Guiana dolphin

The Guiana dolphin (Sotalia guianensis), also known as the estuarine dolphin or costero, is a dolphin found in the coastal and estuary waters to the north and east of South America, and east of Central America. It is a member of the oceanic dolphin family (Delphinidae).

During its 2008 Annual Meeting in Santiago, Chile, as proposed by Flores et al. (2008), the Scientific Committee of the International Whaling Commission (IWC) endorsed "Guiana dolphin" as the common English name for (Sotalia guianensis) in its IWC List of Recognized Cetacean Species (LRCS). Following this endorsement, Flores and colleagues also made the case for the adoption of the English name in the Latin American Journal of Aquatic Mammals.

The Guiana dolphin is frequently described as similar to the bottlenose dolphin in appearance, but it is typically smaller, at only up to 2.1 m (6.9 ft) in length. Individuals are light to bluish grey in coloration on their back and sides. The ventral region is light grey. The dorsal fin is typically slightly hooked, with a triangular shape. The beak is well-defined and of moderate length.

The Guiana dolphin is very similar in appearance to the closely related Tucuxi (Sotalia fluviatilis) with most differences only apparent in skull shape and body size. The Guiana dolphin is the larger of two at a maximum mass of 121 kilograms versus 53 kilograms for the tucuxi.

Researchers have recently shown that the Guiana dolphin has an electroreceptive sense, and speculate this may also be the case for other odontocetes.

Although described as species distinct from the tucuxi Sotalia fluviatilis by Pierre-Joseph van Bénéden in 1864, the Guiana dolphin Sotalia guianensis was subsequently synonymized with Sotalia fluviatilis with the two species being treated as subspecies, or marine and freshwater varieties. The first to reassert differences between these two species was a three-dimensional morphometric study of Monteiro-Filho and colleagues. Subsequently, a molecular analysis by Cunha and colleagues unambiguously demonstrated that Sotalia guianensis was genetically differentiated from Sotalia fluviatilis. This finding was reiterated by Caballero and colleagues with a larger number of genes. The existence of two species has been generally accepted by the scientific community.

The Guiana dolphin is found close to estuaries, inlets and other protected shallow-water areas around the eastern and northern South American coast. It has been reported as far south as southern Brazil and north as far as Nicaragua and possibly Honduras. This species has been observed to tolerate a wide range of temperatures and salinities

This species generally forms small groups averaging about 2-6 individuals, but does occasionally form larger aggregations of up to several hundred animals. They are quite active and may jump clear of the water (a behaviour known as breaching), somersault, spy-hop or tail-splash. They are unlikely, however, to approach boats. Guiana dolphins feed mainly on a wide variety of bony fish and occasionally on shrimps, cephalopods, and crabs. Studies of growth layers suggest the species can live more than 40 years.