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Post‐release monitoring is critical for evaluating the success of rehabilitating stranded cetaceans, yet such data are scarce for many species in the South China Sea (SCS). We satellite‐tracked a rehabilitated subadult male short‐finned pilot whale (Globicephala macrorhynchus; named “Haitang”), following a live stranding on Hainan Island, China. We collected tracking locations and behavioral data over a 52‐day period and conducted a dedicated 3‐day expedition to resight Haitang at sea in the sixth week post‐release. Results confirm Haitang's survival beyond the critical 6‐week benchmark. Its daily movement distance (6.2–145.9 km) and speed (0.6–5.9 km/h) were consistent with those of healthy, free‐ranging conspecifics. Furthermore, diving behavior including time‐at‐depth budgets, maximum dive depth (621 m), diel patterns, and thermal‐depth profiles reflected natural foraging activity and environmental adaptation. Notably, high density and spatial proximity of local conspecifics during the post‐release expedition indicate favorable conditions for social integration and long‐term survival. Movement trajectories suggest that the Qiongdongnan slope represents a critical habitat for this species in the northern SCS. This study provides the first empirical evidence of successful rehabilitation and release of short‐finned pilot whale in the SCS, supporting future stranding response and conservation initiatives. This study presents the first empirical evidence of successful rehabilitation and post‐release monitoring of a short‐finned pilot whale in the South China Sea—a region where such data are critically lacking despite frequent stranding events. Using satellite telemetry and a dedicated resighting expedition, we documented the 52‐day movement, diving behavior, and social reintegration potential of a rehabilitated subadult male, “Haitang”. Our findings not only confirm his survival beyond the critical six‐week benchmark but also provide novel insights into the species' habitat use, diel diving patterns, and behavioral recovery in a poorly studied oceanic region.

Beibu Gulf’s (BBG) Indo-Pacific humpback dolphins present both a genetic differentiation and phenotypical differences from conspecifics from other areas of the South China Sea. Given the recent urbanization and industrialization in southern China, humpback dolphins from the BBG warrant conservation attention. However, this population’s demographic trend is unclear, making it hard to take conservation measures. To assess the population status of humpback dolphins in the BBG, photo-identification surveys were conducted between 2015 and 2019 in the inshore region surrounding the Dafeng River Estuary, which represents the most urbanized and industrialized coastal area of the BBG region. Robust design modeling suggested a constant survival for the female adults (0.89, 95% CI: 0.83–0.94). In comparison, the survival of the juvenile and sex-undetermined adults dropped from 0.92 (95% CI: 0.75–0.98) in 2015 to 0.86 (95% CI: 0.71–0.94) in 2016 and bounced back to 0.89 (95% CI: 0.80–0.94) in 2018. The low level of survival may justify the rapid decline in the annual population size from 156 (95% CI: 133–184) in 2015 to 102 (95% CI: 98–107) in 2019. We found little impact of emigration on the dolphin demographic process. Instead, the low and fluctuating survivals, although with overlapping confidence intervals, seemingly suggested a presence of strong marine stressor(s). Our study highlighted that obtaining high-resolution data is essential to improving our understanding of the demographic dynamics. Moreover, the anthropogenic stress in the BBG region should be quantitatively studied in both temporal and spatial perspectives, to help depict the ecological response of the dolphins to anthropogenic activities.

Passive Acoustic Monitoring (PAM) is increasingly being adopted as a non-invasive method for the assessment of ocean ecological dynamics. PAM is an important sampling approach for acquiring critical information about marine mammals, especially in areas where data are lacking and where evaluations of threats for vulnerable populations are required. The Indo-Pacific humpback dolphin (IPHD, Sousa chinensis) is a coastal species which inhabits tropical and warm-temperate waters from the eastern Indian Ocean throughout Southeast Asia to central China. A new population of this species was recently discovered in waters southwest of Hainan Island, China. An array of passive acoustic platforms was deployed at depths of 10-20 m (the preferred habitat of humpback dolphins), across sites covering more than 100 km of coastline. In this study, we explored whether the acoustic data recorded by the array could be used to classify IPHD echolocation clicks, with the aim of investigating the spatiotemporal patterns of distribution and acoustic behavior of this species. A number of supervised machine learning algorithms were trained to automatically classify echolocation clicks from the different types of short-broadband pulses recorded. The best performance was reported by a cubic support vector machine (Cubic SVM), which was applied to 19215 five-min recordings (~ 4.2 TB), collected over a period of 75 d at six locations. Subsequently, using spectrogram visualization and audio listening, human operators confirmed the presence of clicks within the selected files. Additionally, other dolphin vocalizations (including whistles, buzzes and burst pulses) and different sound sources (soniferous fishes, snapping shrimps, human activities) were also reported. The detection range of IPHD clicks was estimated using a Transmission Loss model and the performance of the trained classifier was compared with data synchronously collected by an acoustic data logger (A-tag). This study demonstrates that the distribution and habitat use of a coastal and resident dolphin species can be monitored over a large spatiotemporal scale, using an array of passive acoustic platforms and a data analysis protocol that includes both machine learning techniques and spectrogram inspection.

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.

Group size is a key social trait influencing population dynamics of group-living animals. The Indo-Pacific humpback dolphins (IPHDs), Sousa chinensis , a shallow water delphinid species, display a fission-fusion social system. Yet little is known about how social organization of this species vary with temporal scales and behavioral state. In this study, we sampled group size estimates from the world’s second largest population of humpback dolphins ( Sousa spp.), which inhabit the eastern waters of Zhanjiang, China. IPHD group sizes changed seasonally and inter-annually, but not with tidal phases. Group sizes also changed with behavioral state of IPHD groups and with number of mother-calf pairs present. IPHDs formed larger groups in the autumn than in other seasons, which might be related to seasonal changes in food availability and reproductive cycle. Of the groups observed, we recorded the presence of mother-calf pair in 85 groups (i.e., nursery groups: 47 ones with one pair, 25 ones with two pairs, and others with three pairs). Notably, nursery groups were about 2–4 times larger than non-nursery groups. In addition, group sizes greatly increased with the number of mother-calf pairs. Living in relatively large groups, more protection, food, and resources might be available for IPHD mothers and calves, and such social strategy provide higher reproduction efficiency and survival success for this species. During our observations, feeding (45.5%) and traveling (25.2%) represented the majority of IPHD’s behavioral budget, while socializing (8.4%) and resting/milling (6.8%) were not frequently observed. Resting/milling groups were approximately 50% smaller than feeding, traveling, or socializing groups, while the latter three types had a similar mean group size. Large groups when IPHDs foraged, traveled, or socialized, might provide more added group benefits. For the first time, our findings clearly revealed intra-population variability in IPHD group sizes across different behavioral and temporal variables, and provided a better understanding of IPHDs’ adaptations to various biological processes and ecological constraints.

This study aimed to develop of a rapid and effective method to occlude dentinal tubules using carboxymethyl chitosan and lysozyme (CMC/LYZ) nanogels with encapsulated amorphous calcium phosphate (ACP) based on the transformation of ACP to HAP. In this work, CMC/LYZ was used to stabilize ACP and form CMC/LYZ-ACP nanogels, and then the nanogel-encapsulated ACP was applied to exposed dentinal tubule surfaces. The morphology of the nanogels was examined by transmission electron microscopy (TEM). Distribution and quantity of elements in CMC/LYZ-ACP nanogels were determined by element mapping and energy dispersive X-Ray spectroscopy (EDX). Scanning electron microscopy (SEM) images, XRD measurements and nanoindentation were applied to check the efficacy of tubular occlusion. TEM revealed that CMC/LYZ-ACP nanogels were spherical dense gel particles with size approximately 50–500 nm. Element mapping and EDX indicated that C, N, O, Ca, P, and S in the microspheres are thoroughly represented. SEM images shows that the thickness of the coating layer was approximately 1–2 μm and the depth to which the mineralized substance enters the dentinal tubule was approximately 4–8 μm. XRD measurements and nanoindentation indicated that the occluding mineralized substance observed were similar to nature dentin. CMC can form spherical dense nanogels loaded with ACP under the participation of lysozyme. The CMC/LYZ-ACP nanogels could increase the dentinal tubule occluding effectiveness. These results indicated that finding and developing novel nanomaterials of CMC/LYZ-ACP would be an effective strategy for the treatment of dentin hypersensitivity.

To compare the preventive effects of various mineralization solutions on tooth demineralization and their influence on the metabolism of . Pure water, Ca/P mineralization solution, Ca/P mineralization solution with fluoride, Ca/P mineralization solution with zinc, Ca/P mineralization solution with magnesium, and Ca/P mineralization solution with strontium (Sr) were prepared. Tooth fragments were immersed in these solutions at 37°C for 24 h. Surface morphology was examined by scanning electron microscopy (SEM). The relative proportions of surface elements were analyzed, and new substances formed on the tooth surface were identified. Acid-etching was performed to evaluate changes in anti-demineralization ability and wear resistance. was inoculated onto tooth surfaces, bacterial adhesion was observed using SEM, and water contact angles were measured. Changes in pH and metabolites of bacterial culture media were assessed. KEGG enrichment pathway analysis was conducted to explore metabolic pathways. Amino acids and organic acids in metabolites and bacterial proliferation were evaluated. RT-PCR was used to measure key glycolysis-related gene expression to verify the production of acidic metabolites. New substances were observed adhering to tooth surfaces by SEM; surfaces treated with zinc and Sr solutions were the roughest. Elemental proportion analysis indicated zinc had the highest adhesion potential, while Sr had the lowest. Newly formed substances included fluorapatite, magnesium hydroxide, and phosphate complexes. All experimental groups demonstrated improved acid resistance and good wear resistance. Sr treatment rendered tooth surfaces more hydrophilic and increased bacterial adhesion. All experimental groups inhibited acid production by , particularly the fluoride group. Antibacterial tests indicated fluoride and zinc had the strongest antibacterial effects. KEGG pathway analysis suggested that the primary signaling pathways influenced by these substances were related to bacterial antibiotic formation and acid-salt metabolism. Metabolite analysis showed that experimental groups significantly inhibited the formation of acidic amino acids and organic acids, with fluoride exhibiting the most notable effect. RT-PCR results indicated experimental groups suppressed transcription of the glycolysis-related bacterial gene , most notably fluoride. Additionally, transcription of bacterial adhesion genes decreased across experimental groups, with Sr markedly inhibiting expression.

Marine mammals are a diverse group of aquatic animals that exhibit wide variation in body size, living conditions, breeding habitat, social behaviour and phylogeny. Although case studies about prenatal investment in cetaceans and pinnipeds have been investigated, comparative studies across different marine mammal taxonomic groups have not yet been conducted systematically. Here, six life history parameters from 75 marine mammal species were collected based on a meta-analysis of the existing literature, and prenatal investment patterns for different taxonomic groups were explored using an unsupervised artificial neural network of a self-organizing map (SOM). Most marine mammal species can be clearly divided into two clusters of small-bodied taxa (small-bodied toothed whales, pinnipeds) and large-bodied taxa (baleen whales, sperm whales and beaked whales, large-bodied toothed whales) based on their distribution within SOM feature maps. Gestation periods and breeding intervals are significantly shorter in pinnipeds than in small-bodied toothed dolphins despite being similar in body size, indicating their adaption to birthing and nursing on land or ice floes. Specific deep-dive feeding behaviour seems to have no impact on the prenatal investment of beaked whales and sperm whales, as these species exhibit a similar capital breeding strategy to baleen whales. Medium-bodied sirenians adopt an intermediate strategy between small-bodied and large-bodied toothed whales, suggesting their prenatal investment strategy is not affected by herbivorous habits. Overall, our results support the body-size hypothesis and breeding-substrate hypothesis and indicate that prenatal investment strategies of marine mammals are possibly not influenced by feeding habits or social behaviour. We suggest that effective conservation measures for small-bodied toothed whales and pinnipeds should prioritize the protection of habitats and minimize human disturbance, whereas conservation measures for large-bodied whales and beaked whales should focus on strategies to prevent substantial declines in population size.

Observer-based counts and photo-identification are two well-established methods with an extensive use in cetacean studies. Using these two methods, group size has been widely reported, especially for small dolphins. Both methods may come with potential errors in estimating the group size, yet there is still a lack of comparison between both methods over a broad range of group size. Particularly, biogeographical variances in group size estimates were often mixed with methodological variances, making it difficult to compare estimates from different geographic regions. Here, group size estimates of a small, shallow-water, and near-shore delphinid species, Indo-Pacific humpback dolphins ( Sousa chinensis ), were simultaneously sampled using observer-based counts and photo-identification at three regions in the northern South China Sea. Data showed that dolphin group size from two methods were highly variable and associated with sampling regions. Generalized linear mixed models (GLMMs) indicated that dolphin group size significantly differed among regions. Statistical examinations further demonstrated dolphin group size could be affected by a complex combination of methodological and biogeographical variances. A common hurdle to examine potential factors influencing the estimation process is the inability to know the true group size at each sample. Therefore, other methods that could generate comparable estimates to represent true group size are warranted in future studies. To conclude, our findings present a better understanding of methodological and biogeographical variances in group size estimates of humpback dolphins, and help yield more robust abundance and density estimation for these vulnerable animals.

Satellite-tagging is increasingly becoming a powerful biotelemetry approach to obtain remote measurement through tracking free-living cetaceans, which can fill knowledge gaps on cetaceans and facilitate conservation management. Here, we made a first biologging attempt on baleen whales in Chinese waters. An adult Bryde’s whale in the Beibu Gulf was tagged to investigate potential occurrence areas and migration routes of this poorly studied species. The whale was satellite-tracked for ~6 days with 71 filtered Argos satellite locations, resulting in a linear movement distance of 464 km. At each satellite-tracking location, the water depth was measured as 42.1 ± 24.8 m on average. During the satellite-tracking period, the whale’s moving speed was estimated at 5.33 ± 4.01 km/h. These findings expanded the known distribution areas of Bryde’s whales in the Beibu Gulf and provided an important scientific basis for the regional protection of this species. We suggest that fine-scale movements, habitat use, and migratory behavior of Bryde’s whales in the Beibu Gulf need more biotelemetry research, using long-term satellite-tracking tags and involving enough individuals. Furthermore, the genetic relationship and possible connectivity of Bryde’s whales in the Beibu Gulf and adjacent waters should be examined.