Relating straight-line to over-the-curve carapace measurements in loggerheads
Marine Turtle Newsletter
There is a need among marine turtle researchers to compare their findings with information gathered by others. Some investigators measure carapace lengths over-the-curve (OC) with meter tapes; others take straight-line measurements (SL) with calipers. Using data gathered on loggerheads at Kennedy Space Center, Florida, we computed an equation by which SL measurements can be converted to OC, and vice versa. Carapace lengths were measured to the nearest 0.1 cm with both meter tapes and calipers from the center of the nuchal (precentral) scute to the distal tip of the longest posterior marginal scute. Because both measurements are subject to error, Model I regression is inappropriate. We used Bartlett's 3-group method for Model II regression (Sokal and Rohlf 1969). In the figure below, the line represents the equation: OC = a + b(SL) = 5.24 + 1.02(SL), (N = 366; r = .9783; p < .01). The 95% confidence limits for the slope, b, indicate that 0.986< b < 1.045.
Frazer, N. B. and L. M. Ehrhart. 1983. Relating straight-line to over-the-curve carapace measurements in loggerheads. Marine Turtle Newsletter 24:4-5.