High predation of marine turtle hatchlings near a coastal jetty

Growing human populations are driving the development of coastal infrastructure such as port facilities. Here, we used passive acoustic telemetry to examine the effects of a jetty and artificial light on the rates of predation of flatback turtle (Natator depressus) hatchlings as they disperse through nearshore waters. When released near a jetty, around 70% of the tagged hatchlings were predated before they could transit the nearshore, irrespective of the presence or absence of artificial light. Only 3 to 23% of hatchlings encountered predators at a second study site nearby where there was no jetty and a similar amount of nesting activity. Evidence for predation was provided by rapid tag detachment due to prey handling by a predator or the extensive movement of the tags within the receiver array suggesting that the tag (and hatchling) was inside the stomach of a predator. We found that 70% of the fish predators that consumed tags used the jetty as a refuge during the day and expanded their range along nearshore waters at night, predating on hatchlings in areas adjacent to the jetty with the highest nesting density. Sampling of potential predators including lutjanid reef fishes under the jetty revealed the presence of turtle hatchlings in their gut contents. By providing daytime refuges for predators, nearshore structures such as jetties have the potential to concentrate predators and they may pose a significant threat to populations of vulnerable species. Such effects must be taken into consideration when assessing the environmental impacts associated with these structures.