The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The declining health of the world’s coral reefs and tropical seas is adding pressure to vulnerable marine fauna. To guide mitigation efforts, understanding the complex dynamics of marine communities has become a top priority, particularly trophic interactions involving threatened or endangered species. Being slower and more conspicuous swimmers than most reef fishes, sea turtle hatchlings would presumably be a more accessible food source for the underwater predators.  In a unique case study at one of Malaysia’s most productive turtle nesting sites (Chagar Hutang Turtle Sanctuary (CHTS), Redang Island) we investigated the occurrence and abundance of large predator fishes and their trophic interaction with the sea turtle hatchlings via field observation and stable isotope analysis approach. We hypothesized that large predators such as sharks and groupers would hunt on hatchlings during the turtle nesting season and, when available, may favour turtle hatchlings over alternative prey. Predation by the blacktip reef sharks Carcharhinus melanopterus and the grouper Epinephelus quoyanus on sea turtle hatchlings in Chagar Hutang bay were discovered during the fieldwork. One juvenile of blacktip reef sharks fed exclusively up to eight sea turtle hatchlings, while one individual grouper fed exclusively up to two hatchlings.  Based on the stable isotope analysis δ¹³C and δ¹⁵N, the mixing model suggested that the hatchlings become the main diet to the sharks and grouper primarily during the peak nesting season. The present study provides valuable insights on the trophic dynamics of the underwater predators, as it combines direct field observations with stable isotope analysis, providing a more comprehensive picture of the predators' dietary preferences during the peak turtle nesting season. The findings emphasize the critical role that large predatory fishes play in shaping the survival rates of sea turtle hatchlings, which in turn can affect the long-term viability of turtle populations at Chagar Hutang Bay, one of Malaysia's key nesting sites.
 

prey-predator, trophic ecology, marine conservation, stable isotopes, sharks, sea turtles, groupers