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The social structure of animal populations is a fundamental component of their biology, influencing gene flow, habitat use, competition and co-operation around resources, and communication. However, ecological and social relationships can be challenging to describe in most marine mammals, who spend the majority of their lives underwater. The finless porpoise (Neophocaena asiaeorientalis) is one such cetacean species with a largely unknown social structure. Recent advances in drone technology enable more systematic surveys, photogrammetry, and photo-identification for diverse animal species. The present study aimed to validate new survey methods and provide a preliminary description of the spatiotemporal distribution of free-ranging finless porpoises in the coastal open-sea area of Ariake Sound, Japan. A vertical take-off and landing (VTOL) drone equipped with an action camera yielded GPS location datasets through line and area surveys, covering a total sea area of 120 km2. The results suggest highly flexible and varied aggregation sizes in finless porpoises. Distance analysis across individuals and aggregations revealed a cohesive tendency among groups, compared to solitaries and in pairs. Therefore, the present VTOL drone surveys both elucidated some social aspects of the study population and confirmed the efficacy of these standardized research protocols involving automated, programmed, and repeatable flight missions.

Social group dynamics are known to impact odontocetes' health and welfare in captivity. Social dominance and agonistic interactions that occur to establish and maintain these relationships might express themselves differently between species and groups, and could be used to monitor social changes. This is the first comparative and quantitative study of agonistic interactions and dominance relationships among three groups of captive odontocetes–Yangtze finless porpoises (YFPs; Neophocaena asiaeorientalis asiaeorientalis), East Asian finless porpoises (EAFPs; Neophocaena asiaeorientalis sunameri), and bottlenose dolphins (BDs; Tursiops truncatus)–and the first use of two methods, including the Elo-Rating Method, to assess dominance in odontocete groups. In this article, we also describe agonistic behaviours in finless porpoises (FPs) for the first time. Agonistic behaviours differed among groups, and BDs' agonistic encounters lasted significantly longer than FPs' ([chi square]= 441.77, df = 2, p < 0.0001). In the three groups, males were more frequently engaged in agonistic interactions than females (YFPs: [chi square] = 8.1144, df = 1, p = 0.004392; EAFPs: [chi square] = 6.3229, df = 1, p = 0.01192; and BDs: [chi square] = 4.5977, df = 1, p = 0.03201). Unlike BD females, YFP females initiated agonistic interactions more frequently than males. YFPs and BDs engaged more often in agonistic interactions when an unusual social event occurred (e.g., reunion of social groups or introduction of new animals). Finally, there was no influence of sex in the dominance hierarchy of FPs whereas BD males were dominant over females in this study. In FPs, younger individuals were found to be the highest ranked for both sexes. We recommend daily monitoring of agonistic behaviour and social dominance in captive odontocete groups using the method described herein for detecting social changes early that might develop to threaten an animal's physical and psychological health and welfare.

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is a critically endangered species, as the whole population in the wild suffered sharp decline and fragmentation. Observations of the local spatial and temporal distribution dynamics can help establish better conservation strategies. In order to understand the characteristics of habitat chosen, a continuous 15 months observation on the distribution patterns of the Yangtze finless porpoise at the confluence of Yangtze and Wanhe rivers was conducted. The results showed that the distribution of the porpoise changed seasonally. From October 2013 to March 2014 and from December 2014 to January 2015, the observation rate ranged from 12.5% to 100% of each observation day, with the average being 60%. The average maximum number of individuals observed per day was 4 (range, 1-8).Porpoises was not observed in September 2013 and from April 2014 to September 2014. Spatial distribution dynamics analyses showed that from the six different hydrological zones of the confluence, the porpoise was more likely to prefer the flow deflection and flow stagnation zones of the confluence. The average occurrence rate in the flow deflection and flow stagnation zones was 32% and 44%, respectively. Based on these observations, we concluded that the confluence of the Yangtze and Wanhe rivers is a popular habitat of the Yangtze finless porpoise in autumn and winter. Conservation measures should be taken to conserve this kind of habitat.

Hearing is considered the primary sensory modality of cetaceans and enables their vital life functions. Information on the hearing sensitivity variability within a species obtained in a biologically relevant wild context is fundamental to evaluating potential noise impact and population-relevant management. Here, non-invasive auditory evoked-potential methods were adopted to describe the audiograms (11.2–152 kHz) of a group of four wild Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) during a capture-and-release health assessment project in Poyang Lake, China. All audiograms presented a U shape, generally similar to those of other delphinids and phocoenids. The lowest auditory threshold (51–55 dB re 1 µPa) was identified at a test frequency of 76 kHz, which was higher than that observed in aquarium porpoises (54 kHz). The good hearing range (within 20 dB of the best hearing sensitivity) was from approximately 20 to 145 kHz, and the low- and high-frequency hearing cut-offs (threshold > 120 dB re l μPa) were 5.6 and 170 kHz, respectively. Compared with aquarium porpoises, wild porpoises have significantly better hearing sensitivity at 32 and 76 kHz and worse sensitivity at 54, 108 and 140 kHz. The audiograms of this group can provide a basis for better understanding the potential impact of anthropogenic noise.

Finless porpoises (Neophocaena asiaeorientalis) currently face population decline caused by significant human activities and are categorized as endangered on the International Union for Conservation of Nature (IUCN) Red List; however, information on their habitats is currently insufficient. Although conducting visual surveys to determine the distribution of cetaceans is common, visual observation of finless porpoises is challenging owing to their specific morphological and ecological characteristics. In this study, we developed an environmental DNA (eDNA) assay for species-specific detection of finless porpoises. To test the utility of the assay, we conducted a visual survey in parallel with an eDNA survey by collecting water samples from 50 sites throughout Osaka Bay. We visually found a finless porpoise at one location and detected eDNA at nine sites, including sites near the visual observation site and those with rare sightings of finless porpoises. Therefore, in this study, we suggest that the use of eDNA analysis for distribution surveys of finless porpoises will enable more efficient surveys. The proposed eDNA technique can not only be applied to the distribution surveys finless porpoises but also to those of other cetacean species.

The East Asian finless porpoise, Neophocaena asiaeorientalis sunameri , is an endangered species that inhabits the coastal marine environments of East Asia. In the present study, we investigated the overall infection status of anisakid nematodes in East Asian finless porpoises from three sea sectors off the Korean Peninsula. The genetic diversity and population genetic structure of the identified nematode species were evaluated. The prevalence of all stages of anisakid nematodes collected from the stomach was 57.55% (61 among the 106 porpoises examined), and 16 of the hosts were found to have adult worms. The mean number of infected adults was 211 (± 419.54, 5–1455 per host). Only one species of anisakids, Anisakis pegreffii , was identified from randomly selected worms by molecular approaches. Analysis of the mitochondrial (mt) cox2 partial gene in 50 newly generated sequences of A. pegreffii revealed 24 haplotypes, including 14 new haplotypes. We observed below-average levels of nucleotide diversity and haplotype diversity compared to other seas around the world. The mtDNA cox2 haplotypes of the species in the three Korean sea areas showed no genetic structure, suggesting well-connected gene flow within these areas. This study represents the first record of a definitive host of A. pegreffii in Korean waters, providing important information regarding anisakids genetic diversity in the cetacean species inhabiting limited regions.

This is a culture-dependent study with the objective of pure culturing and characterizing pathogenic bacteria from the blowhole, lung, stomach and fecal samples of a neonatal crucially endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) that died 27 days after birth. Bacteria were inoculated using a swab onto blood and MacConkey agar plates and representative isolates were identified through 16S rRNA gene sequence analysis. A total of three Clostridium perfringens type C strains from the fecal samples were isolated. Toxin genes, including cpa, cpb and cpb2, were detected by PCR amplification, whereas the etx, iap and cpe genes were not detected. Biofilm formation of the three strains was then examined. Only one strain was capable of biofilm formation. In addition, isolates showed strong resistance against the antibiotics amikacin (3/3), erythromycin (1/3), gentamicin (3/3), streptomycin (3/3), and trimethoprim (3/3), while sensitivity to ampicillin (3/3), bacitracin (3/3), erythromycin (2/3), penicillin G (3/3), and tetracycline (3/3). The results suggested C. perfringens type C could have contributed to the death of this neonatal porpoise.

A female narrow-ridged finless porpoise (Neophocaena asiaeorientalis) stranded on a beach on Jeju Island showed epithelial proliferative skin lesions on its body. Two false killer whales (Pseudorca crassidens), caught using nets near Gangneung and Samcheok, respectively, had multiple plaques on their penile epidermis. Histological examination of the epidermis revealed that all the lesions had common features, including accentuated rete pegs, ballooning changes, and eosinophilic intranuclear inclusion (INI) bodies. Based on the histopathological results, herpesvirus infection was suspected, and thus further analysis was conducted using herpesvirus-specific primers. Based on nested polymerase chain reaction (PCR) tests using the herpesvirus-detectable primers, the PCR products demonstrated two fragments: a 222-base-pair (bp) sequence of the DNA polymerase gene, SNUABM_CeHV01, showing 96.4% identity with a bottlenose dolphin herpesvirus from the Jeju narrow-ridged finless porpoise; and a 222 bp sequence of the DNA polymerase gene, SNUABM_CeHV02, showing 95.95% identity with the same bottlenose dolphin herpesvirus from the Gangneung and Samcheok false killer whales. The significance of this study lies in its ability to demonstrate the existence of novel cetacean herpesviruses in South Korean seawater, representing an important step forward in studying potentially harmful pathogens that affect endangered whale and dolphin populations.

Background Post-mortem imaging has become indispensable in marine mammal research, offering non-destructive alternatives to conventional necropsy. While micro-computed tomography (microCT) provides high resolution for small specimens, its utility in cetacean fetal studies is limited by long scanning time, accessibility, and high cost. Diffusible iodine-based contrast-enhanced CT (diceCT) using clinical-grade scanners presents a potential solution, particularly for endangered species like the narrow-ridged finless porpoise ( Neophocaena asiaeorientalis ) (NRFP), where fetal specimens are exceptionally rare. This study pioneers the application of clinical CT-based diceCT for NRFP fetal imaging, addressing the gap in developmental morphology research. Results A 41 cm NRFP fetus was recovered from a stranded pregnant female and preserved for iodine-enhanced CT imaging. The specimen underwent 22 weeks of staining in 1% iodine-ethanol solution, with weekly solution replacement and biweekly clinical CT scans (100 kVp, 300 mAs, 0.3 mm slice thickness) to monitor progression. Complete staining was confirmed by clear radiographic differentiation between adjacent tissue, variance of Hounsfield unit (HU) values of the specimen, and a plateau in the signal-to-noise ratio (SNR) among all scans within the liver. High-resolution 3D reconstructions successfully visualized the gastrointestinal tract, urogenital structures, and cardiovascular network, with preserved spatial relationships. Conclusions Clinical-grade diceCT provides a practical alternative to microCT for cetacean fetal imaging by achieving organ-scale resolution. The protocol enabled comprehensive 3D morphological analysis without tissue destruction. The archived dataset and destained specimen offer enduring value for conservation research, education, and method development.

The Shandong Peninsula is located on the western coast of the Pacific and is adjacent to the Bohai Sea (BS) and the Yellow Sea (YS) to the east. The East Asian finless porpoise Neophocaena asiaeorientalis sunameri, a subspecies of the narrow-ridged finless porpoise N. asiaeorientalis, is the dominant cetacean resident along the Shandong Peninsula. However, there is insufficient monitoring data to determine the status of the cetacean species in this region. Based on the publicly available literature, media, and internet social website, this study investigated the spatial–temporal distribution of porpoise stranding and bycatch along the coast of the Shandong Peninsula. Data on over five hundred porpoises from two hundred reports between 2000 and 2018 were compiled and analyzed. Results showed that the bycatch and stranding of porpoises occurred widely across the peninsula throughout all months and increased rapidly between 2010 and 2017. The incidents were more frequent in the area where the BS and YS converged during the spring and early summer than in other seasons. The mean body length of bycaught porpoises was smaller than that of those found stranded. Fishing activities could be the principal cause of local finless porpoise incidents. However, limited data hindered a quantitative evaluation of the living conditions of finless porpoises in this area. Establishing a comprehensive monitoring system, which includes standardized reporting, rescue operations, and scientific research, is essential to finless porpoise protection along the Shandong Peninsula.