Estuarine connectivity through the lens of a top predator. Movement ecology of Lontra longicaudis as a management tool for coastal ecosystems

Long-term ecological datasets are essential for understanding how landscape connectivity changes through time, yet such datasets remain exceptionally rare for tropical estuarine predators. The Neotropical Otter Project has continuously monitored Lontra longicaudis on Santa Catarina Island, southern Brazil, since 1986. This study analyzes a standardized 20-year monitoring dataset (2004–2023) to investigate movement ecology, functional connectivity, and habitat use across a freshwater–estuarine–marine landscape. Monthly field surveys conducted at six monitoring sites recorded 9,531 spraints, which were integrated with microsatellite DNA identification to reconstruct movement pathways and evaluate connectivity among habitat compartments. The analyses demonstrate that L. longicaudis regularly moves across freshwater, brackish, and marine environments through supralittoral rocky corridors, maintaining functional connectivity within a metapopulation occupying approximately 610 km 2 . Temporal analyses revealed a pronounced decline in movement intensity over the 20-year study period. During the same period, Santa Catarina Island experienced substantial urban expansion and infrastructure development, highlighting the need to better understand how landscape change may influence functional connectivity. These findings indicate that long-term monitoring of movement patterns provides a sensitive indicator of changes in estuarine landscape connectivity that are not detected by conventional habitat assessments. Building upon these ecological patterns, we propose the Otter Health Index (OHI), a field-based framework that integrates movement integrity, shelter availability, and dietary diversity to support rapid assessments of estuarine condition and to assist conservation planning and ecological restoration. Our results demonstrate the value of long-term movement ecology as an effective approach for evaluating functional connectivity in coastal ecosystems and reinforce the role of the Neotropical otter as a practical bioindicator of estuarine ecosystem integrity.