Aquatic Mammals 2011, 37(2), 208-212, DOI 10.1578/AM.37.2.2011.208 Short Note Tagging Giant Otters (Pteronura brasiliensis) (Carnivora, Mustelidae) for Radio-Telemetry Studies Leandro Silveira, 1 Mariana M. Furtado, 1, 2 Fernando C. W. Rosas, 3 Luis C. L. C. Silva, 4 Márcia M. M. Cabral, 3 Natália M. Tôrres, 1, 5 Rahel Sollmann, 1, 6 Andrew Kouba, 7 and Anah T. A. Jácomo 1 1 Jaguar Conservation Fund/Instituto Onça-Pintada, Caixa Postal 193, CEP: 75830-000, Mineiros-GO, Brazil E-mail address (M. M. Furtado): marianafurtado@jaguar.org.br 2 Universidade de São Paulo, Faculdade de Medicina Veterinária e Zootecnia, Departamento de Medicina Veterinária Preventiva e Saúde Animal, Av. Dr. Orlando Marques de Paiva, 87, Cidade Universitária, 05508-270, São Paulo-SP, Brazil 3 Instituto Nacional de Pesquisas da Amazônia (INPA), Laboratório de Mamíferos Aquáticos, Caixa Postal 478, 69011-970, Manaus-AM, Brazil 4 Universidade de São Paulo, Faculdade de Medicina Veterinária e Zootecnia, Departamento de Cirurgia, Av. Dr. Orlando Marques de Paiva, 87, Cidade Universitária, 05508-270, São Paulo-SP, Brazil 5 Universidade Federal de Goiás, ICB, Departamento de Biologia Geral, Caixa Postal 131, 74001-970, Goiânia-GO, Brazil 6 Leibniz Institute for Zoo and Wildlife Research, Research Group for Evolutionary Ecology, Alfred-Kowalke-Strasse 17, 10315, Berlin, Germany 7 The Memphis Zoo, 2000 Prentiss Place, Memphis, TN 38112, USA The giant otter (Pteronura brasiliensis) is an endan- gered, social carnivore endemic to the freshwater ecosystems of South America (Rosas et al., 2008; International Union for Conservation of Nature [IUCN], 2010). The species depends on good water quality and preserved riverine habitat to survive (Rosas et al., 2008); and as a top predator, it regu- lates prey populations. The species was extensively hunted for its pelt until the 1960s and was almost extinct in some areas of its distribution. Today, the destruction of natural habitats is the main threat to giant otters (Rosas, 2004; Rosas et al., 2008). In spite of the species’ conservation concern and ecological importance, there are few studies focus- ing on the ecology and conservation of free-rang- ing giant otters (Duplaix, 1980; Carter & Rosas, 1997; Staib, 2005; Utreras et al., 2005; Garcia et al., 2007; Rosas et al., 2007; Leuchtenberger & Mourão, 2008). This is probably related to the difficulties of following giant otter individuals and groups during the entire hydrological cycle; their habitat is seasonally flooded and the animals disperse throughout extensive and dense flooded forests during the high-water season. During the dry season, despite the fact that encounters with giant otter groups tend to increase, navigation of several water bodies is extremely difficult due to low water, precluding following giant otter move- ments and estimating reliable home-range sizes by direct observation (Rosas et al., 2007). Radio-telemetry is one of the most frequently used methods to acquire demographic, behavioral, and ecological data for cryptic species (White & Garrott, 1990). This technology has brought two major advantages to wildlife research: (1) the ability to identify individual animals and (2) the possibility to locate each individual when desired (Mech & Barber, 2002). Here, we employed this tool to gather data on giant otters to overcome the challenges of conventional methods. Capturing and tagging an animal depends on a good under- standing of the species’ behavior and ecology. The expertise required to tag individuals for telemetry is often underestimated (Ebner, 2009). Otters are unsuited to standard collar-mounted transmitters due to the similar circumference between their neck and head (Ó Neill et al., 2008). In the case of the social giant otters, a collar would likely be easily removed by the radio-tagged animal or by other members of its group during their extensive grooming behavior. In European otters (Lutra lutra; Ruiz-Olmo et al., 1995), river otters (Lontra canadensis; Hoover, 1984; Hernandez- Divers et al., 2001), sea otters (Enhydra lutris; Garshelis & Siniff, 1983; Williams & Siniff, 1983), beavers (Castor canadensis; Davis et al., 1984), grizzly bears (Ursus arctos; Philo et al., 1981), and black bears (Ursus americanus; Jessup & Koch, 1984)—species with similar characteristics—surgically implanted transmitters