The giant otter Pteronura brasiliensis, categorized as Endangered on the IUCN Red List, was once widely distributed throughout South America. By the middle of the 20th century the giant otter had become locally extinct along the main rivers of the Orinoco basin. Although some populations seem to have recovered, the paucity of information available does not permit a full evaluation of the species' conservation status. The objective of this study was to estimate the abundance and density of the giant otter population along the Orinoco river in the municipality of Puerto Carreño, Vichada, Colombia, where there is important commercial and recreational fishing. Thirty-nine linear km were surveyed, repeatedly, with a total of 315 km of surveys. Population size was estimated by direct counts of individuals. All individuals detected were photographed and identified individually from their throat pelage patterns. In total, 30 otters were identified, giving a minimum density of 0.77 individuals per km, one of the highest reported for the species in Colombia. Given the high density in this well-developed area, our results highlight the importance of this population for the conservation of the species.

The giant otter Pteronura brasiliensis was hunted almost to extinction in the Peruvian Amazon during a period of professional trade in wild animal skins during 1920–1973. In 1973 the Department of Agriculture of Peru (INRENA) prohibited commercial hunting in the Peruvian Amazon, and the giant otter was included in Appendix I of CITES. From 1973 to 2004 giant otter populations experienced a slow recovery in numerous rivers of the Peruvian Amazon. Here, we report the population growth of the giant otter on the Yavarí-Mirín and Yavarí Rivers in north-east Peru. The first evaluations of giant otter populations in these rivers, in which no individuals were sighted, were in 1992–1993. During surveys in 1996 and 1997 two individuals were sighted. In 2001, 19 individuals were sighted and in 2003 and 2004, 41 individuals were observed. This increase demonstrates a slow recovery and shows that the population has not yet reached its carrying capacity. The prohibition of international trade in otter skins by CITES, supported by INRENA, helped the population recover and was important in the conservation of this species.

Data on the occurrence and habitat use of giant otters Pteronura brasiliensis in the 4,437 km2 of Balbina hydroelectric lake in central Amazonia, Brazil, were collected from September 2001 to December 2005. Twenty-nine groups of giant otters were recorded in an area corresponding to 10% of the total reservoir. Despite the fact that it is a hydroelectric lake, the water level can vary annually by up to 3.5 m with the Amazonian seasonal flood pulse. A total of 210 dens, communal latrines and campsites of giant otters were located. An average of 37% of the dens observed were classified as in use, and the species was recorded in the lake throughout the year. Giant otters started their daily activities between 05.23 and 08.05. The average height of den openings was 28.77 ± SD 10.00 cm, with an average width of 56.11 ± SD 19.17 cm. Births in Balbina occur mainly during the period of high and receding water level, as reported for giant otters in other Amazonian areas. There are at least two conditions that enable the species to inhabit hydroelectric reservoirs: (1) presence of the species in the area before dam construction and (2) absence or low numbers of human communities around the reservoir. The potential use of hydroelectric lakes for the conservation of the giant otter in the Amazon is discussed.