Symmetry: the key to diagnosing propeller strike injuries in sea mammals

Abstract

The fresh carcass of a neonatal Indo-Pacific bottlenose dolphin (Tursiops aduncus) was recovered from a suburban beach near Adelaide, South Australia, by officers of the Australian Marine Wildlife Research and Rescue Organisation (AMWRO). The carcass was incomplete with loss of the tail and three deep parallel incised/chop wounds to the torso and tail (Fig. 1). At necropsy the carcass was that of an otherwise healthy Indo-Pacific bottlenose dolphin neonate of around 1–2 weeks of age. The animal was normally formed and well nourished, with milk in its mouth and stomach indicating that recent breast feeding had occurred. Frothy white foam was present in the upper airway. The most significant findings consisted of a series of four curvilinear parallel incised/chop wounds predominately to the right side of the body (Fig. 2). The most rostral injury was a clean incised wound of the upper back and right side of the chest which shelved into paraspinal muscles (Fig. 3). No major vessels had been damaged and the chest cavity had not been opened. Within the chest cavity, however, the deepest part of the chop wound was associated with fracture-dislocation of the midthoracic spine (Fig. 4) with spinal cord transaction. There were also fractures of the posterior aspects of the first to sixth ribs on the right side with fresh paravertebal soft tissue hemorrhage bilaterally. Thoracic organs and vessels were intact. Fifty-nine centimeters caudal to this was a second incised/chop wound which passed from the right side through the anterior aspect of the dorsal fin (Figs. 1, 2). Although no body cavities or major vessels had been opened the wound shelved caudally with fracturing of the underlying spine and adjacent fresh interstitial hemorrhage. Caudal to this was a deep curved incised wound that also shelved caudally and extended into paravertebral muscles with a chopping injury to the lateral aspect of the vertebral bodies, with underlying fractures. The final injury consisted of amputation of the tail (Fig. 5). There were no congenital defects, underlying organic diseases or parasitic infestations identified that could have caused or contributed to death. Death was, therefore, due to multiple incised/chop wounds typical of boat propeller injuries with subsequent exsanguination. Amputation of the tail and transaction of the mid thoracic spinal cord would have also have prevented the animal from swimming.