Field monitoring and rescue
The severely injured SC, named “Hope” by the media in Hong Kong and hereafter referred to as WL212 (also known as SC15-16/01 in the Hong Kong cetacean stranding records managed by the Agriculture, Fisheries and Conservation Department of the Hong Kong Special Administrative Region Government), was first sighted in coastal waters near Tai O, Lantau Island, Hong Kong (22º15’N, 113º50’E) on 16th January 2015 by local cetacean researchers. Through established photo-identification catalogues, the individual was matched to a known individual (WL212) that had been repeatedly sighted in Hong Kong waters since 2012 [24]. Based on the body size and colour pattern, WL212 was classified as a subadult [25] (or as a “speckled” individual between juvenile and adult [26, 27]). Externally, WL212 suffered from four deep lacerations to the dorsal aspect of the caudal region (X1-X4; Fig. 1a), and the deepest wound was at the caudal peduncle with suspected underlying vertebral fractures. Continuous field monitoring of WL212 was carried out via collaboration between the Agriculture, Fisheries and Conservation Department of the Hong Kong Special Administrative Region Government, Ocean Park Conservation Foundation Hong Kong, and local cetacean research groups.
The dolphin was unable to use its fluke effectively and mostly dragged the tail fluke behind. Despite of this, it was able to evade approaching vessels by paddling with its pectoral flippers. Monitoring of the dolphin was also hindered by weather conditions and the limited visibility of the waters. However, it was observed that the body condition of WL212 deteriorated over a short time, and it became emaciated. The wounds gaped more and the soft tissues around X4 appeared more macerated and infected. WL212 started to display begging behaviours and began to accept fish offered by local fishermen and the rescue team. Over the three weeks of field monitoring, multiple rescue attempts were unsuccessful due to adverse weather, lack of expertise in dolphin capture, inadequate equipment, and logistical difficulties. On the third week, oral sedation using 80 mg diazepam (0.6 mg/kg) and 50 mg butorphanol (0.37 mg/kg) was mixed into fish and offered to WL212 during the sixth rescue attempt [28]. The dolphin was in a suitable location and sufficiently sedated three hours later and was captured from a vessel using a hoop net and swimmers. It was then placed in a stretcher and lifted onto the stern platform of the vessel for on-site assessment.
On-site assessment and decision-making
Immediate assessment of WL212 revealed that dolphin had four lacerations on the dorsal aspect and was severely emaciated (cachexia) because of the traumatic injuries and sepsis. In particular, the peduncle wound (X4) was the most severe, appeared gangrenous, and was foul smelling with exposed vertebrae that were also necrotic. Hence, the possibility of recovery after one-off medical treatment and immediate release was deemed impossible. Despite the severity of the peduncle wound, thermography and venipunctures revealed that the blood supply to the tail fluke was still present (Fig. 1b); therefore, there was no indications for immediate euthanasia. As the dolphin was unsuitable for immediate release, the attending veterinarians decided to transport WL212 back to medical facilities for further veterinary assessment, supportive medical care, and rehabilitation.
Veterinary interventions
Upon admission, antibiotic and analgesic medications were administered to WL212, including intramuscular injection of carprofen (2 mg/kg, Rimadyl®, Zoetis, MI, USA), cefovecin (8 mg/kg, Convenia®, Zoetis, MI, USA), and diazepam (0.22 mg/kg, ilium Diazepam®, Troy Animal Healthcare, Australia), and intravenous injection of ceftazidime (30 mg/kg, Sandoz®, Sandoz, Australia). The dolphin was also tube fed with 2.5 L of fluids and fish mash for rehydration and sustenance. Poolside radiography (Fig. 2a) revealed that several vertebral bodies at the peduncle wound were fractured and luxated, while all surrounding intervertebral disc spaces were collapsed. In addition, the spinous process of a caudal vertebra at X3 was also fractured. Consistent with the earlier thermography assessment, blood supply to the tail fluke was still present and it was possible to sample blood from all four major fluke vessels. Intravenous antibiotics were administered in the dorsal fin to avoid accidentally damaging the fluke vessels (phlebitis). Preliminary blood analysis showed a moderate leucocytosis (13,460 cells/µL), elevated fibrinogen (665 mg/dL), mildly elevated urea (22.1 mmol/L), and hyperglycaemia (10.2 mmol/L) based on comparisons to other cetacean species as there are no published reference ranges for SC. On gross examination, the dolphin had a near absence of blubber, chronic muscle wastage, and was severely underweight (135 kg) relative to its body size (233 cm). The prognosis for the animal was poor considering the severe traumatic injuries, chronic sepsis, and emaciation. The animal was placed in a pool with water 8 °C warmer than the winter waters (~ 14 °C) and with access to a warm water pipe delivering water at 28–30 °C (Fig. 2b).
Following initial medical treatment, WL212 was stable but still in critical condition. The demeanour and strength of the dolphin improved with hydration and warmer water. The soft tissues around the peduncle wound showed signs of improvement and under the influence of the anxiolytic (diazepam repeated every 8 h), the dolphin appeared settled and started to accept fish. However, radiographs had revealed the gravity and irreversibility of the lesions. On the third day in rehabilitation, blood tests showed severe leucocytosis (29,850 cells/µL). The dolphin began to vomit after feeding. As the frequency of vomiting increased over time, feeding was halted, and the dolphin was only provisioned with gavage fluids, as well as injectable antiemetics and antibiotics. On the following morning (10th February 2015), the dolphin’s condition had further deteriorated and was unable to stay afloat unassisted. Blood analysis revealed a significant decrease in total white blood cell count (from ~ 30,000 to 8,000 cells/µL), as well as severe electrolyte and biochemical derangements, including hypernatraemia (187 mmol/L), hyperkalaemia (7.08 mmol/L), hyperphosphataemia (4.25 mmol/L), hypoglycaemia (2.2 mmol/L), and uraemia (38.8 mmol/L). With these added signs of irreversible multiple organ failure, it was decided to humanely euthanise WL212 through intravenous lethal injection.
Postmortem examination
Within one hour of euthanasia, the carcass of WL212 was transported to a local veterinary imaging centre for the virtopsy examination using postmortem computed tomography and magnetic resonance imaging (PMCT and PMMRI). As part of the local cetacean stranding response programme, all retrieved stranding cases undergo routine PMCT scanning prior to conventional necropsy [29]. PMCT was performed in prone position using a Toshiba 16-row multi-slice spiral CT scanner Alexion™ (Toshiba Medical Systems, Tochigi, Japan) (Fig. 3a), with the following scan parameters: 120 kV, 80 mA, 1 mm slice thickness, and scan field of view of 390 mm. Subsequently, a focal examination of the peduncle area using PMMRI was performed with a 0.25 Tesla Esaote Vet-MR Grande scanner with a standard quadrature abdominal coil (Esaote, Genoa, Italy). The following MR sequences were performed: T1-weighted sagittal (18 slices, 3.5 mm thickness, TR 524.3 ms, TE 8.0 ms, reconstruction matrix of 768 × 768, and FOV of 449 mm) and T2-weighted sagittal (18 slices, 4 mm thickness, TR 3000 ms, TE 120 ms, reconstruction matrix of 1280 × 1280, and FOV of 450 mm). Both CT and MR scans were reconstructed in the TeraRecon Aquarius iNtuition workstation (TeraRecon, San Mateo, CA) and interpreted by a board-certified radiographer and imaging researcher with experiences in cetacean virtopsy (BCWK) alongside certified veterinarians (PRM, SMC). After virtopsy, the carcass was transported back to Ocean Park Hong Kong for a gross necropsy carried out by the attending veterinarians (PRM, SMC, NF, FKL).
PMCT of WL212 showed the four lacerations on the dorsal aspect from the lower lumbar region to caudal peduncle corresponding to earlier observations (Fig. 3b-d). The two wounds immediately caudal to the dorsal fin (X1 and X2) extended only into the blubber, whereas X3 severed the paraspinal muscles and fractured the spinous process of the 4th caudal vertebra. The wound at the caudal peduncle (X4) penetrated the vertebral column and caused open comminuted fractures of the 10th to 12th caudal vertebrae. Misalignment and misangulation of the caudal peduncle region were noted with some degree of adaptation. PMMRI was used for a more detailed assessment on X4 and the adjacent areas (Fig. 3e). Discontinuation of the spinal cord with complete closure of the spinal canal, as well as the open comminuted fracture at X4 was noted on PMMRI. There was also evidence of healing with the proliferation of granulation tissues around the fractured vertebrae and the spinal canal. Moderate fluid accumulation indicative of localised oedema and inflammation was also observed in the muscles ventral to the vertebral column. Aside from the traumatic injuries, PMCT revealed focal consolidation and diffuse ground-glass opacification patterns in both lungs, especially the left lung, and the presence of fluid in the pleural cavity (Fig. 4a), suggestive of pulmonary oedema and mild pleural effusion. Hyperattenuated content was noted in the stomach and compacted faecal content was seen in the intestines (Fig. 4b), with abnormal appearance of the intestinal lining across several sections of the intestines, indicating impaction and possible enteritis.
Detailed assessment upon gross necropsy showed that the peduncle wound (X4) had exposed the three fractured vertebral bodies and was the site of deep bone infections. The exposed soft tissues appeared macerated and secondarily infected. Granulation tissues was also present around the wound. The other three cut wounds (X1, X2, X3) measured 5 cm, 4 cm, and 12 cm in depth, respectively (Fig. 1c-1d). The individual was also confirmed to be sexually mature based on the presence of spermatozoa when examined microscopically (although in rare numbers likely due to chronic injuries). Histopathological assessment of the soft tissues at the peduncle wound revealed focally extensive acute inflammation with necrosis and haemorrhage, with fibroangiomatosis peripheral to the inflammation. Concurring with PMCT, pulmonary oedema was observed in both lungs, with reddish foam seen grossly and multifocal bronchoalveolar oedema and haemorrhage diagnosed microscopically. In the peritoneal cavity, inflammation was seen on the serosal surfaces of the omentum and the cranial portion of the small intestines. Undigested fish bones were found in the stomach chambers, while the distal small intestine and the proximal large intestine were filled with dehydrated and compacted faeces. Multifocal ulcers and haemorrhages of the mucosal surface were seen throughout the stomach chambers and small intestines, especially in the fundic stomach and duodenum, where severe and extensive gastroenteritis was also diagnosed microscopically. Other findings included generalised inflammation of the spleen, kidneys, and bladder. The severe traumatic injuries and the resulting chronic septicaemia and emaciation developed over weeks in the wild, led to the health conditions justifying the humane euthanasia of WL212. The attempted rehabilitation was further compromised by gastrointestinal complications and respiratory disease.