Energy expenditure of freely swimming adult green turtles (Chelonia mydas) and its link with body acceleration

Abstract

SUMMARYMarine turtles are globally threatened. Crucial for the conservation of these large ectotherms is a detailed knowledge of their energy relationships, especially their at-sea metabolic rates, which will ultimately define population structure and size. Measuring metabolic rates in free-ranging aquatic animals, however, remains a challenge. Hence, it is not surprising that for most marine turtle species we know little about the energetic requirements of adults at sea. Recently, accelerometry has emerged as a promising tool for estimating activity-specific metabolic rates of animals in the field. Accelerometry allows quantification of the movement of animals (ODBA/PDBA, overall/partial dynamic body acceleration), which, after calibration, might serve as a proxy for metabolic rate. We measured oxygen consumption rates (V O2 ) of adult green turtles (Chelonia mydas; 142.1±26.9kg) at rest and when swimming within a 13m-long swim channel, using flow-through respirometry. We investigated the effect of water temperature (T w ) on turtle V O2 and tested the hypothesis that turtle body acceleration can be used as a proxy for V O2 . Mean massspecific V O2 (sV O2 ) of six turtles when resting at a T w of 25.8±1.0°C was 0.50±0.09ml min . sV O2 increased significantly with T w and activity level. Changes in sV O2 were paralleled by changes in respiratory frequency (f R ). Deploying bi-axial accelerometers in conjunction with respirometry, we found a significant positive relationship between sV O2 and PDBA that was modified by T w . The resulting predictive equation was highly significant (r 2 0.83, P<0.0001) and associated error estimates were small (mean algebraic error 3.3%), indicating that body acceleration is a good predictor of V O2 in green turtles. Our results suggest that accelerometry is a suitable method to investigate marine turtle energetics at sea.

Surfacers change their dive tactics depending on the aim of the dive: evidence from simultaneous measurements of breaths and energy expenditure

“…In most previous studies conducted under limited experimental conditions, turtles took only a few breaths (e.g. [23,25]). However, our study in the wild revealed that NB usually varied within the range of 1 -12, indicating that it is important to conduct an experiment under natural conditions to correctly understand the respiratory physiology of sea turtles.…”

“…Dynamic acceleration was calculated by subtracting static from raw acceleration [15]. We estimated oxygen consumption rate during dives from ODBA using conversion equations given in previous reports by Halsey et al [24] and Enstipp et al [23]. These studies demonstrated that ODBA was useful for estimating oxygen consumption rate ( _ V O2 ) in green turtles.…”

“…where PDBA is partial dynamic body acceleration, which is almost the same as ODBA but is calculated from two-axis acceleration (surge and heave) [23]. The equation of Enstipp et al [23] included T w (water temperature) in the model, whereas the equation of Halsey et al [24] did not.…”

“…The equation of Enstipp et al [23] included T w (water temperature) in the model, whereas the equation of Halsey et al [24] did not.…”

“…For more details, see Okuyama et al [27]. Breath events were counted using a head-mounted acceleration logger or direct observation based on an animal-borne video logger, and oxygen consumption was estimated by measuring ODBA and using equations developed by Enstipp et al [23] and Halsey et al [24] to convert ODBA to oxygen consumption. The objectives of this study were to clarify how green turtles manage their energy expenditure during a dive and subsequent respiratory patterns based on the purpose of the dive (resting, foraging and other) under natural conditions and to determine which dive tactics they use.…”