Fatal systemic bacterial infections in two harbour porpoises (Phocoena phocoena) secondary to bite wounds from grey seals (Halichoerus grypus).

Mycoplasma phocicerebrale, the causative agent of seal ('speck') finger, a zoonotic disease, is a common commensal in the oral cavity of various seal species. Historically associated with seal hunters, it remains a significant risk for those handling or rehabilitating marine mammals. While primarily known for causing severe cellulitis in humans, M. phocicerebrale can also lead to severe infections in seals, including osteomyelitis and sepsis. Recent studies have revealed the predatory behaviour of grey seals (Halichoerus grypus) on harbour porpoises (Phocoena phocoena). Examination of scarring patterns on stranded animals suggest that some initial predation attempts are unsuccessful, and porpoises escape only to succumb to infection originating from bite wounds. Here we describe two cases in which the isolation of M. phocicerebrale and other bacterial species from chronically infected bite wounds, the lungs and other internal organs of harbour porpoises suggest failed predation attempts by grey seals. Therefore, the impact of delayed, indirect mortality from sympatric predation attempts may be a significant additional and underestimated cause of mortality in harbour porpoises. One of the cases examined in this study involved a harbour porpoise with gross and histological evidence of a failed predation attempt and a fatal systemic M. phocicerebrale infection. These findings highlight the severe consequences of such infections and underscore the importance of understanding the ecological implications of grey seal predation on harbour porpoise populations.