This three-year study investigated the effects of wavelength, light intensity, and selected lights on the sea-finding orientation and disorientation behavior of hatchling sea turtles. A total of 9075 loggerhead hatchlings (Caretta caretta), 325 green turtle hatchlings (Chelonia mydas), 40 leatherback hatchlings (Dermochelys coriacea), and 410 pen-reared loggerhead yearlings were used in tests during the 1986-1988 nesting seasons. Hatchlings were taken from both hatchery and in situ nests in Florida located at Delray Beach in Boca Raton, Palm Beach County, and City of Jupiter Island, Martin County. Each test was conducted by releasing 15 hatchlings 10 ft. in front of an experimental light source, shown either from the dune, water, northward, or southward direction on the beach. A series of longpass filters, which have low transmission of light in the shorter wavelengths and high transmission in the long wavelength end of the spectrum, were used to determine hatchling responses to light wavelengths. A low-pressure sodium (55 watt) light, which is a commercially available monochromatic long wavelength light source, was also used to test hatchling responses.

For this study, those hatchlings orienting directly toward the light source as well as sideways (perpendicular to the light) were considered to be disoriented. Hatchling loggerheads were positively phototaxic/disoriented with lights containing the shorter (blue) wavelengths and negatively phototaxic with long (yellow, red) wavelength lights which exclude wavelengths shorter than 530 nm (Figure 1a). Hatchlings also oriented away from the light when a long wavelength light source was shown from any direction other than the dune (Table 1). Loggerhead hatchlings were attracted to lights containing 375 nm wavelengths at intensities as low as 0.12 x 10^14 quanta/sec/cm^2. The mean number of hatchlings orienting sideways dramatically increased in the 400-530 nm wavelength range (Figure 1b.) Preliminary tests on hatchling leatherback and green turtles showed similar responses; however, tests with the yearlings showed mixed reactions in response to long wavelength light. If properly positioned, long wavelength lights, such as low-pressure sodium vapor lights, light the used in beach areas without disorienting hatchlings. However, before widespread use of long wavelength lights occurs, additional research is needed on the effects on hatchling leatherback and green turtles and the adults of all species.

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