Abstract:

Aims: The Eurasian otter (Lutra lutra) was once widely distributed across China but has become nearly extinct due to severe habitat destruction and overhunting in recent history. Fortunately, recent studies have shown that Eurasian otters have reappeared on several islands in Zhejiang Province. Among these, Jintang Island stands out for its relatively high frequency of otter sightings, despite the presence of both natural and human-dominated environments. This study aims to investigate how Eurasian otters adapt to human disturbances in urban environments and their ecological interactions with sympatric species on Jintang Island.

Methods: This study deployed 100 camera traps across Jintang Island from August 2023 to February 2024. To investigate the adaptation of Eurasian otters to human disturbance on the island and their coexistence with sympatric species, we used the kernel density method to estimate the diel activity patterns and temporal overlap of all species based on independent detections from camera traps. Pianka’s niche overlap index was then used to quantify spatial interactions between otters and sympatric species (i.e., rodents, shrews, Mustela sibirica, Hydropotes inermis, cats, dogs, and other livestock and poultry). Additionally, we conducted Spearman correlation analyses to explore the relationships between Eurasian otters, sympatric species, and human presence across all camera trap sites. The significance of these correlations was assessed using P-values.

Results: The camera traps recorded a total of 13,969 effective camera days, yielding 9,214 independent detections. The results showed that Eurasian otters on Jintang Island exhibit strong nocturnal activity patterns and experience significant temporal overlap (Δ > 0.60) with most local sympatric species. Among sympatric species pairs, otters showed low spatial overlap with Mustela sibirica, rodents, shrews, dogs, and other livestock and poultry (Pianka’s index < 0.3). The lowest spatial overlap was recorded between otters and Hydropotes inermis (Pianka’s index = 0.02), with a significantly negative Spearman rank correlation. In contrast, the temporal overlap between Eurasian otters and human activities was extremely low (Δ = 0.17, 95% CI = 0.14-0.19), whereas their spatial overlap was the highest among all species (Pianka’s index = 0.43), accompanied by a highly significant Spearman rank correlation (P < 0.001). Notably, electrofishing events predominantly occurred during otter active hours, showing a high overlap (Δ = 0.81, 95% CI = 0.67-0.91), posing a significant threat to otter conservation.

Conclusion: These findings reveal the activity patterns and adaptive strategies of Eurasian otters in response to human disturbances on Jintang Island. The study enhances our understanding of the mechanisms behind the coexistence of otters with both humans and sympatric species in human-dominated landscapes. It also provides valuable insights and recommendations for the conservation of Eurasian otters on coastal islands amidst ongoing urbanization.

Key words: Eurasian otter (Lutra lutra), human disturbance, camera trapping method, activity pattern, spatial and temporal overlap