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May 27, 2024
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Local Variation in Feeding Ground Utilization of Dugongs (Dugong dugon) Across Two Intertidal Seagrass Beds in Talibong Island, Thailand

Author(s):

Chiaki Yamato, Kotaro Ichikawa, Kongkiat Kittiwattanawong, and Nobuaki Arai

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Document: Article

Abstract: In this study, we describe the population characteristics and residency patterns of dugongs (Dugong dugon) across two intertidal seagrass beds in Talibong Island, Thailand: Site A, covering an area of 2.0 × 105 m2, and Site B, covering an area of 2.8 × 105 m2. Transect and individual identification surveys were conducted under clear water conditions using drones: 16 separate days over 11 months at Site A and 10 separate days over 3 months at Site B. Sixty-four individuals were identified from 180 videography sessions. The results confirmed at least two distinct patterns of seagrass habitat utilization among sites located approximately 5 km apart. Site A was characterized by a lower population density, higher year-round site fidelity, occupancy by relatively large individuals, and an absence of feeding aggregations. In contrast, Site B was characterized by a higher population density, lower site fidelity, occupancy by individuals with a wider range of body lengths, and the presence of feeding aggregations. The average population density at Site B was three to five times higher than that at Site A. Site A had a median nearest neighbor distance of 320 m with no significant bias in its distribution, whereas Site B had a median of 20 m with a significant bias. The mean site fidelity index for Site A (0.62 ± 0.08; n = 16) was significantly higher than that for Site B (0.39 ± 0.14; n = 10). Dugongs at Site A might have monopolized this site to some extent, while those at Site B might have benefited from increased opportunities for social interaction provided by aggregations. These findings highlight the importance of fine-scale monitoring of feeding ground utilization by dugongs, taking into consideration individual-specific details such as body lengths and resighting rates for a better understanding of their spatial distribution.

Key Words: habitat use, feeding, drone, dugong, Dugong dugon, population characteristics, photo identification

DOI: https://doi.org/10.1578/AM.50.3.2024.237

Page Numbers: 237-251

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