Data from: Accelerometers can measure total and activity-specific energy expenditure in free-ranging marine mammals only if linked to time-activity budgets

1. Energy expenditure is an important component of foraging ecology, but is extremely difficult to estimate in free-ranging animals and depends on how animals partition their time between different activities during foraging. Acceleration data has emerged as a new way to determine energy expenditure at a fine scale but needs to be tested and validated in wild animals.
2. This study investigated whether vectorial dynamic body acceleration (VeDBA) could accurately predict the energy expended by marine predators during a full foraging trip. We also aimed to determine whether the accuracy of predictions of energy expenditure derived from acceleration increased when partitioned by different types of at-sea activities (i.e., diving, transiting, resting and surface activities) vs calculated activity-specific metabolic rates. 3. To do so, we equipped 20 lactating northern (Callorhinus ursinus) and 20 Antarctic fur seals (Arctocephalus gazella) with GPS, time-depth recorders and tri-axial accelerometers, and obtained estimates of field metabolic rates using the doubly-labelled water (DLW) method. VeDBA was derived from tri-axial acceleration, and at-sea activities (diving, transiting, resting and surface activities) were determined using dive depth, tri-axial acceleration and traveling speed. 4. We found that VeDBA did not accurately predict the total energy expended by fur seals during their full foraging trips (R2 = 0.36). However, the accuracy of VeDBA as a predictor of total energy expenditure increased significantly when foraging trips were partitioned by activity and used activity-specific VeDBA paired with time activity budgets (R2 = 0.70). Activity-specific VeDBA also accurately predicted the energy expenditures of each activity independent of each other (R2 > 0.85). 5. Our study confirms that acceleration is a promising way to estimate energy expenditures of free-ranging marine mammals at a fine scale never attained before. However, it shows that it needs to be based on the time-activity budget that make up foraging trips rather than being derived as a single measure of VeDBA applied to entire foraging trips. Our activity-based method provides a cost-effective means to accurately calculate energy expenditures of fur seals using acceleration and time-activity budgets, a stepping stone for numerous other research fields.

1. 能量消耗是觅食生态学的重要组成部分，但在自由活动的野生动物中极难估算，且取决于动物在觅食过程中分配于不同活动的时间比例。加速度数据已成为精细尺度下估算能量消耗的新方法，但仍需在野生动物中开展测试与验证。
2. 本研究旨在探究矢量动态身体加速度（vectorial dynamic body acceleration, VeDBA）能否精准预测海洋捕食者在完整觅食旅程中消耗的能量。此外，本研究还希望明确：相较于计算特定活动代谢率，当按照不同海上活动类型（即潜水、巡游、休憩与水面活动）划分数据时，基于加速度的能量消耗预测精度是否会提升。
3. 为此，我们为20头泌乳期北太平洋海狗（Callorhinus ursinus）与20头南极海狗（Arctocephalus gazella）佩戴了全球定位系统（GPS）、时间深度记录仪与三轴加速度计，并通过双标水（doubly-labelled water, DLW）法获取了野外代谢率的估算值。我们从三轴加速度数据中提取VeDBA指标，并结合潜水深度、三轴加速度与行进速度判定个体的海上活动类型（潜水、巡游、休憩与水面活动）。
4. 研究结果显示，VeDBA无法精准预测海狗在完整觅食旅程中的总能量消耗（R²=0.36）。但当按照活动类型划分觅食旅程数据，并将特定活动VeDBA与时间活动预算相结合时，VeDBA作为总能量消耗预测因子的精度显著提升（R²=0.70）。此外，特定活动VeDBA还可独立精准预测各类活动的能量消耗（R²>0.85）。
5. 本研究证实，加速度技术可作为一种极具前景的方法，在前所未有的精细尺度下估算自由活动海洋哺乳动物的能量消耗。但同时也表明，该方法需基于构成觅食旅程的时间活动预算，而非仅通过单一VeDBA指标应用于完整觅食旅程。我们提出的基于活动的方法，结合加速度数据与时间活动预算，可实现成本高效的海狗能量消耗精准估算，这一方法可为众多其他研究领域提供重要基石。