Analysis of distribution of river dolphins (Inia and
Sotalia) in protected and transformed areas in the
Amazon and Orinoco basins
Federico Mosquera-Guerra 1,2, Fernando Trujillo1, Danni Parks3, Marcelo Oliveira-da-
Costa4, Miriam Marmontel5, Dolors Armenteras-Pascual2, Saulo Usma4, Daphne Willems4,
Juan David Carvajal-Castro6, Hugo Mantilla-Meluk6, Nicole Franco1, Diego Amorocho4,
Roberto Maldonado4, Karina Berg4, Lila Sainz4, Paul A. Van Damme7, Elizabeth Cambell8.!
1 Fundación Omacha: Calle 84 No. 21 – 64 - Barrio el Polo - Bogotá, D.C,
2 Grupo de Ecología del Paisaje y Modelación de Ecosistemas-ECOLMOD: Departamento
de Biología, Universidad Nacional de Colombia - Cra 30 No. 45-03 - Bogotá D.C,
3 Whitley Fund for Nature : 110 Princedale Road l - London W11 4NH, United Kingdom.!
4 WWF – Brazil; Bolivia; Colombia; Ecuador, Peru, Netherlands; Deutschland; United
Kingdom. Rue Mauverney, 28 1196 Gland, Switzerland
5 Mamiraguá: Estrada do Bexiga, 2.584 Bairro Fonte Boa Cx. Postal 38 69.553-225 – Tefé
6 Universidad del Quindiìo: Programa de Biologiìa, Carrera 15 No. 12 Norte. Quindiìo -
Armenia - Colombia.!
7 Faunagua: Av. Max Fernández final s/n - Plazuela del Chillijchi (Arocagua) –
8 Prodelphinus: Enrique Palacios 630 – 204, Lima 18 – Miraflores - Lima, Peru.!
The South American river dolphins have evolved in the continental aquatic
ecosystems of the Amazon, Grande, Iténez - Mamoré, Araguaia - Tocantis and Orinoco
rivers. The spatial and temporal distribution and the habitat use of these cetaceans do in
these systems, are determined by distinct environmental characteristics such as
precipitation regimes, elevation, productivity and biomass specific to each system. In
addition, geomorphological accidents, such as rapids, have emerged as barriers that
separate dolphin populations, potentially promoting processes of speciation. To date, there
is no comprehensive analysis of river dolphins distribution and representativeness in
protected areas or areas transformed by hydroelectric plants. In the present work, through
niche and spatial modeling tools, we research the representativeness of both protected areas
and areas transformed by hydroelectric plants in the Amazon and Orinoco basins in the
distribution of river dolphins (Inia and Sotalia). The models presented here were
constructed using the MaxEnt algorithm through the integration of 35,594 georeferenced
records and 19 environmental variables derived from the Bioclim and Hydroshed database,
which were parameterised in the R programme. A good representation of the distribution of
river dolphins within the protected areas was evidenced, although the limited management
of the aquatic ecosystems inside the protected areas does not guarantee the conservation of
these species. A major threat identified for river dolphins in South America is the loss of
habitat and fragmentation as a result of the construction of hydroelectric dams. We
examined the degree of overlap between the distribution of Inia and Sotalia and
hydroelectric projects in construction, operation and planning phases and provided an initial
quantification of this tensor. Finally, we consider that the cumulative impacts
(fragmentation, regulation of the flood pulse, retention of limiting nutrients and alteration in
the levels of productivity) generated by this type of infrastructure at the macrobasin scale
will exacerbate the level of the threats to the conservation of river dolphins and their
habitats in the Amazon and Orinoco basins.
Key words: Conservation,!distribution,!human!impact,!hydroelectric!dams,!
The South American river dolphins are represented by the subspecies and species of
the genus Inia and Sotalia. They are widely distributed in the aquatic ecosystems of the
Amazon, Orinoco, Tocantins basins and Orinoco delta (Caballero et al. 2007; Reeves et al.
2011; Secchi et al. 2012; Carvajal-Castro et al. 2015; Caballero et al. 2017). Throughout
their distribution it has been identified that geological interruptions, particularly rapids, act
as effective barriers separating natural populations of river dolphins and promoting
processes of differentiation between populations (Rice 1998).
To date, three subspecies of Inia geoffrensis are recognized with distribution
throughout the Amazon basin (I. g. geoffrensis) and the Orinoco basin (I. g. humboldtiana)
with a suggested vicarious isolation caused by the formation of the Canal del Casiquiare on
the ecological border between the Colombian Orinoquia and the Venezuelan Amazon (Da
Silva & Martin 2000). I. g. boliviensis seems to have been isolated from I. g. geoffrensis
because of the 400 km of rapids from Porto Velho on the Madeira river to Riberalta on the
Beni river in Bolivia (Rice 1998). Currently the Bolivian bufeo (I. g. boliviensis) occurs in
the basin of the Madeira, Iténez and Grande river basins in Bolivia and Brazil (Trujillo et
al.1999; Banguera- Hinestroza et al. 2002; Ruiz-García et al. 2008; Ruiz-García 2010;
Reeves et al. 2011; 2013). However, the taxonomy for the genus Inia has been discussed
and even a new species has been described: the Araguaia river dolphin (Inia
araguaiaensis), present in the hydrographic complex formed by the Araguaia - Tocantins
rivers (Hrbek et al. 2014).
The genus Sotalia includes two species based on cranial morphology and genetic
evidence (Madeira et al. 2004; Cunha et al. 2005; Caballero et al. 2007; 2010; 2017).
Sotalia guianensis (P-J. Van Bénedén 1864) presents populations distributed along the
coasts and estuaries of the Atlantic Ocean from Honduras to Brazil, and in the north of
South America, including individuals established in Lake Maracaibo, middle and delta
parts of the Orinoco river in Venezuela. Recent genetic studies determined that there is a
divergence of 600,000 years between continental and coastal populations (Carvajal-Castro
et al. 2015; Caballero et al. 2017). The species Sotalia fluviatilis (Gervais y Deville, In
Gervais 1853) is found in the Amazon river basin (riparian zone) and is sympatric with Inia
geoffrensis in Brazil, Colombia, Ecuador, Peru and French Guiana in the Amazon river
basin (Borobia et al. 1989; Da Silva 1994; Martin y Da Silva 2004; Cunha et al. 2005;
Caballero et al. 2007; Flores and Da Silva 2009; Trujillo et al. 2010; Secchi et al. 2012;
Carvajal-Castro et al. 2015; Caballero et al. 2017).
Although river dolphins are obligate aquatic mammals, external environment
variables external to this environment associated with the river basins they inhabit, such as
precipitation and atmospheric temperature, may be determining aspects of their ecology,
directly or indirectly affecting their occurrence in a particular area. Historically, the
Orinoco, Amazon and the Araguaia-Tocantins complexes have been identified as different
biogeographical and ecological units characterized by contrasting climatic conditions
(McClain and Naiman 2008; Edmond et al. 1996; WCS 2017). These deferring conditions
affect in many ways the hydric dynamics of their basins, determining the composition and
structure of the biota associated with the course of its main and tributary rivers. Despite
analyses of the potential influence that external variables may have on aquatic biota, to
date, there is no comprehensive analysis in the South American territory on the
representativeness of the distribution of river dolphins in protected areas or areas
transformed by hydroelectric plants.
New tecnological approaches based on Geographic Information Systems (GIS),
currently allow the characterisation of the availability of habitat for species in a given area
through suitability models at a regional scale. Regionally, ecological conditions such as
elevation, temperature and precipitation in combination with latitude, determine, among
others, the vegetation cover, which consequently at a local scale define aspects such as
productivity, nutrient flow and conductivity in the related water ecosystems at a local scale.
Although the relationship between regional and local variables has been studied relatively
poorly, GIS analysis opens a window of possibility to understand the distribution and
ecology of aquatic organisms such as river dolphins at the continental level.
In the present study, the results from river dolphin monitoring, based on sightings
are integrated with environmental information through niche modeling tools, with the
purpose of investigating the representativeness of the different species and subspecies in
protected areas and areas transformed by hydroelectric plants in the Amazon and Orinoco
Material and Methods
Obtaining records and environmental variables
The environmental conditions included 19 bioclimatic variables from the Worldclim
database (Hijmans et al. 2005), in addition, radiation was obtained as an approximation of
primary productivity. To obtain this information, the values of the 12 months of the year
provided by Worldclim v.2 are averaged (Fick and Hijmans 2017). All the variables
presented a resolution of 30 arc-seconds (~1 km2 in Ecuador) (Table 1).
Table 1. Bioclimatic variables used in the potential distribution models of river dolphins
(Inia and Sotalia) in the Amazon and Orinoco river basins.!
Height in meters above sea level
Annual average temperature
Average daytime range (Mean of the month
(Max Temp - Min Temp))
Isothermality ((Bio 2/Bio 7) * 100)
Seasonality of temperature (Standard
deviation * 100)
Maximum temperatura of the hottest month
Minimum temperature of the coldest month
Annual temperature range (Bio 5 - Bio 6)
Average temperature of the wettest quarter
Average temperature of the driest quarter
Average temperature of the warmest quarter
Average temperature of the coldest quarter
Precipitation of the wettest month
Precipitation of the driest month
Seasonality of precipitation (Coefficient of
Precipitation of the wettest quarter
Precipitation of the driest quarter
Precipitation of the warmest quarter
Precipitation of the coldest quarter
Potential distribution models
The models of potential distribution of the subspecies and species of the genera Inia
and Sotalia were generated using the environmental variables and the georeferenced
records obtained through sightings in expeditions carried out within the framework of the
South American River Dolphin Conservation Programme (2006-2018) and the records
issued by river dolphins tagged with satellite telemetry in Colombia, Brazil and Bolivia
(Table 2, Figures 1& 2). The algorithm used was the maximum entropy (MaxEnt) (Phillips
et al. 2006). MaxEnt was chosen because it has been widely used and its best performance
has been demonstrated to estimate the potential distribution of the species more accurate
than other approaches (Graham and Hijmans 2006; Townsend et al. 2007). As MaxEnt only
works with information on the presence of species, it must generate pseudoausencias, more
appropriately called ‘background’ in order to obtain a calibration of the model (Phillips and
Dudík 2008). Therefore, 10000 randomly generated points (background) were used through
the northern zone of the Neotropic. 10 replicas were generated to perform an assembly
methodology (Araújo and New 2007) and thus obtaining a consensus model among the
Table 2. Records of river dolphins (Inia and Sotalia) in the Amazon, Orinoco and
Tocantins-Araguaia river basins.
Records issued by
dolphins marked with
I. g. geoffrensis
I. g. humboldtiana
I. g. boliviensis
Figure 1. Georeferenced records for genus Inia in South America.
Figure 2. Georeferenced records for genus Sotalia in South America.
To evaluate the performance of the model, a "k fold partitioning" approach was
used, with an area under the receiver curve (AUC) as the evaluation metric, using 75% of
the occurrence data to perform modeling and 25% of the remaining occurrence data to test
the model. The AUC value is used to evaluate the discrimination ability of the model: AUC
values close to 1 are considered as a perfect prediction and values of 0.5 or less reflect that
the model is not better than a random model. These analyses were carried out using the R
software, using the dismo libraries (Hijmans et al. 2015), SDMTools (VanDerWal et al.
2014) and raster.
The consensus model generated by MaxEnt is a probability map, on which the
probability of the presence of species is shown. This probability map was used to make a
binary map representing the presence and absence of dolphins, establishing a threshold
value as a criterion, defined as the maximum sum of specificity and sensitivity (MSS).
Therefore, the probability values (probability map) that were equal to or greater than this
threshold value were considered as demostrating the presence of river dolphins (the value
of the pixel equal to 1); on the other hand, values below this threshold were considered as
species’ absence (pixel value equal to 0).
Representation of protected and transformed areas in the potential distribution of river
dolphins (Inia and Sotalia)
A statistical analysis was carried out overlapping the models of potential
distribution, with the protected areas (WDPA) (UNEP-WCMC 2010) downloaded from
(www.protectedplanet.net) and areas transformed by hydroelectric plants in Brazil, Bolivia,
Colombia, Ecuador, Peru and Venezuela (Anderson et al. 2018, Latrubesse et al. 2017).!The
number of pixels intersecting the distribution of species and protection zones were
quantified as an indirect measure of the ability of protected areas to protect dolphins.!At the
same time, the areas transformed by hydroelectric dam construction, operation and
planning in the Amazon, Orinoco and Araguaia-Tocantins basins were quantified in order
to demonstrate the impact of this type of infrastructure on river dolphin populations. For the
purpose of calculating these areas, the function of the library rgeos was used in the
statistical software R.
Potential distribution models
The generated models demonstrate a high correlation, with AUC values of 0.8852
(I. g. geoffrensis), 0.889 (I. g. humboldtiana), 0.9189 (I. g. boliviensis), 0.9738 (I .
araguaiaensis), 0.948 (Sotalia fluviatilis) and 0.933 (S. guianensis). Figure 3 shows the
modelled potential distrubution of the South American river dolphin species and subspecies
(Inia and Sotalia).
Figure 3. Modelled potential distrubution of the South American river dolphins (species and
subspecies) Inia and Sotalia, derived from the algoritm MaxEnt. A. I.g. geoffrensis. B. I.g.
humboldtiana. C. I.g.boliviensis. D. I. araguaiaensis. E. Sotalia fluviatilis. F. S. guianensis.
Representation of protected and transformed areas in the potential distribution of river
dolphins (Inia and Sotalia)
Potential distribution areas for the South American river dolphins (Inia and Sotalia) and
their representation in the aquatic ecosystems in Amazon protected areas were calculated in
order to establish their representativeness for each taxa. (Table 3). In the category of
protected areas, strict figures were included, such as National Parks and regional parks, and
other figures such as sustainable reserves and Ramsar sites were included.
Table 3. Representativeness of protected areas in the distribution of South American river
dolphins (Inia and Sotalia).
Areas of aquatic ecosystems in conservation km2
Figure 4. Distribution of the genus Inia in Amazon protected areas
Figure 5. Distribution of of the genus Sotalia in Amazon protected areas.
The areas transformed by hydroelectric plants were calculated in phases of planning,
construction and operation, and the representation of these in the potential distribution areas
of the South American river dolphins (Table 4).
Table 4. Representativeness of transformed areas by hydroelectric plants in the distribution
of South American river dolphins (Inia and Sotalia).
Areas transformed by hydroelectric plants in
different phases km2
I. g. geoffrensis
I. g. humboldtiana
Figure 6. Spatialisation of habitats transformed by hydroelectics in the operation phase for
the genus Inia.
Figure 7.!Spatialisation of habitats transformed by hydroelectics in the constrution phase
for the genus Inia.
Figure 8. Spatialisation of habitats transformed by hydroelectics in the planning
phase for the genus Inia.
Figure 9. Spatialisation of habitats transformed by hydroelectics in the operation phase for
the genus Sotalia.
Figure 10. Spatialisation of habitats transformed by hydroelectics in the constrution phase
for the genus Sotalia.
Figure 11. Spatialisation of habitats transformed by hydroelectics in the planning
phase for the genus Sotalia.
Potential distribution models
River dolphins (Inia and Sotalia) occur in 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). For the genus Inia
three geographic populations have been recognised as subspecies: I. g. geoffrensis in the
Amazon basin, except for the Madeira basin in Bolivia upstream, from the Teotonio rapids,
I. g. boliviensis in the upper Madeira basin, and I. g. humboldltiana in the Orinoco basin
(Rice 1998, Reeves et al. 2011). Genetic studies reveal the relevance of these geographical
barriers in the generation of vicariant speciation processes, as is the case with Inia
araguaiaensis, a species recently described, whose populations are isolated by the
Araguaia-Tocantins hydrographic complex (Hrbek et al. 2014).
For I. g. geoffrensis, the distribution generated by the model coincide with the
distribution presented by de Best and da Silva (1989a), (1989b) and Leatherwood (1996),
who place its occurence in the rivers Xingu, Tapajós, Madeira (downstream from the rapids
of Teotonio), Purus, Juruá, Ucayali and Marañón (and Samiria tributary) that flow
generally towards the north, and the Negro river with itstributaries Caquetá (Japurá),
Apaporis, Putumayo (Iça) and Napo.
In relation to the distribution of I. g. humboldtiana, the model outcome matches
what was reported by Pilleri y Gihr (1977); Best y da Silva (1989a), (1989b); Meade and
Koehnken (1991); Velásquez-Roa et al. (2015), identifying the subspecies’ presence in the
Apuré tributaries (Portuguesa and Guanmar), Capanaparo, Cinaruco, Meta, Bita, Vichada,
Tomo, Tuparro, Guaviare (tributary Guayabero), Inírida and Atabapo (and Temi tributary)
that flow to the south and east, and the tributaries Aro, Caura, Parquaza, Ventauri (San Juan
tributary) that flow to the north and west, as well as the Casiquiare Canal, which connects
the Orinoco with the Negro river (a tributary of the Amazon), above and below the two
series of rapids in Puerto Ayacucho, which are the main barriers that are expected to
separate the dolphin populations of the Amazon and the Orinoco (Reeves et al. 2011).
Nevertheless, river dolphins have been seen crossing the first group of rapids in Puerto
Ayacucho (Atures) during the high tide (Fernando Trujillo, personal communication with
The modelled distribution generated for Inia boliviensis coincides with what is
stated by Pilleri and Gihr (1977); Best and da Silva (1993); Aliaga-Rossel et al. (2006); Da
Silva (2009); Aliaga-Rossel (2010); Tavera et al. (2010); Cella-Ribeiro et al. (2013), and
Gravena et al. (2014), that this unique aquatic mammal is present in the sub-basins of the
rivers Abuna, Guaporé, Iténez or Guaporé basin (including Verde and Iporuporé
tributaries), Mamoré basin and its primary and secondary tributaries: Pirai, Grande, Ichilo,
Chapare, Ibaré, Tijamuchi, Apere, Yacuma and Yata, Beni (and Orton tributary); on the
Madeira river, its distribution is considered below the Tetonio rapids located upstream from
Porto Velho. According to Cella-Ribeiro et al. (2013), the Bolivian river dolphin presents
an estimated evolutionary divergence of 3.1 million years of genetic isolation generated by
the geographic barrier formed by a series of 18 rapids along a stretch of 290 kilometers on
the Madeira river. These rapids are thought to act as a barrier to the movement of dolphins
and thus restrict the distribution of I.g.boliviensis upstream of the rapids, and I.g.geoffrensis
downstream of the rapids.!
This example is similar to the recent description of the species Inia araguaiaensis
(Hrbek et al. 2014) distributed in the Araguaia-Tocantins river hydrographic complex,
currently isolated from the Amazon river basin (Rossetti and Valeriano 2007; Goulding et
al. 2003). The two basins have been disconnected, although not completely isolated from
each other in the transition from Pliocene to Pleistocene (Rossetti and Valeriano 2007).
Currently, only a narrow channel west of the island of Marajo joins the delta of the Amazon
river with the Para river, which drains the Araguaia-Tocantins river. The connectivity
between the Araguaia-Tocantins and Amazon basins is restricted by a series of important
rapids in the lower Tocantins river, becoming an important biogeographical element to
generate speciation processes (Hrbek et al. 2014).
The results obtained in relation to the distribution of S. fluviatilis coincide with the
reports generated by Layne (1958); Obregón et al. (1988); Borobia et al. (1991); Trujillo
(1992), (1994a), (2000); Vidal et al. (1997); McGuiere and Henningsen (2007); Gómez-
Salazar et al. (2010); Carvajal-Castro et al. (2015) and Caballero et al. (2017). All report its
presence in the Amazon basin as far inland as southern Peru, eastern Ecuador and
southeastern Colombia. This presents a sympatric distribution with I. g.geoffrensis (Secchi
2012), although S. fluviatilis does not occur in the Beni/ Mamoré river basin ,in Bolivia nor
in the upper part of the Negro river (Flores y da Silva 2009). The results obtained by
modeling identy limitations for the distribution of S. fluviatilis in the Caqueta/Japura river
basin, determined by the rapid of Cordoba and reported by Trujillo (1994b); Trujillo
(1995), Galindo (1997); Trujillo et al. (2006); Gómez-Salazar et al. (2010); Pavanato et al.
(2014) and Caballero et al. (2017); in the Apaporis river, its distribution is limitated by the
rapids of Estrella and Puerco (Gómez-Salazar et al. 2010).
In relation to S. guianensis, the presence of the species in the Colombian Orinoco is
not corroborated, which suggests that its distribution is restricted to the middle basin and
delta of the Orinoco. This can be explained by the rapids of Maipures, Atures and the Dead
between the Ayacucho and Samariapo Ports in the Venezuelan Orinoco, probably
restricting the species’ distribution (Gómez-Salazar et al. 2010; Herrera-Trujillo 2012).
Representation of protected and transformed areas in the potential distribution of river
dolphins (Inia and Sotalia)
In the Amazon and Orinoco basins there are important areas under conservation
management, such as national natural parks and Ramsar sites. Among these, there are areas
of distribution of river dolphins (Trujillo et al. 2014). However, the remoteness of these
areas, the limited resources for their control and surveillance, the constant threat of
extractive economies such as gold mining, deforestation of riparian forest, commercial
fishing and directed catches, as well as the terrestrial approach of the initiatives of
conservation initiatives, make the management of aquatic ecosystems within protected
areas still limited (Mosquera-Guerra et al. 2015).
The transformation of the heterogeneous and complex aquatic ecosystems in the
Amazon through the construction of more than one hundred hydroelectric plants causes the
ecological homogenisation of these systems, changes in the flood pulses downstream of the
dams and the retention of limiting nutrients for primary productivity in aquatic food webs
such as the N and P (Forsberg et al. 2017; Latrubesse et al. 2017; Anderson et al. 2018).
It also causes significant losses in fluvial connectivity exactly where the greatest diversity
of river dolphins and fish on the planet are found (Mosquera-Guerra et al. 2015; Anderson
et al. 2018).!These tensors have caused the transformation of extensive areas occupied by
river dolphins in South America. Arauho and Wang (2014), report the effects on
populations of I. araguaiaensis due to the presence of seven hydroelectric projects
constructed in their distribution area and for I.g. boliviensis, I.g. geoffrensis and Sotalia
fluviatilis are reported a total of three new ones.
!These effects are not only limited to the fragmentation of complex and
heterogeneous aquatic systems such as the Araguaia, Tocantins and Madeira rivers. These
ecosystems are made up of habitats types essential for feeding, reproduction and refuge of
dolphins such as confluences, tributaries, lakes and main rivers and tributaries with
different origins, Andean in the case of white waters, jungle in the black and clear rivers
influenced by the Brazil shield
Another type of cumulative negative effect at the macrobasin scale is reported by
Forsberg et al. (2017), which predicts that upon entry into operation of the Rositas dams,
Angosto Del Bala, Inambari, Tam 40, Pongo De Aguierre and Pongo De Monseriche, will
reduce the supply of sediment by 69%, phosphorus by 67% and nitrogen by 57% in the
Andean region and in the entire Amazon basin by 64, 51 and 23%, respectively. These
large reductions in the supply of sediments and nutrients will have a great impact on the
geomorphology of the channels, the fertility of the floodplains and the aquatic productivity
(Latrubesse et al. 2017).
These effects will be greater near the dams and will extend to the lowland flood
plains (Latrubesse et al. 2017). It is expected that the attenuation of the downstream flood
pulse will alter the survival, phenology and growth of the floodplain vegetation and reduce
the primary and secondary productivity of the floodplain food source for fish in its different
phases. This reduction in the biomass of these systems could potentially exacerbate the
conflicts between the river dolphins and the artisanal and commercial fisheries due to the
decrease of fishing resource in the Amazon.
When analyzing the representativeness of protected areas, it is evident that in the
case of Inia boliviensis and Inia araguiaensis it is relatively low. That is why it is advisable
to encourage the creation of aquatic ecosystem conservation figures that generate protection
mechanisms for these species. Ramsar sites with implemented management plans can be
efficient and suitable for river dolphins.
This research was conducted as part of the South America River Dolphins
Conservation Programme sponsored by Whitley Found for Nature, Foundation Segre,
WWF, Nature Serve and Colciencias. The authors thank the researchers and local and
national authorities who participated in the 28 expeditions carried out in South America and
satellite telemetry project to study the ecology of the movement of river dolphins in the
Amazon and Orinoco.
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