Striped dolphins show only moderate geographical variation in skeletal morphometrics, and little if any geographical variation in pigmentation pattern. However, several authors found slight but significant differences in body size between local populations in the eastern North Atlantic, the north-western Mediterranean, and the south-western Mediterranean (Rice, 1998). Calzada and Aguiar (1995) studied the variation in maximum body size of striped dolphins, in various areas of the Mediterranean Sea. Animals inhabiting the southern part of the Mediterranean are larger than those inhabiting the northern fringe. The southern fringe is characterised by stronger seasonality and lower density of dolphins, both factors likely to favour larger maximum individual body sizes in a population. The variation observed may reflect population stratification leading to a degree of genetic isolation within the western Mediterranean Sea. MtDNA differentiation also suggests that NE-Atlantic striped dolphins form a separate population from the Mediterranean population (Garcia-Martinez et at., 1999).
The striped dolphin is distributed world-wide in tropical and temperate waters. It ranges north in the Atlantic to Newfoundland, southern Greenland, Iceland, the Faroes, and Denmark, including the Mediterranean Sea; and in the Pacific to the Sea of Japan, Hokkaido, about 40°N across the western and central Pacific, and British Columbia (Canada). The southern limit of its range is Buenos Aires in Argentina, Cape Province, Western Australia, New Zealand, and Peru (Archer and Perrin, 1999; Rice, 1998; van Waerebeek et al. 1998; Baird et al. 1994).
Würsig et al. (1998) assessed cetacean responses to survey ships and aircraft and found that S. coeruleoalba moved to avoid the ships in 33% of sightings. Their data indicate that density estimates for this species may tend to be biased downwards.
Based on sighting data in 1983-91, the total current striped dolphin population in Japanese waters is estimated at 821,000 with a standard error of 182 000 although questions of stock identity remain Two concentrations of striped dolphin In the western North Pacific were identified. The first, estimated to comprise about 7,000 animals, was found between 20° and 30°N. The second, a large concentration of around 350,000 animals was located between 30° and 40°N. Relatively few striped dolphins were present in the nearshore waters off Japan, with an approximate population of 2,300 individuals (Perrin et al. 1994, and refs. therein).
In the eastern tropical Pacific, "relative" population estimates from annual survey cruises in 1986-90 range from 635,000 to 2,251,300 (Perrin et al. 1994, and refs. therein). Barlow (1995) estimated the abundance of Stenella coeruleoalba in California waters at 12,300 individuals between the coast and approximately 555 km offshore. Balance and Pitman (1998) found that S. coeroleoalba was the second most important species sighted in the West Tropical Indian Ocean (14% of all cetaceans) compared to the Eastern Tropical Pacific (33%) and Gulf of Mexico (10%).
Goujon (1996) conducted a sighting survey in 1993 and estimated population sizes of 74,000 striped dolphins in the fishing grounds of the albacore tuna driftnet fishery in the Bay of Biscay. In the western Mediterranean, it is the most common cetacean. The post-epizootic western Mediterranean population was estimated at 225 000 individuals. It was the most abundant species (43.5%) in recent surveys of the central Mediterranean (Perrin et al. 1994, Reyes, 1991 and refs. therein).
In the regions of Valencia and Murcia (Spain) in the western Mediterranean the absolute density estimated was 0.416 individuals/km² and total abundance was 12,010 individuals (Gomez de Segura et al. 2003). Mean relative density in the whole area was 0.43 individuals/nm. A very high dolphin density area was found in the north of the Ibiza channel with a highest relative density of 9.2 individuals/nm. There were no find seasonal changes in either the absolute density or in the distribution of this species in the area.
Classification: Stenella coeruleoalba was described by Meyen in 1833. Coerulealba is derived from the Latin caeruleus ('sky-blue') and albus ('white').
Local Names: Euphrosyne Dolphin; Whitebelly; Blue-White Dolphin; Meyen's Dolphin; Gray's Dolphin; Streaker Porpoise. Description: This dolphin is well-shaped, with no remarkable features, and a prominant beak. Its dorsal fin is tall and curved, with a dark blue-grey cape. The flanks are a lighter grey, leading to pink-white undersides and black flippers. There are a number of dark stripes, one running from the eye to the anus (between the grey and white areas), and others running from the eye backwards onto the white ventral surface, often linking with the flipper. The grey on the flanks forks upward and away, curving onto the dorsal cape just before the fin. Adults measure between 1.8 and 2.5m, and weigh from 90-150kg. Recognition at sea: The Striped Dolphin is easy to identify, with its tell-tale go-faster stripes. Habitat: The Striped Dolphin occupies both offshore and inshore waters. Food & Feeding: This species takes midwater fish and squid, with laternfish making up at least one-third of the catch. Behaviour: Groups range from a few animals to a few thousand, but often number bteween 100-500. Within each group are three segregations: non-mating adults, mating adults and juveniles. Striped Dolphins are an active species, regularly bowriding and leaping from the water. They vocalise with whistles and clicks. Longevity: Unknown. Estimated Current Population: Unknown. The Influence of Man: Striped Dolphins are taken in drive fisheries in the western Pacific - often numbering an average of 14,000 per year between 1950-69. By the 1980s, these numbers had fallen to between 2,000 and 4,000. Animals in the eastern Atlantic are harpooned from fishing boats to provide the crew with meat. Some individuals have been held in captivity, but have not successfully trained.