to 100 individuals ; those inhabiting coastal areas generally form the smallest schools, of 5 to 15 dolphins . These schools, which may be segregated by age and sex, have a fluid structure, with dolphins joining and splitting into smaller groups, although long-term bonds are also formed within this gregarious social system . In the Bahamas, Atlantic spotted dolphins are often known to associate with bottlenose dolphins as they travel and search for fish, squid and bottom-dwelling invertebrates on which to feed .
The Atlantic spotted dolphin is a vigorous swimmer, quite active at the surface doing forward flips and hurling itself into the air. It also has a complex communication system that is made up of narrow-band whistles. These whistles differ enough between individuals that the human ear can distinguish between individual dolphins. The dolphins are able to communicate with each other by whistling, clicking their tongues, cackling and uttering sharp cries.
Often observed in the clear, shallow waters surrounding the Bahamas, the Atlantic spotted dolphin is said to be an intermediate in appearance between the bottlenose dolphin and pantropical spotted dolphin . Its sturdy body is light grey, with a dark grey 'cape' on the back, and a white belly . A light streak extends up the shoulder, ending just below the dorsal fin, one feature which differentiates this species from the similar pantropical spotted dolphin . As the name suggests, many individuals are patterned with spots, although not all. All calves are unspotted, although some will develop spots as they age, with a number of dolphins becoming so heavily spotted they appear white from a distance . The beak of the Atlantic spotted dolphin is fairly long and sharply demarcated from the melon, and the dorsal fin is tall and sickle-shaped. Atlantic spotted dolphins inhabiting the far-offshore waters of the Gulf Stream can be smaller and completely unspotted, even as adults .
The Atlantic spotted dolphin, is found in the tropical and temperate waters of the Atlantic Ocean (Wilson and Reeder, 1993). It occurs from southern Brazil to New England in the west, to the coast of Africa in the east , generally between 50°N and 25°S .
Along the southeastern and Gulf coasts of the U.S., Stenella frontalis inhabits the continental shelf, usually within 250-350 km of the coast. In the Bahamas, the Atlantic spotted dolphin spends most of its time in the shallow water over sand flats.
The Atlantic spotted dolphin inhabits tropical and warm temperate waters. It is found most often in waters over the continental shelf, but may also inhabit deep oceanic waters in some areas . In the Bahamas, this species can be observed in clear, shallow waters, between 6 and 12 metres deep, over sandflats .
It is known to be preyed on by sharks, but killer whales and other small-toothed whales may also be predators of this dolphin .
In the Bahamas, Atlantic spotted dolphins are often known to associate with bottlenose dolphins as they travel and search for fish, squid and bottom-dwelling invertebrates on which to feed .
The diet of Stenella frontalis varies with location. They eat a variety of invertebrates, as well as small eels and herring. They have even been known to follow trawlers to eat discarded fish. Other feeding habits include feeding at or near the surface and "tracking" schools of small fish.
IUCN Data Deficient
The cost and complexity of the tuna fishery has been increased because of regulations that have been designed to lessen the number of dolphins killed by tuna fisherman.
While the Atlantic spotted dolphin has been extensively studied in the Bahamas , information on the global status of this species is lacking . Further research may be required to determine this dolphin's conservation status and what, if any, conservation measures need to be implemented. While hunting of the Atlantic spotted dolphin continues in some areas , elsewhere, dolphin-watching tours give the opportunity for people to see these charismatic animals at sea , and provide an incentive for local people to conserve them.
There are two potential threats facing this dolphin; it is hunted in the Caribbean Sea, and possibly elsewhere along the coast of South America and West Africa, for food or bait , and it is killed incidentally in fisheries in many parts of its range when it becomes entangled in fishing gear . However, it is not known how many Atlantic spotted dolphins are killed in this manner, and therefore it is not known to what extent this species is threatened with extinction; consequently, the IUCN have classified this species as Data Deficient .
In the past dolphin flesh was considered a delicacy. Besides being used for food, certain parts of its body were used for medicinal purposes. For example, the oil from the liver was used to treat ulcers. Today zoologists are interested in dolphins because they have a high intelligence level. Due to their high intelligence level, dolphins have been trained to help in underwater salvage operations and have even taken part in military exercises. (Stephen, 1973).
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