Protecting nests of the Critically Endangered South Pacific loggerhead turtle Caretta caretta from goanna Varanus spp. predation
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Protecting nests of the Critically Endangered South
Pacific loggerhead turtle Caretta caretta from goanna
Varanus spp. predation
CHRISTINE A. MADDEN HOF, GABRIELA SHUSTER, NEV MCLACHLAN
BEV M C L A C H L A N , S A R A N N E G I U D I C E , C O L I N L I M P U S and T O M O H A R U E G U C H I
Abstract The South Pacific subpopulation of the loggerhead Supplementary material for this article is available at
turtle Caretta caretta is categorized as Critically Endangered https://doi.org/./S
on the IUCN Red List because of significant population de-
clines. Five Queensland beaches support high-density nesting
of this subpopulation, but egg and hatchling survival are low
Introduction
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,
at Wreck Rock beach, one of the turtle’s major nesting bea-
T here is one genetic subpopulation for the loggerhead
turtle Caretta caretta in the South Pacific Ocean
(Bowen et al., ; Limpus et al., ; Boyle et al., )
ches. In addition, we conducted an experiment to determine and most breeding females from this subpopulation nest on
the efficacy of a nest protection device. Predation rates at beaches in eastern Australia and New Caledonia (Limpus &
Wreck Rock beach were .% for treatment and .% for Limpus, ; Limpus, ). Post-hatchlings emerging at
non-treatment clutches during the – nesting season. these beaches undertake trans-Pacific migrations to the
A higher probability of predation (%) was predicted for the west coast of South America, reaching the coastal waters
northern beach. Although nests were only partially predated of Peru and Chile (Kelez et al., ; Boyle et al., ;
(.% of the total number of eggs), nest loss to predators and Donoso & Dutton, ; Alfaro-Shigueto et al., ).
beach erosion (caused by a cyclone) was .%. If left unman- Along the east coast of Australia, sandy beaches in Queens-
aged, the cumulative impact of predation and other threats, land support the majority of nesting, with c. % occurring
including those exacerbated by climate change, can cause at five beaches: Wreck Island, Woongarra Coast, Tryon
unsustainable loss of loggerhead turtle nests. This study Island, Erskine Island and Wreck Rock (Limpus, ;
provides one of the first quantitative data sets on rates of Limpus & Casale, ).
loggerhead turtle clutch predation in the South Pacific. It Despite its protected status and several decades of
enhances our understanding of goanna predation impacts conservation effort, particularly in Queensland, the South
and identifies an efficient predator exclusion device for Pacific subpopulation of the loggerhead turtle continues to
mitigating the effects of terrestrial predators at Wreck Rock decline (Limpus et al., ; Limpus & Casale, ) and was
beach, and for protecting marine turtle nests across northern categorized as Critically Endangered on the IUCN Red List
Australia and globally. in (Limpus & Casale, ). In recent years, although
Keywords Automated cameras, Caretta caretta, eastern the number of nesting loggerhead turtles has been increas-
Australia, feasibility study, goanna predation, loggerhead ing (Limpus et al., ), the escalated mortality of post-
turtle, predator exclusion device, Varanus hatchlings from synthetic debris ingestion in the first
few months after leaving the nesting beaches (Boyle &
Limpus, ) and bycatch mortality of large post-
hatchlings caught in long-line fisheries in Peru and Chile
CHRISTINE A. MADDEN HOF (Corresponding author) and GABRIELA SHUSTER World
Wide Fund for Nature Australia, Level 1, 17 Burnett Lane, Brisbane, QLD 4000,
(Donoso & Dutton, ; Alfaro-Shigueto et al., ) have
Australia. E-mail chof@wwf.org.au hampered population recovery.
NEV MCLACHLAN and BEV MCLACHLAN TurtleCare Volunteers Queensland Inc., In this context, reducing mortality from other causes at
Buderim, Australia nesting beaches could support population growth. Such
SARANNE GIUDICE Burnett Mary Regional Group for Natural Resource causes include the predation of eggs and hatchlings by
Management, Bundaberg, Australia introduced and native predators, the hatchling loss asso-
COLIN LIMPUS Queensland Department of Environment and Science, Brisbane, ciated with light pollution, and beach degradation caused
Australia
by anthropogenic and natural events (Limpus, ; Berry
TOMOHARU EGUCHI Marine Mammal and Turtle Division, Southwest Fisheries et al., ; Limpus & Casale, ).
Science Center, National Marine Fisheries Service, National Oceanic and
Atmospheric Administration, La Jolla, USA Increasing hatchling production by reducing clutch pre-
Received August . Revision requested October . dation is a recommended and common practice for marine
Accepted December . First published online November . turtles (Mroziak et al., ; Engeman et al., , ;
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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. https://doi.org/10.1017/S0030605318001564324 C. A. Madden Hof et al.
O’Connor et al., ). Native and feral predators include within and adjacent to various land tenure (Fig. ). With a
the red fox Vulpes vulpes, raccoon Procyon lotor and pig coastline exposed to onshore winds and largely unprotected
Sus scrofa. Strategies to reduce depredation of marine turtle by the reef, the coastal dunes are a naturally dynamic eco-
eggs have been used with varying levels of success; e.g. system characterized by coastal scrubs, eucalypt woodlands,
predator control through shooting or baiting, deployment wet heaths and sedge lands. Delineated by camp and beach
of exclusion devices (fencing, cages) and scent deterrents, access points, Wreck Rock beach is divided into north and
and clutch relocation (Stancyk et al., ; Addison & south beach sectors and marked every m with timber
Henricy, ; Addison, ; Ratnaswamy et al., ; Yerli pegs. Pegs on the north beach sector are numbered –
et al., ; Blamires & Guinea, ; Baskale & Kaska, ; and on the south beach sector –. The north beach is
Norris et al., ; Kurz et al., ; Engeman et al., ; located adjacent to Deepwater National Park. There are
Lamarre-DeJesus & Griffin, ). However, there are few two public access campsites (Middle Rock and Wreck
in situ studies examining the effectiveness of these strategies Rock) within the Park (Fig. ).
for loggerhead turtles (Schroeder, ; Macdonald et al.,
; Yerli et al., ; O’Connor et al., ). Methods
Wreck Rock beach supports the second largest number of
loggerhead turtles nesting on the eastern Australian main- Data collection
land, with c. nests per season (Limpus, ). Clutch
loss on Wreck Rock beach results from two primary sources: The Wreck Rock Turtle Research Team, under the guid-
storm surge erosion and flooding of nests, which varies ance of the Queensland Government’s Queensland Turtle
widely between years (C.J. Limpus, , pers. comm.), Research Programme, has monitored the Wreck Rock
and depredation by goannas Varanus spp., which may beach study site for loggerhead turtle nesting activity for
now have the greatest impact on hatchling production at more than years, since . During the – nest-
this beach (McLachlan et al., ). Historically, predation ing season ( December – March ), in addition to
by feral foxes was a major threat, with predation levels carrying out the standard nesting and hatchling emergence
reaching c. –% of clutches laid prior to the mid s census for all turtle species (loggerhead, green Chelonia
(Limpus, ). A baiting programme was introduced in mydas and flatback Natator depressus turtles), we moni-
and led to the near-complete elimination of clutch pre- tored predator activity at experimental loggerhead turtle
dation by foxes. Although clutch loss to native goannas was clutches ( treatment and control) daily. Following ovi-
considered negligible historically, anecdotal evidence now position, we marked each nest with flagging tape during the
suggests reduced fox numbers have shifted the balance of night patrol, and designated them for control or treatment
predator–prey interactions, resulting in increased goanna plots (with an exclusion device installed at the latter) the
predation of turtle nests at Wreck Rock beach. Although following day. Treatment and control nests were spread
goannas have long been known to consume marine turtle throughout the study area to ensure sufficient representa-
eggs (Marquez, , p. ), their predation rates on logger- tion of both on the north (control = , treatment = )
head turtle clutches at Wreck Rock beach remained un- and south beaches (control = , treatment = ; Fig. ). It
quantified (Lei & Booth, a). In addition, there is a was not possible to place control and treatment plots
dearth of information on varanid ecology, behaviour and randomly in space and time.
predation cues to develop effective goanna management We constructed predator exclusion devices, modelled
strategies for this region. after those developed and deployed successfully on the
Here we report on the outcome of experiments that suc- Sunshine Coast (O’Connor et al., ), from interlocking
cessfully reduced goanna predation on loggerhead turtle aluminium mesh panels. We chose aluminium mesh be-
clutches at Wreck Rock beach. We quantify goanna predation cause it has been used successfully in previous studies and
rates, provide an effective method to decrease predation and is unlikely to disrupt the hatchlings’ magnetic imprinting
present alternative management interventions to reduce the (Irwin & Lohmann, ). Each exclusion device (cage)
threat of goanna predation on clutches, which can be applied consisted of a m top panel and four side flaps of – cm
widely at nesting beaches in northern Australia and globally. width (Supplementary Plate ). The mesh size of mm was
sufficiently large to allow hatchlings to emerge, but small
Study area enough to prevent access by varanid and mammalian
predators. We placed predator exclusion devices at a
The study site at Wreck Rock (Fig. ) comprises km of depth of c. cm below the sand surface over treatment
east-facing beaches from Broadwater Creek to Red Rock. nests and left control nests unprotected.
The site lies at the southern end of the Great Barrier Reef We conducted predator activity surveys of the treatment
Coast Marine Park (Queensland State Government) and and control plots during daylight hours at low tide using a
Great Barrier Reef Marine Park (Commonwealth), situated 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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. https://doi.org/10.1017/S0030605318001564Protecting loggerhead turtle nests 325
recorded within a . cm (total length of the measuring
tape used) radius from each marked nest centre as a stand-
ard measure and distance of likely plot predation. We
collected the following data: sand disturbance or predator
tracks (species identified as goanna, fox, dog, ghost crab);
attempted predation (holes had been dug but no empty egg
shells were found); predation: holes dug, number of empty
egg shells (if greater than half a shell) and number of un-
developed or unhatched eggs on sand surface; and the dis-
tance between the nest centre and the egg remains farthest
away from it. After recording the data, we manually re-
moved signs of predator activity using footwear, so as to
minimize human scent at the nest site.
In addition, we monitored nests ( treatment and two
control nests) for predator activity throughout the incuba-
tion period, using infrared wildlife motion-sensor cameras
(Reconyx Hyperfire HC, Reconyx, Holmen, USA).
Cameras were secured onto timber marker posts using bun-
gee cords and positioned to aim at the centre of each nest.
The cameras recorded ambient air temperatures and still
images whenever movement was detected. If a camera-
monitored nest was destroyed by predators, we moved the
camera to another nest. We identified species that visited
the clutches from the recorded camera images. Goannas
were not individually identified and we assumed a new
visitation event after s of no recording.
We excavated the clutches when the hatchlings emerged,
or after days of incubation, to determine hatching suc-
cess. We calculated hatching success using data from the
unpredated clutches and the following equation:
Hatching success = (no. of empty shells)/(no. of un-
hatched eggs + no. of undeveloped eggs + no. of empty
shells). We then used the median hatching success to esti-
mate the total hatchling production of the beach throughout
the nesting season.
Statistical analysis
We calculated clutch loss as the proportion of clutches lost
to all causes (predation and erosion) out of the total number
of control clutches. Predation rates were computed as the
proportion of clutches lost to predation out of the total
number of control clutches. Nest monitoring was inter-
rupted during January– February because a cyclone
made landfall nearby. Therefore, we calculated loss of nests
FIG. 1 Study site at Wreck Rock beach, land tenure and location in two distinct periods: before (quantified predation rate)
of camp sites. Markers pegs – are on the north beach and and after (quantified predation + cyclone-caused nest loss)
– on the south beach. C and D indicate the numbers of the cyclone event.
control and treatment (deployment of a predator exclusion
To determine the effectiveness of the exclusion devices
device) loggerhead turtle Caretta caretta clutches, respectively,
on a stretch of beach between the marker pegs shown. The size on loggerhead turtle clutches, we considered five logistic re-
of the circles represents the total nesting activity, including gression models, using three predictor variables: days since
failed nesting attempts, per year on the respective beach the beginning of the experiment (Days), location of the nests
stretches. measured by the peg numbers (Location), and treatment
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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with a predator exclusion device (Treatment; Table ). We % CI = .–.%) than after the cyclone (.%, of
compared models using the Akaike information criterion control plots depredated; % CI = .–.%). The major-
(AIC; Akaike, ). Using the best model from the analysis ity of predation of control nests occurred on the northern
on the effectiveness of the treatment, we predicted the prob- beach (/ = %; % CI = .–.%).
ability of predation at all observed nest locations along the Exclusion devices appeared to be effective in reducing
entire beach. clutch predation. With exclusion devices deployed at
To determine whether the exclusion device delayed pre- nests, only one hatchling became entrapped during emer-
dation, we compared the mean number of days from laying gence. Compared with the control plots ( of control
to predation between control and treatment plots using a nests; .%; % CI = .–.%), fewer treatment plots
Bayesian t test. We hypothesized that the mean number of were depredated during the nesting season ( of treatment
days between laying and predation would be greater for the nests; .%; % CI = .–.%). The point estimate of pre-
treatment plots than for the control plots. dation with exclusion devices was % (/; % CI = .–
To estimate the total number of hatchlings on the entire .%) prior to the cyclone, and % (/; % CI = .–
beach, we used a parametric bootstrap procedure. For all .%) after the cyclone. Although the point estimate was
observed clutches at the nesting beach, we estimated the greater for the treatment plots than control (.% vs
probability of predation using the logistic regression models. .%), the binomial % CI overlapped (.–.% vs .–
The median nest size and median hatching success rate were .%). Because of the large uncertainties associated with
used to compute the total number of hatchlings for the small sample sizes, they were not statistically different.
unpredated nests. We repeated this process , times to Amongst the models used to determine the effects of the
obtain the uncertainty in the estimate from the predation exclusion device on the predation of loggerhead turtle
probability. clutches, Model had the smallest AIC value, although dif-
We conducted all statistical analyses in R .. (R Core ferences in AIC values between the top models were , ,
Team, ) with packages ggplot (Wickham, ) and indicating that these models were not substantially different
gamm (Wood & Scheipl, ). Bayesian computations (Table ). In the following analyses, we use the best model,
were conducted using jags .. (Plummer, ) through which included treatment, location, and their interactions.
rjags (Plummer, ) in R. The interaction term was significant at α = . (Table ),
indicating that the effectiveness of the treatment varied sig-
nificantly along the beach. This can be seen in Fig. , where
Results the predicted probability of predation decreases with in-
creasing peg number (i.e. from north to south along the
During the – nesting season ( December –
beach) for the control plots, but increases for the treatment
March ) we recorded loggerhead, green and
clutches. However, because of the small sample sizes in the
flatback turtles laying one or more clutches at Wreck Rock
area farthest from the field station, on the south beach,
beach (Supplementary Table ). Of the loggerhead turtles,
confidence intervals are wide in this area. For the area
were new recruits and were recaptures from previous
with larger sample sizes, on the north beach, the predicted
nesting seasons. During the nesting season, we recorded
probability of predation was smaller for the treatment than
loggerhead nesting activities, with successful nests and
for the control plots.
failed attempts. Of the successful nesting events,
The main effect of the exclusion device was also signifi-
clutches were laid on the north and on the south beach.
cant at α = . (Table ), indicating that the devices signifi-
We used of the successfully laid nests in our study,
cantly reduced the predation of loggerhead turtle clutches.
deployed exclusion devices on treatment clutches and
This is supported by the percentage of predated clutches
used as control. During the study, plots (eight treat-
in control vs treatment plots (. vs .%, respectively).
ment and controls) were lost to erosion when cyclone
Dylan made landfall near Wreck Rock beach on
January .
Hatching success
Clutch loss The mean clutch size was . ± SE . (n = ; median )
and the mean hatching success was . ± SE .
During the – season, of control clutches were (n = ; median .). Using the most parsimonious logis-
depredated (mean = .%, % CI = .–.%), an add- tic regression model (Model ) from the previous analysis,
itional were lost to erosion. In total, clutch loss to preda- we predicted the probability of predation at all observed nest
tors and erosion events (exacerbated by a cyclone) was .% locations; i.e. extrapolated to the entire beach (Fig. ). Using
(% CI = .–.%). The predation rate was greater prior the probability of predation, median hatching success,
to the cyclone (.%, of control plots depredated; median clutch size, and a parametric bootstrap analysis,
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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TABLE 1 Logistic regression models used to determine the effective- TABLE 2 Estimated linear model coefficients of the best-performing
ness of predator exclusion devices on loggerhead turtle Caretta ca- model (Model ), with standard deviations and P values.
retta clutches, showing predictor variables and difference in Akaike The model was Predation * Intercept + Treatment + Location +
information criterion values from best-performing model (ΔAIC). Treatment × Location.
Model Variables1 ΔAIC Parameter Estimate P
Model 4 Treatment × Location 0.00 (Intercept) −1.40 ± SE 0.38 0.00
Model 3 Treatment 0.57 Treatment −0.64 ± SE 0.37 0.08
Model 2 Treatment + Location 1.22 Location −0.16 ± SE 0.41 0.70
Model 1 Treatment + Location + Days 3.12 Treatment:Location 0.71 ± SE 0.40 0.08
Model 5 Treatment × Days 4.45
Days, days since the beginning of the experiment; Location, location of
the nests measured by the peg numbers along the beach; Treatment, clutch on emerging hatchlings at Wreck Rock beach. On several
treatment with a predator exclusion device. occasions we observed predation on nests adjacent to
control plots (i.e. on nests not included in this study).
We recorded goanna visitation events to logger-
we estimated the total number of hatchlings produced at
head turtle nests monitored by automated cameras. The
Wreck Rock beach during the nesting season to be ,
yellow spotted monitor was found most frequently (
with a % CI of ,–, (Supplementary Fig. ).
recorded visits) followed by the lace monitor ( visits). Of
Some loggerhead turtle clutches were only partially pre-
the monitored clutches, were visited multiple times by
dated. Although sample sizes were small, the mean number
the same species on occasions ( times by yellow spotted
of predated eggs per nest was c. ± SE . (.%, n = ).
monitors and times by lace monitors). The remaining
Undeveloped eggs (unhatched eggs with no obvious em-
four nests were visited once by one goanna species, and at
bryo) also accounted for % of the total eggs in nests.
two of these nests the second species continued to visit
The Bayesian equivalent of a two-sampled t test
multiple times after the first species had visited.
indicated there was no significant difference in the tim-
Ambient air temperature during goanna visits to the
ing of predation between treatment and control nests
clutches was – °C. We found differences between the
(Supplementary Fig. ). Further, the % posterior interval
mean temperatures at visits by the two goanna species and
(Gelman et al., ) of the contrast coefficient (control vs
other species (birds and mammals; Supplementary Fig. )
treatment effects) included zero (−., .). For both
Lace monitors visited turtle nests at a lower ambient tem-
control and treatments, however, predation seemed to
perature (mean = . ± SE . °C, n = ) than yellow
occur either in the early or late stages of incubation
spotted monitors (. ± SE . °C, n = ).
(Supplementary Fig. ).
Predation Discussion
With individual cameras operating for – days, the total As the South Pacific loggerhead turtle subpopulation con-
camera-trapping time was , hours over a period of tinues to decline, it requires renewed attention to decrease
days. Species recorded by automatic cameras included mortality at all life history stages. Nest predation by terres-
hares Lepus sp., kites Milvus sp., cats Felis sp., foxes trial predators may significantly reduce recruitment and
Vulpes sp., emus Dromaius sp., pied butcherbirds Cracticus could lead to additional declines in the already depleted
nigrogularis and wallabies Macropus sp. The two species population (CMS, ). This study provides new infor-
of goannas recorded near turtle nests were the yellow mation about goanna depredation and demonstrates that
spotted or Argus monitor Varanus panoptes and the lace exclusion devices effectively reduce predation. We also pro-
monitor Varanus varius (A. Amey, , pers. comm.). A vide a recent estimate of the predation rate on loggerhead
third goanna Varanus gouldii may be present, but the turtle clutches at a major nesting beach in the South
species identification could not be confirmed. As expected, Pacific.
goanna activity tended to occur during daylight hours The predation rate of loggerhead turtle clutches (.%)
(.–.). at Wreck Rock beach was lower than that reported at
Based on tracks, predation at both treatment and control other nesting beaches. For example, % of flatback turtle
plots was carried out by goannas, with only one incidence of clutches were predated at Fog Bay (Blamires, ; Blamires
fox predation recorded, at a treatment plot. On one occa- & Guinea, ), –% of flatback turtle clutches at
sion, more than six goannas were observed predating on Pennefather beach (J. Doherty and Cape York Peninsula
loggerhead turtle hatchlings as they emerged from a nest. Development Association, unpubl. data in Whytlaw et al.,
This was the first recorded observation of goanna predation ), –% of green and loggerhead turtle clutches in
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FIG. 2 Predicted probability of loggerhead turtle nest predation FIG. 3 Predicted predation probabilities with respect to beach
as a function of location on the beach and control vs predator marker pegs (location) and time since the beginning of the
exclusion device treatment. Shaded areas correspond to % experiment (days). The size of the points corresponds to the
confidence intervals. probabilities.
Turkey (Macdonald et al., ), and –% of loggerhead Repos (mean % loss of entire clutches from natural causes,
turtle clutches in North America (Stancyk et al., ; range .–.%; Limpus, ), clutches are regularly
Engeman et al., ). During the – and – lost to natural erosion and flooding at Wreck Rock beach
nesting seasons at Wreck Rock beach, Lei & Booth (N. McLachlan, unpubl. data). These events will continue
(a) reported .% and .% of clutches predated by to be exacerbated with severe cyclones, floods and storms
goannas, respectively. However, their study was confined to predicted to increase in frequency with climate change
a -km stretch of beach, whereas we monitored the entire (IPCC, ). During the study, a natural tide storm surge
-km stretch. The difference in results may be a result of and wind additionally exposed turtle nests to predation and
this spatial difference in sampling effort and the heterogen- increased the total number of clutches lost. This loss was
eity of predation across a rookery (Blamires, ). It is also greater for the treatment nests, probably because the exclu-
possible that predation is temporally variable because of sion devices provided visual cues for the predators. In add-
fluctuations in predator and prey density. ition, hatchlings are affected by light pollution associated
In recent years, as also evidenced in Lei & Booth (a), with coastal development. Overall, Wreck Rock beach
goannas have been the primary predators of turtle eggs and grossly exceeds a sustainable level of annual clutch loss of
hatchlings at Wreck Rock beach. For the first time, we ob- c. % (CMS, ). Consequently, it is important to
served predation of hatchlings by multiple goannas. Foxes develop ongoing predator management (cognizant of the
are now minor predators of loggerhead turtle clutches, pre- threat posed by extreme weather events) as this may be the
sumably the result of the long-term fox baiting programme. only threat that can be addressed effectively in a timeframe
Yellow spotted and lace monitors were the most promi- that allows the population to recover.
nent visitors to turtle nests at the study site. A third species, The deployment of exclusion devices, although effective,
Varanus gouldii, is frequently found in close proximity to may not be feasible for nesting beaches with moderate to
yellow spotted monitors (Shine, ; A. Amey, , pers. high turtle numbers (e.g. . turtles per night). Devices
comm.) but further studies are needed to confirm its may impede nesting attempts (Kurz et al., ), and re-
presence. sources are often limited (Lei & Booth, b; Lei et al.,
In this study, the aluminium cage predator exclusion ). A suite of alternative predator control methods
devices were effective in reducing predation of loggerhead (some of which are already being applied at Wreck Rock
turtle nests at Wreck Rock beach. With only one entrapped beach) should be included in future studies to develop a con-
hatchling amongst cage deployments, the devices were servation strategy considerate of the main predator species,
deemed successful for reducing predation and letting habitat and climatic conditions, and budgetary and logistical
hatchlings pass through. The same conclusion was also constraints. Additional types of predator exclusion devices
reached by Lei & Booth (b) in subsequent years. that could be deployed include plastic mesh nest protectors
Given Wreck Rock beach is predicted to produce c. , (Lei & Booth, b) and flat chain link screening or less
hatchlings per season, the use of these anti-predator devices rigid wire mesh cages, if not disruptive to hatchlings
should result in increased hatchling production. magnetic imprinting (Addison & Henricy, ; Addison,
The loss of clutches observed in this study (from preda- ). The application of scent deterrents such as habanero
tion and other causes combined) was .%, which is a cause powder (see Ratnaswamy et al., ; Lamarre-DeJesus &
for concern. Historically only quantified for beaches at Mon Griffin, ; Lei et al., ), human scent (see Burke
Oryx, 2020, 54(3), 323–331 © 2019 Fauna & Flora International doi:10.1017/S0030605318001564
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. https://doi.org/10.1017/S0030605318001564Protecting loggerhead turtle nests 329
et al., ), visual disturbance (such as flags, see Burke could uncover vital information regarding the timing of pre-
et al., ), or the use of pheromones (goanna’s own or dation (Ferreira, ; Welicky et al., ), repeated visi-
other species such as cane toads) may be effective in deterring tation by predators, and complete (Limpus, ) vs partial
goannas. Nest relocation (including into hatcheries) should clutch loss (Chatto & Baker, ). For example, further re-
only be trialled as a last resort because it could reduce hatch- search could provide insights into why control clutches were
ling imprinting and success (see Kornaraki et al., ). predated less than anticipated, and why nests not included
Culling of goannas to protect turtle nests is not viable as in this study but directly adjacent to control plots were also
they are protected in Australia. Coastal populations of the predated (as per the simulation in Blamires & Guinea,
yellow spotted monitor may be the species’ last stronghold, ). Although the lace monitor was not previously con-
as many inland populations have declined as a result of sidered a predator of turtle eggs, this species accounted for
a toxic diet of cane toads (Ujvari & Madsen, ; Shine, more than one-third of total predation and visited turtle
). Because the species is not categorized as threatened nests at a lower temperature than the yellow spotted moni-
on the IUCN Red List, Lei & Booth (b; Lei et al., ) tor ( vs °C, respectively).
suggest the temporary removal of male yellow spotted Until further studies are undertaken, interim manage-
monitors (the primary predators of turtle eggs) during the ment is recommended particularly for the north beach.
turtle nesting season. However, given the monitor’s eco- Camp site usage and waste management should be reviewed
logical role as a mesopredator, resource managers must as a priority to reduce goanna activity in this area. This
first understand the local predator–prey interactions and could be achieved with relatively little effort through educa-
the ecosystem-level effects of any predator control method tion and enforcement. Future site-specific management is
selected (Prugh et al., ; Welicky et al., ). Studies on necessary to maximize hatchling success. The exclusion
the raccoon Procyon lotor, another mesopredator that tar- devices deployed in this study are effective in reducing
gets marine turtle clutches, showed its removal had no effect depredation on marine turtle nesting beaches, but are not
on mainland clutch depredation (Ratnaswamy et al., ; cost-effective for Wreck Rock beach because of high nest-
Barton & Roth, ). Tsellarius et al. () suggested ing numbers and limited resources. An alternative predator
goannas scent-mark territorial boundaries to keep strangers control programme should be explored, to provide the
out and control local population sizes, so the removal of in- most efficient allocation of resources and management. This
dividual goannas from a local populations could potentially will be the most robust strategy to maximize hatchling
lead to an increase in goanna numbers. production and thus contribute to future recruitment of
Goanna predation and nest selectivity is probably dri- the declining and Critically Endangered South Pacific subpo-
ven by olfactory and visual cues and influenced by spatial pulation of the loggerhead turtle.
and temporal nest deposition (Blamires & Guinea, ;
Blamires, ; Welicky et al., ), proximity to urbanized Acknowledgements We thank the volunteers of TurtleCare’s
Wreck Rock Turtle Research Team and the Gidarjil Aboriginal
areas (Smith & Engeman, ; Blamires & Guinea, ; Corporation for their assistance with field work; and Kirsten Wortel
Prange et al., ) and human and goanna conspecific and the Burnett Mary Regional Group (BMRG) for assistance with
activity (Ferreira, ). In contrast to Welicky et al. (), mapping. We acknowledge funding from WWF-Australia and BMRG.
predation risk in this study was more probable on the
north beach in areas heavily utilized by humans, with Author contributions Study design: all authors; data collection:
CAMH, GS, NM, BM, SG; data analysis: CAMH, GS, TE; writing:
campsites and food waste. This raises the question of why CAMH; revisions: all authors.
goannas have become more abundant at Wreck Rock beach
(they were considered uncommon in the s; C. Limpus, Conflicts of interest None.
, pers. comm.) and what drives their behaviour. It is
possible that the control of apex predators (dingoes and Ethical standards This research abided by the Oryx guidelines on
ethical standards. Research protocols for this study were approved by
foxes) has altered predator–prey relationships and reduced
an authorised ethics committee (SA 2015/11/531) and authority under
competition for goannas. This, together with increased the Nature Conservation Act 1994.
human activity and camp site waste (particularly on the
north beach), could have increased food availability for
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