We accessed 57 literature references (dated between 1980 and 2021) to obtain information on the use of Amazon River dolphins as bushmeat, medicinal and traditional purposes, and human consumption. The search and selection of publications followed the PRISMA methodological approach (Moher et al., 2009; Nakagawa et al., 2017). A search for information was conducted in the following databases: (1) Scopus, (2) Science Direct, (3) Springer Link, and (4) Google Scholar. Different search terms were used: (1) Amazon River dolphin (TI) AND targeted captures AND bushmeat AND piracathinga fishery*, (2) Amazon River dolphin (TI) AND flesh and blubber OR bushmeat (TI) AND piracathinga fishery*, (3) [TITLE-ABS KEY (Amazon River dolphin * AND piracathinga fishery) * AND (flesh * OR blubber * OR bushmeat * OR traditional medicine * AND piracathinga fishery *) AND TITLE (Amazon River dolphin *)]. In addition, 14 structured surveys were carried out with researchers of Bolivia, Brazil, Colombia, Perú, and Venezuela to identify areas where Amazon River dolphin are captured and opportunistic uses are reported. Subsequently, the information was classified in a database considering the following criteria: (1) country, (2) locality, (3) river, (4) basin, (5) subspecies, (6) category of use: traditional/medicinal purposes, bycatch/bushmeat, and consumption, (7) period(s) of recorded bushmeat use (1980-2000/2001-2021), and (8) references.

Spatial analyses included the mapped localities of use of Inia spp. in the assessed basins, derived from the literatura review. Additionally, 39,135 georeferenced locations from 23 boat-surveys (n = 11,519 locations) conducted in the Amazon (n = 16), Tocantins (n = 1) and the Orinoco basins (n = 6), and 33 tagged individuals from satellite monitoring (n = 27,616 locations) in Amazon (n = 20 individuals) and Orinoco basins (n = 13 individuals; Figure 1 ) were integrated into a kernel density (KD) estimation analysis on percentage volume contours from (K₁₀) 10% to (K₉₀) 90% at 10% intervals (Oshima et al., 2010; Sveegaard et al., 2011; Wells et al., 2017; Mosquera-Guerra et al., 2021). This means that the area within the (K₁₀) 10% contour represented the areas with the highest density or core area and the (K₉₀) 90% contour represented almost the entire range of Amazon River dolphins (Sveegaard et al., 2011). Kernel density analyses allowed us to spatially locate the Inia spp. populations at greater risk from use by calculating the following spatial metrics: (1) number of the core areas (K₅₀), (2) distance from the nearest the Amazon River dolphin core area to a locality use, and (3) distance from the nearest core area to a protected area for the assessed basin (Protected Planet Report, 2020). Mapping was performed using the geostatistical analyst and spatial analyst extensions in ESRI ArcGIS version 10.8.1 (ESRI Environmental Systems Research Institute, 2021; Table 1 ).

Shapiro-Wilk normality test was performed to the variables: (1) Inia spp. population size, (2) Inia spp. population density, (3) Number of the Amazon River dolphin use localities, (4) Number of core areas (K₅₀) in the assessed river basin sections, (5) Distance of core area (K₅₀) to the nearest locality of use, and (6) Distance of core area (K₅₀) to the nearest protected areas. These tests were developed using the open-source software R.4.0.3 (R Core Team, 2020). In all cases, a value of p < 0.05 was considered statistically significant.

We identified 57 localities where Inia spp. individuals were used under the evaluated categories in the study areas, and reported two more on the Brazilian Atlantic coast. The localities were distributed in the basins as follow: Amazon (n = 33, 58%), Tocantins (n = 2, 3%), and Orinoco basins (n = 22, 39%). Based on the number of records, the country with the highest number of localities is Brazil (n = 20, 34%), followed by Venezuela (n = 17, 29%), Peru (n = 13, 22%), Colombia (n = 7, 12%), and Bolivia (n = 2, 3%; see Figure 2 and Supplementary Table 1 ).

Kernel density analyses show that most of the core areas (K₅₀) of Inia spp. are in heterogeneous habitat types as follow: (1) main rivers, (2) confluences, (4) lagoons, and (5) channels of the river basins. In the Amazon basin there are four core areas: (1) Napo-Amazonas rivers confluence, (2) Loretayacu-Amazonas rivers confluence, including the wetland complex of Tarapoto, (3) Iténez River, and (4) Tapajós River. The Orinoco basin has three core areas: (1) Guayabero River, (2) Guaviare-Inírida rivers confluence, and (3) Meta-Bita-Orinoco rivers confluence, and in the Tocantins basin, the core area was in the lower basin ( Figure 3 ).

The values of the Shapiro-Wilk normality test concluded that the data for all variables do not come from a normal distribution ( Table 2 ).

Our results are in line with previous reports on the widespread use of Amazon River dolphin (Inia spp.), such as bait in the C. macropterus fisheries. This practice is an unsustainable practice that is widespread in the Amazonian countries of Bolivia, Brazil, Colombia, and Peru, along the lower Tocantins River in Brazil, and along the Orinoco basin shared between Colombia and Venezuela. It is considered a significant threat to the populations of these species (Brum, 2011; Iriarte and Marmontel, 2013a; Iriarte and Marmontel, 2013b; Mintzer et al., 2013; Botero-Arias et al., 2014; Brum et al., 2015; da Silva V.M.F. et al., 2018; Mintzer et al., 2018; Trujillo et al., 2020).

In the last thirty years, the increase of the human population in the hydrographic areas assessed, as well as the internal and external demand for the fishery resources in these countries, have led to overexploitation and the rapid decline of stocks of fishes of commercial interest to fisheries (e.g., large catfish Brachyplatystoma spp.), and has resulted in a shift of target species of fisheries from increasingly scarce large fish to smaller species (e.g., small catfishes with C. macropterus; Gómez et al., 2008; Barthem, 2013; Barthem et al., 2017). Change in the fisheries in the Amazon, Tocantins and Orinoco basins has involved the use of unsustainable practices (e.g., monofilament nets, trammel nets, and even the use of endangered species such as bait) thus increasing the biological and operational interactions with aquatic vertebrates (e.g., Amazon River dolphins). These events generally result in the incidental capture and retaliatory killing of individuals that in some cases are traded in the bushmeat markets for bait or traditional purposes and in lower proportions for consumption (Hernández and Gonzalves, 2009; Diniz, 2011; da Silva et al., 2011; da Silva V.M.F. et al., 2018; Escobar-WW et al., 2020; Trujillo et al., 2020; Brum et al., 2021).

Governments of Brazil and Colombia have generated instruments such as moratoriums to regulate or prohibit the commercialization of C. macropterus (da Silva V.M.F. et al., 2018; Trujillo et al., 2020). This interaction is considered a serious threat for Inia spp. populations in management plans formulated in Brazil, Bolivia, Colombia, Peru, and Venezuela. However, the implementation of actions proposed in these strategies for the mitigation of this threat has not been effective due to factors such as a: (1) lack of transboundary regulatory instruments for the management of the fishery resource (e.g., moratoriums and ban unified between neighboring countries), (2) reduced institutional capacity to control extensive areas in transboundary zones, and (3) high levels of economic vulnerability and low levels of education of the local communities that facilitate their insertion into extractive models (e.g., illegal trade of wild species), and the use of species of fauna (e.g., river dolphins) for the treatment of diseases without scientific evidence.

Our kernel density results (K₁₀ – K₉₅) coincide with those reported by Mosquera-Guerra et al. (2021) on the heterogenous distribution of the core areas in the different habitat types used by Amazon River dolphins (e.g., confluences, channels, tributaries and lagoons) that are influenced by the ecology of the species and environmental aspects of the basin, such as: (1) wide variations in the home range sizes (K₉₅ = 6.2 – 234 km², mean = 59 ± 13.5 km²), and core area sizes (K₅₀ = 0.6 – 54.9 km², mean = 9 ± 2.6 km ²), (2) broad and specific habitat uses, (3) movements influenced by the lateral and longitudinal migration of fish, (4) sexual segregation of Inia individuals, and (5) ecological characteristics of the aquatic systems where they occur (productivity levels; Mosquera-Guerra et al., 2021).

Although Inia spp. is distributed over >1,000,000 km² of the Amazon, Orinoco, and Tocantins basins, its occurrence is represented by only 15% of their distribution inside protected areas (Mosquera-Guerra et al., 2018). This is evidence that Inia spp. populations throughout much of their range are exposed to different types of human-induced threats such as bycatch (Hernández and Gonzalves, 2009; da Silva et al., 2011; Diniz, 2011; da Silva V.M.F. et al., 2018; Escobar-WW et al., 2020; Trujillo et al., 2020; Brum et al., 2021).

The results obtained through our statistical analysis show that the variables do not come from a normal distribution. This condition may be due to the widespread occurrence of this practice on the Inia spp. and the reduced management and control of the protected areas in the basins evaluated (da Silva V.M.F. et al., 2018; Trujillo et al., 2020). The population aspects considered in our analyses-such as population size of Amazon river dolphins- are influenced by: (1) the abundance and availability of fish prey, (2) the accessibility to foraging locations, determined mainly by the flooding pulse and river geomorphology, and (3) group sizes (Martin and da Silva, 1998; McGuire and Winemiller, 1998; Trujillo, 2000; Martin and da Silva, 2004; McGuire and Henningsen, 2007; Yamamoto et al., 2015; Mintzer et al., 2016; Mosquera-Guerra et al., 2021). Amazon River dolphins make up one of the smallest group sizes among odontocetes as a strategy to increase individual fitness and reduce competition for prey during declines in fish abundance during the high-water period (Gómez-Salazar et al., 2011).

Additionally, the spatial ecology of Amazon River dolphins is influenced by strong sexual segregation of individuals. The documented differential behaviors in the intensity of habitat use between males and females is reported by Trujillo (2000) for the lakes of Tarapoto and the Colombian Amazonas, Martin and da Silva (1998) and Martin and da Silva (2004) using data from 24 individuals monitored with radio telemetry in the Mamirauá Sustainable Development Reserve, and Mosquera-Guerra et al. (2021) from 24 individuals monitored by satellite in Bolivia, Brazil, Colombia, and Peru. This sexual segregation of Inia spp. differentially exposes males and females to targeted or incidental captures as well as other types of threats (Mintzer et al., 2016). The interactions between Amanimals with 20 individuals killed for use as bait inazon River dolphins and fisheries generally occur in highly productive habitats, such as: (1) confluences, (2) channels, and (3) lagoons, where capturing mostly sexually mature individuals and possibly larger numbers of females that have minor movements and are restricted to specific habitats where they care for their calfs. This could explain the rapid population decline in their area of occurrence (Williams et al., 2016; Martin and da Silva, 2021), possibly due to the special reproductive conditions of Inia spp. including (1) extended periods to reach sexual maturity of individuals that on average is considered to be 9.7 years, (2) extensive gestation periods (12.3–13 months), (3) prolonged parental care of calves (1.5–5.8 years), and (4) average intervals between births of 4.6 years (Martin and da Silva, 2018).

Our study highlights the need to continue with Inia population trend studies in order to monitor in a standardised way the fast population decline of Amazon River dolphins reported in the last three decades in the study areas (Williams et al., 2016; Martin and da Silva, 2021). This information is essential to complement spatial analyses and to focus conservation efforts in priority areas. Population studies conducted in the upper and middle Amazon and Orinoco rivers highlight the negative impact of bycatch on I. g. geoffrensis populations. For example, Williams et al. (2016) assess Amazon River dolphin abundance estimates made in the Colombian Amazon trapezoid in 1993, 2002 and 2007, and report an annual decline probability for I. geoffrensis of > 0.75. Hernández and Gonzalves (2009) report that the population of I. geoffrensis in the Javari River, a tributary of the Amazon River, is 250 animals with 20 individuals killed for use as bait in C. macropterus fisheries annually (8%). da Silva et al. (2011), and Martin and da Silva (2021) report between the 5.5–10% annual decline of populations of I. g. geoffrensis in the Central Amazon in the vicinity of the Mamiruá Reserve and document that 1650 Amazon River dolphins are captured annually near the Brazilian Amazonian city of Tefé. Finally, in the Venezuelan Orinoco basin, Diniz (2011) estimates that 840 individuals are killed for piracatinga fisheries (da Silva V.M.F. et al., 2018). In this context, it is a priority to continue with this type of population dynamic studies and thus contribute to an understanding of the effect of this threat on the health of Inia populations.

In this context, it is necessary to clarify the taxonomy of the genus Inia using integrative taxonomy studies since currently only two subspecies are recognized (Committee on Taxonomy, 2021); I. g. geoffrensis distributed across the Amazon, and Orinoco basins and I. g. boliviensis, found along the Mamoré, Iténez, and Madeira rivers (Aliaga-Rossel, 2002; Aliaga-Rossel et al., 2006; Gravena et al., 2014; da Silva and Martin, 2014; da Silva V. et al., 2018; Aliaga-Rossel and Guizada-Durán, 2020; Pivari et al., 2021). This condition does not allow for evidence of possible effects on the loss of genetic diversity for the genus caused by the reduction of populations. This is the case of the Inia spp. that are pressured by targeted and incidental catches in the middle Amazon (Bolivia and Brazil), and Tocantins Basins (Brazil). It has been proposed that I. boliviensis corresponds to a valid species (Banguera-Hinestroza et al., 2002; Ruíz-García, 2010, and Gravena et al., 2014); in the same way, Hrbek et al. (2014) have suggested I. araguaiaensis (Tocantins basin) as a new species in the genus, with a population size >3,000 individuals, seriously threatened by infrastructure projects like dams (Hrbek et al., 2014; Paschoalini et al., 2020; Brum et al., 2021). Although these taxa have not yet been recognized as valid species by a section of the scientific community (Committee on Taxonomy, 2021), a precautionary principle should be considered and efforts should be made to preserve the taxonomic diversity of the genus Inia (Trujillo et al., 2010; da Silva V.M.F. et al., 2018).

Additionally, it is a priority to promote the implementation of public health programs in the countries of the region that monitor concentrations of heavy metals in aquatic ecosystems as well as the zoonotic risks generated by the illegal bushmeat market. The best biological models for evidence of mercury concentrations in aquatic food webs are top predators (e.g., Amazon River dolphins; Mosquera-Guerra et al., 2019a; Barbosa et al., 2021), and benthic fish with omnivorous habits (C. macropterus; Mosquera-Guerra et al., 2015). These aquatic vertebrates are extensively used in the region, and this situation could become a public health problem for local communities and external consumers who make multiple uses of these species.

Finally, the bushmeat markets are widely distributed in the Neotropical region, illegally trading massive numbers of wildlife rodents, primates, xenarthrans, and ungulates (Olival et al., 2017), with a significant increment in the trading of Inia since the 2000s for bait for C. macropterus fisheries, and more recently for human consumption. The use of other products of Inia such as oil, eyes, and genitals organs for traditional purposes and non-evaluated treatments of respiratory ailments since the 1980s (Cravalho, 1999; Gravena et al., 2008; Loch et al., 2009; Trujillo et al., 2010; Martins, 2015; Cosentino and Fisher, 2016; Santos, 2017; da Silva V.M.F. et al., 2018; Mintzer et al., 2018; Siciliano et al., 2018), constitutes a risk for the emergence and transmition of zoonotic diseases and future pandemics. Bushmeat markets are centers for the interaction of viral loads of various vertebrate species (Olival et al., 2017), that could, at any time, cause a zoonotic jump in densely populated places with the Amazon basin where recent censuses have reported more than 40 million inhabitants.