Toxic traces: First insights into metals and metalloids in dugongs (Dugong dugon) from India.

Unmanned aerial vehicles (UAVs) are widely used for mapping and monitoring coastal ecosystems due to their high accuracy and efficiency, providing surveys that are less costly and time-consuming compared to vessel-based methods. This study demonstrates the utility of using UAV imagery combined with ground surveys to evaluate the spatial distribution of dugong (Dugong dugon) foraging based on their feeding trails and associated intertidal seagrass beds in (1) Dugong Tower and (2) Juhoi, Libong Island, Thailand, and (3) Saco, Inhaca Island, Mozambique, as well as the temporal distribution of dugong feeding trails on Mook Island, Thailand. Ground survey results showed that small- and medium-sized seagrass species are the most preferred by dugongs. RGB images capture detailed plant characteristics, while NDVI images assess vegetation density, with higher values indicating denser vegetation. In denser areas (e.g., Juhoi), both images detected feeding trails, with RGB identifying distinct trails and NDVI highlighting contrasts. In sparse areas (e.g., Dugong Tower and Saco), NDVI provided clearer detection. However, UAVs may be limited by restricted flight endurance and sea state conditions, as well as by water level, turbidity, and sun glint. This study highlights the potential of drones to survey and monitor dugong populations indirectly, assisting coastal managers in assessing seagrass availability for dugongs and observing dugong behavior in their natural habitat, particularly in hotspot areas.

The Japanese Dugong (Dugong dugon) Is Still Alive

The dugong (Dugong dugon) is the first marine megafauna to be declared functionally extinct in China, yet its historical range and extinction dynamics remain poorly understood. Sighting histories were thus collected from 841 fishers to investigate this information based on a large-scale interview survey across the entire dugong historical range in 2024. Apart from a single incidental capture reported in 2021, there have been no other records reported by informers since the last stranding in 2008, with the average date of the last sighting being in 1983 ± 14. A notable discovery was that dugongs were once sighted in Shantou, extending the known historical range northward by 500 km in mainland China. We also document extensive past dugong sightings and seagrass meadows in the South China Sea, beyond the previously known range. The spatio-temporal analysis indicates that dugongs disappeared almost simultaneously across their entire historical range, without undergoing significant range contraction. These findings confirm previous conclusions that dugongs are now functionally extinct in China. Our study reveals how a once widely distributed marine mammal experienced a population crash within just 20–30 years, serving as a serious warning for dugong conservation worldwide and highlighting the urgent need to protect other marine megafauna in the South China Sea.

Dugongs (Dugong dugon), classified as vulnerable marine mammals, are increasingly impacted by infectious diseases, yet the role of septicemia and disseminated intravascular coagulation (DIC) in their mortality remains uncharacterized. This study aimed to investigate the pathological and microbiological features associated with an acute mortality event in a juvenile dugong during rehabilitation in southern Thailand. Comprehensive histopathological and microbiological analyses were conducted on tissue samples collected postmortem. Bacterial isolation and identification were performed using standard culture techniques and the VITEK-2 system. Histological examination revealed multisystemic lesions, including fibrin thrombi, hemorrhage, hepatocellular degeneration, pancreatic necrosis, lymphoid depletion, and neuronal damage. Oxidative stress and DNA damage were confirmed in brain tissues through immunofluorescence detection of 4-hydroxynonenal (4-HNE) and 8-hydroxy-2'-deoxyguanosine (8-oxodG). Achromobacter xylosoxidans, an opportunistic pathogen, was isolated from multiple organs, consistent with acute systemic infection. These findings represent the first evidence of septicemia-associated DIC in dugongs caused by A. xylosoxidans, highlighting a previously undocumented cause of mortality in dugongs. The results emphasize the role of opportunistic bacteria in triggering oxidative damage and coagulopathy and underscore the importance of early detection and targeted therapeutic strategies to improve survival in stranded or rehabilitated dugongs.

From pasture to sea: Assessing the viability of ruminant forage species for dugong (Dugong dugon) domestication and welfare

Graphical Abstract Highlight Research 1. The study successfully identified the utilization of coastal and marine areas within the research site. 2. Oceanographic parameters across the study area have been analyzed, providing insights into variations in environmental conditions favoring seagrass ecosystem resilience. 3. The structure of seagrass vegetation has been thoroughly observed, revealing differences in species composition, density, and coverage. 4. Furthermore, the study establishes the connectivity between coastal and marine spatial utilization, oceanographic factors, and seagrass ecosystem dynamics, highlighting their interdependent relationships. Abstract This study aims to assess the ecological status of seagrass meadows and their relationship with dugong (Dugong dugon) habitats across four distinct ecological regions in East Java, Indonesia. Field assessments were conducted to evaluate seagrass community structure, oceanographic parameters, and the intensity of human activities. Seagrass distribution was mapped using Sentinel-2A satellite imagery, while seagrass health was evaluated through the Seagrass Ecological Quality Index (SEQI) and Importance Value Index (IVI). Statistical analyses, including Analysis of Variance (ANOVA) and Principal Component Analysis (PCA), were employed to identify significant differences and key environmental drivers. The results revealed marked spatial variation in oceanographic characteristics and seagrass coverage (p < 0.05). PCA showed that anthropogenic factors—particularly marine space utilization such as aquaculture and coastal development—were major contributors to seagrass degradation. Elevated nutrient concentrations were also associated with declining seagrass health, indicating land-based pollution as a dominant stressor. These findings underline the urgent need for integrated coastal zone management. Strengthening conservation policies, reducing terrestrial runoff, and implementing sustainable marine spatial planning are critical to safeguard seagrass ecosystems and ensure the long-term survival of dugong populations in Indonesian waters.

Exploring the skin Microbiome of free-ranging Dugong dugon in new Caledonia

Abstract The monitoring of body condition, reflecting the state of individuals' energetic reserves, can provide early warning signals of population decline, facilitating prompt conservation actions. However, environmental and anthropogenic drivers of body condition are poorly known for rare and elusive marine mammal species over their entire ranges. We assessed the global patterns and drivers of body condition for the endangered dugong (Dugong dugon) across its Indo‐Pacific range. To do so, we applied the body condition index (BCI) developed for the related manatee based on the ratio of umbilical girth (approximated as maximum width times π), to straight body length measured in drone images. To cover the entire dugong's range, we took advantage of drone footage published on social media. Combined with footage from scientific surveys, social media footage provided body condition estimates for 272 individual dugongs across 18 countries. Despite small sample sizes relative to local population sizes, we found that dugong BCI was better, that is, individuals were ‘plumper’, in New Caledonia, the United Arab Emirates, Australia and Qatar where populations are the largest globally. Dugong BCI was comparatively poorer in countries hosting very small dugong populations such as Mozambique, suggesting a link between body condition and population size. Using statistical models, we then investigated potential environmental and anthropogenic drivers of dugong BCI, while controlling for seasonal and individual effects. The BCI decreased with human gravity, a variable integrating human pressures on tropical reefs, but increased with GDP per capita, indicating that economic wealth positively affects dugong energetic state. The BCI also showed a dome‐shaped relationship with marine protected area coverage, suggesting that extensive spatial protection is not sufficient to maintain dugongs in good state. Our study provides the first assessment of dugong body condition through drone photogrammetry, underlining the value of this non‐invasive, fast and low‐cost approach for monitoring elusive marine mammals.

The study aims to explore the distribution, habitat, tracks, and migration tracks of cetaceans in the tropical seawater at Lamalera, Pantar, Alor, Ombai strait, Pura Island, Kabola Beach and Savu Sea East Nusa Tenggara for its management plan. The field explorative survey discovered several local wisdoms in this area such as managing Dugong dugon feeding on specific seagrass species Halophila ovalis and Enhalus acoroides at Kabola Beach Alor by an elderly key person, later set as the nucleus zone and limited ecotourism. Traditional whale hunting at Lamalera Beach Lembata Island is controlled by a local elderly priest, and the spatial whale track at Pantar, Alor and Ombai strait is set as a limited zone and developed for whale-watching ecotourism. The cold seawater upwelling phenomena that attract school’s dolphin and whale in Alor strait is set for limited zone and ecotourism. The anemone-city as a specific coral-reef ecosystem living above the volcanic underwater sea mount at Pura Island is set for the nucleus zone and limited diving ecotourism. Result of FGD and considering those specific ecological factors, the stakeholders agree to describe the adaptive local wisdom to develop the conservation and sustainable ecotourism of the Cetacean. The novelty is the development of a new paradigm of Marine-Geopark Cetacean management strategy for conservation and sustainable ecotourism. That is, the integration of coastal geo-morphological underwater sea mounts, ecological factors, local wisdom, social-economy, and sustainable generating income activities by the local community, as the first concept of scientific, community-based, and adaptive local wisdom policy will lead to an active participatory sustainable management plan. The study had implied progressively with four Governor Regulations of East Nusa Tenggara Province for the Cetacean sustainable resources management are Task-force Team for Integrated Coastal zonation and Management Plan, Diving spots-ecotourism, Co-management by stake-holders, and Development of Integrated and sustainable ecotourism.

Abstract. Dewi CSU, Wahyudi S, Tarno H, Wiadnya DGR, Iranawati F, Sukandar, Martinah A, Sani LMI, Subhan B, Herandarudewi SM, Faiqoh E, Ciptadi G. 2025. Genetic of stranded Dugong dugon (Müller 1776) in the Java Sea, Indonesia, through COX1-based DNA barcoding. Biodiversitas 26: 951-962. The dugong (Dugong dugon (Müller 1776)), an endangered herbivorous marine mammal, is listed as the Red List of the IUCN and CITES Appendix I. Considering its protected categorizing, its population is persistently decreasing globally, particularly in Indonesia, accordingly requiring significant conservation measures. This study aimed to assess the conservation status of the species, analyze the morphology, morphometry, and genetic profile of stranded dugongs, and evaluate surrounding seagrass meadows. Fieldwork undertaken in February, March, and September 2023 concentrated on stranded dugongs, gathering morphological, morphometric, and genetic data, in addition to surveying seagrass habitats using satellite photography. Morphological observations encompassed 14 criteria, whilst tissue samples from pectoral fins were utilized for genetic profiling by phylogenetic analysis. Geographic coordinates identified stranded dugongs, whereas seagrass regions were assessed with Sentinel-2 data and QGIS. The results indicated that genetic investigation verified the species' strong affinity with populations in the Java Sea and New Zealand, with more divergence from dugongs in Kerala, India. The seagrass beds adjacent to the dugongs' habitat ranged from 0.21 to 16.68 hectares within a larger network of 55.38 to 85.35 hectares, underscoring their potential as a protection zone. These findings underscore the essential link between dugong conservation and seagrass ecosystem conservation, making it clear that both aspects are interconnected and necessitate combined protection methods.

The Persian Gulf hosts the second-largest population of Dugongs. The International Union for the Conservation of Nature (IUCN) lists them as Vulnerable to Extinction species. Incidental fishing, vessel strikes, environmental pollution, habitat degradation, and infectious diseases currently threaten these sirenians. While research focused on the abovementioned threats, little is known about pathogen infections, particularly waterborne parasites. The current study aimed to investigate the prevalence of the waterborne parasites, namely Blastocystis, Cryptosporidium, Dientamoeba fragilis, Giardia duodenalis, and Toxoplasma gondii in the Qatar Dugongs population. Hence, twenty-three tissues from stranded Dugongs' carcasses were collected postmortem and subjected to DNA extraction and parasite qPCR screening. Only Blastocystis and Cryptosporidium species were detected in different tissues across the tested animals harboring genotypes ST1 and Cryptosporidium hominis IbA9G3, respectively, with the first-time report of Blastocystis sp. within sirenian hosts. Continuous monitoring should be provided to shed lights about the contamination sources of these endangered species and clarify the zoonotic potential transmission routes between wildlife and humans.

Cetaceans and sirenians are endangered marine mammals that are threatened by stranding and mortality. In Thailand's Andaman Sea, limited data exist on the causes and patterns of these events. This retrospective study investigated the characterization and underlying causes of cetacean and sirenian mortality events in the Andaman Sea from 2018 to 2023 using information from the Department of Marine and Coastal Resources, Thailand. Data on 363 stranded marine mammals, including both live and dead strandings, species types, carcass condition, and necropsy findings and diagnoses, were gathered and analyzed to classify and determine the main factors contributing to mortality, encompassing both direct human-related and non-direct human-related causes. From 2018 to 2023, 231 cetaceans and 132 sirenians were documented, representing six families and 19 species. Of these animals, 18.18% (66/363) were stranded alive and 81.81% (297/363) were found dead. The most common species were dugong (Dugong dugon) and Indo-Pacific humpback dolphin (Sousa chinensis). Detailed postmortem analyses of 107 specimens showed that 17.76% (19/107) of deaths were anthropogenic, affecting 8 sirenians and 11 cetaceans. The majority of deaths were non-anthropogenic, involving 34 sirenians and 54 cetaceans. In addition, 223 stranded animals could not be fully assessed due to carcass condition. A high cetacean and sirenian mortality rate in the Andaman Sea can be attributed to non-anthropogenic factors. The dugong and Indo-Pacific humpback dolphin were the most frequently encountered species. This report enhances our understanding of marine mammal mortality in Thailand and underscores the need for improved health management and diagnostic responses.

Context A better understanding of animal habitat use informs fundamental ecology and can provide underpinnings for effective management. Aims This study explored the temporal variation in feeding ground utilisation by dugongs (Dugong dugon) in two intertidal seagrass beds in Talibong Island, Thailand (Sites A and B), focusing on the distribution and direction of dugong feeding trails. Methods Drone-based aerial photography was conducted quarterly over 1 year and daily over 2 weeks to observe feeding trails and behaviour. Key results During five and seven separate photography periods over 1 year, 0.04 ± 0.01% (range: 0.03–0.06%) of Site A (200,000 m2) was covered with new feeding trails daily, while 0.35 ± 0.31% (range: 0.07–0.96%) of Site B (278,000 m2) was covered daily. This temporal variation in the feeding trail area corresponded to that in seagrass coverage. Daily observations over 2 weeks during six separate photography periods revealed a significant decrease in overlapping rates (intersection over union) of the core areas (50% kernel density estimation [KDE]) as time elapsed. The 1-year observation highlighted relatively higher overlapping rates of home ranges (95% KDE) (Site A: 0.27 ± 0.09; Site B: 0.49 ± 0.08) and low overlapping rates of core areas (Site A: 0.02 ± 0.03; Site B: 0.09 ± 0.09). The relative frequencies of the feeding trail direction remained consistent across survey seasons, and the most and least dominant directions were common across all survey seasons and sites. The circular correlation coefficient between the directions of dugong body axis and the estimated tidal current was 0.45, suggesting that feeding generally occurred in the upstream direction. The direction and spatial range of dugong feeding may be affected by temporally consistent factors. One factor that can affect the feeding direction is the tidal current. Conclusions Overall, dugongs may feed and move within seagrass beds in a temporally consistent manner, even when there are shifts in feeding hotspots. Implications This research enhances our understanding of how dugongs utilise their feeding grounds and highlights the importance of not only identifying feeding hotspots but also predicting their feeding routes by considering the direction and distribution of feeding trails.

Remote Underwater Video Confirms the Presence of Dugongs (Dugong dugon) at Ashmore Reef Australian Marine Park in the Eastern Indian Ocean

Abstract Deterioration of seagrass beds worldwide has raised concern about the future of dugongs because almost all aspects of their life history depend on availability of seagrass. Understanding their energy metabolism and consequently how much seagrass they need will inform protective conservation strategies for dugongs. This study determined resting metabolic rate (RMR) in five wild‐caught adult dugongs by measuring oxygen consumption (O2). Measurement conditions met assumptions for RMR, except that dugongs were not postabsorptive, thus a postprandial (pp) allometric equation for herbivorous mammals of similar size was used to predict an expected RMRpp for dugongs of known mass. O2 was measured for 30 min in a metabolic tank after brief habituation. Dugongs' RMRpp was approximately half that predicted for their body mass but was higher than for manatees. Based on dugongs' RMRpp and considering plant caloric and water content, the daily minimum intake of fresh weight seagrass was 40–65 kg Halophila ovalis, or 20–40 kg Halodule spp. Greater seagrass intake would be required for growing and reproducing dugongs. Slow growth and protracted reproductive rates of dugongs are likely related to limitations in seagrass energy and nutrients. To ensure viability of this vulnerable species, it is critically important to conserve extensive healthy seagrass beds.

Sirenia, an iconic marine taxon with a tropical and subtropical worldwide distribution, face an uncertain future. All species are designated 'Vulnerable' to extinction by the IUCN. Nonetheless, a comprehensive understanding of geographic structuring across the global range is lacking, impeding our ability to highlight particularly vulnerable populations for conservation priority. Here, we use ancient DNA to investigate dugong (Dugong dugon) population structure, analysing 56 mitogenomes from specimens comprising the known historical range. Our results reveal geographically structured and distinct monophyletic clades characterized by contrasting evolutionary histories. We observe deep-rooted and divergent lineages in the East (Indo-Pacific) and obtain new evidence for the relatively recent dispersal of dugongs into the western Indian Ocean. All populations are significantly differentiated from each other with western populations having approximately 10-fold lower levels of genetic variation than eastern Indo-Pacific populations. Additionally, we find a significant temporal loss of genetic diversity in western Indian Ocean dugongs since the mid-twentieth century, as well as a decline in population size beginning approximately 1000 years ago. Our results add to the growing body of evidence that dugong populations are becoming ever more susceptible to ongoing human action and global climate change.

This follow-up study to the first assessment of Philippine marine mammal strandings (1998 to 2009) assesses the spatiotemporal variation of strandings and the top five most frequently stranded species from a 2005-2022 dataset. It identifies stranding hotspot areas, estimates species stranding rates/status, and examines species composition and other stranding information. The 18-year database contained 1,368 stranding events with an annual average of 76 events. The total annual stranding frequency increased over the initial study period but fluctuated in the last seven years. Of the 30 species of marine mammals known in the Philippines, 27 species (26 cetaceans and one sirenian) were recorded in stranding records, and the top five most frequently stranded were (1) spinner dolphins (Stenella longirostris), (2) dugongs (Dugong dugon), (3) Risso’s dolphins (Grampus griseus), (4) Fraser’s dolphins (Lagenodelphis hosei), and (5) melon-headed whales (Peponocephala electra). Strandings consisted mostly of single animals (95%), and 55% of animals stranded alive. For each of the top five species, the frequency of stranding events increased annually. There was a peak in stranding frequency during the pre-southwest inter-monsoon season (March-April-May) for spinner and Risso’s dolphins as well as melon-headed whales, with no seasonal trend for the Fraser’s dolphins and dugongs. We identified stranding hotspots within 15 × 15 km grids along the coastline of the major island groups: Luzon, Visayas, and Mindanao. Thirty-five percent (497 of 1,422 grids) of the Philippine coastline had stranding records, with the majority in Luzon (n = 238), followed by Mindanao (n = 130) and Visayas (n = 128). Thirty-five stranding hotspots were identified: 24 in Luzon, 10 in Mindanao, and one in Visayas. Species stranding status categories were generated from log transformed stranding rates per species into standardized classification by quartiles. The stranding status of the top five most frequently stranded species was “very frequent” for spinner dolphins, and “frequent” for Fraser’s and Risso’s dolphins, dugongs, and melon-headed whales. The spatiotemporal variation of stranded marine mammals reflects the dynamic nature of the Philippine archipelago driven by monsoons and inter-monsoons and is exacerbated by fishing pressure and illegal activities. This study showed the importance of robust long-term marine mammal stranding databases for monitoring strandings and generating relevant information essential for their conservation.

Sirenians of the superorder Afrotheria were the first mammals to transition from land to water and are the only herbivorous marine mammals. Here, we generated a chromosome-level dugong (Dugong dugon) genome. A comparison of our assembly with other afrotherian genomes reveals possible molecular adaptations to aquatic life by sirenians, including a shift in daily activity patterns (circadian clock) and tolerance to a high-iodine plant diet mediated through changes in the iodide transporter NIS (SLC5A5) and its co-transporters. Functional in vitro assays confirm that sirenian amino acid substitutions alter the properties of the circadian clock protein PER2 and NIS. Sirenians show evidence of convergent regression of integumentary system (skin and its appendages) genes with cetaceans. Our analysis also uncovers gene losses that may be maladaptive in a modern environment, including a candidate gene (KCNK18) for sirenian cold stress syndrome likely lost during their evolutionary shift in daily activity patterns. Genomes from nine Australian locations and the functionally extinct Okinawan population confirm and date a genetic break ~10.7 thousand years ago on the Australian east coast and provide evidence of an associated ecotype, and highlight the need for whole-genome resequencing data from dugong populations worldwide for conservation and genetic management.

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.