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.

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.

Tooth rake marks are usually used as an indicator of received aggression in odontocetes whose social interactions are difficult to observe directly. Photographic data from five locations of the northern South China Sea were used to analyze seasonal, demographic, and geographic effects on the density of tooth rake marks and dorsal fin notches in Indo-Pacific humpback dolphins (Sousa chinensis, IPHDs). The analysis revealed that fresh tooth rake marks were most frequent during the dry season. Males exhibited significantly higher rake mark density than females and rake density declined significantly with age. The density of notches was also significantly higher for males than for females, and lower for young dolphins than for mid-aged and adult ones. Geographically, tooth rake mark and notch density were the highest in Sanniang Bay and Southwestern Hainan. These results provide indirect evidence of variation in social interactions across seasons, across the lifespan of an individual, between sexes, and among different locations. This variation may result from changes in biological parameters, differences in social lives, and habitat characteristics.A model to determine the sex of dolphins was tested, and after further validation, such sex assignment could contribute to understanding IPHDs' social structure.

No abstract

Indo‐Pacific humpback dolphins (Sousa chinensis) inhabiting the Chinese coastline of the northern South China Sea are subject to intense human activity. To investigate potential impacts to dolphins, photographs taken from 2010 to 2021 in five different locations were analyzed. Among individual dolphins (N = 1,159), 10.6% presented human‐induced injuries. Adults were more frequently injured than young dolphins, and individuals from around Jiangmen, Hainan, and Sanniang Bay presented the highest injury prevalence. More research should be conducted in areas that have been subject to less research, such as Jiangmen and Hainan, and the dolphin watching activities occurring in Sanniang Bay should be monitored and regulated. Forty‐seven percent of dolphins presented skin conditions, with orange patches being the most frequent (41.5%). Orange patches and hyper‐pigmented pink spots were significantly less prevalent in summer and fall than in winter and spring. Orange patches were less frequent in females than in males, as well as with calves relative to older age classes. Seasonal patterns may be linked to water temperatures, while demographic patterns may be associated with immune defenses. These findings allow for a better understanding of the potential impact of human activities on Indo‐Pacific humpback dolphins and should inform further conservation measures.

No abstract

No abstract

The Indo-Pacific humpback dolphin is characterized by a particular ontogenic change in body color from dark gray at birth to pure white (or with a few dark-gray spots) after reaching adulthood. Here, we report a spectrum of anomalous body color patterns observed on Indo-Pacific humpback dolphins off southern China. The occurrence of hypopigmentation and hyperpigmentation was described and compared among six putative dolphin populations. Low rates of anomalies in body color patterns were observed (<1%), except for hypopigmentation, which was prevalent in dolphins residing in the mid-Pearl-River-Delta region (3.3%).