A reliable method for sexing giant otters (Pteronura brasiliensis) in the wild


  • Jessica Groenendijk Cocha Cashu Biological Station, San Diego Zoo Global - Institute for Conservation Research
  • Frank Hajek Servicios Ecosistémicos Perú




Giant Otter, Pteronura brasiliensis, Sexing, Gender


Sexing of giant otters under field conditions is only possible when individuals are entirely out of the water, usually when basking or grooming. Body size is not indicative of gender, and the breeding pair does not necessarily consist of the largest animals in the group. Sexing is facilitated by the presence, in adult, parous females, of four permanently elongated teats (due to repeated and prolonged lactation) and, in mature males, of a visible scrotum. Identification of the breeding male is sometimes assisted his behaviour, specifically that of marking, and by his year-on-year permanence in the group. However, sexing is more difficult in adult females that have not lactated, or in sub-adults, juveniles, and cubs of both sexes. Here, we present a reliable method of sexing wild Giant otters of all ages and sexual status, tested with known sex individuals.

Author Biographies

Jessica Groenendijk, Cocha Cashu Biological Station, San Diego Zoo Global - Institute for Conservation Research

Education and Outreach Coordinator, Cocha Cashu Biological Station, Manu National Park, Peru

Frank Hajek, Servicios Ecosistémicos Perú

Director, Servicios Ecosistémicos Perú


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How to Cite

Groenendijk, J., & Hajek, F. (2015). A reliable method for sexing giant otters (Pteronura brasiliensis) in the wild. Latin American Journal of Aquatic Mammals, 10(2), 163-165. https://doi.org/10.5597/lajam00211