Besides the Amazon mainstem, I. g. geoffrensis has been recorded in the Tocantins (and das Mortes and Verde affluents), Xingu, TapajÃ³s, Madeira (below the Teotonio rapids), Purus, JuruÃ¡, Ucayali, and MaraÃ±on (and Samiria affluent) tributaries flowing generally north, and in the Negro, Caqueta (JapurÃ¡), 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), ItÃ©nez or GuaporÃ© Basin (and Verde and IporuporÃ© affluents), and MamorÃ© Basin and its tributaries and afluents: Pirai, Grande, Ichilo, Chapare, IbarÃ©, 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 ApurÃ© (and Portuguesa and Guanmar affluents), Capanaparo, Cinaruco, Meta, Bita, Vichada, Tomo, Tuparro, Guaviare (and Guayabero affluent), InÃrida, 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.
- UNESCO-IOC Register of Marine Organisms
Habitat and Ecology
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).
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
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 ApurÃ© River, Venezuela in 1981 (Pilleri et al. 1982); 0.20 dolphins/km observed in a 201-km segment of the ApurÃ© 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).
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 TucuruÃ 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 CaronÃ, 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 TucuruÃ 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.
Research is needed to evaluate better the impact of threats, and to design effective conservation measures.
Relevance to Humans and Ecosystems
IUCN Red List Category
- IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
Amazon river dolphin
Inia geoffrensis, commonly known as the Amazon river dolphin, is a freshwater river dolphin endemic to the Orinoco, Amazon and Araguaia/Tocantins River systems of Brazil, Peru, Bolivia, Ecuador, Colombia and Venezuela. It was previously listed as a vulnerable species by the IUCN due to pollution, overfishing, excessive boat traffic and habitat loss but in 2011 it was changed to data deficient due to a lack of current information about threats, ecology, and population numbers and trends.
The Amazon river dolphin is one of the river dolphins formerly included in the superfamily Platanistoidea, making it paraphyletic; it has since been moved to Inioidea. Although not a large cetacean in general terms, this dolphin is the largest freshwater cetacean; it can grow larger than a human. Body length can range from 1.53 to 2.4 m (5.0 to 7.9 ft), depending on subspecies. Females are typically larger than males. The largest female Amazon river dolphins can range up to 2.5 m (8.2 ft) in length and weigh 98.5 kg (217 lb). The largest male dolphins can range up to 2.0 m (6.6 ft) in length and weigh 94 kg (207 lb).
They have unfused neck vertebrae, enabling them to turn their heads 90 degrees. Their flexibility is important in navigating through the flooded forests. Also, they possess long beaks which contain 24 to 34 conical and molar-type teeth on each side of the jaws.
In colour, these dolphins can be either light gray or carnation pink.
The species was described by Henri Marie Ducrotay de Blainville in 1817. Rice's 1998 classification lists a single species, Inia geoffrensis in the genus Inia, with three recognised subspecies. Some older classifications, as well as some recent publications, listed the boliviensis population as a separate species. In 2012 the Society for Marine Mammalogy began considering the Bolivian (Inia geoffrensis boliviensis) and Amazonian (Inia geoffrensis geoffrensis) subspecies as full species Inia boliviensis and Inia geoffrensis, respectively; however, much of the scientific community consider the boliviensis population to be a subspecies of Inia geoffrensis. The genus Inia separated from its sister taxon during the Miocene epoch.
The two currently recognized species are:
- I. g. geoffrensis — distributed in the Amazon and Araguaia/Tocantins basins (excluding the Madeira River drainage, upstream of the Teotonio Rapids in Rondônia)
- I. g. humboldtiana — distributed in the Orinoco basin
- I. boliviensis — distributed in the Bolivian sub-basin of the Amazon basin upstream of the Teotonio Rapids in Rondônia
The Amazon river dolphin is closely related to the newly identified Araguaian river dolphin which is believed to have become physically separated and diverged into two separate species. Araguaian Boto have fewer rows of teeth than their closely related Amazon Boto.
The Amazon river dolphin is found throughout the Amazon and Orinoco. It is particularly abundant in lowland rivers with extensive floodplains. During the annual rainy season, these rivers flood large areas of forests and marshes along their banks. The Amazon river dolphin specialises in hunting in these habitats, using its unusually flexible neck and spinal cord to maneuver among the underwater tree trunks, and using its long snout to extract prey fish from hiding places in hollow logs and thickets of submerged vegetation.
When the water levels drop, the dolphins move either into the main river channels or into large lakes in the forest, and take advantage of the concentrated prey in these reduced water bodies. They feed on crustaceans, crabs, small turtles, catfish, piranha, shrimp, and other fish.
Adult males have been observed carrying objects in their mouths, objects such as branches or other floating vegetation, balls of hardened clay. The males appear to carry these objects as a socio-sexual display which is part of their mating system. The behaviour is "triggered by an unusually large number of adult males and/or adult females in a group, or perhaps it attracts such animals into the group. A plausible explanation of the results is that object carrying is aimed at females and is stimulated by the number of females in the group, while aggression is aimed at other adult males and is stimulated by object carrying in the group."
The male reaches sexual maturity at about 2 metres (6.6 ft) and the female at about 1.7 metres (5.6 ft). Most calves are born between July and September after a gestation period of 9 to 12 months; they are about 0.81 metres (2.7 ft) long at birth and weigh about 6.8 kilograms (15 lb). The young follow their parents closely for a few months, and often two adults are seen swimming with two or more small juveniles.
The Amazon river 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 organized by tailored agreements. In September 2012, Bolivian President Evo Morales enacted a law to protect the dolphin and declared it a national treasure.
In popular culture
In traditional Amazon River folklore, at night, an Amazon river dolphin becomes a handsome young man who seduces girls, impregnates them, and then returns to the river in the morning to become a dolphin again. This dolphin shapeshifter is called an encantado. It has been suggested that the myth arose partly because dolphin genitalia bear a resemblance to those of humans. Others believe the myth served (and still serves) as a way of hiding the incestuous relations which are quite common in some small, isolated communities along the river. In the area, there are tales that it is bad luck to kill a dolphin. Legend also states that if a person makes eye contact with an Amazon river dolphin, he or she will have lifelong nightmares. Local legends also state that the dolphin is the guardian of the Amazonian manatee, and that, should one wish to find a manatee, one must first make peace with the dolphin.
Associated with these legends is the use of various fetishes, such as dried eyeballs and genitalia. These may or may not be accompanied by the intervention of a shaman. A recent study has shown, despite the claim of the seller and the belief of the buyers, none of these fetishes are derived from the boto. They are derived from Sotalia guianensis, are most likely harvested along the coast and the Amazon River delta, and then are traded up the Amazon River. In inland cities far from the coast, many, if not most, of the fetishes are derived from domestic animals such as sheep and pigs.
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- R.R. Reeves, T.A. Jefferson, L. Karczmarski, K. Laidre, G. O'Corry-Crowe, L. Rojas-Bracho, E.R. Secchi, E. Slooten, B.D. Smith, J.Y. Wang, & K. Zhou (2011). "Inia geoffrensis". IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature and Natural Resources.
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