95
mined. Studies on navigational ability in migratory seabirds
showed that there can be many potential cues, for instance,
olfactory, hydrodynamic, sky polarization, sun and star positions (Muheim et al. 2006; Lohmann et al. 2008; Gagliardo
et al. 2013). However, detecting the geomagnetic field was,
for example, in black-browed albatross Diomedea melanophris not one of them (Bonadonna et al. 2003). As such,
we need to remind ourselves that experimental studies are
never able to look at the full spectrum of natural conditions
that occur during migration and, therefore, cannot eliminate
particular cues completely.
Bio-telemetry already enables scientists to study the
migratory routes of marine top predators in detail. However,
at present, many questions remain, especially concerning the
drivers and the processes that shape migration. This opens up
interesting opportunities for future research and invites scientists to think outside the box to tackle current practical
problems. Again, inter- and multidisciplinary collaborations
could provide solutions.
Challenges and Ethics of Bio-telemetry
Attaching a device to an animal necessarily raises ethical
questions (Wilson and McMahon 2006), which still remain
largely understudied (Vandenabeele et al. 2011). Is it appropriate to equip an animal with an instrument that may impact
its natural behavior or may even affect its breeding success
and survival? What is regarded as acceptable practice? Does
the acquisition of knowledge outweigh the potential adverse
effects of a tag? In this section we will first highlight, separately for each top predator group, the difficulties of attaching a tag to an animal, and then list the known tag effects for
each group. Finally, we mention approaches for improvements in the field of bio-telemetry and give recommendations from the perspective of animal welfare.
First of all, it is far from easy to equip an animal with a
tag. It usually involves capturing and physically restraining
the animal for a certain period of time. Sometimes even
chemical immobilization is necessary, particularly in large
pinnipeds (Gales and Mattlin 1998; Bornemann et al. 2013).
The capture itself causes short-term stress for the animal, but
does not usually have long-term consequences (Baker and
Johanos 2002; McMahon et al. 2005; Blanchet et al. 2014).
The tag attachment techniques vary considerably between,
and even within, the different taxa, but can generally be
divided into invasive and non-invasive attachments.
Most bio-telemetry devices for pinnipeds are non- invasive
and commonly glued to the fur by using epoxy resin (Fedak
et al. 1983; Lowther et al. 2013; Nachtsheim et al. 2017), or
more recently, superglue (Cronin et al. 2016). The devices
are either actively recovered or remain on the animal for up
to one year until they fall off during the next annual molt.
The attachment procedure itself, i.e., gluing the device to the
fur, can cause small superficial abrasions or even lesions in a
few cases, however, these injuries heal completely soon after
the tag has been shed (Field et al. 2012). There is evidence
that the placement of particularly large and bulky tags
increases the hydrodynamic drag, potentially causing elevated metabolic costs and leading to behavioral changes in
the short term (Walker and Boveng 1995; Hazekamp et al.
2010; Blanchet et al. 2014; Maresh et al. 2015; Rosen et al.
2017). However, long-term studies on the mass gain and survival of seals could not find adverse effects of bio-telemetry
devices (Baker and Johanos 2002; McMahon et al. 2008;
Mazzaro and Dunn 2010).
The attachment of non-invasive telemetry devices on
cetaceans has proven to be challenging. The smooth and rapidly regenerating skin of whales, dolphins and porpoises
hampers the attachment of external tags. A commonly used
non-invasive method is deploying tags, such as DTAGs, with
suction cups (Fig. 2f). These devices usually stay on the animal for a few hours or days (Aguilar Soto et al. 2008;
Wisniewska et al. 2016). This method is obviously not sufficient to study large-scale migration patterns and hence,
invasive tags are frequently used on cetaceans. The tag is
either anchored in the blubber or muscle tissue, especially on
large whales and dolphins (Weller 2008; Hauser et al. 2010;
Reisinger et al. 2014; Gendron et al. 2015), or pinned through
the dorsal fin of small dolphins and porpoises (Irvine et al.
1982; Teilmann et al. 2007; Balmer et al. 2014). While the
former can be remotely deployed (e.g., using a crossbow),
the latter requires physically capturing the animals. The
wound-healing and long-term effects of invasive tagging
have rarely been studied, particularly due to the elusive
nature of most cetaceans. Although swellings, cavities, and
scars are frequently observed at the tag site in large whales,
even over a period of multiple years, these injuries, however,
had no impact on the body condition, overall health or reproductive success of the animals (Best and Mate 2007; Mate
et al. 2007; Weller 2008; Gendron et al. 2015; Norman et al.
2017). In small cetaceans, dorsal fin-mounted tags can fall
off due to corrosion of the pins. In some cases, mild inflammatory responses have been reported around the pin holes,
but they usually heal without complication, resulting in the
formation of scar tissue (Sonne et al. 2012; Heide-Jørgensen
et al. 2017). More severe is the migration of dorsal fin tags
through the tissue over time due to the constant hydrodynamic drag, ultimately leading to tag loss and fin damage
(Irvine et al. 1982; Martin et al. 2006; Balmer et al. 2014).
This raises the concern of whether or not such tags negatively affect the natural behavior of small cetaceans (van der
Hoop et al. 2014). However, on the long term, body condition, survival rates and reproductive success of tagged small
cetaceans were not affected (Martin et al. 2006; HeideJørgensen et al. 2017)
Bio-telemetry as an Essential Tool in Movement Ecology and Marine Conservation
mined. Studies on navigational ability in migratory seabirds
showed that there can be many potential cues, for instance,
olfactory, hydrodynamic, sky polarization, sun and star positions (Muheim et al. 2006; Lohmann et al. 2008; Gagliardo
et al. 2013). However, detecting the geomagnetic field was,
for example, in black-browed albatross Diomedea melanophris not one of them (Bonadonna et al. 2003). As such,
we need to remind ourselves that experimental studies are
never able to look at the full spectrum of natural conditions
that occur during migration and, therefore, cannot eliminate
particular cues completely.
Bio-telemetry already enables scientists to study the
migratory routes of marine top predators in detail. However,
at present, many questions remain, especially concerning the
drivers and the processes that shape migration. This opens up
interesting opportunities for future research and invites scientists to think outside the box to tackle current practical
problems. Again, inter- and multidisciplinary collaborations
could provide solutions.
Challenges and Ethics of Bio-telemetry
Attaching a device to an animal necessarily raises ethical
questions (Wilson and McMahon 2006), which still remain
largely understudied (Vandenabeele et al. 2011). Is it appropriate to equip an animal with an instrument that may impact
its natural behavior or may even affect its breeding success
and survival? What is regarded as acceptable practice? Does
the acquisition of knowledge outweigh the potential adverse
effects of a tag? In this section we will first highlight, separately for each top predator group, the difficulties of attaching a tag to an animal, and then list the known tag effects for
each group. Finally, we mention approaches for improvements in the field of bio-telemetry and give recommendations from the perspective of animal welfare.
First of all, it is far from easy to equip an animal with a
tag. It usually involves capturing and physically restraining
the animal for a certain period of time. Sometimes even
chemical immobilization is necessary, particularly in large
pinnipeds (Gales and Mattlin 1998; Bornemann et al. 2013).
The capture itself causes short-term stress for the animal, but
does not usually have long-term consequences (Baker and
Johanos 2002; McMahon et al. 2005; Blanchet et al. 2014).
The tag attachment techniques vary considerably between,
and even within, the different taxa, but can generally be
divided into invasive and non-invasive attachments.
Most bio-telemetry devices for pinnipeds are non- invasive
and commonly glued to the fur by using epoxy resin (Fedak
et al. 1983; Lowther et al. 2013; Nachtsheim et al. 2017), or
more recently, superglue (Cronin et al. 2016). The devices
are either actively recovered or remain on the animal for up
to one year until they fall off during the next annual molt.
The attachment procedure itself, i.e., gluing the device to the
fur, can cause small superficial abrasions or even lesions in a
few cases, however, these injuries heal completely soon after
the tag has been shed (Field et al. 2012). There is evidence
that the placement of particularly large and bulky tags
increases the hydrodynamic drag, potentially causing elevated metabolic costs and leading to behavioral changes in
the short term (Walker and Boveng 1995; Hazekamp et al.
2010; Blanchet et al. 2014; Maresh et al. 2015; Rosen et al.
2017). However, long-term studies on the mass gain and survival of seals could not find adverse effects of bio-telemetry
devices (Baker and Johanos 2002; McMahon et al. 2008;
Mazzaro and Dunn 2010).
The attachment of non-invasive telemetry devices on
cetaceans has proven to be challenging. The smooth and rapidly regenerating skin of whales, dolphins and porpoises
hampers the attachment of external tags. A commonly used
non-invasive method is deploying tags, such as DTAGs, with
suction cups (Fig. 2f). These devices usually stay on the animal for a few hours or days (Aguilar Soto et al. 2008;
Wisniewska et al. 2016). This method is obviously not sufficient to study large-scale migration patterns and hence,
invasive tags are frequently used on cetaceans. The tag is
either anchored in the blubber or muscle tissue, especially on
large whales and dolphins (Weller 2008; Hauser et al. 2010;
Reisinger et al. 2014; Gendron et al. 2015), or pinned through
the dorsal fin of small dolphins and porpoises (Irvine et al.
1982; Teilmann et al. 2007; Balmer et al. 2014). While the
former can be remotely deployed (e.g., using a crossbow),
the latter requires physically capturing the animals. The
wound-healing and long-term effects of invasive tagging
have rarely been studied, particularly due to the elusive
nature of most cetaceans. Although swellings, cavities, and
scars are frequently observed at the tag site in large whales,
even over a period of multiple years, these injuries, however,
had no impact on the body condition, overall health or reproductive success of the animals (Best and Mate 2007; Mate
et al. 2007; Weller 2008; Gendron et al. 2015; Norman et al.
2017). In small cetaceans, dorsal fin-mounted tags can fall
off due to corrosion of the pins. In some cases, mild inflammatory responses have been reported around the pin holes,
but they usually heal without complication, resulting in the
formation of scar tissue (Sonne et al. 2012; Heide-Jørgensen
et al. 2017). More severe is the migration of dorsal fin tags
through the tissue over time due to the constant hydrodynamic drag, ultimately leading to tag loss and fin damage
(Irvine et al. 1982; Martin et al. 2006; Balmer et al. 2014).
This raises the concern of whether or not such tags negatively affect the natural behavior of small cetaceans (van der
Hoop et al. 2014). However, on the long term, body condition, survival rates and reproductive success of tagged small
cetaceans were not affected (Martin et al. 2006; HeideJørgensen et al. 2017)
Bio-telemetry as an Essential Tool in Movement Ecology and Marine Conservation