Prey-inflicted interactions in aquatic ecosystems: a framework to quantify body marking patterns on marine fauna with a case study on the white shark (Carcharodon carcharias) in Atlantic Canada.

Context: Predator-prey interactions are fundamental ecological processes that expose both predators and prey to risks of injury or mortality. However, the ecological costs of these interactions are difficult to assess in marine systems where direct observations are challenging. Body marking analysis, which uses distinctive markings from injurious animal interactions, offers a means to examine their occurrence, frequency, timing and possible causes. However, the absence of standardized approaches limits meaningful comparisons across studies. Aims: This study aimed to (i) develop a standardized framework for classifying and quantifying external markings on marine animals and (ii) evaluate its utility by examining prey-inflicted markings on white sharks (Carcharodon carcharias) in Atlantic Canada. Methods: A literature review of body markings on marine animals was conducted to derive a systematic approach for classifying markings. The framework was tested using photographs of white sharks taken underwater with Baited Remote Underwater Video (BRUV) and above-water when sharks were lifted out during tagging procedures. Observed markings were cross-referenced with scientific literature to determine likely species interacting with focal study animal (i.e., white shark), approximate time since interaction (i.e., recent or old), and nature of interactions using location on the body (i.e., head wounds suggesting hunting/feeding). Key Results: Analysis of 14 white sharks (photographed underwater, n = 6; above-water, n = 8) identified four distinct markings categories, two from interactions with grey seals (Halichoerus grypus) or harbour seals (Phoca vitulina; claw and bite marks) and two of unknown origins (serious, and unidentified markings). Claw marks, present on all individuals, primarily on the dorsal head regions, comprised over 90% of recorded markings and increased in frequency with shark size. Furthermore, open claw marks, observed only on photographs taken above-water, suggested recent encounters with seals. Conclusions: The framework derived here indicated that interactions between white sharks and seals are common, providing a baseline for future research on pinniped-white shark dynamics in Atlantic Canada. Implications: This study provides a framework that future research can use to standardize marking assessments in marine animals, promoting greater consistency and comparability across studies and advancing our understanding of ecological interactions across species and ecosystems.