Atlantic spinner dolphin  (Stenella clymene)

One of the most recently recognised species of dolphin (2) (4), the Atlantic spinner dolphin remains among the least known of the Delphinidae (2). In appearance it is very similar to the spinner dolphin (Stenella longirostris), which is largely why it was not recognised until 1981 as a distinct species. It is a small but stocky dolphin, with a fairly long beak and a dorsal fin that is triangular to sickle-shaped. Males are larger and heavier than females, but both sexes have a white belly, light grey flanks and a dark grey cape, and a dark grey line runs down the top of the beak (2) (4). The one distinctive feature that separates the Atlantic spinner dolphin on appearance from the spinner dolphin is the black marking, somewhat like a moustache, on top of the beak (2).

Occurs in the tropical and warm temperate waters of the Atlantic Ocean, including the Caribbean and Gulf of Mexico (5).

Atlantic spinner dolphins have been generally observed in deep, offshore, tropical and warm-temperate waters, at depths of 44 to 4,500 metres (2) (5).

Atlantic spinner dolphins have been seen singly, amongst groups of spinner dolphins, and in large groups of around 100 animals (5). These schools may sometimes be divided by age and sex (2), and sometimes swim in the company of a group of common dolphins (Delphinus delphis) (4). Atlantic spinner dolphins appear to feed in midwater during the night, on fishes and squids, and many bear bite marks and scars from cookie-cutter sharks (Isistius brasiliensis) (4).

These attractive and acrobatic dolphins have been observed riding the bow waves of boats and spinning out of the water, hence their name, although the spins are not as high or as complex as those of performed by the spinner dolphin (4).

While the Atlantic spinner dolphin is currently not known to be facing any serious threats, the lack of research on this species means that the problems could simply be undocumented (2). These dolphins are harpooned in the Lesser Antilles and are sometimes caught in fishing gear in other areas (1). By-catch is likely to occur in many parts of its range, but is thought to be most significant in the eastern tropical Atlantic, off West Africa, where considerable numbers may be taken in tuna purse seines (1) (2).

The Atlantic spinner dolphin is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any international trade in this species should be carefully monitored to ensure its compatibility with the species' survival (3). The lack of information regarding this species current status has led to the World Conservation Union (IUCN) being unable to assess its risk of extinction, and thus it is classified as Data Deficient (1). Further research into this enchanting marine mammal is clearly needed, particularly into the impact of by-catch in West Africa, so that conservation measures can be promptly implemented if required.

For further information on dolphins and their conservation see:

• American Cetacean Society:
  www.acsonline.org

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