Sea-Finding Experiment

SEA-FINDING EXPERIMENT

Hatchlings were tested in an orientation arena where they could be exposed to different combinations of silhouette heights, degree of slope, and light intensity and direction. Each hatchling was tethered to a central post in the arena and then released in the center so that it could crawl in any direction it chose. For example:

Results:

Hatchlings oriented down-slope when no light was present. If light was present, then visual cues appeared to override slope cues.

If light was provided in all directions and the arena was level, then hatchlings preferred the side of the arena where the intensity of light was the brightest.

Hatchlings oriented away from dark silhouettes that were placed close to the horizon, suggesting that they prefer the lowest illuminated horizon, or perhaps prefer the direction that has the brightest illumination in an area close to the horizon .

Summary:

When hatchling sea turtles emerge from their nests, they move toward the brighter light reflected from the ocean surface and away from the elevated silhouettes of dunes and vegetation. Because beaches normally slope down toward the water, moving toward the brighter, lower horizon reliably guides turtles to the ocean. Once in the water, they need to use other cues to guide them as they swim away from land.

The experiments described on this page are based on the following reference:

Salmon, M., Wyneken, J., Fritz, E., and Lucas, M. 1992. Seafinding by hatchling sea turtles: role of brightness, silhouette, and beach slope as orientation cues. Behaviour. 122: 56-77.

Reviews of Sea-finding:

Lohmann, K. J., and C. M. F. Lohmann. 2003. Orientation mechanisms of hatchling loggerheads. In: Loggerhead Sea Turtles (eds. A. B. Bolten and B. E. Witherington), pp. 44-62. Smithsonian Books: Washington.

Lohmann, K. J., Witherington, B. E., Lohmann, C. M. F., and M. Salmon. 1997. Orientation, navigation, and natal beach homing in sea turtles. In: The Biology of Sea Turtles (eds. P. Lutz and J. Musick), pp. 107-135. CRC Press: Boca Raton.

Witherington, B. E. 1992. Sea-finding and the use of photic orientation cues by hatchling sea turtles. Ph.D. dissertation, University of Florida, Gainesville, Florida, U.S.A.

Witherington, B. E. 1997. The problem of photopollution for sea turtles and other nocturnal animals. In: Behavioral Approaches to Conservation in the Wild (eds. J. R. Clemmons and R. Buchholz), pp. 303-328. Cambridge University Press: Cambridge.

Additional Studies of Sea-finding in Sea Turtles:

Ehrenfeld, D. W. 1968. The role of vision in the sea-finding orientation of the green turtle (Chelonia mydas). 2. Orientation mechanism and range of spectral sensitivity. Animal Behaviour 16: 281-287.

Limpus, C. J. 1971. Sea turtle ocean finding behaviour. Search 2: 385-387.

Mrosovsky, N. 1972. The water-finding ability of sea turtles: behavioral studies and physiological speculations. Brain Behavior and Evolution 5: 202-225.

Mrosovsky, N. 1978. Orientation mechanisms of marine turtles. In: Animal Migration, Navigation, and Homing (eds. K. Schmidt-Koenig and W. T. Keeton), pp. 413-419. Springer-Verlag: Berlin.

Mrosovsky, N., and S. F. Kingsmill. 1985. How turtles find the sea. Zeitschrift fur Tierpsychologie 67: 237-256.

Verheijen, F. J., and J. T. Wildschut. 1973. The photic orientation of hatchling sea turtles during water finding behaviour. Netherlands Journal of Sea Research 7: 53-67.

last edited 09/28/2003