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 ( o 2) 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 o 2 over an hour in a green turtle from measures of ODBA and mean flipper length (R2 = 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 o 2. A o 2-ODBA equation for the loggerhead hatchling data was also significant (R2 = 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.
Highlights
Measuring metabolic rate of sea turtles is difficult
Histograms of V O2 and overall dynamic body acceleration (ODBA) for all experiments together indicated that these variables were reasonably normally distributed
There was an interaction between ODBA and turtle ID (P,0.003) indicating that the slopes of the V O2ODBA relationships varied among individual animals
Summary
Measuring metabolic rate (energy expenditure) of sea turtles is difficult. Values obtained using the doubly-labelled water (DLW) technique [3] can sometimes be spurious due mainly to the high water flux and low rate of carbon dioxide production of turtles [2,4]. While in some species the DLW technique is valid during feeding periods [5] (but not during fasting [2]), it only provides a single value for mean metabolic rate over the experimental period. Data on the metabolic rates of free-ranging sea turtles, at a range of temporal resolutions, are important for understanding the physiology of these animals, their population dynamics and, in turn, managing their conservation (Wallace and Jones 2008). There are a number of methods for estimating energy expenditure in animals that should be applicable to sea turtles. The carapace makes turtles suitable for instrumenting with data loggers (e.g. [6]), affording the opportunity to measure a pertinent physiological or behavioural proxy of energy expenditure
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