First published online April 23, 2004
Journal of Experimental Biology 207, 1771-1778 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00946
Navigation and seasonal migratory orientation in juvenile sea turtles
Larisa Avens1,2,* and
Kenneth J. Lohmann1
1 Department of Biology, University of North Carolina, Chapel Hill, NC
27599-3280, USA
2 NOAA Fisheries, Beaufort, NC 28516-9722, USA
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Fig. 1. Map of the coastal areas of North Carolina indicating the location of the
testing site (NOAA Laboratory) and the locations where turtles were
captured.
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Fig. 2. Diagram of the experimental arena and the data acquisition system used to
monitor the orientation of juvenile sea turtles (turtle not drawn to scale).
Each turtle was outfitted with a nylon–LycraTM harness and tethered
to a rotatable arm in the arena. The data acquisition computer was located in
a shed approximately 5 m to the south of the arena. See text for details.
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Fig. 3. Summer and autumn orientation of juvenile loggerhead turtles. Each dot
within a circular diagram represents the mean angle of orientation for a
single turtle during its 10-min trial. Triangles on the outsides of the
circles correspond to the most direct routes back to the capture areas for
each group of turtles. The broken lines represent the 95% confidence interval
for the mean heading. (A) Orientation of loggerheads captured at locations
east–northeast of the test site and tested between May and September
1998–2001. Turtles were significantly oriented with a mean angle of
83° (N=122, r=0.29, P<0.0005
V-test, 95% confidence interval ±25°). The confidence
interval overlaps the direction to the capture area (74°). (B) Orientation
of loggerheads captured at locations west–southwest of the test site and
tested between May and September 1999–2002. Turtles were significantly
oriented with a mean angle of 271° (N=11, r=0.43,
P<0.05 V-test, 95% confidence interval ±76°).
The confidence interval overlaps the direction to the capture site (255°).
(C) Autumn orientation of loggerheads tested in October and November
1998–2000. Turtles were significantly oriented with a mean angle of
190° (N=15, r=0.61, P<0.005 Rayleigh test,
95% confidence interval ±33°). This direction coincides with the
direction of orientation exhibited by wild turtles during their autumn
migration.
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Fig. 4. Summer and autumn orientation of juvenile green turtles. Each dot within a
circular diagram represents the mean angle of orientation for a single turtle
during its 10-min trial. The triangle on the outside of each circle
corresponds to the direction towards the capture area for each group of
turtles. The broken lines represent the 95% confidence interval for the mean
angle. (A) Orientation of green turtles tested between May and September
1998–1999. Turtles were significantly oriented with a mean angle of
50° (N=9, r=0.71, P<0.0025 V-test,
95% confidence interval ±37°). The confidence interval overlaps the
direction to the capture site (74°). (B) Autumn orientation of green
turtles tested in October and November 1998 and 2001. Turtles were
significantly oriented with a mean angle of 199° (N=7,
r=0.76, P<0.02 Rayleigh test, 95% confidence interval
±39°). This direction of orientation is consistent with that
observed in wild turtles during the autumn migration.
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© The Company of Biologists Ltd 2004
