Jeju Island Dolphin Postmortem Uncovers Traumatic Jaw Injury and Fatal Opportunistic Pneumonia

A multidisciplinary postmortem investigation of a well-known resident Indo-Pacific bottlenose dolphin (Tursiops aduncus) off Jeju Island, Republic of Korea, has detailed a complex pathological progression linking chronic blunt-force trauma to reactive tumor growth and ultimately fatal aspiration pneumonia. The male dolphin, cataloged as TA25-0630 and known locally as Tuckee, was followed in coastal waters over a six-year period, including three years of intensive longitudinal field tracking conducted by veterinary and marine conservation researchers. The animal had initially drawn widespread public concern and scientific attention after being filmed in October 2019 for the television documentary MBC Special Warning from the Ocean: The Vanishing Whales, which highlighted a noticeable facial deformity and a protruding oral mass. Following its stranding and death in the summer of 2025, researchers carried out an exhaustive postmortem study combining high-resolution diagnostic imaging, histopathology, molecular sequencing, bacteriological assays, virology, and environmental toxicology to clarify the precise nature of the mass and establish the cascade of factors leading to the animal’s demise.

Long-term observational data gathered over four years of field monitoring provided rare behavioral context prior to the animal’s death, with research teams tracking Tuckee and associated pods across more than 300 days annually and averaging eight hours per daily observation session. Observers used high-resolution digital cameras equipped with telephoto lenses from shore alongside complementary drone flights utilizing DJI Mavic 3 Cine and Pro systems operated at altitudes between 20 and 30 meters to minimize acoustic and behavioral disturbance. Throughout this multi-year surveillance, Tuckee actively participated in the fission-fusion social dynamics typical of the local Jeju dolphin population, alternating between large aggregations and small subgroups while maintaining locomotor patterns and overall vitality comparable to healthy conspecifics. However, the prominent oral growth prevented normal jaw closure, causing a permanent open-mouth posture while swimming and forcing the dolphin to adopt an unusual foraging strategy. Tuckee was repeatedly observed preying on olive flounder (Paralichthys olivaceus), maneuvering the flat-bodied fish sideways through the narrow lateral oral gap, thereby maintaining fair body condition despite extensive anatomical impairment.

Behavioral changes were first detected roughly three weeks before death, when the animal began lagging behind conspecific pods and engaging in extended solitary periods. On the day preceding stranding, vertical aerial drone imaging captured the dolphin swimming alongside two companions, exhibiting a lower jaw visibly deviated 25 degrees to the left of the midline without apparent lip hemorrhage. The following day, the carcass was recovered from nearshore waters by the Korea Coast Guard at latitude 33.242673 degrees North and longitude 126.418391 degrees East. Physical examination revealed an adult male measuring 278 centimeters in total length and weighing 208 kilograms in fair nutritional state. Age estimation was established using three mutually supportive methodologies: growth layer groups counted in sectioned left mandibular teeth yielded an age of 19 years; skeletal evaluation across sixteen anatomical centers of the pectoral flipper indicated approximately 18 years of maturity; and ventral and lateral body surface speckling patterns aligned with speckle Phase IV, representing an age span of 16 to 18 years, confirming a chronological age of approximately 18 to 19 years.

To investigate internal skeletal trauma and soft-tissue alterations before dissection, the frozen carcass was transported to Jeju National University Equine Hospital for post-mortem computed tomography scanning on a 16-row, 32-slice helical Aquilion Lightning scanner. Due to gantry bore limitations of 780 millimeters in diameter, scanning was conducted in two separate sections, encompassing the rostrum-to-pectoral flipper region and the caudal segment at 120 kilovolt peak and 225 milliampere-seconds with one-millimeter slice thickness. Three-dimensional volume rendering and multiplanar reconstruction using Synapse 3D software demonstrated extensive chronic bilateral mandibular injuries consistent with severe, high-impact blunt trauma sustained years earlier. The left mandible exhibited a comminuted fracture with its rostral segment rotated 80 degrees to the left of normal anatomical alignment alongside pronounced bone remodeling caudal to tooth number twelve, while the right mandible showed an oblique fracture caudal to tooth number two with bony union and ventral fusion. CT imaging confirmed the primary soft-tissue mass originated from the left mandibular gingiva and extended along the tongue toward the esophagus, exhibiting poorly defined margins blending into adjacent musculature.

Subsequent macroscopic necropsy and histopathological assessments revealed that the oral lesion was a reactive, non-malignant traumatic fibroma rather than an aggressive neoplastic transformation. Gross examination identified a large, firm, lichenified mass lining the left mandibular gingival margin, a smaller lichenified nodule on the rostral right gingiva, and diffuse apical thickening of the tongue with protruding sublingual nodules. Histological sections stained with hematoxylin and eosin demonstrated marked epithelial hyperplasia, pronounced neovascularization, and widespread chronic inflammatory infiltration surrounding dense, poorly circumscribed proliferations of fibroblasts. Masson’s trichrome staining highlighted abundant collagen bundles that stained intensely blue, reinforcing a benign fibromatous architecture. Immunohistochemistry demonstrated diffuse cytoplasmic positivity for vimentin in dermal spindle cells and smooth muscle actin positivity restricted to vascular walls, whereas beta-catenin was negative without nuclear accumulation and CD34 was entirely negative. Furthermore, polymerase chain reaction amplification and direct sequencing of exon 3 of the CTNNB1 gene identified no mutations, successfully ruling out aggressive fibromatosis or desmoid tumors, while transmission electron microscopy across three tumor areas detected no viral particles.

Transcriptomic profiling of formalin-fixed paraffin-embedded tongue tissue was performed using Quant-Seq 3-prime mRNA sequencing to explore the gene expression profile of the reactive growth. Sequencing produced over 21.3 million clean reads, of which approximately 15.96 million reads were mapped to the reference genome of the common bottlenose dolphin (Tursiops truncatus) with an overall mapping alignment rate of 74.6 percent. Gene ontology functional classification of highly expressed transcripts highlighted four predominant biological themes: secretory proteolysis and digestive enzyme-related functions, extracellular matrix organization and stromal tissue remodeling, cytoskeletal contractile fiber organization, and epithelial differentiation with keratinization signatures. The prominent representation of secretory proteolysis-associated transcripts was consistent with chronic local inflammation and salivary gland-derived cellular activity, while pathways linked to extracellular matrix deposition and myofibroblast activation reflected persistent mechanical irritation rather than malignant cellular proliferation. The authors noted that without matched normal control tissues from the same individual, these transcriptomic patterns provide exploratory insight into reactive hyperplastic mechanisms under sustained biomechanical stress.

Gross internal examination demonstrated that the ultimate cause of death was severe, debilitating respiratory disease characterized by near-total functional failure of the left lung. Large volumes of foamy fluid filled the tracheal lumen, and computed tomography scans demonstrated marked nasal sinus congestion with distinct air-fluid levels and extensive upper airway swelling that rendered the trachea non-patent. The left lung exhibited multifocal to coalescing suppurative nodular abscesses concentrated predominantly in the caudoventral parenchyma, filled with thick, yellow, creamy purulent material, accompanied by fibrous pleural adhesions and marked reactive enlargement of twenty-six regional mediastinal and hyoid lymph nodes measuring up to 4.96 centimeters in diameter. Cross-sectional computed tomography of the thoracic cavity illustrated diffuse consolidation and severe ground-glass opacities creating an extensive crazy-paving pattern across the left pulmonary field, whereas the right lung displayed only mild ground-glass opacities without gross suppurative lesions.

Histopathology of the left lung confirmed severe, multifocal to coalescing, chronic-active suppurative and necrotizing pneumonia, showing widespread alveolar destruction, extensive necrotic debris, abundant dense basophilic bacterial colonies, and heavy neutrophil and lymphocyte infiltration. Examination of the right lung identified partially compressed alveolar spaces containing pale eosinophilic proteinaceous fluid, diffuse interalveolar septal thickening, and localized bacterial colonization of bronchial mucosal walls. An impression smear of the left lung stained using Ziehl-Neelsen confirmed the absence of acid-fast mycobacteria while revealing incidental intact diatoms within pulmonary tissue sections. Concurrently, necropsy identified focal mucosal ulceration accompanied by subepithelial chronic inflammatory cell infiltration at the left laryngeal inlet. The combination of chronic laryngeal ulceration, foreign diatoms within lung parenchyma, and caudoventral accumulation of suppurative exudate supported seawater aspiration, wherein hydrodynamic forces generated during forward swimming drove ingested seawater and oral pathogens directly past the deformed, unsealed oral cavity and larynx into the bronchial tree.

Microbiological characterization uncovered a striking polymicrobial infection dominated by an unexpected anaerobic pathogen, contrasting sharply with routine aerobic culture outcomes. Standard aerobic cultivation of pulmonary abscess swabs isolated nine bacterial species, including Proteus mirabilis, Leclercia adecarboxylata, Shewanella algae, Acinetobacter calcoaceticus, Vagococcus fluvialis, Alcaligenes faecalis subsp. faecalis, Leucobacter chromiireducens, a Glutamicibacter species, and organisms within the Bacillus cereus group. However, amplicon-based 16S ribosomal RNA metagenomic sequencing revealed that the anaerobic bacterium Parvimonas micra accounted for more than 85 percent of the total microbial community in the left pulmonary abscess, co-occurring alongside secondary populations of Fusobacterium and Actinomyces species. Diagnostic polymerase chain reaction assays further amplified Parvimonas micra and Fusobacterium species from oral tumor tissue and multiple internal organs, indicating systemic hematogenous dissemination. While Parvimonas micra is widely recognized in human clinical medicine as an opportunistic oral commensal involved in periodontal breakdown and deep-seated lung abscesses, this finding represents its first confirmed documentation as a primary contributor to fatal pulmonary abscessation in any marine mammal.

Toxicological screening for halogenated organic contaminants across blubber, liver, melon, kidney, and stomach tissues revealed substantial chemical accumulation consistent with the dolphin’s advanced age and apex trophic position. Gas chromatography-mass spectrometry normalized to lipid weight demonstrated that legacy contaminants dominated blubber tissues, with total dichlorodiphenyltrichloroethane concentrations reaching 66,500 nanograms per gram lipid weight and polychlorinated biphenyls measuring 11,900 nanograms per gram lipid weight. Intermediate concentrations were recorded for chlordanes at 2,500 nanograms per gram lipid weight, polybrominated diphenyl ethers at 1,040 nanograms per gram lipid weight, and hexachlorobenzene at 241 nanograms per gram lipid weight, while novel flame retardants appeared at low levels, including novel brominated flame retardants at 2.64 nanograms per gram lipid weight and Dechlorane Plus at 1.90 nanograms per gram lipid weight. While blubber burdens exceeded established toxicity thresholds for immune disruption identified in other marine mammals, tissue distribution remained uniform across internal organs, arguing against rapid lipid mobilization or terminal emaciation, and indicating that environmental pollutants likely acted as indirect physiological stressors rather than direct causes of death.

Subject of Research: Multidisciplinary postmortem investigation of a resident Indo-Pacific bottlenose dolphin linking chronic mandibular trauma to fatal aspiration pneumonia

Article Title: From traumatic oral fibroma to fatal pneumonia: a multidisciplinary postmortem investigation in a long-term monitored Indo-Pacific bottlenose dolphin (Tursiops aduncus)

Article References: Park, J.-H., Lee, K. L., Lee, Y. M., Choi, J. Y., Heo, Y. R., Oh, S. M., Lee, D., Kim, S., Lee, H. W., Poon, C. T. C., Hong, W. H., Moon, H.-B., Mok, S., Lee, C.-Y., Kim, M.-A., Yuen, A. H. L., Seok, S. H., Kim, B. Y., & Kim, S. W. (2026). From traumatic oral fibroma to fatal pneumonia: a multidisciplinary postmortem investigation in a long-term monitored Indo-Pacific bottlenose dolphin (Tursiops aduncus). BMC Zoology, 11(1), Article 30. https://doi.org/10.1186/s40850-026-00277-z

Image Credits: AI Generated

DOI: 10.1186/s40850-026-00277-z

Keywords: marine mammal pathology, Indo-Pacific bottlenose dolphin, Tursiops aduncus, traumatic oral fibroma, mandibular fracture, Parvimonas micra, aspiration pneumonia, veterinary postmortem imaging, Jeju Island wildlife, halogenated organic contaminants, traumatic, oral