River otters serve as sentinel species for freshwater ecosystem health, with their individual welfare reflecting the cumulative effects of water quality, prey availability, and habitat connectivity.
River otter welfare as a sentinel concept frames individual animal health as a direct indicator of ecosystem health, creating alignment between conservation, ecological, and welfare goals. Otters with poor body condition, high contaminant loads, or disease prevalence indicate watershed problems that affect the entire aquatic community and potentially human health. Monitoring otter welfare therefore provides early warning of ecosystem stressors at low cost compared to comprehensive water quality or fish community surveys. The recovery of otter populations across their historical range demonstrates that when ecosystem conditions improve — cleaner water, recovering fish communities, reduced persecution — individual otter welfare improves alongside population-level metrics. Protecting otter habitat is simultaneously protecting individual otter welfare and the ecological services of healthy freshwater systems.