Queensland Department of Environment and Science, Brisbane, Queensland, Australia.
Biopixel Oceans Foundation, James Cook University, Smithfield, Queensland, Australia.
PLoS One. 2020 Jun 4;15(6):e0228524. doi: 10.1371/journal.pone.0228524. eCollection 2020.
Nester abundance is a key measure of the performance of the world's largest green turtle rookery at Raine Island, Australia, and has been estimated by mark-resight counts since 1984. Nesters are first marked by painting their carapace with a longitudinal white stripe. Painted and unpainted turtles are then counted by a surface observer on a small boat in waters adjacent to the reef. Unmanned aerial vehicles (UAV) and underwater video may provide more cost-effective and less biased alternatives to this approach, but estimates must be comparable with historical estimates. Here we compare and evaluate the three methods. We found comparatively little variation in resighting probabilities between consecutive days of sampling or time of day, which supports an underlying assumption of the method (i.e. demographic closure during sampling). This lack of bias in the location availability for detection of painted versus unpainted turtles and further supported by a parallel satellite tracking study of 40 turtles at Raine Island. Our results demonstrated that surface observers consistently reported higher proportions of marked turtles than either the UAV or underwater video method. This in turn yielded higher population estimates with UAV or underwater video compared to the historical surface observer method, which suggested correction factors of 1.53 and 1.73 respectively. We attributed this to observer search error because a white marked turtle is easier to spot than the non-marked turtle. In contrast, the UAV and underwater video methods allowed subsequent frame-by-frame review, thus reducing observer search error. UAVs were the most efficient in terms of survey time, personnel commitment and weather tolerance compared to the other methods. However, underwater video may also be a useful alternative for in-water mark-resight surveys of turtles.
巢区丰度是衡量澳大利亚雷岛（Raine Island）世界上最大的绿海龟筑巢地表现的关键指标，自 1984 年以来，一直通过标记重见计数进行估计。巢区筑巢者首先通过在龟甲上绘制一条纵向的白色条纹来标记。然后，在靠近珊瑚礁的水面上，一艘小船的水面观察员对已标记和未标记的海龟进行计数。无人机（UAV）和水下视频可能提供更具成本效益且偏差更小的替代方法，但估算结果必须与历史估算值可比。在这里，我们比较和评估了这三种方法。我们发现，在连续几天的采样或一天中的不同时间，重见概率之间的变化相对较小，这支持了该方法的一个基本假设（即在采样期间存在人口封闭）。这种对已标记和未标记海龟的检测位置可用性的偏差很小，并且进一步得到了对雷岛 40 只海龟的平行卫星跟踪研究的支持。我们的结果表明，水面观察员一致报告标记海龟的比例高于无人机或水下视频方法，这反过来又导致使用无人机或水下视频的种群估算值高于历史上的水面观察员方法，这表明分别需要 1.53 和 1.73 的校正因子。我们将其归因于观测者搜索错误，因为白色标记的海龟比未标记的海龟更容易被发现。相比之下，无人机和水下视频方法允许随后逐帧审查，从而减少了观测者搜索错误。与其他方法相比，无人机在调查时间、人员投入和天气容忍度方面效率最高。然而，水下视频也可能是海龟水标记重见调查的有用替代方法。
