Predation on sea turtles at sea: A multi-source synthesis and research perspectives

Predation is a key ecological process shaping sea turtle populations, yet - unlike predation of eggs, hatchlings and adults on nesting beaches - its role at sea remains poorly quantified due to observational challenges. This study synthesizes multiple, rarely integrated data sources-including unpublished data-to examine global patterns of sea turtle predation at sea. Sources include field observations (turtles found stranded, nesting, admitted to rescue centers, or captured in-water for research), literature records, predator diet data, and non-conventional online sources (NCS; images and videos). A literature review compiled 206 report/predator/turtle species/turtle life stage/area combinations involving all seven extant sea turtle species and 51 predator species. Although predators span several taxa (including teleost fishes, crocodilians, and mammals), most reports involve a few shark species. To estimate predation rates, we analysed 156,726 turtle records (dead or alive), of which 5,107 individuals (3.3%) showed evidence of shark-bite injuries. These rates varied significantly among species, size classes, regions, and over time. Stomach content analysis of 3,927 sharks from 12 species identified turtle remains only in tiger and white sharks, with tiger sharks emerging as the dominant predator. NCS yielded 34 shark-turtle interactions, 73% of which were videos that offered rare insights into sea turtle defensive behaviours such as dorsal shielding, rapid manoeuvring, fleeing, and even counterattacks. Together, these multiple approaches provide complementary insights and highlight the dominant role of large sharks, particularly tiger sharks, in sea turtle predation. However, current knowledge is largely confined to predation in neritic waters because of the inherent difficulties of studying this topic in oceanic environments. Predation on small juveniles and in oceanic waters remains the most significant knowledge gap due to the likelihood of whole-body ingestion and occurrence in oceanic habitats. Tracking such early life stages may become feasible with advances in tag miniaturization. Meanwhile, visible shark-bite injuries on large turtles-if adequately standardized-represent a promising tool for monitoring spatial and temporal trends in predation pressure on large turtles in coastal waters. With improved data collection, analytical methods, and citizen science contributions through NCS, we can begin to address critical knowledge gaps in the at-sea predation ecology of sea turtles.