Stenella frontalis

Atlantic Spotted Dolphin

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Atlantic Spotted Dolphin Atlantic Spotted Dolphin

 

Description

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 (4). Its sturdy body is light grey, with a dark grey 'cape' on the back, and a white belly (4). 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 (2). As the name suggests, many individuals are patterned with spots, although not all. All calves are unspotted (4), but some will develop spots as they age, with a number of dolphins becoming so heavily spotted they appear white from a distance (2). 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 (2).

Geography

This species is found only in the Atlantic Ocean, from southern Brazil to the United States (New England) in the west, and to the coast of Africa in the east (the exact limits off West Africa are not well known – Perrin 2002a,b). A discontinuity in the range of the species exists in the western South Atlantic Ocean (Moreno et al., 2005).

Ecosystem

Habitat and Ecology

Distribution is mostly over the offshore continental shelf, but these dolphins also inhabit deep oceanic waters. The species is known from far-offshore Gulf-stream waters and the mid-tropical Atlantic (Perrin et al. 1987). The large, heavily spotted form of the Atlantic spotted dolphin along the south-eastern and Gulf coasts of the United States inhabits the continental shelf, usually being found inside or near the 200 m isobath (within 250-350 km of the coast), but sometimes coming into very shallow water adjacent to the beach seasonally, perhaps in pursuit of migratory fish (Perrin et al. 1987). In the Bahamas, Atlantic spotted dolphins spend much time in shallow water (6-12 m) over sand flats. The smaller and less-spotted forms that inhabit more pelagic offshore waters and waters around oceanic islands are less well known in their habitat requirements (Perrin et al. 1994; Jefferson and Schiro 1997. In the north-central and western Gulf of Mexico. Atlantic spotted dolphins were consistently found in the shallowest waters on the continental shelf and along the shelf break within the 250-m isobath (Davis et al. 1998). In addition, the bottom depth gradient (sea floor slope) was less for Atlantic spotted dolphins than for any other species.

Conservation

Although the species is widespread, abundance has not been estimated for the mid- and eastern Atlantic. Bycatches in West Africa are of unknown scale and potentially large.

 

Threats

Major Threats

No direct killing is known, other than occasional catches in small Caribbean dolphin fisheries, possible off West Africa and possibly in the Azores (Jefferson et al. 1993; Perrin et al. 1994). 

Incidental catches in fisheries are known for several areas of the range (Brazil, the Caribbean, off the east coast of the United States, and in Mauritania). Some are probably also taken incidentally in tuna purse seines off the West African coast (Van Waerebeek et al. 2000). There are no reliable estimates of the number of animals taken in any of these fisheries (Jefferson et al. 1993). Atlantic spotted dolphins are also captured incidentally in gillnets in Brazil and Venezuela (Zerbini and Kotas 1998). In Venezuela, the dolphin carcasses are used for shark bait and for human consumption (Perrin et al. 1994). Mignucci-Giannoni et al. (1999) found that the most common human-related causes observed in strandings were entanglement and accidental captures, followed by animals being shot or speared. Niero et al. (1999) reported that in 1995, a large number of Atlantic spotted dolphins washed ashore on the sandy beaches north of Nouakchott, the capital of Mauritania. Workers surveyed the coastline to assess the number of corpses and the cause of death, which was attributed to fishery interaction.
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