How to Reduce the Risk of Predation of Green Turtle Nests by Nile Monitors

Abstract. Predation of nests and hatchlings can significantly reduce sea turtle reproductive output. On Cavalos island, João Vieira and Poilão Marine National Park, Bijagos archipelago, Guinea-Bissau, one of the primary threats to green turtle nests is predation by Nile monitors (Varanus niloticus). In this study, we tested 3 different nest protection techniques—disguising scent cues, disguising visual cues, and placing a metal net over the nest—to reduce predation on green turtle (Chelonia mydas) nests by Nile monitors. Nests were monitored for 10 d after they were laid, and we found that using metal nets and disguising scent cues led to a significant increase of the number of days it took for Nile monitors to find and predate the nests. Overall reduction in predation rates also approached significance when metal nets or disguising scent cues were used. We used the Risk Reduction metric to compare the effectiveness of our experiment with other nest protection techniques; our results corresponded to a > 50% decrease in the risk of predation, a value comparable to or better than other techniques used elsewhere. We suggest that camouflaging a nest's scent may be the most cost-efficient management option to reduce predation rates by Nile monitors in sensitive areas without damaging the local ecosystem.