Protecting loggerhead turtle nests 329
et al., 2005), visual disturbance (such as flags, see Burke et al., 2005), or the use of pheromones (goanna’s own or other species such as cane toads)may be effective in deterring goannas. Nest relocation (including into hatcheries) should only be trialled as a last resort because it could reduce hatch- ling imprinting and success (see Kornaraki et al., 2006). Culling of goannas to protect turtle nests is not viable as
they are protected in Australia. Coastal populations of the yellow spotted monitor may be the species’ last stronghold, as many inland populations have declined as a result of a toxic diet of cane toads (Ujvari & Madsen, 2009; Shine, 2010). Because the species is not categorized as threatened on the IUCN Red List, Lei & Booth (2017b; Lei et al., 2017) suggest the temporary removal of male yellow spotted monitors (the primary predators of turtle eggs) during the turtle nesting season. However, given the monitor’s eco- logical role as a mesopredator, resource managers must first understand the local predator–prey interactions and the ecosystem-level effects of any predator control method selected (Prugh et al., 2009;Welicky et al., 2012). Studies on the raccoon Procyon lotor, another mesopredator that tar- gets marine turtle clutches, showed its removal had no effect on mainland clutch depredation (Ratnaswamy et al., 1997; Barton & Roth, 2007). Tsellarius et al. (2011) suggested goannas scent-mark territorial boundaries to keep strangers out and control local population sizes, so the removal of in- dividual goannas from a local populations could potentially lead to an increase in goanna numbers. Goanna predation and nest selectivity is probably dri-
ven by olfactory and visual cues and influenced by spatial and temporal nest deposition (Blamires & Guinea, 2003; Blamires, 2004;Welicky et al., 2012), proximity to urbanized areas (Smith & Engeman, 2002; Blamires & Guinea, 2003; Prange et al., 2004) and human and goanna conspecific activity (Ferreira, 2012). In contrast to Welicky et al. (2012), predation risk in this study was more probable on the north beach in areas heavily utilized by humans, with campsites and food waste. This raises the question of why goannas have become more abundant atWreck Rock beach (they were considered uncommon in the 1970s; C. Limpus, 2017, pers. comm.) and what drives their behaviour. It is possible that the control of apex predators (dingoes and foxes) has altered predator–prey relationships and reduced competition for goannas. This, together with increased human activity and camp site waste (particularly on the north beach), could have increased food availability for goannas, supporting them in greater numbers (Prugh et al., 2009). Research with a focus on goanna ecology and loggerhead
turtle clutch predation could improve management inter- ventions for Wreck Rock beach. Such studies should include research into the biology and behaviour of goannas, exam- ination of long-term predation effects and human impacts on predator behaviour. An examination of clutch predation
could uncover vital information regarding the timing of pre- dation (Ferreira, 2012; Welicky et al., 2012), repeated visi- tation by predators, and complete (Limpus, 1971) vs partial clutch loss (Chatto & Baker, 2008). For example, further re- search could provide insights into why control clutcheswere predated less than anticipated, and why nests not included in this study but directly adjacent to control plots were also predated (as per the simulation in Blamires & Guinea, 2003). Although the lace monitor was not previously con- sidered a predator of turtle eggs, this species accounted for more than one-third of total predation and visited turtle nests at a lower temperature than the yellow spotted moni- tor (33 vs 37 °C, respectively). Until further studies are undertaken, interim manage-
ment is recommended particularly for the north beach. Camp site usage and waste management should be reviewed as a priority to reduce goanna activity in this area. This could be achieved with relatively little effort through educa- tion and enforcement. Future site-specific management is necessary to maximize hatchling success. The exclusion devices deployed in this study are effective in reducing depredation on marine turtle nesting beaches, but are not cost-effective for Wreck Rock beach because of high nest- ing numbers and limited resources. An alternative predator control programme should be explored, to provide the most efficient allocation of resources and management. This will be the most robust strategy to maximize hatchling production and thus contribute to future recruitment of the declining and Critically Endangered South Pacific subpo- pulation of the loggerhead turtle.
Acknowledgements We thank the volunteers of TurtleCare’s Wreck Rock Turtle Research Team and the Gidarjil Aboriginal Corporation for their assistance with field work; and Kirsten Wortel and the Burnett Mary Regional Group (BMRG) for assistance with mapping. Weacknowledge funding from WWF-Australia and BMRG.
Author contributions Study design: all authors; data collection: CAMH, GS, NM, BM, SG; data analysis: CAMH, GS, TE; writing: CAMH; revisions: all authors.
Conflicts of interest None.
Ethical standards This research abided by the Oryx guidelines on ethical standards. Research protocols for this study were approved by an authorised ethics committee (SA 2015/11/531) and authority under the Nature Conservation Act 1994.
References
ADDISON, D.S. (1997) Galvanized wire cages can protect nest depredation. Marine Turtle Newsletter, 76, 8–11.
ADDISON, D.S.&HENRICY,S. (1994) A comparison of galvanized wire mesh cages vs flat chain-link screen in preventing Procyon lotor depredation of Caretta caretta nests. NOAA Technical Memorandum, 351, 174.
AKAIKE,H. (1974) A new look at the statistical model identification. IEEE Transactions on Automatic Control, 19, 716–723.
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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