Protecting nests of the Critically Endangered South Pacific loggerhead turtle Caretta caretta fromgoanna Varanus spp. predation CHRI S TIN E A. MADDEN HOF,GAB R I EL A SHUSTER,NEV MCLACHLAN


BEV MCLACHLAN,S AR A N NE GIUDICE,COL IN L IMPUS and TOMOHARU EGUCHI


Abstract The South Pacific subpopulation of the loggerhead turtle Caretta caretta is categorized as Critically Endangered on the IUCN Red List because of significant population de- clines. FiveQueensland beaches support high-density nesting of this subpopulation, but egg and hatchling survival are low at some beaches because of feral and native terrestrial preda- tors. We quantified predation of loggerhead turtle eggs by two species of goanna, Varanus panoptes and Varanus varius, atWreck Rock beach, one of the turtle’s major nesting bea- ches. In addition, we conducted an experiment to determine the efficacy of a nest protection device. Predation rates at Wreck Rock beach were 15.2% for treatment and 45.8%for non-treatment clutches during the 2013–2014 nesting season. Ahigher probability of predation (64%)was predicted for the northern beach. Although nests were only partially predated (16.4%of the total number of eggs), nest loss to predators and beach erosion (caused by a cyclone)was 91.7%. If left unman- aged, the cumulative impact of predation and other threats, including those exacerbated by climate change, can cause unsustainable loss of loggerhead turtle nests. This study provides one of the first quantitative data sets on rates of loggerhead turtle clutch predation in the South Pacific. It enhances our understanding of goanna predation impacts and identifies an efficient predator exclusion device for mitigating the effects of terrestrial predators at Wreck Rock beach, and for protectingmarine turtle nests across northern Australia and globally.


Keywords Automated cameras, Caretta caretta, eastern Australia, feasibility study, goanna predation, loggerhead turtle, predator exclusion device, Varanus


CHRISTINE A.MADDENHOF (Corresponding author) andGABRIELA SHUSTER World Wide Fund for Nature Australia, Level 1, 17 Burnett Lane, Brisbane, QLD 4000, Australia. E-mail chof@wwf.org.au


NEV MCLACHLAN and BEV MCLACHLAN TurtleCare Volunteers Queensland Inc., Buderim, Australia


SARANNE GIUDICE Burnett Mary Regional Group for Natural Resource Management, Bundaberg, Australia


COLIN LIMPUS Queensland Department of Environment and Science, Brisbane, Australia


TOMOHARU EGUCHI Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, USA


Received 28 August 2018. Revision requested 16 October 2018. Accepted 20 December 2018. First published online 29 November 2019.


Supplementary material for this article is available at https://doi.org/10.1017/S0030605318001564


Introduction


(Bowen et al., 1994; Limpus et al., 2006; Boyle et al., 2009) and most breeding females from this subpopulation nest on beaches in eastern Australia and New Caledonia (Limpus & Limpus, 2003; Limpus, 2008). Post-hatchlings emerging at these beaches undertake trans-Pacific migrations to the west coast of South America, reaching the coastal waters of Peru and Chile (Kelez et al., 2005; Boyle et al., 2009; Donoso & Dutton, 2010; Alfaro-Shigueto et al., 2011). Along the east coast of Australia, sandy beaches in Queens- land support the majority of nesting, with c. 80% occurring at five beaches: Wreck Island, Woongarra Coast, Tryon Island, Erskine Island and Wreck Rock (Limpus, 2008; Limpus & Casale, 2015). Despite its protected status and several decades of conservation effort, particularly in Queensland, the South Pacific subpopulation of the loggerhead turtle continues to decline (Limpus et al., 2013; Limpus &Casale, 2015) and was categorized as Critically Endangered on the IUCN Red List in 2015 (Limpus & Casale, 2015). In recent years, although the number of nesting loggerhead turtles has been increas- ing (Limpus et al., 2013), the escalated mortality of post- hatchlings from synthetic debris ingestion in the first few months after leaving the nesting beaches (Boyle & Limpus, 2008) and bycatch mortality of large post- hatchlings caught in long-line fisheries in Peru and Chile (Donoso & Dutton, 2010; Alfaro-Shigueto et al., 2011) have hampered population recovery. In this context, reducing mortality from other causes at


T


nesting beaches could support population growth. Such causes include the predation of eggs and hatchlings by introduced and native predators, the hatchling loss asso- ciated with light pollution, and beach degradation caused by anthropogenic and natural events (Limpus, 2008; Berry et al., 2013; Limpus & Casale, 2015). Increasing hatchling production by reducing clutch pre-


dation is a recommended and common practice for marine turtles (Mroziak et al., 2000; Engeman et al., 2003, 2006;


Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564


here is one genetic subpopulation for the loggerhead turtle Caretta caretta in the South Pacific Ocean


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