The Giant Otter inhabits large rivers, streams, lakes and swamps (Duplaix 1980, Carter and Rosas 1997). In Suriname, the species seems to prefer black water creeks and rivers with sandy or rocky bottoms (Duplaix 1980). In Peru, large lowland rivers with gentle flow and oxbow lakes with high fish densities are preferred (Schenck 1999). In Bolivia, both clear and white water floodplains are used (Zambrana Rojas et al. 2012).  Since giant otters build dens and use campsites along the banks of water bodies, some habitat traits are important determinants of presence, such as gentle slopes and vegetation cover and proximity to the water’s edge (Lima et al. 2012). In seasonally flooded habitats, the availability of banks and other habitat features may change, and induce changes in habitat selection (Leuchtenberger et al. 2013). During the peak inundation in the southern Pantanal, when no banks were available, giant otter groups used emerged shrubs as refuges and latrines (Leuchtenberger et al. 2015). At such times, when prey is more dispersed, giant otters were observed in flooded forest, swamps and grasslands adjacent to the river (Leuchtenberger et al. 2013). Territoriality and population density may lead some groups to use unusual sites, such as artificial lakes along roads in the southern Pantanal (Leuchtenberger et al. 2013), even adapting their diet (Ribas et al. 2012). Giant otters also use agricultural channels (Laidler 1984) and the reservoirs of dams (Palmeirim et al. 2014). The preferred habitat for giant otters seem to be undisturbed water bodies, with high-quality vegetation cover and abundant prey density.

Giant Otters are one of the most social members of the otter family. A giant otter group consists of a dominant breeding pair, non-breeding subadults and offspring. Group size can range from two to 16 individuals that may or may not be related (Ribas et al. 2016). Reproduction is related to the capacity of the group to defend high-quality territories, usually a function of group size (Groenendijk et al. 2015, Leuchtenberger et al. 2015), possibly explaining the advantage of having non-related individuals in the group (Leuchtenberger and Mourão 2008, Ribas et al. 2016). Giant otters attain sexual maturity at around 2.5 years old (Oliveira et al. 2011, Sykes-Gatz 2004), and the earliest breeding may occur at age three years (Groenendijk et al. 2015). A group usually produces one litter a year, ranging from 1-6 young, but averaging 2 (Duplaix 1980, Staib 2005, Groenendijk and Hajek 2006, Leuchtenberger and Mourão 2008).

Groups live in well-established territories that are constantly defended by scent-markings at latrines, campsites and dens along the banks of lakes and rivers (Leuchtenberger and Mourão 2009), and warning vocalizations (Leuchtenberger et al. 2014, Mumm Knörnschild 2017). Conflict encounters are common when an intruder is detected, and may lead to serious injuries or even death (Schweizer 1992, Rosas and Mattos 2003, Ribas and Mourão 2004). Territories vary in size from 0.5 km to 18 km in the dry season, and 8 to 24 km in the wet season (Utreras et al. 2005, Leuchtenberger et al. 2015), and appears to be related to group size (Groenendijk et al. 2015; Leuchtenberger et al. 2015). The size of neighbouring groups may limit the expansion of territory (Leuchtenberger et al. 2015).

The diet of Giant Otters consists almost exclusively of fish, but may also include caiman and other vertebrates (Ribas et al. 2012, Rosas-Ribeiro et al. 2012). The species is opportunistic in its diet and adapts its diet according to prey availability.

The average reproductive lifespan is about five years for females and males (Groenendijk et al. 2014). This, in tandem with a mortality of about 50% (Groenendijk et al. 2014), a suspected high transient mortality, and difficulty to establish new groups (Schenck and Staib, 1998), means that population recovery and colonization of new areas can be slow.

Pteronura brasiliensis is endemic to South America and is distributed east of the Andes in the Orinoco, Amazonas, and Parana basins, and the hydrographic networks of the Guianas. The northern limit of its distribution occurs in northern Venezuela, and the southern limit in Misiones, Argentina. The Giant Otter’s range has become discontinuous and fragmented due to local extinctions; the Uruguayan and Argentine populations are extinct or nearly so (Gil pers. comm., Buschiazzo pers. comm.), and the species is reduced to a single, small subpopulation in Paraguay, occupying less than 2% of its former distributional range. It is also extinct to the east of the Tocantins and Paraná basins in Brazil. In the Brazilian Cerrado a population persists in the face of intense habitat modification. Important subpopulations are still found in parts of the Amazon, in the Pantanal region, and, possibly, in the Guianas.

The Giant Otter is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES) and as Endangered under the United States Endangered Species Act, 1973. The Global Otter Conservation Strategy for the species (Leuchtenberger et al. 2018) recommends priority actions that include:

• Establish protected areas in all range countries, including fish corridors to connect fragmented populations and protect stable populations.
• Implement reintroduction programs to recover lost historical populations in Argentina (Corrientes) and Brazil (Paraná Basin).
• Establish national conservation plans throughout the species range.
• Foster multinational cooperation (i.e. Amapá-Brazil and French Guiana, Suriname and Guyana, Southern Amazon and the Pantanal) to coordinate management of transboundary or connected protected areas, control of illegal mining and the integrity of continuous otter habitat.
• Create protocols in all range countries to regulate mitigation and compensation for projects like hydroelectric dams, gold mining, agriculture, deforestation and overfishing in Giant Otter habitat.
• Implement resilience/recovery projects in areas of human activities to help the return of Giant Otters after threat mitigation.
• Create global guidelines for Giant Otter watching by ecotourists including mandatory responsible behaviour.
• Train locals to participate as field assistants in research activities, or as ecotourism guides.
• Promote the value of Giant Otters through environmental education programs in communities that coexist with otters.
• Develop management plans to regulate overfishing to reduce conflicts and protect the prey base.
• Implement sustainable economic alternatives for communities that coexist with Giant Otters by training locals to guide otter watchers and strengthen local networks to participate in the regional decision-making processes.
• Create a map of risk and decision scenarios for stakeholders, incorporating otter presence and the current and future threats.
• Conduct population surveys in areas with poor or no knowledge about Giant Otter occurrence in the last 10 years.
• Establish long-term Giant Otter conservation programs for key populations in Brazil (Pantanal, Amazonia, Cerrado), Bolivia (Amazonia), Peru (Amazonia), and Colombia (Orinoco).
• Conduct population surveys in parts of Uruguay, Argentina, Brazil (Paraná Basin) where there is little or no knowledge about Giant Otter presence in the last decade.
• Document the illegal trade in Guyana where animals are taken from the wild by traders either to trade or breed for pets.
• Build strong local networks to create the capacity for local communities to participate in the regional decision-making process.