324 C. A. Madden Hof et al.
O’Connor et al., 2017). Native and feral predators include the red fox Vulpes vulpes, raccoon Procyon lotor and pig Sus scrofa. Strategies to reduce depredation of marine turtle eggs have been used with varying levels of success; e.g. predator control through shooting or baiting, deployment of exclusion devices (fencing, cages) and scent deterrents, and clutch relocation (Stancyk et al., 1980; Addison & Henricy, 1994; Addison, 1997; Ratnaswamy et al., 1997;Yerli et al., 1997; Blamires & Guinea, 2003; Baskale & Kaska, 2005; Norris et al., 2005; Kurz et al., 2011; Engeman et al., 2012; Lamarre-DeJesus & Griffin, 2013). However, there are few in situ studies examining the effectiveness of these strategies for loggerhead turtles (Schroeder, 1981; Macdonald et al., 1994;Yerli et al., 1997;O’Connor et al., 2017). WreckRock beach supports the second largest number of
loggerhead turtles nesting on the eastern Australian main- land, with c. 400 nests per season (Limpus, 2008). Clutch loss onWreck Rock beach results from two primary sources: storm surge erosion and flooding of nests, which varies widely between years (C.J. Limpus, 2017, pers. comm.), and depredation by goannas Varanus spp., which may now have the greatest impact on hatchling production at this beach (McLachlan et al., 2015). Historically, predation by feral foxes was a major threat, with predation levels reaching c. 90–95% of clutches laid prior to the mid 1980s (Limpus, 2008). A baiting programme was introduced in 1987 and led to the near-complete elimination of clutch pre- dation by foxes. Although clutch loss to native goannas was considered negligible historically, anecdotal evidence now suggests reduced fox numbers have shifted the balance of predator–prey interactions, resulting in increased goanna predation of turtle nests at Wreck Rock beach. Although goannas have long been known to consume marine turtle eggs (Marquez, 1990,p. 51), their predation rates on logger- head turtle clutches at Wreck Rock beach remained un- quantified (Lei & Booth, 2017a). In addition, there is a dearth of information on varanid ecology, behaviour and predation cues to develop effective goanna management strategies for this region. Here we report on the outcome of experiments that suc-
cessfully reduced goanna predation on loggerhead turtle clutches atWreckRock beach.We quantify goanna predation rates, provide an effective method to decrease predation and present alternative management interventions to reduce the threat of goanna predation on clutches, which can be applied widely at nesting beaches in northern Australia and globally.
Study area
The study site at Wreck Rock (Fig. 1) comprises 22 km of east-facing beaches from Broadwater Creek to Red Rock. The site lies at the southern end of the Great Barrier Reef Coast Marine Park (Queensland State Government) and Great Barrier Reef Marine Park (Commonwealth), situated
within and adjacent to various land tenure (Fig. 1). With a coastline exposed to onshore winds and largely unprotected by the reef, the coastal dunes are a naturally dynamic eco- system characterized by coastal scrubs, eucalypt woodlands, wet heaths and sedge lands. Delineated by camp and beach access points, Wreck Rock beach is divided into north and south beach sectors and marked every 100 m with timber pegs. Pegs on the north beach sector are numbered 0–65 and on the south beach sector 66–210. The north beach is located adjacent to Deepwater National Park. There are two public access campsites (Middle Rock and Wreck Rock) within the Park (Fig. 1).
Methods
Data collection The Wreck Rock Turtle Research Team, under the guid- ance of the Queensland Government’s Queensland Turtle Research Programme, has monitored the Wreck Rock beach study site for loggerhead turtle nesting activity for more than 40 years, since 1977. During the 2013–2014 nest- ing season (1 December 2013–12 March 2014), in addition to carrying out the standard nesting and hatchling emergence census for all turtle species (loggerhead, green Chelonia mydas and flatback Natator depressus turtles), we moni- tored predator activity at 57 experimental loggerhead turtle clutches (33 treatment and 24 control) daily. Following ovi- position, we marked each nest with flagging tape during the night patrol, and designated them for control or treatment plots (with an exclusion device installed at the latter) the following day. Treatment and control nests were spread throughout the study area to ensure sufficient representa- tion of both on the north (control = 14, treatment = 22) and south beaches (control = 10, treatment = 11; Fig. 1). It was not possible to place control and treatment plots randomly in space and time. We constructed predator exclusion devices, modelled
after those developed and deployed successfully on the Sunshine Coast (O’Connor et al., 2017), from interlocking aluminium mesh panels. We chose aluminium mesh be- cause it has been used successfully in previous studies and is unlikely to disrupt the hatchlings’ magnetic imprinting (Irwin & Lohmann, 2003). Each exclusion device (cage) consisted of a 1 m2 top panel and four side flaps of 20–25 cm width (Supplementary Plate 1). The mesh size of 70mmwas sufficiently large to allow hatchlings to emerge, but small enough to prevent access by varanid and mammalian predators. We placed predator exclusion devices at a depth of c. 20 cm below the sand surface over 33 treatment nests and left 24 control nests unprotected. We conducted predator activity surveys of the treatment
and control plots during daylight hours at low tide using a pro-forma datasheet. For reasons of practicality, data were
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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