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Regional Magnetic Fields as Navigational Markers for Sea Turtles
Kenneth J. Lohmann, Shaun D. Cain, Susan A. Dodge, and Catherine M. F. Lohmann
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Supplementary Material
Supplemental Figure 1. Diagram (not to scale) of the orientation arena, magnetic coil system, and data acquisition system. Each hatchling was tethered to a rotatable lever-arm mounted on a digital encoder (located inside the central post of the orientation arena). The lever arm tracked the direction toward which the turtle swam; signals from the encoder were relayed to the data acquisition computer, which recorded the orientation of the turtle every 10 s. The arena was partially filled with sea water and enclosed by a computerized magnetic coil system consisting of two different coils arranged orthogonally. One coil controlled the horizontal component of the field while the other controlled the vertical component. Each coil measured 2.27 m on a side and was constructed in accordance with the 4-coil design of Merritt
et al. (
1). The turtles were tethered in the center of the coil where field uniformity was highest (
1, 2). Movement was restricted to a horizontal area defined by a circle of radius 25 cm or less and a vertical area of 5 cm or less. In this region, calculated (
1, 2) and measured deviations from perfect field uniformity were less than 1%.
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References
1. R. Merritt, C. Purcell, G. Stroink, Rev. Sci. Instrum. 54, 879 (1983).
2. J. L. Kirschvink, Bioelectromagnetics 13, 401 (1992).
