An evaluation of nest predator impacts and the efficacy of plastic meshing on marine turtle nests on the western Cape York Peninsula, Australia

Eric J Nordberg,Stewart Macdonald,Gina Zimny,Andrew Hoskins,Anders Zimny,Ruchira Somaweera,Janine Ferguson,Justin Perry

doi:10.1016/j.biocon.2019.108201

Abstract

Nest predation is considered to be one of the most significant biotic threats to marine turtle populations globally. The introduction of feral predators to nesting beaches has dramatically increased nest predation, reaching near total egg loss in some regions. We monitored a 48 km stretch of beach along western Cape York Peninsula, Australia, from June – November 2018. We recorded a total of 360 nests comprising 117 flatback and 243 olive ridley nests. We installed plastic meshing (90 cm × 100 cm) on 110 olive ridley nests (45.2% of total olive ridley clutches laid) within the study area. We classified all nest predation attempts into three categories: complete, partial, or failed predation events. In total, 109 (30.2%) of all marine turtle nests were depredated by a variety of predators, including feral pigs, dingoes, goannas, and humans. The addition of plastic meshing reduced the likelihood of dingoes gaining access to eggs, but not goannas or feral pigs. Further, we found no difference in the proportion of hatchling emergence between meshed and un-meshed nests. Additionally, while hatchling emergence was reduced in nests that had been partially depredated, these nests still produced live hatchlings and contributed to recruitment. The success of particular predator control methods is often predator, and/or regionally, specific. Our findings highlight a thorough understanding of predator guilds and their relative impacts is required to deploy targeted and predator-specific strategies to maximize conservation results. We present a strong case for data-driven adaptive management that has implications for designing optimal predator management plans.

Highlights

Marine turtles face a series of threats globally
This study was conducted along a 48 km stretch of coastline between the Love and Kirk Rivers managed by the Aak Puul Ngantam (APN) Aboriginal ranger group, located approximately 30 km southwest of Aurukun, on the west coast of Cape York Peninsula, Queensland, Australia (Fig. 1)
Predation events showed little pattern in their spatial distribution; goanna and dingo predation was evenly distributed along the beach, predation by humans was centered around an indigenous traditional owner camp in the middle of the beach, and predation by feral pigs was clustered in the northern stretches of the beach near a large freshwater wetland

Summary

Introduction

Marine turtles face a series of threats globally. Their populations suffer from pressures both on land and at sea, ranging from pollution (Eckert, 1995; Lazar and Gračan, 2011), fisheries bycatch (Hall et al, 2000; Pandav et al, 1997), and challenges from rising sea water, including nest inundation, and lack of suitable nesting beaches due to erosion or beach habitat loss (Fish et al, 2005; Fuentes et al, 2010; Whytlaw et al, 2013). Excessive predation rates from native and feral animals (Davis and Whiting, 1977; Whytlaw et al, 2013) lead to reduced recruitment and population declines (Engeman et al, 2003; Hamann et al, 2010; Stancyke, 1982). While native animals have sustainably harvested turtle nests for thousands of years, turtle populations are at risk due to a lack of recruitment as a result of additional predation pressure from feral animals among other threats (Limpus, 2008; Whytlaw et al, 2013). In Australia, feral red foxes (Vulpes vulpes) and feral pigs (Sus scrufa) are responsible for high levels of predation, exceeding 90% nest predation in some regions prior to predator control or nest protection programs (Limpus et al, 1993; Limpus, 2008; Whytlaw et al, 2013)

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