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Case Study: Antarctic Project
In 2009, a group of researchers from several countries conformed the Southern
Ocean Researh Partnership (SORP), a collaborative consortium to develop and
implement non-lethal methods for cetacean research in the Southern Ocean, which
aims to maximize conservation efforts for cetaceans populations around Antarctica
after many of them were almost depleted by commercial whaling from the end of
nineteenth century and during the twentieth century. This program was endorsed by
the International Whaling Commission becoming the IWC-SORP. Argentina, as
one of the member countries of the SORP, has been participating in this program by
conducting a yearly ship-based survey on-board an Argentinean Coastguard cutter,
around the western Antarctic Peninsula during austral summer since 2014. The aim
of this project is to determine year-round relative abundance, distribution, and seasonality of cetaceans and correlate them with oceanographic features and possible
impact driven by climate change.
Line-transect surveys are conducted from the ship collecting simultaneous visual
and acoustic data on cetacean presence. Acoustic recordings are collected using a
linear array of hydrophones which is towed behind the vessel. Each element of the
array is equipped with an omni-directional sensor with an approximately flat frequency response from 30 Hz to 200 kHz, and each sensor is connected to a custombuilt preamplifier board and bandpass filter. One channel of the array records at
500 kHz sample rate and the others at 192 kHz which means that recordings are
obtained up to 250 kHz and 96 kHz, respectively. Acoustic recordings are monitored in real time by an acoustician who is communicated by radio with the marine
mammal observers located in the bridge. When sounds are recorded on several
channels, the difference in the time of arrival at each sensor can be used to localize
vocalizing animals and try to confirm the species producing that sound visually. The
good thing of combining visual and acoustic monitoring is that there are some species that are more detectable through one method or the other, and in this way the
detection probability overall increases. For example, given that the array is towed
behind the vessel, the ship noise masks the low-frequency sounds from baleen
whales preventing their detection. However, most toothed whales signals are in a
frequency range that can be recorded by the array without being overlapped by ship
noise, using the proper equipment. Besides, some deep diving species like sperm
whales and beaked whales can be very hard to detect visually in the surface, but they
can be easily recognized by their characteristic sounds.
One of the great advantages of using PAM to study cetaceans is that it gives us
the possibility of collecting continuous data during day and night, all year around,
in such a remote area as it is the Southern Ocean. Thus, in addition to the real time
visual and acoustic monitoring, in February 2014, an acoustic bottom-mounted,
autonomous recorder called HARP, was deployed near Elephant Island at a depth of
approximately 1000 m in order to collect sounds for the whole year. This equipment
samples at a rate of 200 kHz, obtaining acoustic signals from 10 Hz to 100 kHz,
which covers all baleen whale calls and most of the odontocetes known to inhabit
these waters. The HARP was successfully recovered and redeployed during a second SORP cruise in 2015, and again in a third cruise in 2016. Recovery, refurbishM.L. Melcón et al.
Case Study: Antarctic Project
In 2009, a group of researchers from several countries conformed the Southern
Ocean Researh Partnership (SORP), a collaborative consortium to develop and
implement non-lethal methods for cetacean research in the Southern Ocean, which
aims to maximize conservation efforts for cetaceans populations around Antarctica
after many of them were almost depleted by commercial whaling from the end of
nineteenth century and during the twentieth century. This program was endorsed by
the International Whaling Commission becoming the IWC-SORP. Argentina, as
one of the member countries of the SORP, has been participating in this program by
conducting a yearly ship-based survey on-board an Argentinean Coastguard cutter,
around the western Antarctic Peninsula during austral summer since 2014. The aim
of this project is to determine year-round relative abundance, distribution, and seasonality of cetaceans and correlate them with oceanographic features and possible
impact driven by climate change.
Line-transect surveys are conducted from the ship collecting simultaneous visual
and acoustic data on cetacean presence. Acoustic recordings are collected using a
linear array of hydrophones which is towed behind the vessel. Each element of the
array is equipped with an omni-directional sensor with an approximately flat frequency response from 30 Hz to 200 kHz, and each sensor is connected to a custombuilt preamplifier board and bandpass filter. One channel of the array records at
500 kHz sample rate and the others at 192 kHz which means that recordings are
obtained up to 250 kHz and 96 kHz, respectively. Acoustic recordings are monitored in real time by an acoustician who is communicated by radio with the marine
mammal observers located in the bridge. When sounds are recorded on several
channels, the difference in the time of arrival at each sensor can be used to localize
vocalizing animals and try to confirm the species producing that sound visually. The
good thing of combining visual and acoustic monitoring is that there are some species that are more detectable through one method or the other, and in this way the
detection probability overall increases. For example, given that the array is towed
behind the vessel, the ship noise masks the low-frequency sounds from baleen
whales preventing their detection. However, most toothed whales signals are in a
frequency range that can be recorded by the array without being overlapped by ship
noise, using the proper equipment. Besides, some deep diving species like sperm
whales and beaked whales can be very hard to detect visually in the surface, but they
can be easily recognized by their characteristic sounds.
One of the great advantages of using PAM to study cetaceans is that it gives us
the possibility of collecting continuous data during day and night, all year around,
in such a remote area as it is the Southern Ocean. Thus, in addition to the real time
visual and acoustic monitoring, in February 2014, an acoustic bottom-mounted,
autonomous recorder called HARP, was deployed near Elephant Island at a depth of
approximately 1000 m in order to collect sounds for the whole year. This equipment
samples at a rate of 200 kHz, obtaining acoustic signals from 10 Hz to 100 kHz,
which covers all baleen whale calls and most of the odontocetes known to inhabit
these waters. The HARP was successfully recovered and redeployed during a second SORP cruise in 2015, and again in a third cruise in 2016. Recovery, refurbishM.L. Melcón et al.