115
which can be towed behind vessels (Jaquet and Whitehead 1999; Whitehead 2002;
Watwood et al. 2006; Barlow et al. 2013), allowing to record sounds continuously.
Passive acoustic detection systems have been successfully used on a number of cetacean surveys (Gannier et al. 2002; Barlow and Taylor 2005; Leaper et al. 2003; Hastie
et al. 2003; Lewis et al. 2007; Fais et al. 2016). Acoustic monitoring provides an opportunity to collect data in conditions unsuitable for visual observations such as darkness,
poor visibility and high sea states (Evans and Hammond 2004; Mellinger et al. 2007;
Ward et al. 2012). The use of simple towed hydrophones to monitor cetacean vocalizations enables quantifiable data to be collected at minimal cost (Whitehead 2002).
The implementation of acoustic survey associate to visual effort can maximize
the results, knowing that a relative large amount of ship time would be lost due to
bad weather or night fall, a passive acoustic towed-array device can increase search
effort. Some researchers have demonstrated the advantages of acoustic towed arrays
in comparison to visual survey methods specially to detect species that spend most
of their time in deep divings, such as beaked whales and sperm whales (Jaquet and
Whitehead 1999; Whitehead 2002; Watwood et al. 2006; Barlow et al. 2013; Yack
et al. 2013; Schorr et al. 2014). On the other hand, this technique has disadvantages
as the need to manage a heavy cable when the moving platform stops, loss of
maneuverability of the moving platform, risk of damaging the propellers, requires
an experienced crew and is a lengthy process to initiate the survey (Evans and
Hammond 2004; Nielsen and Møhl 2006).
This chapter will present a general overview of the equipment which has being used
to cetaceans acoustic survey in the Western South Atlantic Ocean. Also, will give a basic
bioacoustic analysis introduction and will present a general description of acoustic
parameters of different species registered. Recordings were obtained opportunistically
from 2012 to 2015 during a survey mostly dedicated to visual monitoring of cetacean
occurrence and distribution along the western South Atlantic continental shelf break.
Research cruises were performed between 26°S and 38°S over the continental shelf
break and slope. Acoustic tracklines comprised an average of 780 nm of effort per survey. Concurrent environmental and GPS data were logged automatically using WinCruz
software. Visual positive identifications were associated to the acoustic recordings. The
wave files were analyzed using partially automated detections tools complemented with
visual and aural searched for species confirmation whenever possible.
5.2 Towed Array Equipment
The system consists of a three-elements hydrophone array (Fig. 5.1) on a cable
towed 150–300 m behind the vessel) coupled to a recording system, configured to
give a variable frequency response from 499 Hz (High Pass Filter) to 100,000 Hz
(Fig. 5.2). This system is mostly used as an additional method to visual surveys
commonly applied to marine mammals (Bittle and Duncan 2013), allowing real
time or post data analysis. It has being used from different platforms and contexts
5 Marine Mammal Bioacustics Using Towed Array Systems in the Western South…
which can be towed behind vessels (Jaquet and Whitehead 1999; Whitehead 2002;
Watwood et al. 2006; Barlow et al. 2013), allowing to record sounds continuously.
Passive acoustic detection systems have been successfully used on a number of cetacean surveys (Gannier et al. 2002; Barlow and Taylor 2005; Leaper et al. 2003; Hastie
et al. 2003; Lewis et al. 2007; Fais et al. 2016). Acoustic monitoring provides an opportunity to collect data in conditions unsuitable for visual observations such as darkness,
poor visibility and high sea states (Evans and Hammond 2004; Mellinger et al. 2007;
Ward et al. 2012). The use of simple towed hydrophones to monitor cetacean vocalizations enables quantifiable data to be collected at minimal cost (Whitehead 2002).
The implementation of acoustic survey associate to visual effort can maximize
the results, knowing that a relative large amount of ship time would be lost due to
bad weather or night fall, a passive acoustic towed-array device can increase search
effort. Some researchers have demonstrated the advantages of acoustic towed arrays
in comparison to visual survey methods specially to detect species that spend most
of their time in deep divings, such as beaked whales and sperm whales (Jaquet and
Whitehead 1999; Whitehead 2002; Watwood et al. 2006; Barlow et al. 2013; Yack
et al. 2013; Schorr et al. 2014). On the other hand, this technique has disadvantages
as the need to manage a heavy cable when the moving platform stops, loss of
maneuverability of the moving platform, risk of damaging the propellers, requires
an experienced crew and is a lengthy process to initiate the survey (Evans and
Hammond 2004; Nielsen and Møhl 2006).
This chapter will present a general overview of the equipment which has being used
to cetaceans acoustic survey in the Western South Atlantic Ocean. Also, will give a basic
bioacoustic analysis introduction and will present a general description of acoustic
parameters of different species registered. Recordings were obtained opportunistically
from 2012 to 2015 during a survey mostly dedicated to visual monitoring of cetacean
occurrence and distribution along the western South Atlantic continental shelf break.
Research cruises were performed between 26°S and 38°S over the continental shelf
break and slope. Acoustic tracklines comprised an average of 780 nm of effort per survey. Concurrent environmental and GPS data were logged automatically using WinCruz
software. Visual positive identifications were associated to the acoustic recordings. The
wave files were analyzed using partially automated detections tools complemented with
visual and aural searched for species confirmation whenever possible.
5.2 Towed Array Equipment
The system consists of a three-elements hydrophone array (Fig. 5.1) on a cable
towed 150–300 m behind the vessel) coupled to a recording system, configured to
give a variable frequency response from 499 Hz (High Pass Filter) to 100,000 Hz
(Fig. 5.2). This system is mostly used as an additional method to visual surveys
commonly applied to marine mammals (Bittle and Duncan 2013), allowing real
time or post data analysis. It has being used from different platforms and contexts
5 Marine Mammal Bioacustics Using Towed Array Systems in the Western South…