DOI: 10.5061/dryad.ns1rn8prc
title: Data from: Overall dynamic body acceleration measures activity differently on large vs small aquatic animals

description: Acceleration-based proxies for activity and energy expenditure are widely
 used in bio-logging studies of animal movement and locomotion to explore
 biomechanical strategies, energetic costs of behaviour, habitat use and
 the impact of anthropogenic disturbance. The foremost such proxy is
 Overall Dynamic Body Acceleration (ODBA) along with variants VeDBA and
 PDBA. This technique, which involves summing the magnitude of
 high-pass-filtered acceleration signals (the so-called dynamic
 acceleration) over a reference interval, has been applied to animals as
 diverse as shags, lobsters, humans and whales. The relationship between
 ODBA and energy use has been tested empirically on animals small enough to
 house in laboratory facilities and arguments have been offered for why the
 method should be generally applicable, however validations on larger
 animals are scant. Here, we examine how body size impacts ODBA and its
 variants under steady locomotion in large aquatic animals, using cetaceans
 as model species. To do this, we first develop a simplified mathematical
 model for the acceleration signals that would be measured by a tag on a
 swimming animal. We then test this model with empirical data gathered
 using bio-logging tags on whale species covering nearly an order of
 magnitude difference in body length from 1.3 m harbour porpoises to 12 m
 sperm whales. We show that the motions measured by ODBA can be
 fundamentally different in small compared to large aquatic animals.
 Whereas dynamic acceleration in small animals is predominantly due to
 specific acceleration (i.e., actual accelerative motions generated by
 muscle action), in larger aquatic animals body rotations (i.e., changes in
 orientation that accompany swimming and manoeuvring) can dominate the
 measured acceleration. As body rotations do not necessarily increase in
 magnitude as swimming speed increases, ODBA may under-estimate the
 relative cost of behaviours or responses to disturbance in large aquatic
 animals. This does not lessen the value of ODBA for small animals, but it
 raises a caution against uncritical use on larger animals. For large
 aquatic animals, activity proxies that specifically remove body rotations
 using gyroscopes or magnetometers may provide more consistent estimates of
 energy use although these methods are yet to be validated.
description: Data was collected on 6 sperm whales (<i>Physeter
 macrocephalus</i>, Pm), 6 Blainville´s beaked whales
 (<i>Mesoplodon densirostris, </i>Md) and 6 harbour porposise
 <i>(Phocoena phocoena</i>, Pp) using suction cup attached
 multi-sensor tags (DTAGs version 2 and 3). Tags were attached to sperm
 whales between 2003-2010 in Norway, Italy, the U.S. North Atlantic, and
 the Azores, to Blainville's beaked whales between 2003-2010 off the
 coast of El Hierro (Canary Islands, Spain) and to harbour porpoises, which
 were bycaught in a pound net fishery in inner Danish waters between
 2012-2014 and tagged upon release. The tags included a pressure sensor,
 triaxial magnetometers, and triaxial accelerometers sampled at 50-200 Hz
 with 16-bit resolution. These sensor streams were decimated to a common 25
 Hz sampling rate in post processing. The triaxial accelerometer and
 magnetometer signals were rotated to correct for the orientation of the
 tag on the whale which was estimated at each surfacing from the
 stereotypical movements during respiration. Software tools from
 <i>www.animaltags.org</i> in Matlab R2019a were used for data
 processing.
description: Here we present a different nc-file for each of the 18 tagged
 animals, 6 individuals per species. nc files are named after the tag ID,
 i.e., the code comprises the first letter for each species initials in
 Latin, the year it was tagged (two digits), the Julian day, and the tag
 deployment of the day (a single letter). Each nc-file contains
 "P", "A" and "M" variables sampled at 25Hz
 for 10 randomly-selected data blocks ("block") of 10 consecutive
 swimming strokes. "P" corresponds to depth in
 meters. "A" corresponds to the measured
 animal-frame triaxial accelerometer signal in g; columns correspond to the
 acceleration components a<sub>x</sub>,
 a<sub>y</sub> and a<sub>z</sub>, which correspond
 to the longitudinal, lateral and dorso-vental axis,
 respectively. "M" corresponds to the measured
 animal-frame triaxial magnetometer signal in μT; columns correspond to the
 magnetometer components m<sub>x</sub>,
 m<sub>y</sub> and m<sub>z</sub>, which correspond
 to the longitudinal, lateral and dorso-vental axis, respectively.
 "block" corresponds to the each of the randomnly selected blocks
 of 10 consecutive swimming strokes. In addition each
 nc.file contains information regarding the data owner and data provider of
 each database.