88
and high costs of conventional VHF radio telemetry (Fancy
et al. 1988). Animal locations are determined through Doppler
shift via communication between an animal-borne satellite
transmitter and polar-orbiting satellites. The estimated locations are provided online by CLS and allow quasi- live tracking
of tagged individuals (Fancy et al. 1988; Costa et al. 2012).
Argos satellite tags represent the first reliable system to
track horizontal movements of marine animals. This information is essential to analyze habitat use or migration patterns.
The first successful deployment was conducted on a basking
shark Cetorhinus maximus and only provided locations over
the course of two weeks (Priede 1984). Nevertheless, this was
sufficient to conclude that the shark was probably feeding on
zooplankton along a frontal system (Priede 1984; Priede and
Miller 2009). Since then, enormous improvements in both the
Argos satellite system and satellite tags have been achieved
(e.g., more polar-orbiting satellites, better sensitivity of satellite sensors, longer transmitter battery life, more streamlined
tag shapes), ultimately leading to a larger quantity of collected data (Hays et al. 2007). Argos satellite tags have been
deployed on a diverse assemblage of marine top predator species, including seabirds (Jouventin and Weimerskirch 1990;
Spencer et al. 2014; Pistorius et al. 2017), sharks (Priede
1984; Eckert and Stewart 2001; Weng et al. 2005), pinnipeds
(Costa et al. 2010a; Dietz et al. 2013; Arcalís-Planas et al.
2015) and cetaceans (Andrews et al. 2008; Edrén et al. 2010;
Hauser et al. 2010; Reisinger et al. 2015).
GPS Tags
Despite the many advantages of Argos satellite tags, one of
the major drawbacks is the relatively low location accuracy,
with errors generally ranging between 500 m and 10 km
(Costa et al. 2010b). Qualitatively poor Argos locations are
especially prevalent in studies involving diving top predators,
since the time spent at the surface to enable successful uplinks
to the satellite is limited (Vincent et al. 2002; Costa et al.
2010b; Patterson et al. 2010). GPS tags provide a much better
accuracy, usually with errors less than 50 m (Costa et al.
2010b; Dujon et al. 2014). Despite this higher location accuracy, most researchers have, for quite some time, refrained
from using GPS tags, mainly due to the length of time (10–
30 min) and high energy demand required to fix a GPS position (Tomkiewicz et al. 2010; Costa et al. 2012). This meant
that they were well suited for seabirds (Fig. 2e) (Ryan et al.
2004; Pinaud and Weimerskirch 2007; Votier et al. 2010), but
less so for diving animals. This problem has more recently
been overcome by the development of a Fastloc® GPS, for
which GPS positions can be obtained within milliseconds,
which enables a successful location fix even within a short
surfacing event (Costa et al. 2010b). Thus, GPS tags are now
also increasingly used on marine mammals (Heide-Jørgensen
et al. 2013; Villegas-Amtmann et al. 2013; McKenna et al.
2015). The GPS positions are either stored on-board the
device and must be downloaded from a recovered tag, or can
be transmitted via the Argos satellite system (Costa et al.
2010b; Patterson et al. 2010). GPS locations can also be
relayed through communication with the Global Systems for
Mobile Communication (GSM)—the mobile phone network
(McConnell et al. 2004; Cronin and McConnell 2008). The
locations are stored internally and transmitted as a text message, together with ancillary information, when the animal is
within the coverage of the GSM network (Cronin and
McConnell 2008). These devices represent a promising tool
for the relatively inexpensive and accurate tracking of coastal
top predator species (Fig. 2c) (Jessopp et al. 2013; Wilson
et al. 2017), especially in the light of the rapidly expanding
GSM network around the globe.
Satellite-linked Data Loggers
For many applications, simultaneous information on both
horizontal movements and specific behaviors, for example,
diving behavior, is required to better understand how marine
animals respond to their environment and use their habitat.
This is achieved by combining a satellite tag (Argos and/or
GPS) with an archival logger (e.g., time-depth recorders,
accelerometers), i.e., a satellite-linked data logger. These
devices not only record an animal’s position, but also log
information on different behaviors and ambient conditions.
Some instruments are able to transmit these data via Argos
satellites, while others need to be recovered for data download. Remotely collected data via satellite only provide compressed and reduced information due to bandwidth
limitations, whereas retrievable instruments offer data in
high resolution. However, it is expected that the impact of
this constraint will continue to lessen with the on-going rapid
technological advance and further developments in the field
of bio-telemetry (see, for example, Cox et al. 2017).
The first satellite-linked data logger was a combination of
a satellite transmitter and a TDR (Merrick et al. 1994). This
provided the opportunity to combine location data with concurrent behavioral data, and thus enabled the analysis of
horizontal and vertical movements (Merrick et al. 1994;
Ryan et al. 2004; Burns et al. 2008; Bestley et al. 2015;
Heerah et al. 2016). The first satellite-linked dive recorders
were effective to study habitat use in relation to diving
behavior, but had restricted applicability, due to the limited
information available about each dive (Merrick et al. 1994;
Burns 1999; Davis et al. 2007; Nachtsheim et al. 2017). The
development of the satellite relay data logger (SRDL) revolutionized the study of top predator movements, providing
locations and compressed time-depth profiles for each dive
via satellite communication (Fedak et al. 2002). These
B. C. Heylen and D. A. Nachtsheim
and high costs of conventional VHF radio telemetry (Fancy
et al. 1988). Animal locations are determined through Doppler
shift via communication between an animal-borne satellite
transmitter and polar-orbiting satellites. The estimated locations are provided online by CLS and allow quasi- live tracking
of tagged individuals (Fancy et al. 1988; Costa et al. 2012).
Argos satellite tags represent the first reliable system to
track horizontal movements of marine animals. This information is essential to analyze habitat use or migration patterns.
The first successful deployment was conducted on a basking
shark Cetorhinus maximus and only provided locations over
the course of two weeks (Priede 1984). Nevertheless, this was
sufficient to conclude that the shark was probably feeding on
zooplankton along a frontal system (Priede 1984; Priede and
Miller 2009). Since then, enormous improvements in both the
Argos satellite system and satellite tags have been achieved
(e.g., more polar-orbiting satellites, better sensitivity of satellite sensors, longer transmitter battery life, more streamlined
tag shapes), ultimately leading to a larger quantity of collected data (Hays et al. 2007). Argos satellite tags have been
deployed on a diverse assemblage of marine top predator species, including seabirds (Jouventin and Weimerskirch 1990;
Spencer et al. 2014; Pistorius et al. 2017), sharks (Priede
1984; Eckert and Stewart 2001; Weng et al. 2005), pinnipeds
(Costa et al. 2010a; Dietz et al. 2013; Arcalís-Planas et al.
2015) and cetaceans (Andrews et al. 2008; Edrén et al. 2010;
Hauser et al. 2010; Reisinger et al. 2015).
GPS Tags
Despite the many advantages of Argos satellite tags, one of
the major drawbacks is the relatively low location accuracy,
with errors generally ranging between 500 m and 10 km
(Costa et al. 2010b). Qualitatively poor Argos locations are
especially prevalent in studies involving diving top predators,
since the time spent at the surface to enable successful uplinks
to the satellite is limited (Vincent et al. 2002; Costa et al.
2010b; Patterson et al. 2010). GPS tags provide a much better
accuracy, usually with errors less than 50 m (Costa et al.
2010b; Dujon et al. 2014). Despite this higher location accuracy, most researchers have, for quite some time, refrained
from using GPS tags, mainly due to the length of time (10–
30 min) and high energy demand required to fix a GPS position (Tomkiewicz et al. 2010; Costa et al. 2012). This meant
that they were well suited for seabirds (Fig. 2e) (Ryan et al.
2004; Pinaud and Weimerskirch 2007; Votier et al. 2010), but
less so for diving animals. This problem has more recently
been overcome by the development of a Fastloc® GPS, for
which GPS positions can be obtained within milliseconds,
which enables a successful location fix even within a short
surfacing event (Costa et al. 2010b). Thus, GPS tags are now
also increasingly used on marine mammals (Heide-Jørgensen
et al. 2013; Villegas-Amtmann et al. 2013; McKenna et al.
2015). The GPS positions are either stored on-board the
device and must be downloaded from a recovered tag, or can
be transmitted via the Argos satellite system (Costa et al.
2010b; Patterson et al. 2010). GPS locations can also be
relayed through communication with the Global Systems for
Mobile Communication (GSM)—the mobile phone network
(McConnell et al. 2004; Cronin and McConnell 2008). The
locations are stored internally and transmitted as a text message, together with ancillary information, when the animal is
within the coverage of the GSM network (Cronin and
McConnell 2008). These devices represent a promising tool
for the relatively inexpensive and accurate tracking of coastal
top predator species (Fig. 2c) (Jessopp et al. 2013; Wilson
et al. 2017), especially in the light of the rapidly expanding
GSM network around the globe.
Satellite-linked Data Loggers
For many applications, simultaneous information on both
horizontal movements and specific behaviors, for example,
diving behavior, is required to better understand how marine
animals respond to their environment and use their habitat.
This is achieved by combining a satellite tag (Argos and/or
GPS) with an archival logger (e.g., time-depth recorders,
accelerometers), i.e., a satellite-linked data logger. These
devices not only record an animal’s position, but also log
information on different behaviors and ambient conditions.
Some instruments are able to transmit these data via Argos
satellites, while others need to be recovered for data download. Remotely collected data via satellite only provide compressed and reduced information due to bandwidth
limitations, whereas retrievable instruments offer data in
high resolution. However, it is expected that the impact of
this constraint will continue to lessen with the on-going rapid
technological advance and further developments in the field
of bio-telemetry (see, for example, Cox et al. 2017).
The first satellite-linked data logger was a combination of
a satellite transmitter and a TDR (Merrick et al. 1994). This
provided the opportunity to combine location data with concurrent behavioral data, and thus enabled the analysis of
horizontal and vertical movements (Merrick et al. 1994;
Ryan et al. 2004; Burns et al. 2008; Bestley et al. 2015;
Heerah et al. 2016). The first satellite-linked dive recorders
were effective to study habitat use in relation to diving
behavior, but had restricted applicability, due to the limited
information available about each dive (Merrick et al. 1994;
Burns 1999; Davis et al. 2007; Nachtsheim et al. 2017). The
development of the satellite relay data logger (SRDL) revolutionized the study of top predator movements, providing
locations and compressed time-depth profiles for each dive
via satellite communication (Fedak et al. 2002). These
B. C. Heylen and D. A. Nachtsheim