Inia boliviensis, d'Orbigny, 1834

Russell A. Mittermeier & Don E. Wilson, 2014, Iniidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 364-379 : 378

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Bolivian Boto

Inia boliviensis

French: Boto de Bolivie / German: Bolivien-Delfin / Spanish: Delfin del Madeira

Other common names: Bolivian Bufeo

Taxonomy. [nia boliviensis d’Orbigny, 1834 ,

“la riviere du Guaporé” (= Itenez) near “Principe de Béira,” Brazil.

Recent studies of mitochondrial control region sequences and the cytochrome b gene by E. Banguera-Hinestroza and colleagues in 2002 and mtDNA and nDNA by W. Gravena in 2013, reinforced earlier morphological evidence provided by V. M. F. da Silva in 1994, suggesting that the Bolivian Botos are an evolutionarily significant unit distinct from those in the Amazon and Orinoco drainages. Monotypic.

Distribution. Bolivian lowlands (NE to the Chiquitano Mts and SW to the piedmont elevations in the subandean region) and SW Brazilian Amazon in the upper Madeira River, and the Beni, Ichilo, Marmoré, Ipurupuru, Iboré, Baré, Abuna, and Iténez (= Guaporé) rivers and their tributaries, all of which drain into the Madeira; recently also recorded below Santo Antonio falls between the cities of Porto Velho and Borba.

Descriptive notes. Only two reliable body length measurements have been published 208 cm and 216 cm (adult females), but size is presumably very similar to the Amazon River Dolphin (1. geoffrensis ) and the Araguaian Boto ( I. araguaiaensis ). Sexual dimorphism is pronounced in all species, with males larger and more robust than females. The main differences between the skull of boto species are the relative length of their rostrums and the number of teeth, which are greater in the Bolivian Boto, and the biparietal skull width which is comparatively narrower in the Bolivian Boto. Relative rostral length: ¢.73% of total skull length vs. ¢.65% in the Amazonian River Dolphin; number of teeth: upper row 31-35 teeth (mean 33-3) and lower jaw from 31-34 teeth (mean 32-3). Each upper and lower tooth row has 9-11 molar-type teeth.

Habitat. Sediment-laden white water and clear water, but not black water, in lowland floodplains (oxbow and “varzea” or white-water lakes). Similar to other botos, it aggregates at confluences and meetings of waters and is present in most of the aquatic habitats ofthe region. Otherwise, the habitat of the Bolivian Boto is quite similar to the other species of botos in the Amazon.

Food and Feeding. There is no specific information available for this species, but examination of stomach contents of two Bolivian Botos suggests a catholic piscivorous diet, similar to that of the Amazon River Dolphin.

Breeding. There is no information available for this species, but it is likely similar to the Amazon River Dolphin, in which the presence of neonates and juveniles has been observed throughout the year, with births peaking during low-water season.

Activity patterns. There is no information available for this species, but it probably moves seasonally due to fish migration and the annual flooding cycle. During the transition from high to low waters dolphins leave lagoons and flooded areas and go to main river channels, as do botos in the Brazilian Amazon and Araguaia river basins.

Movements, Home range and Social organization. Encounter rates of Bolivian Botos are 0-2-5-8 ind/km of waterway, with greater densities in larger rivers. As described for botos elsewhere, this species is commonly sighted singly or in groups of up to four. Larger aggregations occur around a resource or in confluences and bays. Other characteristics of their movements and social organization have not been studied, but are likely similar to those of the Amazon River Dolphin.

Status and Conservation. CITES Appendix I. Classified as Data Deficient on The IUCN Red List (as I. geoffrensis boliviensis ). In Bolivia, this dolphin is indirectly protected by the Political Constitution and the Supreme Decree 25458 of July 1999, with a total ban on the hunting and trade of those native wildlife species considered to be in danger of extinction. In March 2008 the Beni Department issued a Law decreeing the Bolivian Boto as a Natural Heritage. The Bolivian Boto has been mostly separated from the congeneric Amazon River Dolphin living in the lower Madeira by a sequence of rapids, but these have not formed a total barrier to downstream movement; individual Bolivian Botos have been found between and below the rapids. During years of exceptionally high water levels, upstream movements may even have been possible. However, the construction of the Jirau and Santo Antonio hydroelectric dams on the Madeira River in Brazil, begun in 2008 and completed in 2013, have now completely blocked all passage of botos in either direction. There are no quantitative studies of abundance or trends of the Bolivian Boto. Estimated densities for tributaries of the Iténez and Mamoré rivers were 3-2 ind/km and 3-5 ind/km, respectively, with estimated population sizes of 2986 and 1369 individuals. So far, the only known human impact on the Bolivian Botois entanglement in monofilament gillnets.

Bibliography. Aliaga-Rossel (2000, 2002), Aliaga-Rossel et al. (2006), Banguera-Hinestroza et al. (2002), Best & da Silva (1989a, 1989b, 1993), Gravena (2013), Pilleri & Gihr (1977), da Silva (1994), Tavera et al. (2010).

Figures

1. Amazon River Dolphin (Inia geoffrensis), 2. Bolivian Boto (Inia boliviensis), 3. Araguaian Boto (Ima araguaiaensis)

Distribution. Bolivian lowlands (NE to the Chiquitano Mts and SW to the piedmont elevations in the subandean region) and SW Brazilian Amazon in the upper Madeira River, and the Beni, Ichilo, Marmoré, Ipurupuru, Iboré, Baré, Abuna, and Iténez (= Guaporé) rivers and their tributaries, all of which drain into the Madeira; recently also recorded below Santo Antonio falls between the cities of Porto Velho and Borba.