First record of the Neotropical river otter Lontra longicaudis in the Autonomous City of Buenos Aires, Argentina: repeated observations in a highly urbanized estuarine environment

Lobito de río en Buenos Aires

Abstract

The Neotropical river otter (Lontra longicaudis) reaches the southern limit of its known distribution in northeastern Buenos Aires Province, Argentina. This study reports the first record of the species within the Autonomous City of Buenos Aires and discusses the ecological significance of its occurrence in a protected wetland embedded within a highly urbanized landscape. Opportunistic observations collected by recreational fishers between February 2021 and February 2023 were compiled from a pier adjacent to the Reserva Ecológica Costanera Sur. Photographs and videos were used to document the number of individuals, their general behavior, and the occurrence of juvenile otters accompanying an adult. Repeated sightings documented 3 to 4 individuals using the pier surroundings during daylight hours. One observation included an adult female accompanied by two juveniles. Individuals used rocks and artificial structures beneath the pier for resting or feeding,  representing the first confirmed record of the species within the Autonomous City of Buenos Aires. These observations improve current knowledge of the recent distribution of Lontra longicaudis along the Río de la Plata shoreline and show that the species may use a highly anthropized estuarine environment at the southern edge of its distribution. Nevertheless, the available evidence does not allow inference of the origin of the individuals or confirmation of local reproduction. The records highlight the potential importance of urban riparian reserves as components of a habitat mosaic used by the species and emphasize the need for systematic monitoring to better understand habitat use near the southern limit of its distribution.