780 G. Garrote et al.


TABLE 1 The six sectors surveyed for the giant river otter Pteronura brasiliensis in Colombia (Fig. 1), with type of water body, survey method, length of each sector, number of surveys of each sector, and total survey effort.


Sector


Water body


Orinoco Principal river


Method Boat


San José Tributary Foot Tesoro Tributary Foot Negro Tributary Boat


Length (km)


21.30 2.40


2.10 11.20


No. of surveys


9 5


4 8


India Lagoon Canoe 0.70 10 Pañuelo Lagoon Canoe 1.17 Total


5 38.87 41


Total effort (km)


191.70 12.00 89.60 5.85


8.40 7.00


314.55 Giant otters are territorial, diurnal, live in groups and


have irregular pale patterning on their throats that allows individuals to be identified (Duplaix, 1980), facilitating esti- mation of population size by direct counts of groups and individuals (Groenendijk et al., 2005). Given the logistical impossibility of sampling continuously, the area was di- vided into six sectors, which were sampled independently (Table 1). Depending on accessibility, each sector was sampled using either a 9-m motorized aluminium boat with a 25-hp engine or a canoe, or on foot along the banks of streams where access by boat was impossible. Surveys were conducted by three experienced observers during 7.30– 18.00.When we detected an individual or group of otters,we


followed them until the pale throat patterns of each individ- ual could be photographed and the size of the group estab- lished. We recorded group sizes and locations using a GPS, which we also used to calculate the length of each transect. The surveys were carried out during 15 January–9 March 2018 during the dry season, when the otters are easiest to detect (Groenendijk et al., 2005). The study area comprised a total of 38.87 linear km, in-


cluding the main river, its tributaries and lagoons. Each sec- tor was sampled repeatedly, giving a total survey effort of 314.55 linear km (Table 1). Six groups of giant otters and two solitary individuals were detected. The groups consisted of 2–11 individuals, with amean of 4.67 ± SD 3.39 individuals per group. In total, 30 otters were identified, yielding a minimum density of 0.77 individuals per km. Our results show that the giant otter density along the


riverOrinoco and its tributaries and lagoons inthe Puerto Car- reño area is among the highest reported for the species in Colombia (Table 2), similar to the 0.8 individuals per km in the Apaporis river in the Amazon Basin (Botello, 2000) and greater than the 0.17 individuals per km in the Inirida Fluvial Star and the tributaries of the upper Orinoco river (Suarez, 2010). Compared to elsewhere in South America, the density we recorded is similar to the highest densities reported for the species in the Brazilian Pantanal (0.74–1.00 individuals per km; Tomas et al., 2015) but lower than in the river San Martín in Bolivia (3.87 individuals per km; van Damme et al., 2002) and Suriname (1.2 individuals per km; Duplaix, 1980). However, the latter two areas are remote,


TABLE 2 Compilation of studies of the giant otter, with length of water body surveyed (effort) and density of individuals observed. Country Study area


Survey effort (km)


Colombia Orinoco-Bojonawi


Colombia Inirida Fluvial Star, Guaviare Colombia Caño Limón, Arauca Colombia Río Apaporis, Amazonas Bolivia Bolivia Bolivia Bolivia Bolivia Bolivia


Bolivia Bolivia


Brazil Brazil Brazil Brazil Peru Peru Peru


Suriname


Río Verde, Noel Kempff National Park Río Paucerna, Noel Kempff National Park


Río San Martín, Itenez Reserve Río Itenez Guaporé, Itenez Reserve Río Madidi, Madidi National Park


Río Aquidauana, Pantanal Canal Riozinho, Pantanal Río Negro, Pantanal


Jauaperi river, Xixuaú Reserve, Roraima del Manu National Park Las Piedras Los Amigos


39


217 39 30 22 46


Río Itenez Guaporé, Noel Kempff National Park 225 Río Paragua, Noel Kempff National Park Río Negro


45 21


324 23 36 40


179 309 116


291 168 23


Density


(individuals per km) Source 0.77


0.17 0.17 0.83 0.09 0.20 0.12 0.26 0.26 3.87


0.89 0.18


0.30 0.74 1.00 1.00 0.22 0.05 0.04 1.20


This study Suárez (2010)


Armas & Padilla (2010) Botello (2000)


Fraser et al. (1993) Fraser et al. (1993) Fraser et al. (1993)


van Damme et al. (2001) Painter et al. (1994)


Ten (unpubl. data, 2001), in van Damme et al. (2002)


Ten (unpubl. data, 2001), in van Damme et al. (2002) Ayala &Wallace (2009) Tomas et al. (2015) Tomas et al. (2015) Tomas et al. (2015)


Evangelista & Rosas (2011) Mendoza et al. (2017) Mendoza et al. (2017) Mendoza et al. (2017) Duplaix (1980)


Oryx, 2021, 55(5), 779–782 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320000058


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