Giant otters, once targeted by the pelt trade to near extinction, are now legally protected and have made a comeback in some parts of their range. Our state of knowledge about the behavior and ecology of this apex predator has increased substantially since the first studies in the 1970s but remains incomplete. Negative anthropogenic pressures and conflicts affecting giant otters are intensifying and now take many forms, from extensive habitat loss and degradation, pollution, ecotourism with heavy impacts, to gold mining. We review the corpus of giant otter field research and findings since 1980 and discuss new findings and our shortfall of knowledge and their implications for the long-term conservation of the species.Resumo: O abate de ariranhas para o comércio de suas peles no passado levou a espécie quase à extinção. Atualmente a caça à ariranha está proibida e algumas populações têm dado sinais de recuperação em partes de sua distribuição. O conhecimento acerca do comportamento e ecologia deste predador de topo de cadeia aumentou substancialmente desde a realização do primeiro estudo com a espécie na década de 1970, mas permanece incompleto. Conflitos e pressões antrópicas negativas têm se intensificado e abrangem desde a perda extensiva de habitat, poluição, ecoturismo pobremente manejado ou planejado, até a mineração de ouro. Neste artigo nós revisamos o conhecimento atual gerado pelas pesquisas com ariranha após 1980 e discutimos as novas informações, as deficiências de conhecimento ainda existentes e suas implicações para a conservação desta espécie. †

According to the "social intelligence hypothesis," species with complex social interactions have more sophisticated communication systems. Giant otters (Pteronura brasiliensis) live in groups with complex social interactions. It is likely that the vocal communication of giant otters is more sophisticated than previous studies suggest. The objectives of the current study were to describe the airborne vocal repertoire of giant otters in the Pantanal area of Brazil, to analyze call types within different behavioral contexts, and to correlate vocal complexity with level of sociability of mustelids to verify whether or not the result supports the social intelligence hypothesis. The behavior of nine giant otters groups was observed. Vocalizations recorded were acoustically and statistically analyzed to describe the species' repertoire. The repertoire was comprised by 15 sound types emitted in different behavioral contexts. The main behavioral contexts of each sound type were significantly associated with the acoustic variable ordination of different sound types. A strong correlation between vocal complexity and sociability was found for different species, suggesting that the communication systems observed in the family mustelidae support the social intelligence hypothesis.

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