Striped Dolphin Stenella coeruleoalba

Striped dolphins are recognizable by their striking markings, making them one of the most beautiful small cetaceans.    They are found in the Pacific, Indian and Atlantic Oceans and most adjacent seas, in waters roughly between latitudes of 50° North and 40° South.  They are one of the most commonly encountered dolphins in the Mediterranean Sea. They are not always approachable, but when they can be observed, they are appreciated for their impressive acrobatic behavior.

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Not to be confused with:

From a distance striped dolphins could be confused with other smallish long-beaked dolphins, including pantropical spotted, spinner and common dolphins. However, at close range the unique colour pattern of this species, marked by the distinctive interrupted cape and stripes between the eye and flipper and tail stock should make it easy to distinguish.  It also has a slightly more robust or stocky build than the other species.

Distribution 

Striped dolphins are found in the Pacific, Indian, and Atlantic Oceans and many of the adjacent seas, including the Mediterranean. They range further into temperate waters than spinner, spotted, or clymene dolphins, and are generally found between latitudes of 50° North and 40° South, although there are some unusual extra-limital records from areas further north.  Like spinner and spotted dolphins, they are mostly observed in open oceans, except where deep water can be found close to shore.  They are also associated with areas of upwelling of cold, nutrient-rich water^1,2.

Striped dolphins are native to the following countries and territories: Algeria; American Samoa; Anguilla; Antigua and Barbuda; Aruba; Australia; Bahamas; Bangladesh; Barbados; Belize; Benin; Bermuda; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Brazil; British Indian Ocean Territory; Brunei Darussalam; Cambodia; Cameroon; Canada; Cabo Verde; Cayman Islands; China; Cocos (Keeling) Islands; Colombia; Comoros; Congo; Congo, The Democratic Republic of the; Cook Islands; Costa Rica; Côte d'Ivoire; Cuba; Curaçao; Cyprus; Denmark; Djibouti; Dominica; Dominican Republic; Ecuador; El Salvador; Equatorial Guinea; Ethiopia; Fiji; France; French Guiana; French Polynesia; Gabon; Gambia; Germany; Gibraltar; Greece; Greenland; Grenada; Guadeloupe; Guam; Guatemala; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; Hong Kong; India; Indonesia; Iran, Islamic Republic of; Ireland; Israel; Italy; Jamaica; Japan; Kenya; Kiribati; Kuwait; Liberia; Madagascar; Malaysia; Maldives; Marshall Islands; Martinique; Mauritania; Mexico; Micronesia, Federated States of ; Monaco; Morocco; Mozambique; Myanmar; Namibia; Netherlands; New Caledonia; New Zealand; Nicaragua; Nigeria; Niue; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Pitcairn; Portugal; Qatar; Russian Federation; Saint Helena, Ascension and Tristan da Cunha; Saint Kitts and Nevis; Saint Lucia; Saint Martin; Saint Pierre and Miquelon; Saint Vincent and the Grenadines; Samoa; Sao Tomé and Principe; Senegal; Sierra Leone; Singapore; Solomon Islands; Somalia; South Africa; Spain; Sri Lanka; Suriname; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Timor-Leste; Togo; Tonga; Trinidad and Tobago; Turks and Caicos Islands; United Arab Emirates; United Kingdom; United States; Uruguay; Venezuela, Bolivarian Republic of; Viet Nam; Virgin Islands, British; Virgin Islands, U.S.; Wallis and Futuna; Western Sahara; Yemen

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Biology and Ecology

Feeding

Striped dolphins in different regions have developed different diets:  Off the coasts of Japan, South Africa and in the in the northeast Atlantic, they feed predominantly on on lantern fish, a species that follows the diel migration to deep waters during the day and rises towards th surface at night.  In order to reach this deep prey, striped dolphins are able to dive to depths of between 200 and 700m.  In coastal areas of the northeast Atlantic, striped dolphins feed on cod and anchovy, while in the Mediterranean they appear to prefer squid^2,3.

Social structure, Reproduction and growth

Striped dolphins can form groups ranging from fewer than 30 animals to 500, and are sometimes seen in association with other species in mixed species groups of over 1000 animals.  In some ocean basins they form schools that are segregated by age class, with separate schools for juveniles, adults and mixed schools⁴. The adult and mixed schools are further split into those that are breeding or not, with one male likely breeding with multiple females.  A female is pregnant for 12-13 months, and there appear to be two times of year when births are most common – one in summer and one in winter². 

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Threats and conservation

Natural Predators

Killer whales and sharks are known to prey on striped dolphins.  The species has also experienced mass die offs due to morbillivirus breakout in the Atlantic Ocean and Mediterranean Sea^3,5-7.

Human induced threats

Like almost all small cetaceans the world over, striped dolphins are seriously impacted by entanglement in different types of fishing gear throughout their range, and fisheries bycatch has been high and potentially unsustainable in the northeast Atlantic⁸ and the Mediterranean, among other places³.

Striped dolphins have also been the victims of several mass die-offs caused by a virus called morbillivirus^3,7,9. Researchers believe that high levels of contaminants and other environmental factors somehow render this species more susceptible to viral infections^3,10-12.

Conservation status

There have been some directed hunts for striped dolphins in different locations, including Japan, where thousands of individuals were taken through the 1980’s.  But current takes are now limited to fewer than 100 individuals per year¹³.  The species has also been directly hunted either as food or because they were perceived as competition in fisheries in the Caribbean, Sri Lanka, and the Mediterranean^5,13. Despite the ongoing threats and repeated mass die-offs, striped dolphins are numerous throughout their range and are designated globally as Least Concern on the IUCN Red List of Threatened Species¹³.  The Mediterranean population, on the other hand, suffered severe depletion from a morbillivirus die-off in 1990-1992¹⁴, and does not appear to be recovering, possibly due to ongoing threats of contaminants¹⁵ and fisheries bycatch^3,16.  As such, this population is considered Vulnerable on the IUCN Red List of Threatened Species⁵   The species is listed under Appendix II of the Convention on Migratory Species (CMS).

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Striped dolphins and dolphin watching

Due to their predominantly offshore distribution, striped dolphins are not often the primary target of whale and dolphin watching tours. However, they are one of the most frequently encountered small cetacean in the Mediterranean (for example, Spain, Italy and Greece)¹⁷ and can also be observed on tours in locations where there is deep water close to shore, such as the Canary Islands and the Azores.   Different populations appear to react differently to boats, with some fleeing at high speeds – putting on a spectacle of leaps as they go, and others approaching vessels to bow ride¹⁸.  Groups that can be approached sometimes put on impressive displays with leaps and a unique behaviour called ‘roto-tailing’, during which they twist their tail as they leap high out of the water².

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