The species Delphinus delphis was described by Linnaeus in 1758, in his original classification of nature. Since then many different species of common dolphins have been described, and most of these are now considered in the synonymies of either D. delphis or D. capensis.
Size, shape and distinctive characteristics
Short-beaked common dolphins are moderately robust, with tall, slightly-falcate dorsal fins. They have moderately-long, well-defined beaks, and more rounded, bulging melons than their congener. Short-beaked common dolphins are strikingly patterned, with a dark brownish-gray back, white belly, and tan to ochre thoracic patch (giving rise to the species' most characteristic feature: an hourglass pattern on the side). The color pattern is highly variable. There are 41-57 pairs of small, sharp, pointed teeth in each jaw.
Short-beaked common dolphin adults in the eastern Pacific measure 1.6-2.2 m (females) or 1.7-2.3 m (males) long, with occasional specimens to 2.35 m. Those in the northeast Atlantic appear to get much larger, up to about 2.50 m. Some may reach nearly 2.70 m.
Short-beaked common dolphins reach weights up to 200 kg.
The short-beaked common dolphin is an oceanic species that is widely distributed in tropical to cool temperate waters of the Atlantic and Pacific oceans. They apparently do not occur in the Gulf of Mexico, nor in most areas of the Indian Ocean or Caribbean Sea. They are found from nearshore waters to thousands of kilometers offshore. Separate populations apparently occur in some enclosed seas, such as the Mediterranean and Black seas. This species appears to have a preference for upwelling-modified waters and areas with steep slopes (such as seamounts and escarpments).
Ecology and Behaviour
Short-beaked common dolphin are often active, performing different types of breaches and leaps. These animals are energetic bowriders (except in prime tuna fishing zones of the ETP). They also sometimes ride the "bow waves" of large whales at times. Dolphins of this species are highly vocal; sometimes their squeals can be heard above the surface.
Schools range in size from about ten to over 10,000. Large schools of short-beaked common dolphins are often seen whipping the ocean's surface white as they move along at great speed. Schools are often segregated by age and sex. They often associate with other marine mammal species (especially pilot whales). Schools of this species in the eastern tropical Pacific are sometimes associated with yellowfin tuna (although not as often as are spotted and spinner dolphins).
The life history of the short-beaked common dolphin has been studied in several parts of the species' range. They have reported calving intervals of 1-3 years, and age at sexual maturity varies among populations (generally 3-12 years for males and 2-7 years for females). Some of this variation may be attributable to density-dependent responses to different histories of exploitation. Gestation lasts 10-11 months. In the Black Sea, peak calving occurs in summer months (June to August), but calving may be less seasonal in other areas. Short-beaked common dolphins can live for at least 25 years.
These animals feed mostly on small schooling fishes and squid. In some areas (e.g., southern California), common dolphins feed mostly at night on prey linked to the deep scattering layer (DSL), which migrates toward the surface at night. In other areas, they feed mainly on near-surface schooling fish. Squids may form an important part of their diet. Researchers have recorded foraging dives as deep as 200 m.
This is one of the most-abundant dolphin species in the world, with many available estimates for the various parts of its range. There are about 392,700 (western US coast), 3,000,000 (eastern tropical Pacific), 30,000 (eastern US coast), 61,000 (eastern Atlantic continental shelf), 75,000 (Celtic Sea shelf), 14,700 (Alboran Sea), and 96,000 (Black Sea/Turkish Straits System) individuals. So, while certain populations are in danger (e.g., the Mediterranean Sea), overall the species is not currently threatened with extinction by human activities.
The overall species is listed as Least Concern on the IUCN Red List. However, populations in the Mediterranean Sea and Black Sea are listed as Endangered and Vulnerable, respectively.
The eastern tropical Pacific tuna fishery incidentally takes short-beaked common dolphins, and some stocks may have been depleted by past levels of mortality. There are also incidental catches in various fisheries in other parts of the range, in particular gillnets and pelagic trawls, throughout the range. Very large hunts formerly took place in countries bordering the Black Sea. Common dolphin stocks there have declined dramatically and the fishery has apparently not operated since 1983. Some hunting still occurs off Japan and possibly in the Mediterranean Sea. However, the recent common dolphin decline in the Mediterranean Sea appears to have been mostly caused by poor habitat quality and prey depletion.
EVANS, W. E. 1994. Common dolphin, white-bellied porpoise Delphinus delphis Linnaeus, 1758. Pp. 191-224 in Handbook of Marine Mammals, Volume 5: The first book of dolphins (S. H. Ridgway and R. Harrison). Academic Press.
FERRERO, R. C. and W. A. WALKER. 1995. Growth and reproduction of the common dolphin, Delphinus delphis Lineaus, in the offshore waters of the North Pacific Ocean. Fishery Bulletin 93:483-494.
PERRIN, W. F. 2009. Common dolphins Delphinus delphis and D. capensis. Pp. 255-259 in Encyclopedia of Marine Mammals (Second Edition) (W. F. Perrin, B. Wursig and J. G. M. Thewissen). Academic Press.
STOCKIN, K., A. VELLA and P. G. H. EVANS (eds.). 2005. Common dolphins: current research, threats and issues. ECS Newsletter No. 45, 44 pp.