DOI: 10.5061/dryad.n8s3c
title: Data from: Accelerometers can measure total and activity-specific energy expenditure in free-ranging marine mammals only if linked to time-activity budgets

description: 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 have emerged as a new way to determine energy
 expenditure at a fine scale but this needs to be tested and validated in
 wild animals. 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). To
 do so, we equipped 20 lactating northern (Callorhinus ursinus) and 20
 lactating 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 travelling speed. 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 when activity-specific
 VeDBA was 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 &gt; 0·85). 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 budgets
 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,
 that can be transfered to studies on other species.
description: Northern fur seals
 dataData was collected on
 northern fur seal females during the breeding season on St Paul island,
 Bering Sea, Alaska from a daily Diary tag from Wildlife Computers. Column
 headings include "Date", "Time","Depth",
 "External Temperature", "int mX", "int mY",
 "int mZ", "int aX", "int aY", "int
 aZ", "Light Level", "Velocity",
 "Wet/Dry", "Wet/Dry", "Hour", "Battery
 Voltage", "Protocol". int mX, Y, Z refer to magnetic field
 recorded on the 3 body axes, and int aX, Y, Z to the acceleration recorded
 on the same axes.Northern_fur_seals_data.zipAntarctic fur seal dataData was collected on Antarctic fur seal females during the breeding season on Kerguelen Island, Southern Ocean on The Pointe Suzanne colony from a Daily Diary tag from Wildlife Computers. Column headings include "Date", "Time", "Depth", "Temperature", "aX", "aY", "aZ", "Light", "Velocity", "WetDry", "WetDrytxt". aX, Y, Z refer to the acceleration recorded on the 3 body axes.Antarctic_fur_seal_data.zip