328 C. A. Madden Hof et al.
FIG. 2 Predicted probability of loggerhead turtle nest predation as a function of location on the beach and control vs predator exclusion device treatment. Shaded areas correspond to 95% confidence intervals.
Turkey (Macdonald et al., 1994), and 67–95% of loggerhead turtle clutches in North America (Stancyk et al., 1980; Engeman et al., 2003). During the 2014–2015 and 2015– 2016 nesting seasons at Wreck Rock beach, Lei & Booth (2017a) reported 57.7% and 17.4% of clutches predated by goannas, respectively. However, their study was confined to a 6-km stretch of beach, whereas we monitored the entire 22-km stretch. The difference in results may be a result of this spatial difference in sampling effort and the heterogen- eity of predation across a rookery (Blamires, 1999). It is also possible that predation is temporally variable because of fluctuations in predator and prey density. In recent years, as also evidenced in Lei & Booth (2017a),
goannas have been the primary predators of turtle eggs and hatchlings at Wreck Rock beach. For the first time, we ob- served predation of hatchlings by multiple goannas. Foxes are now minor predators of loggerhead turtle clutches, pre- sumably the result of the long-term fox baiting programme. Yellow spotted and lace monitors were the most promi- nent visitors to turtle nests at the study site. A third species, Varanus gouldii, is frequently found in close proximity to yellow spotted monitors (Shine, 1986;
A.Amey, 2014, pers. comm.) but further studies are needed to confirm its presence. In this study, the aluminium cage predator exclusion
devices were effective in reducing predation of loggerhead turtle nests at Wreck Rock beach. With only one entrapped hatchling amongst 33 cage deployments, the devices were deemed successful for reducing predation and letting hatchlings pass through. The same conclusion was also reached by Lei & Booth (2017b) in subsequent years. Given Wreck Rock beach is predicted to produce c. 12,000 hatchlings per season, the use of these anti-predator devices should result in increased hatchling production. The loss of clutches observed in this study (from preda-
tion and other causes combined) was 91.7%, which is a cause for concern. Historically only quantified for beaches at Mon
FIG. 3 Predicted predation probabilities with respect to beach marker pegs (location) and time since the beginning of the experiment (days). The size of the points corresponds to the probabilities.
Repos (mean 13%loss of entire clutches from natural causes, range 8.4–83.0%; Limpus, 2008), clutches are regularly lost to natural erosion and flooding at Wreck Rock beach (N. McLachlan, unpubl. data). These events will continue to be exacerbated with severe cyclones, floods and storms predicted to increase in frequency with climate change (IPCC, 2007). During the study, a natural tide storm surge and wind additionally exposed turtle nests to predation and increased the total number of clutches lost. This loss was greater for the treatment nests, probably because the exclu- sion devices provided visual cues for the predators. In add- ition, hatchlings are affected by light pollution associated with coastal development. Overall, Wreck Rock beach grossly exceeds a sustainable level of annual clutch loss of c. 30%(CMS, 2014). Consequently, it is important to develop ongoing predator management (cognizant of the threat posed by extreme weather events) as this may be the only threat that can be addressed effectively in a timeframe that allows the population to recover. The deployment of exclusion devices, although effective,
may not be feasible for nesting beaches with moderate to high turtle numbers (e.g. .20 turtles per night). Devices may impede nesting attempts (Kurz et al., 2011), and re- sources are often limited (Lei & Booth, 2017b; Lei et al., 2017). A suite of alternative predator control methods (some of which are already being applied at Wreck Rock beach) should be included in future studies to develop a con- servation strategy considerate of the main predator species, habitat and climatic conditions, and budgetary and logistical constraints. Additional types of predator exclusion devices that could be deployed include plastic mesh nest protectors (Lei & Booth, 2017b) and flat chain link screening or less rigid wire mesh cages, if not disruptive to hatchlings magnetic imprinting (Addison & Henricy, 1994; Addison, 1997). The application of scent deterrents such as habanero powder (see Ratnaswamy et al., 1997; Lamarre-DeJesus & Griffin, 2013; Lei et al., 2017), human scent (see Burke
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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