Stenella clymene (Gray, 1850)

Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 410-526 : 510

18.

Clymene Dolphin

Stenella clymene

French: Dauphin clymene / German: Clymene-Delfin / Spanish: Delfin climene

Other common names: Atlantic Spinner Dolphin, Helmet Dolphin, Senegal Dolphin, Short-snouted Spinner Dolphin

Taxonomy. Delphinus clymene Gray, 1850 ,

type locality unknown.

Taxonomy of Stenella is currently in dispute. The genus is likely polyphyletic and probably will be revised in the near future. According to molecular studies, S. frontalis is most closely related to S. coeruleoalba and S. clymene , followed by Delphinus and Tursiops aduncus . These species appear to be more closely related to each other than any of them are to 1. truncatus , S. attenuata or S. longirostris . Monotypic.

Distribution. Tropical and subtropical waters of the Atlantic Ocean including the Caribbean and Gulf of Mexico.

Descriptive notes. Total length up to 197 cm (males) and up to 190 cm (females); weight up to 90 kg. Neonatal length is unknown but thought to be less than 120 cm. The Clymene Dolphin has similar color pattern to the Spinner Dolphin ( S. longirostris ), but it is smaller in size and more robust in build. Clymene Dolphins have moderately sized, falcate dorsal fin and slender, curved flippers. Color pattern is three-toned and comprises a dark-gray dorsal cape, pale-gray flanks, and white-pink belly, throat, and lower jaw. Dorsal cape dips above eye to cover most of melon, and dips again at mid-body below dorsal fin. Lips and beak tip are black or dark gray. There is dark stripe extending longitudinally from beak tip to base of melon, and there are dark streaks running across beak like a moustache. Dark ring encircles eye, and dark band from corner of eye extends posteroventrally to leading edge of flipper joint. There are 39-52 pairs of conical teeth in each upper jaw and 39-48 pairs in lower jaw.

Habitat. Prefers deeper offshore waters with an average depth of 1870 m. The Clymene Dolphin has different distributional extensions on each side of the Atlantic Ocean. Northern limit is ¢.39° N in the western Atlantic Ocean and c.16° N in the eastern Atlantic Ocean. Southern limit is ¢.30° S in the western Atlantic Ocean and c.7° Sin the eastern Atlantic Ocean.

Food and Feeding. Little is known about the diet and preferred prey of the Clymene Dolphin. It appears to be primarily a nocturnal feeder, which is supported by analyses of stomach contents that contain small mesopelagic fish and squid species that are known to be associated with the deep scattering layer. These prey include lanternfish (myctophids), herring smelts (argentinids), and codlets (bregmacerotids). The Clymene Dolphin herds schools of fish by hunting cooperatively during the day in the Gulf of Mexico. This suggests that it has an opportunistic diet that varies geographically and by prey availability.

Breeding. There is no specific information available for this species, but life history parameters are thought to be similar to other species of Stenella . Female Clymene Dolphins may reach maturity at a length of 180 cm.

Activity patterns. The Clymene Dolphin is aerially active and is known to spin on its long axis like the Spinner Dolphin, although with fewer revolutions perjump and less elaborate acrobatics. They are also known to bow-ride.

Movements, Home range and Social organization. The Clymene Dolphin generally lives in small groups consisting of one to several tens of individuals. Average group size is ¢.70 individuals, but groups of up to 1000 individuals have been observed. In the Gulf of Mexico, group sizes are usually less than 200 individuals, and the largest groups tend to have 60-80 individuals. Sex and age classes may segregate within groups, and adult males tend not to travel in groups with mother—offspring pairs. The Clymene Dolphin is often observed in groups or in close association with Spinner Dolphins. They are also observed in groups with Short-beaked Common Dolphins ( Delphinus delphis ) oft western Africa. There are no known migratory patterns of Clymene Dolphins, and there are currently no robust data on movements or home range patterns.

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The IUCN Red List. In the northern Gulf of Mexico, there are ¢.6575 individuals, and off the east coast of the USA, there are ¢.6086 individuals. There are no estimates for total abundance or population trends. The Clymene Dolphin is occasionally taken as direct catch in dolphin harpoon fisheries in the Caribbean (e.g. St. Vincent and the Grenadines), and incidental captures occur occasionally throughout most ofits distribution. Off Brazil and Venezuela, the Clymene Dolphin is susceptible to gillnet fisheries. Incidentally caught corpses are used for shark bait and human consumption. There is no conclusive evidence on whether any of these catches are actually intentional. Overall, exploitation does not appear to be a major threat to the Clymene Dolphin. Several species of ocean dolphins, including the Clymene Dolphin, may be taken in large numbers in tuna purse-seine fisheries off western Africa, but there is currently no monitoring there.

Bibliography. Fertl, Jefferson et al. (2003), Fertl, Schiro & Peake (1997), Hammond et al. (2008k), Jefferson (2009a), Jefferson, Odell & Prunier (1995), Jefferson, Webber & Pitman (2008), LeDuc et al. (1999), Perrin & Mead (1994).

Figures

17. Pantropical Spotted Dolphin (Stenella attenuata), 18. Clymene Dolphin (Stenella clymene), 19. Striped Dolphin (Stenella coeruleoalba), 20. Atlantic Spotted Dolphin (Stenella frontalis), 21. Spinner Dolphin (Stenella longirostris), 22. Rough-toothed Dolphin (Steno bredanensus)

Distribution. Tropical and subtropical waters of the Atlantic Ocean including the Caribbean and Gulf of Mexico.