Artificial light on water attracts turtle hatchlings during their nearshore transit, Western Australia

Examined the effect of artificial light on the nearshore trajectories of turtle hatchlings dispersing from natal beaches. Green turtle (Chelonia mydas) hatchlings were tagged with miniature acoustic transmitters and their movements tracked within an underwater array of 36 acoustic receivers placed in the nearshore zone. A total of 40 hatchlings were tracked, 20 of which were subjected to artificial light during their transit of the array. At the same time, we measured current speed and direction which were highly variable within and between experimental nights and treatments. Artificial lighting affected hatchling behaviour, with 88% of individual trajectories oriented towards the light and spending, on average, 23% more time in the 2.25ha tracking array (19.5 ± 5 mins) than under ambient light conditions (15.8 ± 5 mins). Current speed had little to no effect on the bearing (angular direction) of the hatchling tracks when artificial light was present, but under ambient conditions, it influenced the bearing of the tracks when current direction was offshore and above speeds of ~32.5 cm s-1. This is the first experimental evidence that wild turtle hatchlings are attracted to artificial light after entering the ocean, a behaviour that is likely to subject them to greater risk of predation. The experimental protocol described in this study can be used to assess the effect of anthropogenic (light pollution, noise etc.) and natural (wave action, current, wind, moonlight) influences on the in-water movements of sea turtle hatchlings during the early phase of dispersal.

本研究探究了人工光照对从筑巢海滩（natal beach）孵化后扩散的海龟幼龟近岸运动轨迹的影响。研究对象为绿海龟（Chelonia mydas）幼龟，其被搭载微型声学发射器（acoustic transmitter），并通过布设于近岸海域的36台声学接收器（acoustic receiver）组成的水下阵列追踪其活动；总计追踪了40只幼龟，其中20只在穿越该阵列的过程中接受了人工光照处理。与此同时，本研究同步测量了海流流速与流向，实验夜间及不同处理组间的海流条件均存在高度变异性。研究结果显示，人工光照会显著影响幼龟的行为：88%的个体轨迹朝向光源方向，且其在2.25公顷的追踪阵列内的平均停留时间为19.5±5分钟，相较于自然光条件下的15.8±5分钟，平均多出23%。当存在人工光照时，海流流速对幼龟轨迹的方位（角向）几乎无影响；但在自然光条件下，当海流流向为离岸方向且流速高于约32.5 cm·s⁻¹时，海流会显著影响幼龟轨迹的方位。本研究首次通过实验证实，野生海龟幼龟进入海洋后会被人工光源吸引，该行为大概率会使其面临更高的捕食风险。本研究所述的实验方案，可用于评估人为活动（光污染、噪声污染等）与自然因素（波浪作用、海流、风力、月光）对海龟幼龟扩散早期阶段水下活动的影响。