The Guiana Dolphin (sensu Flores and da Silva 2009) is found mostly in shallow waters near shore and in estuaries along the Atlantic coast of northwestern South America, from Florianópolis, Santa Catarina State, southern Brazil (27º35'S), northwards into the Caribbean Sea and along the coast of Central America to the mouth of the Layasiksa River, the west side of Waunta Lagoon (13°40'N), northeastern Nicaragua (Carr and Bonde 2000) and possibly Honduras (15°58'N, 79°54'W) (Flores and da Silva 2009). In the Orinoco River, there are frequent records of Sotalia dolphins at Ciudad Bolívar, some 300 km upstream, which are suspected to correspond to S. guianensis (da Silva and Best 1996, Meade and Koehnken 1991, Flores and da Silva 2009). Boher et al. (1995) reported a sighting in the middle Orinoco, 800 km inland. Although there are disputed reports of Sotalia dolphins in the upper Orinoco, and even in the Apure River (Hershkovitz 1963, Borobia et al. 1991, but see Boher et al. 1995), there are no confirmed records from the upper Orinoco and Apure Rivers, or in the lower reaches of most of the major Orinoco tributaries, in a compilation of sightings over the period from 1983 to 1990 (Meade and Koehnken 1991). It is assumed that Sotalia dolphins cannot traverse the rapids at the Casiquiare Channel, which connects the Orinoco and Amazon River basins (da Silva and Best 1996).
Habitat and Ecology
S. guianensis is patchily distributed (Borobia et al. 1991, Flores and da Silva 2009) as evident from the relatively small home ranges of individuals. In its southernmost limit at Baia Norte, estimated individual home ranges were only about 10-15 km² (Flores and Bazzalo 2004). In the Cananéia estuary, São Paulo state, where Guiana dolphins were found in water depths ranging from 1 to 23 m, observed home ranges varied from 1.6 to 22.9 km2 (Santos and Rosso 2007).
Guiana dolphins consume both marine and estuarine species such as demersal and pelagic fish of the families Sciaenidae, Clupeidae, Mugilidae, Trichiuridae and Batrachoididae as well as neritic cephalopods, family Loliginidae (Borobia and Barros 1991, da Silva and Best 1994, 1996, Santos et al. 2002, Di Beneditto and Ramos 2004). They also prey on penaeid shrimps (Santos et al. 2002) and crabs (Flores and da Silva 2009). Young age classes of teleost fishes, including over 60 species, are usually the most important items in the diet (Flores and da Silva 2009). In northern Rio de Janeiro, for example, lengths of fish preyed upon by S. guianensis ranged from 1.2 to 106.9 cm and mantle lengths of cephalopods varied from 3.4 to 22.2 cm (Di Beneditto and Ramos 2004). Sciaenid fishes that produce relatively loud sounds by swim bladder contraction were observed as common prey items. Feeding occurs both individually and in large groups.
Predators of Guiana dolphins may include killer whales (Orcinus orca) (Bittencourt 1983) and sharks, although there are no confirmed records other than an observed predation attempt by a bull shark, Carcharhinus leucas (Santos and Gadig in press).
Males reach sexual maturity at 7 years and at body lengths of 170-175 cm. Females mature at 5-8 years of age and at body lengths of 164-169 cm (Di Beneditto and Ramos 2004). Calving is year-round and gestation lasts around 11-12 months, with newborn calves ranging in size from 90 to 100 cm (Di Beneditto and Ramos 2004, Rosas and Monteiro-Filho 2002). The reproductive cycle is estimated at 2 years, with no marked seasonality in ovulation or timing of birth (Santos et al. 2001, Rosas and Monteiro-Filho 2002, Di Beneditto and Ramos 2004). The breeding system is promiscuous (Rosas and Monteiro-Filho 2002) within a fusion-fission society (Santos and Rosso 2008). Females older than 25 years have senescent ovaries (Rosas and Monteiro-Filho 2002). Maximum observed age (uncalibrated Growth Layer Groups) was 29 for males and 30 for females (Rosas et al. 2003, Santos et al. 2003, Di Beneditto and Ramos 2004).
Group size ranged between 1 and 40 individuals, and groups of 2 -10 were most common in Guanabara Bay, southeastern Brazil (Azevedo et al. 2007). In the Cananeia estuary, group size varied from lone individuals to aggregations of up to 60 (mean ± SD: 12.4 ± 11.4 individuals) (Santos and Rosso 2007). No seasonal variation in group size was observed in either of those studies. Nursery groups were twice as large as non-calf groups in Guanabara Bay and much more frequent in the Cananeia estuary. In the Cayos Miskito Reserve, Nicaragua, the mean group size was 3 (Edwards and Schnell 2001). Although Flores and da Silva (2009) reported that Guiana dolphins do not associate with bottlenose dolphins (Tursiops truncatus) in Brazilian waters, there are records of aggression of bottlenose dolphins towards Guiana dolphins in Santa Catarina State (Wedekin et al. 2004).
IUCN Red List Assessment
Red List Category
Red List Criteria
Although Guiana dolphins are certainly affected by several threat factors including bycatch in fisheries, deliberate capture for bait, pollution and habitat deterioration, no formal assessment to evaluate the risks of population decline has been performed. Despite progress on population structure, relevant information for assessment under IUCN's criteria is incomplete for any of the proposed management units. Such assessment cannot be performed before population (management unit)-specific abundance, non-natural mortality rates and other relevant parameters are estimated. Due to a lack of adequate data on these parameters, Sotalia guianensis status cannot as yet be assessed under any of the criteria and it is listed as Data Deficient.
This structuring pattern is probably due to the patchy and discontinuous distribution of Sotalia guianensis (Borobia et al. 1991, Flores and da Silva 2009). Abundance estimates are not available for the total population or for any of the proposed MUs. Although the species appears relatively abundant in many parts of its range, estimates of absolute or relative abundance, such as minimum number sighted, encounter rate, or estimated minimum density, are available only for small areas. Not all estimates are consistent and some lack methodological rigor. Some of the differences observed in the same areas over time might be due to different methodologies rather than decrease or increase. For instance, Geise (1991) estimated that there were just over 400 dolphins in Guanabara Bay (Rio de Janeiro State), southeastern Brazil. More recent estimates using photo-identification mark-recapture analysis indicate that there may be only 69-75 individuals in that area (Pizzorno 1999). It is not clear whether the difference is a result of population decline or of using different estimation methods. Geise et al. (1999) estimated that approximately 704.8 ± 367.7 individuals inhabited the area around Cananéia (São Paulo State), also in southeastern Brazil, where recent mark-recapture estimates suggest there are only 290-360 dolphins (Santos and Zerbini 2006). In Sepetiba Bay (Rio de Janeiro State), density was estimated as 2.79 dolphins/km², implying a total of 1,269 individuals (CI=739-2,196) (Flach et al. 2008). Density and abundance were similar for the entrance and interior of the Bay. In southern Brazil, abundance has been estimated only for Babitonga Bay (Santa Catarina State) where estimates varied from 231 (CI = 147-365; density of 1.44/km²) in 2001 to 154 (CI = 71-332; density = 0.96/km²) in 2003. Density of dolphins in Guaratuba Bay and Paranaguá and Antonina estuaries varied from 0.15/km² in the Bay (Filla 2004) to 11.56-23.16/km² in the estuaries, respectively (Filla 2004, Japp 2004). Bolaños-Jiménez (in IWC 2007) reported observations of groups as large as 70 in Lake Maracaibo, Venezuela. In Colombia, Bossenecker (1978) estimated 100-400 dolphins near the mouth of the Magdalena River and noted that the species was abundant in the Gulf of Cispata, near San Antero (Colombia). In Golfo de Morrosquillo, Colombia, an abundance of 70-90 individuals was estimated based on mark-recapture of photo-identified animals (Dussán-Duque et al. 2006). Sotalia have been described as common in the Marowijne River (border between Suriname and French Guiana) and also in the mouths of the larger rivers of Suriname (Husson, 1978, in da Silva and Best 1994, Duplaix, 1980). In Guyana, they have been reported from the Demerra, Cuyuni, Mazaruni and Essequibo river mouths (Williams 1928, Herald 1967 in da Silva and Best 1994). Edwards and Schnell (2001) estimated that there were about 50 Sotalia in Nicaragua's Cayos Miskito Reserve.
Although there is no evidence of past or recent commercial hunting, molecular data indicated that dolphin-derived products illegally sold in the Brazilian Amazon as amulets or love charms came from S. guianensis instead of from Botos (Inia geoffrensis) as advertised by sellers (Cunha and Solé-Cava 2007, Gravena et al. 2008, Sholl et al. 2008). They were probably accidentally captured in the Amazon estuary and along the adjacent Pará and Amapá coasts. S. guianensis amulets were found not only in Belém (
Pollution from industrial and agricultural activities may be a threat both directly, through the destruction of habitat, and indirectly, through contamination of prey. Large harbours such as Baia de Guanabara (Rio de Janeiro), Santos (São Paulo) and Paranaguá (Paraná), are very polluted with effluent, including heavy metals, posing a serious potential threat (da Silva et al. 2003, Medeiros and Bícego 2004, Bícego et al. 2006). The continued use of insecticides containing substances banned elsewhere is common in
The costero (Sotalia guianensis) is found in the coastal waters to the north and east of South America, and east of Central America. The common name "costero" has been suggested by Caballero and colleagues due to the species' affinity for coastal habitats. The costero is a member of the oceanic dolphin family (Delphinidae). Physically, it resembles the bottlenose dolphin. However, this species is sufficiently different from the bottlenose dolphin that it is given its own genus, Sotalia. It is also known as the Guyana dolphin.
The costero 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 colored light to bluish grey on its back and sides. The ventral region is light gray. The dorsal fin is typically slightly hooked. The beak is well-defined and of moderate length.
Researchers have recently shown that the costero has an electroreceptive sense, and speculate this may also be the case for other toothed whales.
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. 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; however, the IUCN still treats both as a single species, Sotalia fluviatilis.
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.
This species forms small groups of about 10-15 individuals, occasionally up to 30, and swim in tight-knit groups, suggesting a highly developed social structure. They are quite active and may jump clear of the water (a behavior known as breaching), somersault, spy-hop or tail-splash. They are unlikely, however, to approach boats. They feed on a wide variety of fish. 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 costero dolphins in Sepetiba Bay, Brazil. 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. Infanticide has been reported twice before in bottlenose dolphins, but is thought to be generally uncommon among cetaceans.
The costero appears to be relatively common; however, it gets frequently entangled in nets of the coastal fishing fleets. An estimated at least 2,000 animals are killed by entanglement per year in the Amazon River delta region. Many of these animals are used as shark fishing bait, and their organs are sold as fetishes. Another major problem in some areas is collisions with boats. Possible natural predators are the orca and the bull shark.
The Guiana dolphin is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
- 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, E., Smith, B.D., Wang, JY. & Zhou, K. (2008). Sotalia. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 25 February 2009. Includes a lengthy justification of the data deficient category. Treats Sotalia guianensis and Sotalia fluviatilis as subspecies.
- 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, and 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.
- Nicole U. Czech-Damal, Alexander Liebschner, Lars Miersch, Gertrud Klauer, Frederike D. Hanke, Christopher Marshall, Guido Dehnhardt and Wolf Hanke (2011). "Electroreception in the Guiana dolphin (Sotalia guianensis)". Proc. R. Soc. B. doi:10.1098/rspb.2011.1127.
- Borobia, M., S. Siciliano, L. Lodi, and W. Hoek (1991). "Distribution of the South American dolphin Sotalia fluviatilis". Canadian Journal of Zoology 69 (4): 1024–1039. doi:10.1139/z91-148.
- Monteiro-Filho, E.L.D.A., L. Rabello-Monteiro, and 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.
- 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, and 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.
- "Dolphins seen trying to kill calf". BBC News. 18 May 2009. Retrieved 30 April 2010.
- Nery, M. F., and 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.
- Beltrán, S. (1998) Captura accidental de Sotalia fluviatilis (Gervais, 1853) na pescaria artesanal do estuário Amazônico. Masters Thesis in Biology. Universidade Federal do Amazonas, Manaus, AM, Brazil
- Gravena, W., T. Hrbek, V.M.F. da Silva, and I.P. Farias (2008). "Amazon River dolphin love fetishes: From folklore to molecular forensics". Marine Mammal Science 24: 969–978. doi:10.1111/j.1748-7692.2008.00237.x.
- "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: 5th March 2009. Convention on Migratory Species page on the Guiana dolphin
- Flach, Leonardo; Flach, Patricia Amaral; Chiarello, Adriano G (2008). "Density, abundance and distribution of the Guiana dolphin (Sotalia guianensis van Benéden, 1864) in Sepetiba Bay, Southeast Brazil". The Journal of Cetacean Research and Management (International Whaling Commission) 10 (1): 31–36. ISSN 1561-0713. Retrieved January 2013.
- Rosas, Fernando C Weber; Monteiro-Filho, Emygdio LA (2002). "Reproduction of the Estuarine Dolphin (Sotalia guianensis) on the Coast of Paraná, Southern Brazil". Journal of Mammalogy 83 (2): 507–515. doi:10.1644/1545-1542(2002)083<0507:ROTEDS>2.0.CO;2.