Stenella coeruleoalba (Meyen, 1833)

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 : 510-511

19.

Striped Dolphin

Stenella coeruleoalba

French: Dauphin bleu et blanc / German: Streifendelfin / Spanish: Delfin listado

Other common names: Blue-white Dolphin, Euphrosyne Dolphin, Gray's Dolphin, Meyen’s Dolphin, Streaker Porpoise, Whitebelly

Taxonomy. Delphinus coeruleo-albus Meyen, 1833 ,

“an der ostlichen Kiiste von Stidamerika; wir harpunirten ihn in der Gegend des Rio de la Plata,” off coast of Argentina and Uruguay, South America.

Taxonomy of Stenella is currently in dispute. The genus is likely polyphyletic and will probably 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 71. truncatus , S. attenuata or S. longwrostris. Monotypic.

Distribution. Tropical to warm temperate waters from ¢.50° N to ¢.40° S in the Indian, Pacific, and Atlantic oceans, as well as many adjacent seas including the Gulf of California, Sea ofJapan, Bohai, Yellow, and East China seas, and the Mediterranean Sea. Vagrant to the Red Sea and Persian Gulf.

Descriptive notes. Total length 216- 256 cm; weight 131-156 kg. Neonates are 93-100 cm long and c.10-15 kg. Male Striped Dolphins are slightly larger than females. The Striped Dolphin is more robust in build than other species of Stenella . It has moderately long beak that is distinguished from melon by crease; a moderately sized, falcate dorsal fin; and slender, curved, darkgray flippers with tapered and pointed tips. Skin has a three-toned color pattern, with dark bluish-gray dorsal cape, pale-gray flanks, and ventral surface (including throat and lowerjaw) that is whitish-pink up to urogenital area. Pale-gray streak extends from anterior flanks posterodorsally into cape just under dorsal fin. Beak is mostly black, and stripe extends from beak to black ring around eye. From there, stripe continues down to leading edge offlipperjoint. Thin, black band borders white ventral area, and accessory stripe may streak from this border onto white area just above flipper. There are 40-55 slender, conical teeth in each jaw. Striped Dolphins in the south-western Mediterranean Sea tend to be slightly shorter than the species’ average.

Habitat. Prefers deep water and is only found near-shore where deep water occurs near the coast. Striped Dolphins are associated with areas of upwelling in the eastern tropical Pacific Ocean and the Kuroshio Current offJapan. In the western North Atlantic Ocean, they prefer waters to continental slopes. Oceanic populations of Striped Dolphins off South Africa are most abundant in the warm Agulhas Current in waters more than 1000 m deep. Along the mid-Atlantic ridge, they prefer warm sea-surface temperatures of 12-22°C. In the Mediterranean Sea, Striped Dolphins prefer waters with depths of at least 600 m.

Food and Feeding. The Striped Dolphin is known to forage at depths of 200-700 m. Off Japan and South Africa, lanternfish (myctophids) are preferred prey. Cephalopods dominate the diet in the Mediterranean Sea; preferred species include Albraliopsis morisii, common clubhook squid ( Onychoteuthis banksii), European flying squid ( Todarodes sagittatus), common arm squid (Brachioteuthis riser), eye-flash squid (Abralia veranyi), and odd bobtail ( Heteroteuthis dispar). In the north-eastern Atlantic Ocean, Striped Dolphins feed on mesopelagic squid and cephalopods. In the coastal northeastern Atlantic Ocean, dominant prey are cod ( Gadidae ) and anchovy ( Engraulidae ). Foraging of the Striped Dolphin is likely nocturnal.

Breeding. The Striped Dolphin may breed throughout the year, but offJapan, breeding is known to peak in summer and winter. Gestation lasts 12-13 months. Males reach sexual maturity at 7-15 years and females at 5-13 years. Breeding system of the Striped Dolphin is thought to be polygynous. Longevity is thought to be ¢.58 years.

Activity patterns. Off the French Riviera in the Mediterranean Sea, there are known diurnal inshore-offshore movements of Striped Dolphins. They feed close to the continental shelf at night and move offshore during the day. They are fast swimmers and skittish around boats. Acrobatic leaps are common and include a unique behavior known as “roto-tailing,” which involves rotating the tail during a high breach.

Movements, Home range and Social organization. Off Japan, average group size is c.100 individuals, and groups usually consist of less than 500 individuals. In the eastern North Atlantic Ocean, groups of 10-30 individuals are common. In the western Pacific Ocean, groups are segregated by sex and age classes. There are three types of groups: juvenile groups, adult groups, and mixed (breeding and non-breeding) groups. Young offspring join juvenile groups c.1-2 years after weaning. Striped Dolphins move seasonally with oceanic currents. Off Japan, they move north into pelagic waters with the Kuroshio Current during summer and come back south again along the coast and down into the East China Sea during winter. In the Mediterranean Sea, Striped Dolphins move north in May—September to avoid increasing sea-surface temperatures farther south. They become more abundant between the French mainland and Corsica during this time. Abundance then decreases again in December—April.

Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. The subpopulation in the Mediterranean Sea is listed as Vulnerable. Total abundance of Striped Dolphins in the western North Pacific Ocean is ¢.570,000 individuals, including 19,631 individuals off near-shore Japan. In the eastern tropical Pacific Ocean, there are 1,470,854 Striped Dolphins. There are ¢.19,000 individuals off the west coast of the USA, 94,462 individuals off the east coast of the USA, 13,143 individuals off Hawaii, ¢.74,000 individuals in the Bay of Biscay, 3325 in the northern Gulf of Mexico, and 68,379-214,800 individuals in the western Mediterranean Sea. The Striped Dolphin is, in fact, one of the most abundant species of cetaceans in the Mediterranean Sea. Morphology and genetics suggest demographic isolation between Striped Dolphins in the Mediterranean Sea and eastern North Atlantic Ocean due to limited gene flow across the Strait of Gibraltar. Overall abundance of Striped Dolphins is estimated at 2,000,000 individuals, but population trends are unknown. Direct catch of Striped Dolphins has occurred offJapan since at least the late 1800s in a combination of drive fisheries and hand harpoon fisheries. In the late 1970s, catch rate was 15,000-20,000 Striped Dolphins/year, and in the 1980s and 1990s, catch rate ranged from a few hundred to several thousand dolphins per year. In 1993, an annual quota was set at 725 individuals. Nevertheless, this catch is from more than one population and is not currently thought to be a significant threat. Opportunistic catch occurs off Taiwan, in the Solomon Islands drive fishery, and in harpoon and gillnet fisheries off Sri Lanka and St. Vincent and the Grenadines. Small numbers of Striped Dolphins are taken for baiting shrimp traps and human consumption in the Mediterranean Sea (Spain, France, and Italy). The Striped Dolphin is caught incidentally in purse-seine and gillnetfisheries throughout its distribution. High-sea driftnets likely killed many thousands of Striped Dolphins in the 1970s and 1980s before the United Nations introduced a moratorium on high-sea driftnet fishing in 1993. Pelagic driftnets in the western Mediterranean Sea continue to be illegally used by Moroccan, French, Italian, and Turkish fisheries. For example, the Italian fishery kills 5000-15,000 dolphins/year, mostly Striped Dolphins. The Striped Dolphin also is caught incidentally in pelagic trawl and driftnet fisheries off Western Europe. Heavy metal tissue concentrations, including selenium, exceed detrimental thresholds for mammals in the Mediterranean Sea. Tissue concentrations of PCBs and DDT are also much higher than thresholds known to cause reproductive impairment in bottlenose dolphins (7 Tursiops spp. ), although these levels have been declining gradually overthe last 20 years. These contaminants may have contributed to decreased immune function and increased susceptibility to the 1990-92 morbillivirus outbreak in the population of Striped Dolphins in the Mediterranean Sea, and possibly also the 2006-2007 outbreak. High concentrations of heavy metals and organochlorines have also been reported in specimens from Japan. Prey species of Striped Dolphins are being overexploited in the Mediterranean Sea. Even though the Striped Dolphin is classified as Least Concern, populations offJapan and in the Mediterranean Sea are experiencing significant threats.

Bibliography. Aguilar (2000), Aguilar & Borrell (1994, 2005), Bilandzic et al. (2012), Garcia-Martinez et al. (1995), Gomez de Segura et al. (2006), Gomez-Campos et al. (2011), Hammond et al. (2008), Jefferson et al. (2008), Kasuya (1999c), LeDuc et al. (1999), Perrin, Wilson & Archer (1994), Pulcini et al. (1993), Storelli et al. (2012), Wang & Yang Shihchu (2007).

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 to warm temperate waters from ¢.50° N to ¢.40° S in the Indian, Pacific, and Atlantic oceans, as well as many adjacent seas including the Gulf of California, Sea ofJapan, Bohai, Yellow, and East China seas, and the Mediterranean Sea. Vagrant to the Red Sea and Persian Gulf.