Forensic determination of shark species as predators and scavengers of sea turtles in Florida and Alabama, USA

Abstract

Sharks are the primary predator of large immature and mature sea turtles, yet the shark species responsible for both lethal and non-lethal injuries are rarely identified. Forensic analysis of bite wounds can be used to accurately assess size and potential shark species when combined with observations on species-specific feeding behavior, geographic distribution, and habitat preference. The objective of this study was to use forensic analysis of bite damage on sea turtles to infer shark size and species. Photographs from 13 cases of documented shark predation (n = 10) and scavenging (n = 3) attempts on sea turtles were retrospectively analyzed, including nesting, free-ranging, and/or dead stranded loggerhead Caretta caretta, green Chelonia mydas, Kemp’s ridley Lepidochelys kempii, and leatherback Dermochelys coriacea sea turtles in Florida and Alabama, USA, from 2010-2020. Mean interdental distance (IDD) and bite circumference (BC) of wound marks on sea turtles suggest that wounds were generated by white sharks Carcharodon carcharias in 3 cases, tiger sharks Galeocerdo cuvier in 3 cases, and bull shark(s) Carcharhinus leucas in one case. For 3 cases with less distinct wound patterns, 2 likely shark species were identified and thereafter narrowed down to a single species based on bite mark characteristics (e.g. punctures). Due to indistinct IDD and BC ranges of the bite patterns, a single shark species was not identified in 3 cases. Forensic analysis enables more accurate evaluations of which shark species prey on and scavenge sea turtles and is a useful technique for studying the behavioral interactions of sharks and turtles.