|Scientific Name:||Inia geoffrensis|
|Species Authority:||(Blainville, 1817)|
|Taxonomic Notes:||Three subspecies are currently recognized: I. g. geoffrensis in the Amazon River system of Brazil, Peru, and Ecuador, I. g. boliviensis in Bolivia, and I. g. humboldtiana in the Orinoco basin of Venezuela and Colombia (e.g, Rice 1998; Best and da Silva 1993). A recent study of mitochondrial control region sequences and the cytochrome b gene (Banguera-Hinestroza et al. 2002) reinforced earlier morphological evidence (da Silva 1994) suggesting that the Bolivian dolphins are an evolutionarily significant unit distinct from those in the Amazon and Orinoco drainages.|
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K.|
|Reviewer/s:||Brownell Jr., R.L. & Cooke, J.|
The species was previously listed as Vulnerable but is now considered Data Deficient due to the limited amount of current information available on threats, ecology, and population numbers and trends. In areas where botos have been studied, they appear widespread and relatively abundant. However, these areas represent only a small proportion of the species’ total range and often are places where the dolphins have some protection. Therefore, the impressions from those areas may not be representative. Also, much of the information summarized in this assessment is dated and may no longer be valid.
|Range Description:||Botos occur throughout the Amazon and Orinoco river basins, from the deltas upstream to where impassable rapids, waterfalls, lack of water, and possibly low temperatures block their movement (Best and da Silva 1989a,b). Three geographic populations have been recognized as subspecies: I. g. geoffrensis in the Amazon basin, except for the Madeira drainage in Bolivia above the Teotonio rapids, I. g. boliviensis in the upper Madeira drainage, and I. g. humboldltiana in the Orinoco basin (Rice 1998).
Besides the Amazon mainstem, I. g. geoffrensis has been recorded in the Tocantins (and das Mortes and Verde affluents), Xingu, Tapajós, Madeira (below the Teotonio rapids), Purus, Juruá, Ucayali, and Marañon (and Samiria affluent) tributaries flowing generally north, and in the Negro, Caqueta (Japurá), Apaporis, Putumayo, Napo, and Tigre tributaries flowing generally south (partial list from Best and da Silva 1989a,b; Leatherwood 1996).
In addition to the Madeira mainstem above the Teotonio rapids, I. g. boliviensis has been reported from the Beni (and Orton affluent), Iténez or Guaporé Basin (and Verde and Iporuporé affluents), and Mamoré Basin and its tributaries and afluents: Pirai, Grande, Ichilo, Chapare, Ibaré, Tijamuchi, Apere, Yacuma and Yata (Pilleri and Gihr 1977, Aliaga-Rossel et al. 2006, Aliaga-Rossel 2010).
In the Orinoco system, besides the mainstem, I. g. humboldtiana has been recorded in the Apuré (and Portuguesa and Guanmar affluents), Capanaparo, Cinaruco, Meta, Bita, Vichada, Tomo, Tuparro, Guaviare (and Guayabero affluent), Inírida, and Atabapo (and Temi affluent) tributaries flowing south and east, and in the Aro, Caura, Parquaza, Ventauri (San Juan affluent) tributaries flowing north and west, as well as in the Casiquiare Canal, which connects the Orinoco with the Negro River (a tributary of the Amazon), above and below the two sets of rapids at Puerto Ayacucho, which are the principal barriers that may (or may not) separate the Amazon and Orinoco populations (as summarized in Pilleri and Gihr 1977; Best and da Silva 1989a,b; Meade and Koehnken 1991). Botos have been seen crossing the first set of rapids at Puerto Ayacucho (Atures) during high water (Fernando Trujillo pers. comm. to B.D. Smith).
The map shows where the species may occur. 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.
Native:Bolivia, Plurinational States of; Brazil; Colombia; Ecuador; Peru; Venezuela
|Range Map:||Click here to open the map viewer and explore range.|
In the Amazon basin, data are available on abundance and encounter rates for only a few river segments: 107 individuals counted (0.19 dolphins/km; ± 0.06) in a 490-km segment of the Solimões River, Brazil in August 1979 (Magnusson et al. 1980); 0.22 dolphins/km (± 0.04) observed in a 1525-km segment of the Solimões River, Brazil during four surveys in March 1983- February 1984 (Best and da Silva 1989b); 78 individuals counted and 346 individuals estimated (CV=0.12) using line and strip transect methods in a 120-km segment (ca. 250 km²) of the Amazon River bordering Peru and Colombia, including the Atacuari, Loretoyacu, and Amacayacu tributaries, and the Caballo Cocha and Tarapoto-El Correo lake systems in June 1993 (Vidal et al. 1997); 0.147 dolphins/km (± 0.121) observed in a 232-km segment of the Amazon-Marañon River, Peru during 11 surveys in March-August 1991-1993 (Leatherwood and Reeves 1995a); 0.41-0.50 dolphins/km observed in a 95-km segment of the Tigre River, Peru during 14 surveys in March-August 1991-1994 (Leatherwood and Reeves 1995b); and 260 ± 50 individuals in 225 km² of the Mamirauá Lake system of Brazil - extrapolated to about 13,000 individuals in the 11,240 km² Mamirauá Sustainable Development Reserve (Martin and da Silva 2004a).
Counts and encounter rates for segments of the Orinoco basin include: 122 individuals counted (1.16 dolphins/km) in a 105-km segment of the Apuré River, Venezuela in 1981 (Pilleri et al. 1982); 0.20 dolphins/km observed in a 201-km segment of the Apuré River, Venezuela in July-August 1989 (Schnapp and Howroyd 1992); 14-15 individuals counted (0.024 dolphins/km) in a 450-km segment of the Orinoco River, Venezuela in 1981 (Pilleri et al. 1982); 8 individuals counted (0.025 dolphins/km) in a 340-km segment of the Casiquiare River, Venezuela in 1981 (Pilleri et al. 1982).
|Habitat and Ecology:||
Botos swim into flooded forests in the high-water season and often search for prey among the roots and trunks of partially submerged trees. Mark/recapture studies have shown that some individuals are resident to specific areas year-round (Martin and da Silva 2004a), whereas others move several tens to hundreds of kilometers within the rivers, but there does not appear to be any actual seasonal migration (Martin and da Silva 2004a).
Botos are generally concentrated below channel confluences (Magnusson et al. 1980; Mead and Koehnken 1991; Leatherwood 1996; Vidal et al. 1997; Leatherwood et al. 2000), with mixing of white and black waters (Martin et al. 2004). Their affinity for confluences diminishes during the high water season, probably because the animals move into appended lakes and flooded forests (Leatherwood 1996; Leatherwood et al. 2000; Martin and da Silva 2004b). They occur most often within 150 m of the edges of rivers, with lower densities in the centers of large rivers (Martin et al. 2004).
Botos feed on a large variety of fishes (over 43 species), generally near the bottom (see Best and da Silva 1993; da Silva 2002).
Threats include incidental mortality in fishing gear, deliberate killing for fish bait and attractant and for predator control, damming of rivers (although this is, at present, less of a problem than for the river cetaceans in Asia), and environmental pollution from organochlorines and heavy metals (see da Silva 2002; IWC 2007; Reeves et. Al. 1999).
The Mura Indians hunted botos near Barro do Rio Negro, Brazil during the nineteenth century (Pilleri and Arvy 1981) and the Tucuna and Cocama Indians may have killed them in the Amazon near Leticia (Allen and Neil 1958; Layne and Caldwell 1964) and the lower Ucayali River (Mohr 1964), respectively, until at least the 1950s.
Between 1956 and the early 1970s, more than 100 botos were live-captured and exported mostly to the U.S. and Europe (Brownell 1984) and (a few) to Japan (Tobayama and Kamiya 1989). However, in recent decades, there have been no reported live-captures and exports.
Incidental mortality has not been studied systematically in most areas. However, similar to other small cetaceans, botos are vulnerable to entanglement in a variety of nets (lampara seine nets, fixed gill nets, drifting gill nets; Best and da Silva 1993; Martin et al. 2004) as well as to drop traps intended to catch large fish or manatees in the flooded forest in Peru (Leatherwood 1996)
There is an emergent, but already large-scale, problem involving the deliberate killing of botos in Brazil for fish attractant (IWC 2007). Botos are also killed deliberately in some areas because fishermen regard them as competitors and because the dolphins damage fishing nets (F. Trujillo pers. comm. to B.D. Smith).
Fishing with explosives, although illegal in most areas, is common in some areas of the Amazon Basin (Goulding 1983; Smith 1985). This fishing technique threatens botos due to the concussive effects of explosions. Fishermen also reportedly attempt to kill dolphins that are attracted to prey on the stunned or dead fish (Best and da Silva 1989a).
Water development projects have not been as extensive in the Amazon and Orinoco basins as in Asian rivers inhabited by cetaceans. A population of botos was isolated above the Tucuruí dam in the Tocantins River, but there is no information on their current status. The Balbina dam in the Uatuma River may have isolated botos but there is no information on historic or current occurrence of dolphins in this river. Both of these dams in the Amazon basin, and the Guri dam in the Caroní, an Orinoco tributary, have probably degraded downstream habitat due to their effects on flow and temperature regimes (see Ward and Stanford 1989; Ligon et al. 1995; Kondolf 1997). There are many more proposed dams, especially for northward flowing Amazon tributaries that, if built, would restrict dolphin movements (Best and da Silva 1989a) and probably degrade their habitat.
Mercury is often used to separate gold from soil and rock in mining operations along the Amazon (Pfeiffer ,i>et al. 1993). In the Madeira River almost 60% of children under five years old had accumulated levels of mercury, presumably from eating contaminated fish, high enough to cause neurological damage (Boischio and Henshel 1996). A study of mercury in the sediments and floating plants in the Tucuruí Reservoir of the former Tocantins River, Brazil, emphasized the risk of mercury accumulation in the bed of non-flowing waters (Aula et al. 1995). The effects of the bioaccumulation of mercury in botos are unknown but the high levels recorded in the Amazon ecosystem give reason for concern.
The species is in Appendix II of CITES.
Research is needed to evaluate better the impact of threats, and to design effective conservation measures.
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Kondolf, G. M. 1997. Hungry water: effects of dams and gravel mining on river channels. Environmental Management 21: 533-551.
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Martin, A. R. and Da Silva, V. M. F. 2004a. Number, seasonal movements, and residency characteristics of river dolphins in an Amazonian floodplain lake system. Canadian Journal of Zoology 82: 1307-1315.
Martin, A. R. and Da Silva, V. M. F. 2004b. River dolphins and flooded forest: Seasonal habitat use and sexual segregation of botos (Inia geoffrensis) in an extreme cetacean environment. Journal of Zoology (London) 263: 295-305.
Martin, A. R., da Silva, V. M. F. and Salmon, D. L. 2004c. Riverine habitat preferences of botos (Inia geoffrensis) and tucuxis (Sotalia fluviatilis) in the central Amazon. Marine Mammal Science 20(2): 189-200.
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Vidal, O., Barlow, J., Hurtado, L. A., Torre, J., Cendon, P. and Ojeda, Z. 1997. Distribution and abundance of the Amazon river dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) in the upper Amazon River. Marine Mammal Science 13(3): 427-445.
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|Citation:||Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. 2011. Inia geoffrensis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 June 2013.|
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