Scavenging versus predation: shark-bite injuries in stranded sea turtles in the southeastern USA

Abstract

Injuries inflicted by sharks are a frequent observation in stranded sea turtles. Sharks prey on live turtles and scavenge carcasses, which can create uncertainty as to the cause of stranding when sea turtles are found dead with shark-bite wounds. Consequently, attributing the cause of stranding to a shark attack based purely on the presence of the characteristic wounds can overestimate predation by sharks as a cause of mortality. To better characterize the timing of shark-bite wounds relative to death of sea turtles in the southeastern USA, we performed necropsies on 70 stranded turtles that were found dead in which the predominant observation was bite wounds without any grossly evident vital responses (inflammation or healing). Postmortem examination included assessment for evidence of exsanguination and histopathological evaluation of skeletal muscle comprising wound margins. We characterized wounds as antemortem, perimortem, or postmortem based on specific criteria related to the presence or absence of supravital and intravital responses. Most (80%) shark-bite wounds were postmortem, 10% were antemortem, and 10% were perimortem. We found that antemortem and postmortem wounds were similar in extent and location except for wounds that primarily involved the shell, which were never found in cases of scavenging. For sea turtles found dead in the southeastern USA, our findings suggest that most shark-bite wounds without externally evident vital responses are due to scavenging. Additionally, this scavenging can significantly damage a carcass, potentially obscuring the detection of other causes of mortality. These findings should be considered when using data derived from stranded sea turtles to conduct mortality assessments.