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. 2011;6(8):e22311.
doi: 10.1371/journal.pone.0022311. Epub 2011 Aug 4.

Measuring energy expenditure in sub-adult and hatchling sea turtles via accelerometry

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Measuring energy expenditure in sub-adult and hatchling sea turtles via accelerometry

Lewis G Halsey et al. PLoS One. 2011.

Abstract

Measuring the metabolic of sea turtles is fundamental to understanding their ecology yet the presently available methods are limited. Accelerometry is a relatively new technique for estimating metabolic rate that has shown promise with a number of species but its utility with air-breathing divers is not yet established. The present study undertakes laboratory experiments to investigate whether rate of oxygen uptake (VO2) at the surface in active sub-adult green turtles Chelonia mydas and hatchling loggerhead turtles Caretta caretta correlates with overall dynamic body acceleration (ODBA), a derivative of acceleration used as a proxy for metabolic rate. Six green turtles (25-44 kg) and two loggerhead turtles (20 g) were instrumented with tri-axial acceleration logging devices and placed singly into a respirometry chamber. The green turtles were able to submerge freely within a 1.5 m deep tank and the loggerhead turtles were tethered in water 16 cm deep so that they swam at the surface. A significant prediction equation for mean VO2 over an hour in a green turtle from measures of ODBA and mean flipper length (R(2) = 0.56) returned a mean estimate error across turtles of 8.0%. The range of temperatures used in the green turtle experiments (22-30 °C) had only a small effect on Vo₂. A VO2-ODBA equation for the loggerhead hatchling data was also significant (R(2) = 0.67). Together these data indicate the potential of the accelerometry technique for estimating energy expenditure in sea turtles, which may have important applications in sea turtle diving ecology, and also in conservation such as assessing turtle survival times when trapped underwater in fishing nets.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Rate of oxygen uptake against ODBA at 10 min intervals for six green turtles during a range of activity levels and temperatures.
Each type of symbol represents data points for a particular individual. Darker versions of symbols denote higher ambient water temperatures (closed unfilled symbols represent temperatures between and including 22 and 25°C, unclosed symbols 25°C, closed grey-filled symbols 26 and 27°C, and closed black-filled symbols 29 and 30°C). Values for rate of oxygen uptake are shown adjusted for inter-individual differences between turtles (by subtracting from each data point the parameter estimate for Turtle ID obtained from a linear mixed effects model; see Methods). The common slope shown, derived from the linear mixed effects model, is described by formula image
Figure 2
Figure 2. Simulation demonstrating the accuracy of predictions of rate of oxygen uptake from ODBA in green turtles using prediction equation 1, at different values of ODBA, for different sampling scenarios.
The three scenarios are: (1) six turtles measured for one hour each; black dashed lines, (2) one turtle measured for one hour; grey dashed line, (3) 20 turtles measured for one week each; grey stippled lines. In each case, each 10 min period of data is averaged. (a) The 95% confidence intervals. The black solid line represents prediction equation 1 (see Fig. 1). (b) The relative standard error of the estimate ( = SEE/predicted rate of oxygen uptake×100).
Figure 3
Figure 3. Rate of oxygen uptake against ODBA at one minute intervals for two loggerhead turtle (denoted by the two symbol types) Caretta caretta hatchlings while swimming during the first few hours after emerging from the egg.
The common slope for these two turtles, derived from a linear mixed effects model, is described by formula image

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