The marine otter (Lontra felina) as a bioindicator for mercury pollution along the South Pacific coast of Chile.

Mercury (Hg) is one of the 10 environmental pollutants of greatest global concern and a potent neurotoxin that bioaccumulates in marine apex predators, such as marine mammals. The marine otter, or chungungo (Lontra felina), possesses a narrow home range and a clear dietary overlap with humans in coastal settlements, and thus presents as a critical sentinel species for biomonitoring pollution along the Southeast Pacific shoreline. This study presents the first comprehensive assessment of total mercury (THg) in the marine otter, analysing several biological compartments along a broad latitudinal gradient in Chile. Mean THg concentrations ranged from 0.1 to 5.5 μg/g dw in the order: Fur > Liver > Kidney > Muscle > Heart > Brain > Spraints. Blood THg was 0.07 μg/g ww. Fur and brain were positively correlated (r=0.89, p=0.041), providing a non-invasive method to evaluate Hg exposure levels in brain and neurotoxic risk. Risk assessment revealed that 70% of individuals exceeded subclinical neurotoxicity thresholds (brain THg >0.1 μg/g ww), indicating potential neurobehavioural changes and disruption. While no statistically significant latitudinal differences were found, tissue-specific patterns suggest a complex interplay of anthropogenic and natural factors. Northern Marine otters usually show the highest THg levels consistent with high mining pressure and a marked piscivorous diet, however southern otters may be subjected to an unexpectedly high risk of long-term bioaccumulation, as revealed by high fur THg. These findings establish a vital baseline for the Minamata Convention in the Southeastern Pacific, and showcase the marine otter as a useful bioindicator.