Response of turtle hatchlings to light emitting diodes at sea

We used passive acoustic telemetry to examine the effects of five different intensities of Light Emitting Diodes (4000K floodlight) on the movement patterns and predation rates of flatback turtle (Natator depressus) hatchlings as they disperse through nearshore waters. A total of 68 hatchlings were released, 36 of which were released when the light sources were present on a boat located to the east of the hatchling release point and 32 were released when the light sources were present on a boat located to the west of the release location. Five or six hatchlings were released in each treatment (Ambient, 10 watt, 30 watt, 50 watt, 70 watt, 120 watt). Attraction of hatchlings to lights increased with light intensity only when lights were located in the direction that hatchlings preferred to disperse under ambient conditions (west). This suggests that the location of the light source in relation to the preferred direction of travel may be important in determining the impact on hatchlings. When the light source was not in the direction of travel, only 25% of hatchlings were attracted to it. Predation of hatchlings was higher when LEDs were illuminated than under ambient light conditions. We found no clear relationship with predation rates or time spent in the nearshore with light intensity, although a combination of high variability in environmental conditions across nights, low sample sizes, and the relatively low intensity of our light treatments might have affected our ability to detect an effect. The hatchling predation rates we recorded and the finding that hatchlings spent 20% longer in predator-rich nearshore areas for all light intensities on one of the nights suggest that the presence of LEDs, regardless of their intensity, is likely to have a negative impact on the survivorship of hatchlings passing through the nearshore.

本研究采用被动声学遥测（passive acoustic telemetry）技术，探究五种不同强度的发光二极管（Light Emitting Diodes，4000K泛光灯）对平背龟（Natator depressus）幼龟在近岸水域扩散过程中的运动模式与被捕食率的影响。本次实验共放流68只平背龟幼龟，其中36只为在幼龟放流点东侧的船上开启光源时放流，剩余32只为在放流点西侧的船上开启光源时放流。每组实验处理（自然光照组、10瓦、30瓦、50瓦、70瓦、120瓦）各放流5至6只幼龟。
仅当光源位于幼龟在自然光照条件下偏好的扩散方向（西侧）时，幼龟的趋光性随光照强度升高而增强。这表明光源相对于幼龟偏好行进方向的位置，是决定其对幼龟影响程度的关键因素。当光源不在幼龟偏好的行进方向时，仅有25%的幼龟会被其吸引。
开启发光二极管光源时的幼龟被捕食率高于自然光照条件下。尽管夜间环境条件存在高度异质性、样本量有限且本研究的光照处理强度相对偏低，我们未检测到光照强度与幼龟被捕食率、近岸停留时间之间存在明确关联。本研究记录的幼龟被捕食率，以及某次夜间实验中所有光照强度组的幼龟在捕食者密集的近岸区域停留时间均延长20%的发现表明：无论发光二极管光源强度如何，其存在均可能对途经近岸水域的幼龟存活率产生负面影响。