Influences of artificial lighting on the seaward orientation of hatchling loggerhead turtles Caretta caretta

Published source details 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.
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This study is summarised as evidence for the following.

	Action	Category
	Change the colour (spectral composition) of lighting Action Link
	Use low intensity lighting Action Link

Change the colour (spectral composition) of lighting

A replicated, controlled study (years not provided) on a beach in Florida, USA (Witherington & Bjorndal 1991) found that yellow-tinted incandescent lighting did not affect loggerhead turtle Caretta caretta hatchling seaward orientation at high intensity, whereas four other artificial lights did at both low and high intensities. Hatchlings released under high, but not low, intensity yellow-tinted incandescent lighting oriented in a similar direction compared to no lighting (data reported as crawl angle), which was directly seawards on average. High-pressure sodium vapour, low-pressure sodium vapour, red-tinted incandescent and white quartz lighting all affected sea turtle hatchling seaward orientation at high and low intensities compared to no lighting (data reported as crawl angle, see paper for details). Overall, hatchlings tended to be most attracted to white quartz lighting. High-pressure sodium vapour, low-pressure sodium vapour, yellow-tinted incandescent, red-tinted incandescent and white quartz lights were trialled at high and low intensity. 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.

(Summarised by: Maggie Watson, Katie Sainsbury)
Use low intensity lighting

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.

(Summarised by: Maggie Watson, Katie Sainsbury)