Chronic entanglement and fatal septicaemia in a juvenile bottlenose dolphin (Tursiops truncatus): animal welfare implications

Abstract

Case history: A juvenile bottlenose dolphin (Tursiops truncatus) was first observed among a group of approximately 12 dolphins on 10 December 2024, repeatedly breaching off Riverhead, Auckland, New Zealand. On subsequent observations, material consistent with fishing debris was seen entangled around the dorsal fin and tail flukes. While most conspecifics departed the area, a larger dolphin remained in close association with the entangled individual. The pair remained within the local area for at least 29 days prior to human intervention efforts to disentangle the animal. During the interim period, the entangled dolphin exhibited progressive deterioration in body condition and reduced activity compared with the free-swimming conspecific. The animal was found dead shortly thereafter. Pathological findings: Within 48 hours of death, post-mortem MRI and necropsy were conducted on the cadaver, which was scored as decomposition carcass code 1 (within rigor mortis). These identified an emaciated, sexually immature female bottlenose dolphin. Gross examination revealed severe, multifocal to coalescing lacerations and abrasions affecting the dorsal fin and caudal peduncle, with associated soft-tissue loss and irregular wound margins. Histologically, sections from the dorsal fin laceration showed evidence of severe, subacute to chronic, ulcerative necrosuppurative dermatitis with secondary bacterial infection. Pulmonary tissue samples revealed an acute, severe bacterial pneumonia characterised by neutrophilic infiltration and short bacilli. The liver and spleen showed findings of hepatitis and splenitis, suggestive of bacterial septicaemia. Swab isolates from these pooled tissues identified moderate growth of Erysipelothrix rhusiopathiae and Pseudomonas spp. Collectively, in vivo evidence and post-mortem gross and histopathological findings were consistent with poor body condition resulting from a progressive wasting disease primarily associated with chronic entanglement, leading to chronic active deep infectious necrosuppurative dermatitis and subsequent fatal bacterial septicaemia. Diagnosis: Bacterial septicaemia. Clinical relevance: This case highlights the importance of timely intervention in entanglement events to reduce the risk of secondary complications, including impaired foraging, progressive loss of body condition, and infection. Based on post-mortem findings, death was consistent with bacterial septicaemia in the context of a deep skin lesion to the dorsal fin caused by fishing gear and its subsequent pathological effects. From an animal welfare perspective, the prolonged duration of entanglement, progressive debilitation, and evidence of systemic wasting disease support a period of substantial and sustained welfare compromise prior to death. This incident would be classified as high-intensity, long-duration suffering.