Use low intensity lighting

Supporting evidence from individual studies

1. A replicated, controlled study (years not provided) on a beach in Florida, USA (Witherington & Bjorndal 1991) found that using low rather than high intensity lighting did not improve loggerhead turtle Caretta caretta hatchling orientation seawards in any of five types of commercially-available artificial light types, but that one of 10 lighting treatments showed similar ranges of orientation to no lighting. Only high intensity yellow tinted incandescent lighting did not affect hatchling orientation compared when no lighting was used (results presented as crawl angles, see paper for details). Only low intensity low-pressure sodium vapour light did not affect the variation in crawl angle (results presented as crawl angles, see paper for details). Hatchlings in trials with white light sources (low and high intensity) showed the worst seaward orientation (results presented as crawl angles, see paper for details). Five commercially available lights were trialled at low and high intensities: high-pressure sodium vapour, low-pressure sodium vapour, yellow-tinted incandescent, red-tinted incandescent and white quartz. Trials were conducted at night by releasing 30 hatchlings/trial (from 30 different clutches) into the centre of an 8 m diameter sand arena divided into 32 segments, with segment one closest to the sea (0°) and a light positioned 4 m from the eighth segment (90°). After five minutes, the segment location of hatchlings was recorded. Trials were also carried out with no lighting.

   Study and other actions tested

   Referenced paper

   Witherington B.E. & Bjorndal K.A. (1991) Influences of artificial lighting on the seaward orientation of hatchling loggerhead turtles Caretta caretta. Biological Conservation, 55, 139-149.

2. A replicated, site comparison study in 2001 on a sandy beach in Florida, USA (Bertolotti & Salmon 2005) found that when street lighting was embedded in the road, loggerhead turtle Caretta caretta hatchling orientation was more often seawards compared to when overhead lighting was used, though results depended on whether there was a full moon or new moon. Hatchling orientation was similar between embedded and overhead lighting conditions (seawards) in both unshaded and shaded sites during full moons. During the new moon, hatchlings moved seawards at all three sites when embedded lights were used, whereas with overhead lighting, the direction of movement was seaward in shaded areas, but more mixed in unshaded areas. With embedded lights and cloud cover, fewer turtles oriented directly eastwards compared to when there was no cloud cover. The nesting beach was parallel to a road with streetlights. In July–September 2001, loggerhead turtle hatchling orientation was compared between embedded lighting (LED lights in road studs at 9 m intervals) and overhead lighting (150W high-pressure sodium vapour angled away from the beach, 7.5–9 m high on wooden poles at 60–100 m intervals) in two unshaded sites and one site shaded by shrubs. Newly emerged hatchlings were placed in a 4 m diameter arena and exit direction from the arena was recorded. Trials were carried out 2–3 times for each site, lighting condition and moon phase (24 hatchlings from two or more nests/trial, sourced from 76 total nests).

   Study and other actions tested

   Referenced paper

   Bertolotti L. & Salmon M. (2005) Do embedded roadway lights protect sea turtles? Environmental Management, 36, 702-710.

3. A replicated, controlled study in 2000–2001 in a laboratory in Florida, USA (Sella et al. 2006) found that lowering the intensity of a light source led to lower preference for moving towards that light source in laboratory trials with loggerhead Caretta caretta or green Chelonia mydas turtle hatchlings. Hatchlings preferentially crawled towards unfiltered light over orange or red light in four of four trials, but preference for unfiltered light decreased as its intensity decreased (from 2 of 4 trials to 0 of 4 trials with decreasing intensity). At the lowest intensity, turtles showed preference for the filtered light in two of four trials. In comparisons between orange and red filtered light, turtles showed no preference in six of eight trials, but preferred red light when the orange light intensity was reduced to its lowest level (2 of 2 trials). Hatchlings were presented with a choice of two lights to crawl towards. High pressure sodium vapour lights were covered with an orange, red or no filter and the less filtered light in each comparison was tested at four intensity levels. The highest intensity used matched that of a beach adjacent streetlight located 40 or 60 m from a nest, and intensity was reduced using a neutral density filter. In 2000–2001, hatchlings were obtained from two beaches, with 25 used in each trial. Each hatchling was used in only one trial and then released in to the wild.

   Study and other actions tested

   Referenced paper

   Sella K.N., Salmon M. & Witherington B.E. (2006) Filtered streetlights attract hatchling marine turtles. Chelonian Conservation and Biology, 5, 255-261.

4. A replicated, site comparison study in 2005 on a sandy beach on the east coast of Terengganu, Peninsular Malaysia (van de Merwe et al. 2013) found that green turtle Chelonia mydas hatchlings from a hatchery released in low and moderate ambient artificial light took a more direct route to the sea than hatchlings released in high ambient artificial light. Green turtle hatchlings released in low and moderate artificial ambient light dispersed at an angle similar to a direct line towards to the sea (62–76° dispersal angle), while hatchlings released in high ambient light dispersed at a different angle to the most direct route (148° dispersal angle, see original paper for information about directionality). In July–October 2005, sea-finding behaviours were tested on 30 hatchlings from each of 14 hatchery nests (420 hatchlings) under three different ambient lighting scenarios–high ambient light (300 m north of hatchery), moderate ambient light (directly in front of hatchery) and low ambient light (500 m south of hatchery; 10 hatchlings/nest/lighting scenario). All trials were conducted in an 8m wide circular sand arena 20 m from the sea with hatchlings placed under a bucket in the centre before release. The angle of dispersal for each hatchling was calculated using a compass from the centre to the point where the hatchling exited the arena and compared to the angle of the direct route to the sea.

   Study and other actions tested

   Referenced paper

   Van de Merwe J.P., Ibrahim K. & Whittier J.M. (2013) Post-emergence handling of green turtle hatchlings: Improving hatchery management worldwide. Animal Conservation, 16, 316-323.