Sotalia fluviatilis

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	MAMMALIA	CETARTIODACTYLA	DELPHINIDAE

Scientific Name:

Sotalia fluviatilis

Species Authority:

(Gervais & Deville, 1853)

Common Name/s:

English	–	Estuarine Dolphin, Gray Dolphin, Guianian River Dolphin, Tucuxi
French	–	Dauphin De L'Amazon, Sotalie
Spanish	–	Bufeo Negro, Bufo Negro

Synonym/s:

Sotalia fluviatilis <i>sensu</i> IWC, 2007 ssp. fluviatilis

Sotalia fluviatilis Di Beneditto, 2004 ssp. guianensis

Taxonomic Notes:

Recently, it has been recommended that the riverine and marine forms of Sotalia be split into two species, S. fluviatilis in the Amazon and possibly Orinoco systems and S. guianensis in marine and estuarine waters (see Monteiro-Filho et al. 2002, Cunha et al. 2005, Siciliano et al. 2006, Caballero et al. 2007). The evidence for separate species appears convincing and is likely to gain wide acceptance. For immediate assessment purposes, however, the two forms have been treated here as subspecies:

Marine form (S. f. guianensis) - found along the Central and South American coast from Honduras to southern Brazil and Trinidad and Tobago (also on Abrolhos Bank) and up the Orinoco River to Ciudad Bolivar; significantly larger than the freshwater form (reaching up to 2.2 m) with slightly more teeth (28-36 upper and 28-34 lower); size at birth estimated to be 0.8-1.15 m (Di Beneditto et al. 2004).

Freshwater form (S. f. fluviatilis) - found in the Amazon River and possibly the Orinoco system (e.g. near the Colombia-Venezuela border; IWC 2007; significantly smaller (reaching only about 1.5-1.6 m) with fewer teeth (28-35 upper and 26-33 lower); size at birth estimated to be 0.7-0.8 m.

There are no known reliable external differences between the two forms other than total length and girth.

Assessment Information [top]

Red List Category & Criteria:	Data Deficient ver 3.1
Year Assessed:	2008
Assessor/s	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.
Evaluator/s:	Brownell Jr., R.L. & Cooke, J. (Cetacean Red List Authority)
Justification: This species is Data Deficient due to a lack of basic information needed for a proper assessment (e.g. abundance, population structure, bycatch rates). There is strong evidence that the genus Sotalia consists of two living species (Cunha et al. 2005, Caballero et al. 2007) so a re-assessment will be needed. However, for the present, Data Deficient is considered an appropriate designation regardless of whether one or two species are recognized. Current knowledge is restricted to a few portions of the genus’s extensive range and may not be representative. Much of the available information on the freshwater population(s) is outdated. The apparently discontinuous range of marine populations means that local groups of these dolphins would be especially vulnerable to any increases in the bycatch rate. Among the highest priorities for conservation-relevant research on Sotalia are studies of population structure, population size, magnitude of incidental mortality in fisheries, and contaminant status (IWC 2001, 2007).

Geographic Range [top]

Range Description:	Dolphins of the genus Sotalia occur only in South and Central American waters (Borobia 1991). The marine form is found mostly in shallow waters near shore and in estuaries along the Atlantic coast, from Florianopolis, southern Brazil (27ºS), northwards into the Caribbean Sea as far as Panama (perhaps even Honduras at 15ºN) (IWC 2007; Caballero et al. 2007). Carr and Bonde (2000) extended the known range to northeastern Nicaragua, north of the mouth of the Layasiksa River, west side of Waunta Lagoon (13°40'N). The freshwater form is found in the Amazon drainage, as far inland as southern Peru, eastern Ecuador, and southeastern Colombia. Sotalia occur in the Orinoco basin, from the mouth upstream to Ciudad Bolívar but it is unclear to which form these animals belong – they have been provisionally considered S. guianensis (Caballero et al. 2007). During the flood season, riverine animals may move into smaller tributaries, but apparently do not move into the inundated forest to feed (as botos often do), staying mainly in the main river channels, tributaries and lakes (da Silva and Best 1996). Tucuxis are largely sympatric with the boto in the Amazon and Orinoco systems, but generally do not interact with that species.
Countries:	Native: Brazil; Colombia; Costa Rica; Ecuador; French Guiana; Guyana; Nicaragua; Panama; Peru; Suriname; Trinidad and Tobago; Venezuela Presence uncertain: Honduras
FAO Marine Fishing Areas:	Native: Atlantic – western central; Atlantic – southwest
Range Map:	(click map to view full version)

Population [top]

Population:	Although the distribution of marine Sotalia appears patchy and discontinuous (Flores 2002), the overall population structure is unclear. There are no estimates of the total population size for either the freshwater or the marine form, but Sotalia appear relatively abundant in many parts of their range. Estimates of absolute or relative abundance, such as minimum number sighted, encounter rate, and estimates of minimum density, are available only for small areas (IWC 2001, 2007). Not all estimates are consistent. For instance, Geise (1991) estimated that there were just over 400 dolphins in Guanabara Bay (Rio de Janeiro). More recent estimates using photo-identification mark-recapture analysis indicate that there may be only 69-75 individuals in that area (Pizzorno 1999, Flores 2002). It is not clear whether the difference is a result of population decline or due to the use of differing estimation methods. Geise (1988) estimated 3,000 in the area around Cananéia (São Paulo State), where recent mark-recapture estimates suggest that there are only 290-360 dolphins (Santos and Zerbini 2006). Bolaños-Jiménez (in IWC 2007) reported observations of groups as large as 70 individuals in Lake Maracaibo, Venezuela. Elsewhere in Brazil, Flach (2004) estimated 400-500 dolphins in Sepetiba Bay (Rio de Janeiro State). In Colombia, Bossenecker (1978, in da Silva and Best 1994) estimated 100-400 dolphins near the mouth of the Magdalena River and noted that they were abundant in the Gulf of Cispata, near San Antero (Colombia). 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). In the Amazon drainage, an average density (encounter rate) of approximately 1.1 dolphins/km of river was estimated between Manaus and Tefé in the Solimões River (Magnusson et al. 1980). Four boat surveys of about 1,525 km each, from Manaus to Letícia resulted in a mean total of 768 (± 104.7) dolphins per trip or 1.02 individuals/km² (da Silva and Best 1994). About 350 Sotalia were estimated to inhabit the Samiria River system in Peru (Leatherwood 1996). Sotalia are reportedly common in Colombia in the Loretoyacu River, in the Tarapoto River and El Correo Lake system, and in the lower reaches of the Orinoco River (da Silva and Best 1994). Vidal et al. (1997) estimated that in 1993 there were 409 tucuxis (CV=13%) along 120 km of the Amazon River bordering Colombia, Peru, and Brazil. Density (dolphins/km²) was highest in lakes (8.6), followed by areas along main banks (2.8) and around islands (2.0). These are among the highest densities measured to date for any cetacean. Edwards and Schnell (2001) estimated that there were about 50 Sotalia in Nicaragua’s Cayos Miskito Reserve.
Population Trend:	Unknown

Population:

Although the distribution of marine Sotalia appears patchy and discontinuous (Flores 2002), the overall population structure is unclear. There are no estimates of the total population size for either the freshwater or the marine form, but Sotalia appear relatively abundant in many parts of their range. Estimates of absolute or relative abundance, such as minimum number sighted, encounter rate, and estimates of minimum density, are available only for small areas (IWC 2001, 2007). Not all estimates are consistent. For instance, Geise (1991) estimated that there were just over 400 dolphins in Guanabara Bay (Rio de Janeiro). More recent estimates using photo-identification mark-recapture analysis indicate that there may be only 69-75 individuals in that area (Pizzorno 1999, Flores 2002). It is not clear whether the difference is a result of population decline or due to the use of differing estimation methods. Geise (1988) estimated 3,000 in the area around Cananéia (São Paulo State), where recent mark-recapture estimates suggest that there are only 290-360 dolphins (Santos and Zerbini 2006). Bolaños-Jiménez (in IWC 2007) reported observations of groups as large as 70 individuals in Lake Maracaibo, Venezuela.

Elsewhere in Brazil, Flach (2004) estimated 400-500 dolphins in Sepetiba Bay (Rio de Janeiro State). In Colombia, Bossenecker (1978, in da Silva and Best 1994) estimated 100-400 dolphins near the mouth of the Magdalena River and noted that they were abundant in the Gulf of Cispata, near San Antero (Colombia). 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).

In the Amazon drainage, an average density (encounter rate) of approximately 1.1 dolphins/km of river was estimated between Manaus and Tefé in the Solimões River (Magnusson et al. 1980). Four boat surveys of about 1,525 km each, from Manaus to Letícia resulted in a mean total of 768 (± 104.7) dolphins per trip or 1.02 individuals/km² (da Silva and Best 1994). About 350 Sotalia were estimated to inhabit the Samiria River system in Peru (Leatherwood 1996). Sotalia are reportedly common in Colombia in the Loretoyacu River, in the Tarapoto River and El Correo Lake system, and in the lower reaches of the Orinoco River (da Silva and Best 1994). Vidal et al. (1997) estimated that in 1993 there were 409 tucuxis (CV=13%) along 120 km of the Amazon River bordering Colombia, Peru, and Brazil. Density (dolphins/km²) was highest in lakes (8.6), followed by areas along main banks (2.8) and around islands (2.0). These are among the highest densities measured to date for any cetacean. Edwards and Schnell (2001) estimated that there were about 50 Sotalia in Nicaragua’s Cayos Miskito Reserve.

Population Trend:

Unknown

Habitat and Ecology [top]

Habitat and Ecology:	Riverine Sotalia inhabit all three types of water in Amazonia – whitewater, clearwater, and blackwater. Therefore physical factors such as visibility and acidity appear not to affect their distribution directly. Rapids and fast-moving turbulent water are avoided. These dolphins, like the sympatric botos, show a distinct preference for junctions of rivers and channels (da Silva and Best 1996). Marine Sotalia appear to prefer shallow, sheltered estuaries and bays. In Baia de Guanabara, they prefer the deeper channels (25 m depth) and avoid areas shallower than about 6 m (Azevedo et al. 2007). In open coastal areas, the dolphins seem to avoid deep waters (e.g. Edwards and Schnell 2001) although they can be sighted several kilometers from shore in areas where the continental shelf is shallow or in waters over offshore banks (e.g. Abrolhos off Brazil) (Rossi-Santos et al. 2006; IWC 2007). A wide variety of fishes, mostly small schooling species, are eaten by riverine tucuxis. Sotalia in coastal marine waters consume primarily estuarine species such as drums and croakers (Sciaenidae) and neritic cephalopods (N. Barros, in IWC 2007). Feeding occurs both individually and in large groups.
Systems:	Freshwater; Marine

Habitat and Ecology:

Riverine Sotalia inhabit all three types of water in Amazonia – whitewater, clearwater, and blackwater. Therefore physical factors such as visibility and acidity appear not to affect their distribution directly. Rapids and fast-moving turbulent water are avoided. These dolphins, like the sympatric botos, show a distinct preference for junctions of rivers and channels (da Silva and Best 1996).

Marine Sotalia appear to prefer shallow, sheltered estuaries and bays. In Baia de Guanabara, they prefer the deeper channels (25 m depth) and avoid areas shallower than about 6 m (Azevedo et al. 2007). In open coastal areas, the dolphins seem to avoid deep waters (e.g. Edwards and Schnell 2001) although they can be sighted several kilometers from shore in areas where the continental shelf is shallow or in waters over offshore banks (e.g. Abrolhos off Brazil) (Rossi-Santos et al. 2006; IWC 2007).

A wide variety of fishes, mostly small schooling species, are eaten by riverine tucuxis. Sotalia in coastal marine waters consume primarily estuarine species such as drums and croakers (Sciaenidae) and neritic cephalopods (N. Barros, in IWC 2007). Feeding occurs both individually and in large groups.

Systems:

Freshwater; Marine

Threats [top]

Major Threat(s):	River dolphins in the Amazon region are threatened primarily by incidental mortality in fishing gear (IWC 2001). In one study in the central Amazon of Brazil, 74% of 34 Sotalia examined had been killed in gill nets and 15% in seine nets (da Silva and Best, 1985). Other potentially important threats come from pollution caused by oil industry activities (Denkinger 2001), the damming of rivers for hydroelectric projects, and various forms of habitat degradation (da Silva and Best 1994; IWC 2001). The use of pesticides banned in many countries continues to be commonly used in some regions in South America (PNUMA 2002). Mercury is used to refine fluvial gold and then, like the pesticides, enters aquatic food webs. Dams, in addition to fragmenting dolphin populations, can have serious effects on migratory fish populations on which Sotalia feed (such as some siluriform fishes) can be seriously affected by dams and reservoir formation, and the potential suitability of nonmigratory fish for the diet of Sotalia is unknown (da Silva and Best 1994). The increased use of outboard engines and illegal fishing with explosives are also sources of concern in parts of these dolphins’ range (e.g. Utreras et al. 2001, Zapata-Rios and Utreras 2004). Although freshwater dolphins have been protected by superstitions in parts of Amazonia, there was and may still be a small market for the eyes and genital organs, used as love charms (aphrodisiacs) when prepared in a special manner (da Silva and Best 1994). According to V. da Silva (pers. comm.), this market is no longer a significant threat in Brazil, although according to M. Borobia (in IWC 2007) the practice of selling dolphin parts continues in at least some local areas. It is unclear what proportion of the dolphins that supplied or supply this market were taken incidentally in fishing gear as opposed to killed deliberately. Coastal and estuarine Sotalia are also 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). However, there are no records of past or recent commercial hunting. Pollution from industrial and agricultural activities may be a threat both directly, through the destruction of habitat, or indirectly, through contamination of prey. Large harbours such as Baia de Guanabara (Rio de Janiero) and Santos (São Paulo) are extremely polluted (da Silva et al. 2003; Medeiros and Bícego 2004; Bícego et al. 2006). 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).

Major Threat(s):

River dolphins in the Amazon region are threatened primarily by incidental mortality in fishing gear (IWC 2001). In one study in the central Amazon of Brazil, 74% of 34 Sotalia examined had been killed in gill nets and 15% in seine nets (da Silva and Best, 1985).

Other potentially important threats come from pollution caused by oil industry activities (Denkinger 2001), the damming of rivers for hydroelectric projects, and various forms of habitat degradation (da Silva and Best 1994; IWC 2001). The use of pesticides banned in many countries continues to be commonly used in some regions in South America (PNUMA 2002). Mercury is used to refine fluvial gold and then, like the pesticides, enters aquatic food webs. Dams, in addition to fragmenting dolphin populations, can have serious effects on migratory fish populations on which Sotalia feed (such as some siluriform fishes) can be seriously affected by dams and reservoir formation, and the potential suitability of nonmigratory fish for the diet of Sotalia is unknown (da Silva and Best 1994). The increased use of outboard engines and illegal fishing with explosives are also sources of concern in parts of these dolphins’ range (e.g. Utreras et al. 2001, Zapata-Rios and Utreras 2004). Although freshwater dolphins have been protected by superstitions in parts of Amazonia, there was and may still be a small market for the eyes and genital organs, used as love charms (aphrodisiacs) when prepared in a special manner (da Silva and Best 1994). According to V. da Silva (pers. comm.), this market is no longer a significant threat in Brazil, although according to M. Borobia (in IWC 2007) the practice of selling dolphin parts continues in at least some local areas. It is unclear what proportion of the dolphins that supplied or supply this market were taken incidentally in fishing gear as opposed to killed deliberately.

Coastal and estuarine Sotalia are also 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). However, there are no records of past or recent commercial hunting. Pollution from industrial and agricultural activities may be a threat both directly, through the destruction of habitat, or indirectly, through contamination of prey. Large harbours such as Baia de Guanabara (Rio de Janiero) and Santos (São Paulo) are extremely polluted (da Silva et al. 2003; Medeiros and Bícego 2004; Bícego et al. 2006). 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).

Conservation Actions [top]

Conservation Actions:	The species is listed in Appendix II of CITES. Research is needed to evaluate the impacts of threats on this species, and to propose appropriate conservation measures.

Conservation Actions:

The species is listed in Appendix II of CITES. Research is needed to evaluate the impacts of threats on this species, and to propose appropriate conservation measures.

Citation:	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 fluviatilis. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. <www.iucnredlist.org>. Downloaded on 05 July 2009.
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