Protecting loggerhead turtle nests 325
recorded within a 152.4 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 12 nests (10 treatment and two
control nests) for predator activity throughout the incuba- tion period, using infrared wildlife motion-sensor cameras (Reconyx Hyperfire HC600, 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 60 s of no recording. We excavated the clutches when the hatchlings emerged,
or after 60 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
FIG. 1 Study site at Wreck Rock beach, land tenure and location of camp sites. Markers pegs 0–65 are on the north beach and 66–210 on the south beach. C and D indicate the numbers of control and treatment (deployment of a predator exclusion device) loggerhead turtle Caretta caretta clutches, respectively, on a stretch of beach between the marker pegs shown. The size of the circles represents the total nesting activity, including failed nesting attempts, per year on the respective beach stretches.
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 26 January–7 February 2014 because a cyclone made landfall nearby. Therefore, we calculated loss of nests in two distinct periods: before (quantified predation rate) and after (quantified predation + cyclone-caused nest loss) the cyclone event. To determine the effectiveness of the exclusion devices
on loggerhead turtle clutches, we considered five logistic re- gression models, using three predictor variables: days since the beginning of the experiment (Days), location of the nests 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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