Unusual Mortality of Pinnipeds in the United Kingdom Associated with Helical (Corkscrew) Injuries of Anthropogenic Origin

Between June 2008 and December 2010, 76 dead pinnipeds were found on the coast of the United Kingdom with peculiar injuries consisting of a single continuous curvilinear skin laceration spiralling down the body. The skin and blubber had been sheared from the underlying fascia and, in many cases, the scapula also had been avulsed from the thoracic wall. Although previously unreported in the UK, similar distinctive lesions had been described in Canadian pinnipeds where they were referred to as corkscrew injuries. In the UK, identical injuries were seen in both native species of pinniped, with 43 harbor seals (Phoca vitulina) (57%) and 26 grey seals (Halichoerus grypus) (34%) affected, and seven carcasses (9%) for which the species could not be determined. There were two apparent seasonal peaks in incidence; predominantly adult harbor seals were discovered during the summer and juvenile grey seals during the winter. Postmortem examinations of 20 harbor seals revealed they had been alive and healthy when the injuries were sustained, with no evidence of any underlying disease or disability. Based on the pathological findings, it was concluded that mortality was caused by a sudden traumatic event involving a strong rotational shearing force. The injuries were consistent with the animals being drawn through the ducted propellers of marine vessels and, in some cases, there was a direct correlation with the presence of work boats operating in the vicinity. This challenges the conclusions of a previous study in Canada that suggested natural predation by Greenland sharks (Somniosus microcephalus) was likely to be responsible for these injuries.