Guiana dolphin

Guiana dolphin
Guiana dolphin in Mochima National Park
Size compared to an average human
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Delphinidae
Genus: Sotalia
Species: S. guianensis
Binomial name
Sotalia guianensis
(van Bénéden, 1864)
Range of Guiana dolphin(coastal–solid pattern) and tucuxi (inland–hatched pattern)

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

Etymology

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). Furthermore, the common name "Guiana dolphin" has been suggested by Flores and colleagues.[2]

Description

The Guiana dolphin (Sotalia guianensis) is frequently described as looking similar to the bottlenose dolphin. However, it is typically smaller, at only up to 2.1 m (6.9 ft) in length. The dolphin is coloured light to bluish grey on its 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.

Guiana dolphins are very inconspicuous, and considered a "shy" species. It does not bow ride on boats and normally swims away from them.

Researchers have recently shown that the costero has an electroreceptive sense, and speculate this may also be the case for other odontocetes.[3]

Taxonomy

Although described as species distinct from the tucuxi Sotalia fluviatilis by Pierre-Joseph van Bénéden in 1864, the costero Sotalia guianensis has subsequently been synonymized with Sotalia fluviatilis with the two species being treated as subspecies, or marine and freshwater varieties.[4] The first to reassert differences between these two species was a three-dimensional morphometric study of Monteiro-Filho and colleagues.[5] Subsequently a molecular analysis by Cunha and colleagues[6] unambiguously demonstrated that Sotalia guianensis was genetically differentiated from Sotalia fluviatilis. This finding was reiterated by Caballero and colleagues[7] with a larger number of genes. The existence of two species has been generally accepted by the scientific community;.

Distribution

The costero 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. One report exists of an animal reaching Honduras.

34 survive in Guanabara Bay near Rio de Janeiro, down from 70 in 1995 and 400 in 1985.[8]

Behaviour

This species forms small groups of about 2-10 individuals, occasionally up to 100, and swim in tight-knit groups, suggesting a highly developed social structure. 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. They feed on a wide variety of fish, shrimps and squid. Studies of growth layers suggest the species can live up to 30 years.

In December 2006, researchers from the Southern University of Chile and the Rural Federal University of Rio de Janeiro witnessed attempted infanticide by a group of costeros in Sepetiba Bay, Brazil.[9] A group of six adults separated a mother from her calf, four then keeping her at bay by ramming her and hitting her with their flukes. The other two adults rammed the calf, held it under water, then threw it into the air and held it under water again. The mother was seen again in a few days, but not her calf. Since females become sexually receptive within a few days of losing a calf, and the group of attacking males was sexually interested in the female, it is possible that the infanticide occurred for this reason.[10] Infanticide has been reported twice before in bottlenose dolphins, but is thought to be generally uncommon among cetaceans.[10]

Conservation

The costero is listed on Appendix II[11] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II[11] as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.

References

  1. ↑ Reeves, R.R.; Crespo, E.A.; Dans, Jefferson; T.A., Karczmarski; L., Laidre; K., O’Corry-Crowe; G., Pedraza; S., Rojas-Bracho; L., Secchi; E.R., Slooten; et al. (2008). "Sotalia". IUCN Red List of Threatened Species. Version 2008. International Union for Conservation of Nature. Retrieved 25 February 2009. Includes a lengthy justification of the data deficient category. Treats Sotalia guianensis and Sotalia fluviatilis as subspecies.
  2. ↑ Flores, PAC; Bazzalo, M; Santos, MC; Rossi-Santos, MR; Trujillo, F; Bolaños-Jimenez, J; Cremer, MJ; May-Colado, LJ; Silva, FJL; Montiel-Villalobos, MG; Azevedo, AF; Meirelles, ACO. Flach, L; Barrios-Garrido, H; Simões-Lopes, PC; Cunha, HA; van Waerebeek, K (2010). "PROPOSED ENGLISH COMMON NAME FOR THE NEOTROPICAL DELPHINID SOTALIA GUIANENSIS (P-J. VAN BÉNEDÉN, 1864)". Latin America Journal of Aquatic Mammals. 8 (1-2): 179–181. doi:10.5597/lajam00167.
  3. ↑ Nicole U. Czech-Damal; Alexander Liebschner; Lars Miersch; Gertrud Klauer; Frederike D. Hanke; Christopher Marshall; Guido Dehnhardt; Wolf Hanke (2011). "Electroreception in the Guiana dolphin (Sotalia guianensis)". Proc. R. Soc. B. 279 (1729): 663–8. doi:10.1098/rspb.2011.1127. PMC 3248726Freely accessible. PMID 21795271.
  4. ↑ Borobia, M.; S. Siciliano; L. Lodi & W. Hoek (1991). "Distribution of the South American dolphin Sotalia fluviatilis". Canadian Journal of Zoology. 69 (4): 1024–1039. doi:10.1139/z91-148.
  5. ↑ Monteiro-Filho, E.L.D.A.; L. Rabello-Monteiro & S.F.D. Reis (2008). "Skull shape and size divergence in dolphins of the genus Sotalia: A morphometric tridimensional analysis". Journal of Mammalogy. 83: 125–134. doi:10.1644/1545-1542(2002)083<0125:SSASDI>2.0.CO;2.
  6. ↑ Cunha, H.A.; V.M.F. da Silva; J. Lailson-Brito Jr.; M.C.O. Santos; P.A.C. Flores; A.R. Martin; A.F. Azevedo; A.B.L. Fragoso; R.C. Zanelatto & A.M. Solé-Cava (2005). "Riverine and marine ecotypes of Sotalia dolphins are different species". Marine Biology. 148 (2): 449–457. doi:10.1007/s00227-005-0078-2.
  7. ↑ Caballero, S.; F. Trujillo; J. A. Vianna; H. Barrios-Garrido; M. G. Montiel; S. Beltrán-Pedreros; M. Marmontel; M. C. Santos; M. R. Rossi-Santos; F. R. Santos & C. S. Baker (2007). "Taxonomic status of the genus Sotalia: species level ranking for "tucuxi" (Sotalia fluviatilis) and "costero" (Sotalia guianensis) dolphins". Marine Mammal Science. 23 (2): 358–386. doi:10.1111/j.1748-7692.2007.00110.x.
  8. ↑ "Rio 2016: Dolphins threatened by toxic waters where sailing event to be held". Australian Broadcasting Corporation. 27 June 2016. Retrieved 16 July 2016.
  9. ↑ "Dolphins seen trying to kill calf". BBC News. 18 May 2009. Retrieved 30 April 2010.
  10. 1 2 Nery, M. F.; S. M. Simão (2009). "Sexual coercion and aggression towards a newborn calf of marine tucuxi dolphins (Sotalia guianensis)". Marine Mammal Science. 25 (2): 450–454. doi:10.1111/j.1748-7692.2008.00275.x.
  11. 1 2 "Appendix II" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009. Convention on Migratory Species page on the Guiana dolphin
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