157
(Madsen and Wahlberg 2007). A negative aspect of sonobuoys is that they are often
used only one time and end up being trash in the ocean.
Autonomous Recorders there are different designs, but essentially all of them consist of a typical recording system described above, a set of batteries and hard drives
to store the information, and a release system. These devices are deployed onto the
seafloor and recovered after some time that could vary from several days to several
months, depending on the device configuration and capabilities. Generally, when
acoustic recordings are obtained from these autonomous recorders, there is no visual
data to match the sounds to a particular species. In those cases, there are other sources
of information that could provide some cues on species identification, e.g. the number of possible candidates can be reduced by studying which species are likely to
inhabit the sampled area. Also, a preliminary and broad characterization of the signal, along with previous information on acoustic repertoire of some species could
help to further reduce the candidates, e.g. for instance sperm whales can be excluded
if the recorded signals are whistles or NBHF clicks; if recordings consist of upswept
FM clicks any other taxa than beaked whales can be excluded. Later in this chapter
we will explain with a real example how some additional information can help to
have a good approximation of species identity. These systems are not usually used to
study the acoustic repertoire of a species given the lack of visual correlation to confidently determine the species identity of the recorded sounds. Instead, they are suitable to study cetacean presence in a certain area, seasonal patterns and abundance
estimates. In some case behavioral context is possible to be determined.
Acoustic Tags are attached on free-ranging animals and generally used to study the
acoustic repertoire and correlate it with diving and movement patterns. They have
sensors of sound, pressure and temperature, and a very high frequency (VHF) transmitter which stands for radio frequency electromagnetic waves to track the animal
and recover the tag once it is detached from the animal (Johnson et al. 2009). An
advantage of using tags is that usually the recorded sounds can be correlated with
diving patterns of the species of interest. Also source properties of the signals can be
described at an individual level. Among the cons, these tags are expensive and may
result difficult to attach, especially in fast swimming, small odontocetes. Currently
the deployment of the device is invasive and special permits are required to use them.
Equipment improvements over the last decades allowed scientists to get access
to information that some years ago wasn’t available because of the instrument limitations. For instance, the first studies on bioacoustics in Argentina were focused
mostly on Southern right whales and killer whales, and the hydrophones and recorders used by researchers probably would not be able to record frequencies higher
than 100 kHz. Thus, sounds from species like Commerson’s dolphins, Franciscana
dolphins, Peale’s dolphins and porpoises which all produce NBHF clicks would not
be recorded even if they were present and vocalizing. Thus, researchers aiming to
conduct bioacoustics studies need to consider very carefully which technical
requirements the equipment should meet in order to properly record and analyze the
sounds of the species of interest. It is important to consider the sensitivity of the
hydrophone (the sound pressure level required to generate 1 V), and frequency
6 Bioacoustic Techniques Applied to Odontocete Conservation and Management…
(Madsen and Wahlberg 2007). A negative aspect of sonobuoys is that they are often
used only one time and end up being trash in the ocean.
Autonomous Recorders there are different designs, but essentially all of them consist of a typical recording system described above, a set of batteries and hard drives
to store the information, and a release system. These devices are deployed onto the
seafloor and recovered after some time that could vary from several days to several
months, depending on the device configuration and capabilities. Generally, when
acoustic recordings are obtained from these autonomous recorders, there is no visual
data to match the sounds to a particular species. In those cases, there are other sources
of information that could provide some cues on species identification, e.g. the number of possible candidates can be reduced by studying which species are likely to
inhabit the sampled area. Also, a preliminary and broad characterization of the signal, along with previous information on acoustic repertoire of some species could
help to further reduce the candidates, e.g. for instance sperm whales can be excluded
if the recorded signals are whistles or NBHF clicks; if recordings consist of upswept
FM clicks any other taxa than beaked whales can be excluded. Later in this chapter
we will explain with a real example how some additional information can help to
have a good approximation of species identity. These systems are not usually used to
study the acoustic repertoire of a species given the lack of visual correlation to confidently determine the species identity of the recorded sounds. Instead, they are suitable to study cetacean presence in a certain area, seasonal patterns and abundance
estimates. In some case behavioral context is possible to be determined.
Acoustic Tags are attached on free-ranging animals and generally used to study the
acoustic repertoire and correlate it with diving and movement patterns. They have
sensors of sound, pressure and temperature, and a very high frequency (VHF) transmitter which stands for radio frequency electromagnetic waves to track the animal
and recover the tag once it is detached from the animal (Johnson et al. 2009). An
advantage of using tags is that usually the recorded sounds can be correlated with
diving patterns of the species of interest. Also source properties of the signals can be
described at an individual level. Among the cons, these tags are expensive and may
result difficult to attach, especially in fast swimming, small odontocetes. Currently
the deployment of the device is invasive and special permits are required to use them.
Equipment improvements over the last decades allowed scientists to get access
to information that some years ago wasn’t available because of the instrument limitations. For instance, the first studies on bioacoustics in Argentina were focused
mostly on Southern right whales and killer whales, and the hydrophones and recorders used by researchers probably would not be able to record frequencies higher
than 100 kHz. Thus, sounds from species like Commerson’s dolphins, Franciscana
dolphins, Peale’s dolphins and porpoises which all produce NBHF clicks would not
be recorded even if they were present and vocalizing. Thus, researchers aiming to
conduct bioacoustics studies need to consider very carefully which technical
requirements the equipment should meet in order to properly record and analyze the
sounds of the species of interest. It is important to consider the sensitivity of the
hydrophone (the sound pressure level required to generate 1 V), and frequency
6 Bioacoustic Techniques Applied to Odontocete Conservation and Management…