Offshore Dispersal and Predation of Sea Turtle Hatchlings I: A Study of Hawksbill Turtles at Chagar Hutang Turtle Sanctuary, Malaysia

Abstract

Sea turtle hatchlings emerge from underground nests at night, rapidly crawling seaward to swim off shore. Once in the water, hatchlings might experience high predation rates while in shallow water before reaching deeper water where encounters with predators, and consequently mortality rates, likely decline. Behavioral studies have described different swimming strategies used by hatchlings to counter nearshore predation. Coastal and oceanographic conditions are also likely to influence dispersal away from near shore to the open ocean. This study assessed predation rates of Hawksbill Turtle (Eretmochelys imbricata) hatchlings as they dispersed from shore at Chagar Hutang Bay, Malaysia and the role surface currents play in the transport of hatchlings off shore in the nearshore environment. An acoustic doppler current profiler was used to measure surface currents, and direct observations of hatchlings swimming off shore were made from a kayak using GPS loggers to track hatchling swimming paths. Six of the 31 hatchlings tracked (19.4%) were predated, most within 50 m of shore, indicating that predators are more abundant in shallower areas of the bay where a coralline-rocky bottom predominates. Survival tended to be greater under dark conditions when moonlight was absent or minimal. We quantified the relative importance of the tidal current in a hatchling's offshore swim, and found that in most cases, tidal surface currents assisted the offshore movement of Hawksbill hatchlings as they dispersed from the beach. These findings provide a better understanding of how sea turtle hatchling dispersal is affected by predation, moonlight, and physical oceanographic conditions at Chagar Hutang Turtle Sanctuary.