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Background Vessel collision induces blunt and sharp force traumas to aquatic animals and is a leading anthropogenic impact affecting cetaceans worldwide. Vessel collision is an important threat affecting vulnerable coastal cetaceans such as the Indo-Pacific humpback dolphins ( Sousa chinensis ) which reside in coastal waters of Hong Kong amongst heavy marine traffic. Case presentation A severely injured subadult S. chinensis was sighted in the waters off southwestern Hong Kong with four gaping incision wounds on its dorsum. It was in poor body condition and seemed unable to use the fluke effectively. The deepest wound located at the caudal peduncle near the base of the fluke and exposed the underlying fractured caudal vertebrae. The dolphin was monitored in the field over three weeks and eventually captured for medical intervention as veterinary assessment indicated progressive and life-threatening deterioration. During rehabilitation, the dolphin demonstrated initial signs of improvement over the first 36 hours as supported by diagnostic tests but then deteriorated rapidly. It was humanely euthanised after three days of rehabilitation. Postmortem investigation was carried out using virtopsy (postmortem computed tomography and magnetic resonance imaging) and conventional necropsy, with special attention to the traumatic musculoskeletal injuries caused by vessel collision and also revealed acute gastrointestinal compromise and respiratory disease that further hampered the rehabilitation. Conclusion In cetaceans, the prognosis for recovery from injuries caused by vessel collision depends on the extent, location, and gravity of the injuries (i.e., superficial, deep, penetrating, blunt vs. sharp, fresh vs. septic), as well as the health status of the individual and its ability to respond to the insult. Injuries extending deep into the vertebral column may lead to delayed death and associated welfare issues. The prognosis of this case was likely poor given the severity and location of the injuries, but the attempted rehabilitation and postmortem investigation provided valuable insights for clinical management if similar cases are encountered in the future. Being able to non-invasively assess and document traumatic injuries and other pathologies, diagnostic imaging is particularly useful in the clinical assessment and postmortem investigation (virtopsy) of cases with vessel-induced injuries.

As long-lived apex predators, Indo-Pacific humpback dolphins (Sousa chinensis) are key indicators of marine coastal environmental health. Skin marks can be observed on dorsal body surfaces that are visible during mark–recapture studies that rely on photo-identification (photo-ID) methods. Skin mark prevalence may be an indicator of environmental or anthropogenic stressors in the ecosystem, which may lead to individual and/or population-level health concerns. The prevalence of marks of anthropogenic origin was assessed in the Critically Endangered S. chinensis taiwanensis population along the coasts of central Taiwan. Fifty, twenty-eight, and thirty-four individuals were identified in 2018, 2019, and 2021, respectively. At least one category of injuries was observed in 47 of 57 distinctive individuals (82%), and adults showed a higher prevalence of deep injuries than the other coloration stages. At least one category of skin lesion was observed in 33 of 57 distinctive individuals (58%), and high prevalence of skin lesions was found in mature individuals. Given the difficulty in taking direct observations, skin mark prevalence is proposed as a proxy for estimating habitat health and anthropogenic stressors upon S. chinensis taiwanensis. The moderate-to-high prevalence of skin marks in this study was designated as a warning of risks. This study provides important updated information for the assessment of the health and survival of this population. More effective management measures are urgently needed to reverse the observed population decline.

Chinese white dolphin (Sousa chinensis), also known as the Indo-Pacific humpback dolphin, has been classified as “Vulnerable” on the IUCN Red List of Threatened Species. It is a special cetacean species that lives in tropical and subtropical nearshore waters, with significant differences from other cetaceans. Here, we sequenced and assembled a draft genome of the Chinese white dolphin with a total length of 2.3 Gb and annotation of 18,387 protein-coding genes. Genes from certain expanded families are potentially involved in DNA replication and repairing, suggesting that they may be related to adaptation of this marine mammal to nearshore environments. We also discovered that its historical population had undergone a remarkable bottleneck incident before the Mindel glaciation. In addition, a comparative genomic survey on antihypertensive peptides (AHTPs) among five representative mammals with various residential habitats (such as remarkable differences in exogenous ion concentrations and sea depth) revealed that these small bioactive peptides were highly conserved among these examined mammals, and they had the most abundant hits in collagen subunit proteins, especially for two putative AHTP peptides Gly-Leu-Pro (GLP) and Leu-Gly-Pro (LGP). Our genome assembly will be a valuable resource for further genetic researches on adaptive ecology and conservation biology of cetaceans, and for in-depth investigations into bioactive peptides in aquatic and terrestrial mammals for development of peptide-based drugs to treat various human cardiovascular diseases.

A small population of fewer than 80 Sousa chinensis taiwanensis inhabits the western coast of Taiwan. To explore the relationship between environmental factors (water depth, temperature, salinity, turbidity, and pH) and distribution patterns of dolphins, this study was conducted in Yunlin, which has been one of the population's core areas despite being subject to heavy industrial development. 242 day-surveys were conducted along four parallel transect lines between 2008 to 2018, during which sightings of 274 dolphin groups of this species were recorded. The standardized dolphin sighting rate (groups/100km) was used as an index for comparison. Contrasting to the roughly steady distribution in east-west gradient, the north-south gradient exhibited substantial and varied temporospatial changes among three sections (north, middle, and south) off the coast of Yunlin and among three periods. Dolphin sighting rate during spring-summer was significantly higher than that during Autumn-winter. Taking data from inshore surveys for long term comparison, we found that sighting rates at the middle section remained high and relatively stable (around 2-4.6), whereas the rates in the other two sections exhibited opposite trend with high fluctuations, e.g. drastically fluctuated between 0-3.4 in the northern section, while from 3.36 declined to 0.35 in the southern section. We further discovered that rapid changes in three environmental factors, including turbidity, pH, water depth and construction disturbance, could play key roles on dolphin distribution patterns, and can serve as good indicators for habitat suitability for this vulnerable subspecies.

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.

An opportunistic sighting of an Indo-Pacific humpback dolphin (Sousa chinensis) was reported in the nearshore waters off the east Liaodong Peninsula, China. This is the first at-sea sighting in this area, and the northern-most sighting record of this species with a distance >3000 km away from the nearest described conspecific population located in the mid-China. The present sighting occurred in close proximity to the location at which another Indo-Pacific humpback dolphin was found by-caught in 2003. The sighted individual could not be identified through the existing photo-identification catalogues of this species in China (>3500 individuals). Therefore, we suggest that a population of Indo-Pacific humpback dolphins that was never reported might exist in the north of the Yellow Sea.

Age composition is an important population parameter for understanding and managing endangered species. There are very few studies involving cetaceans in estimating the age of individuals in the wild. In this study, we rigorously quantified the body color pattern of 37 stranded Indo-Pacific humpback dolphins (Sousa chinensis) of the Pearl River Estuary (PRE), which showed a significant, albeit with variability between individuals, correlation with age for both the males (between age 1 and 35, r2 = 0.84) and females (between age 1 and 25, r2 = 0.85). The population-averaged correlation (r2 = 0.85) was then applied to a large volume of photo-identification data (2011–2015) to estimate the age composition of the population occurring in the greater deltaic region, which further suggested a spatial difference in age composition and, therefore, a complex demographic process of the humpback dolphin across the region. In particular, the age composition of humpback dolphins in the east PRE (Lingding Bay) is severely aged. Finally, a population viability analysis with the consideration of observed age structure and the simulated age-specific fecundity suggested that 95.75% of the Lingding Bay humpback dolphins are projected to be lost after three generations. Given the sophisticated anthropogenic landscape in the PRE, we suggest that management units of the humpback dolphins should be clearly defined and the regional-specific conservation measures are much needed.

Odontocetes display a wide range of surface behaviors, including aerial and percussive behaviors. However, only a handful of studies have quantitatively investigated the context and function of surface behavioral events in odontocetes. Here, the display of breaching, side breaching, and tail-slapping by Indo-Pacific humpback dolphins (Sousa chinensis) was observed during surveys conducted in three locations of the northern South China Sea. The analysis of 380 encounters revealed that, while breaching was not associated with particular contexts, side breaching was mostly displayed during foraging, probably to gather prey during feeding events, and could therefore be further used to indicate foraging activity. Tail-slapping was displayed significantly more during spring than in other seasons, during socializing and traveling than during other activities, and in larger than in smaller groups. This behavior was mostly displayed by old individuals in a variety of contexts, indicating a potential range of functions including attracting attention, communicating information, expressing an emotional state, or gathering prey together. Unexpectedly, tail slaps were significantly less frequent when the research boat actively followed dolphins, showing that the link between this behavior and human disturbances is not clear. More research is needed to investigate details regarding the display of tail slaps in order to be able to reliably use it as a cue to monitor during surveys that indicates that dolphins are being impacted due to disturbance from boats. Furthermore, differences in the display of surface behavioral events were observed among locations, which may be attributed to differences in foraging and/or communication strategies among different populations. The results obtained here will be useful for behavioral monitoring during field surveys.Significance statementEven though aerial and percussive behaviors are commonly observed in odontocetes, research conducted on these behaviors is scarce and their function(s) are not well understood yet. These functions may vary depending on the species and even on the population. Understanding the context and function of these behaviors is of significant importance for better monitoring animal behavior in the wild (e.g., categorizing the animals’ behavioral state, noticing signs of disturbance). The present study is the first to investigate aerial and percussive behaviors (i.e., breaching, side breaching, and tail slapping) in wild Indo-Pacific humpback dolphins. Dolphins exhibited differences in the frequency at which they display these behaviors depending on the population and the behavioral state of the group. These results inform on the potential communication/foraging strategies differences among populations and provide cues to better monitor dolphins’ behavior in the field.

Trauma, including cuts to the torso and damage to soft and muscular tissues of the torso and fins (dorsal, pectoral, or caudal), has been documented in wild cetaceans. The head contains the brain and other critical anatomy for sensory processing, feeding, and respiration, which are directly related to survival. Damage or deformity to the rostrum (the anterior portion of the upper jaw, sometimes referred to as the mouth or beak) could severely impact foraging and may be fatal in both the short- and long-term. There are few reports on the long-term survival of wild cetaceans with severe damage to the upper rostrum. Wang et al conducted above water surface observations of an Indo-Pacific humpback dolphin (Sousa chinensis) missing most of its upper rostrum. Over a 3-y period, that individual behaved similarly to other apparently healthy individuals. Frainer et al evaluated unusual rostrum conditions in Indian Ocean humpback dolphins (Sousa plumbea) and reported that some individuals survived with injuries for up to 10 y.

Although whistles and high‐frequency clicks of Indo‐Pacific humpback dolphins (Sousa chinensis) had been documented in many wild populations, the small population inhabiting Xiamen Bay has received limited attention. Monthly surveys from 2021 to 2024 recorded a total of 107 whistles and 33,038 high‐quality clicks. Whistles exhibited mean minimum and maximum frequencies of 5.2 ± 2.2 kHz and 7.5 ± 2.7 kHz, respectively, with a mean duration of 247.6 ± 174.2 ms. Clicks had a peak frequency of 86.4 ± 19.5 kHz, a −3 dB bandwidth of 53.3 ± 14.6 kHz, and a duration of 22.3 ± 6.4 μs. Statistically, clicks from dolphins in the West sub‐region had a higher mean peak frequency, broader −3 dB bandwidth, and shorter duration than those from the East sub‐region, suggesting adaptations to local environmental conditions and vessel noise. No significant difference was observed in whistles between the two communities. These findings indicated a potential risk of population subdivision for the Xiamen Bay population, underscoring the urgency of protective measures that sustain connectivity and reduce anthropogenic pressures. The Indo‐Pacific humpback dolphin population in Xiamen Bay was divided into two geographically separated but socially associated communities inhabiting the West and East sub‐regions. Based on 3 years of boat‐based surveys, this study established baseline acoustic characteristics and investigated whether vocal patterns varied with habitat conditions between these two communities. Our findings reveal emerging inter‐community vocal divergence, highlighting the urgency of protective measures to mitigate anthropogenic pressures and reduce the risk of further fragmentation.