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).
The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
- UNESCO-IOC Register of Marine Organisms
Habitat and Ecology
Sotalia 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 seven 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 three (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).
- UNESCO-IOC Register of Marine Organisms
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.
- 2010Data 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.
Guiana Dolphins are vulnerable to incidental mortality in fishing gear, especially monofilament gillnets, seine nets, and shrimp and fish traps (da Silva and Best 1994, IWC 2007). Significant catches have been reported in many parts of their range (e.g. Siciliano 1994, da Silva and Best 1994, 1996, Beltrán 1998, Di Beneditto 2003, IWC 2007). In addition there has been some direct killing for human consumption and for shark and shrimp bait (da Silva and Best 1994, IWC 2007). Beltran (1998) recorded 938 animals taken in drift nets from the port of Arapiranga (Pará State) during the summer of 1996 and a further 125 taken during the winter. These data were collected by interviewing fishermen in the port after trips and collecting carcasses. More recently, Monteiro-Neto et al. (2004) estimated that approximately 90 Guiana Dolphins were killed every year in the passive gill net fisheries along the Brazilian coast. In the metropolitan area of Fortaleza, the capital of Ceará State, 32 bycaught animals were recorded (Monteiro-Neto et al. 2004).
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 (Pará State, at the Amazon Estuary) but also in Manaus, Amazonas State, and Porto Velho, Rondônia State, despite the availability of Botos and Tucuxis in those areas. In one market in Porto Velho, however, 90% of the eyeballs sold as dolphin products were in fact from pigs or sheep (Gravena et al. 2008). It is unclear what proportion of the dolphins that supplied or supply such markets are taken incidentally in fishing gear as opposed to killed deliberately. Dolphin charms may originate both from bycatch in legal fisheries and as a secondary product of the illegal catch of dolphins for bait (Cunha et al. 2010). The catch or bycatch of Guiana Dolphins for such purposes can be high. A single boat had 83 carcasses on board (footage done obtained by IBAMA and broadcast by a Brazilian television network on 07/16/2007), probably intended as bait for the shark fishery. Some Guiana Dolphins taken off the coast of Panamá and Colombia in the late 1970s were kept in captivity in Europe for more than 20 years (Terry 1986). A few dolphins are still kept in Colombian facilities, although since 2005 live-capture for captivity has been illegal (Culik 2004).
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 South America (da Silva and Best 1994, Yogui et al. 2003). Studies that included determination of micropollutant concentrations in Guiana dolphins from Guanabara Bay demonstrated the estuary to be a world hotspot for environmental contamination by persistent bioaccumulative toxicants (PBTs). In general, the PBT concentrations found in Guiana dolphins from this area are in the same range as the levels verified in coastal cetaceans from highly industrialized countries of the Northern Hemisphere. This latter statement holds for dichlorodiphenyltrichloroethane (DDT) and its metabolites, polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB) (Lailson-Brito et al. in press), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzo-p-furans (PCDFs), dioxin-like PCBs (Dorneles et al. 2008a), organotin compounds (Dorneles et al. 2008b), and perfluorooctane sulfonate (PFOS) (Dorneles et al. 2008c), as well as polybrominated diphenyl ethers (PBDEs) (Dorneles et al. 2010). Although the Cananéia estuary is known to be polluted by both chlorinated pesticides and polychlorinated biphenyls (PCBs), organochlorine concentrations were lower in the blubber of Guiana dolphins than in that of small cetaceans from developed areas (Yogui et al. 2003). Mercury is used in the refining of fluvial gold and then, like the pesticides, probably enters the aquatic food chain of the rivers and coasts. Mercury and selenium were found in the livers of two Sotalia from Suriname (da Silva and Best, 1994 and ref. therein). The detection of Cd, Hg and Pb in tissue samples of S. guianensis off the coast of Ceará, Brazil, indicated that heavy metals are locally present in the water and bioaccumulation probably occurs through the food web. Contamination levels were not considered critical, but they could be related to Ceará's growing industrial development (Monteiro-Neto et al. 2002). Exploration for oil in the offshore regions of Brazil, Venezuela and Colombia may not pose a direct threat to Sotalia, but spills in estuaries could affect local subpopulations (da Silva and Best 1994, Culik 2004). In recent years, skin diseases have been observed in estuaries (Van Bressem et al. 2009).
The Guiana dolphin (Sotalia guianensis) is a dolphin found in the coastal waters to the north and east of South America, and east of Central America. 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 in this paper published in the Latin American Journal of Aquatic Mammals. It is also known as the estuarine dolphin. The Guiana dolphin is a member of the oceanic dolphin family (Delphinidae).
The Guiana dolphin 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 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 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;.
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. One report exists of an animal reaching Honduras.
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 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, 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 Guiana dolphins 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 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.
- 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.
- 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.
- 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.
- "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.
- "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.