Abundance of the Bolivian River Dolphin (Inia boliviensis) in Mamore River, Upper Madeira Basin

Encounter rates of the Bolivian river dolphin (Inia boliviensis) in northeastern Bolivia

“…Although most of the encounters were in the main channel as opposed to confluences and meanders, these latter habitats have larger group sizes. Similar observations were described by other studies (Aliaga-Rossel, 2002;Aliaga-Rossel et al, 2006;Gomez-Salazar et al, 2011;Guizada and Aliaga-Rossel, 2016) that concluded that prey density at confluences is higher due to fish becoming disoriented. This increases the benefit to the dolphins to a lower energy cost, leading to the maintenance and support of larger groups (Best and da Silva, 1993;Aliaga-Rossel et al, 2006).…”

“…This difference in a single system can be attributed to seasonal habitat use of the species as mentioned by McGuire and Aliaga-Rossel (2007) who argue that during the rainy season the river is wider, resulting in more area for dolphins and their prey to disseminate in, as opposed to the low-water season, when they tend to be more concentrated in the main channel. This characteristic is true in several other river systems (Gomez-Salazar et al, 2011;Aliaga-Rossel et al, 2012;Guizada and Aliaga-Rossel, 2016).…”

“…This was observed in other tributaries of the basin of the Mamoré with groups of up to 20 individuals (Aliaga-Rossel, unpublished data) and more than 20 in Colombia for Inia geoffrensis 4 . Conversely, during descending and low water season (observed in the Negro and Blanco rivers), the whole group is concentrated in the main channels, causing a forced migration, and a possible increase in the competition cost for resources, further instigating a sexual or group segregation into different habitats (Aliaga-Rossel et al, 2006;McGuire and Aliaga-Rossel, 2007;Guizada and Aliaga-Rossel, 2016).…”

Challenges and priorities for river cetacean conservation

“…In South America, the use of Amazon river dolphin and tucuxi as bait for piracatinga catfish Calophysus macropterus is an ongoing threat (Estupiñan et al 2003, Mintzer et al 2018 and demand remains high (Salinas et al 2014, Perez 2018. The use of Amazonian dolphins as bait was first recorded in Brazil in the early 2000s (Silveira & Viana 2003, Loch et al 2009, Mintzer et al 2013, Brum et al 2015, and the practise has since extended to Bolivia, Colombia, Ecuador, Peru, and Venezuela (Mosquera-Guerra & Trujillo 2015, Guizada & Aliaga-Rossel 2016, Fruet et al 2018, Escobar-WW et al 2020, Trujillo et al 2020b. Such illegal take for use as bait was the primary cause of the halving of both South American river dolphin populations in the Mamirauá Sustainable Development Reserve (Brazil) over a period of 2 decades (da Silva et al 2018a).…”

A case of playful interaction between Bolivian river dolphins with a Beni anaconda

“…The Beni anaconda, Eunectes beniensis , is a large‐sized aquatic Boid snake, usually attaining up to 2 m, and endemic to the floodplains of the Bolivian Amazonia (Quintana et al, 2017). The Bolivian river dolphins, Inia boliviensis , are large‐sized freshwater mammals, that reach up to 2.4 m, and are also endemic to the floodplains of Bolivian Amazonia (Aliaga‐Rossel & Escobar, 2020; Guizada & Aliaga‐Rossel, 2016). The Bolivian river dolphin is considered threatened with extinction, as most populations are facing declines associated with overfishing, hunting, and habitat loss (Guizada & Aliaga‐Rossel, 2016); the Tijamuchin River population (Figure 1), in the floodplains of Beni, is estimated as having 0.52 dolphins per km in both “dry” and “wet” seasons, and specimens appear to prefer river confluences and meanders (Guizada & Aliaga‐Rossel, 2016).…”