HOW IT WORKS?    

A-tag enables you to start acoustic monitoring of cetaceans, which you are interested in. A-tag offers multi-platform observations of cetaceans, originally developped to observe biosonar behavior by tagging on dolphins and porpoises in the wild. In recent years, A-tag has been applied for the acoustic transect to count the number of dolphins and porpoises, and for the long term stationed observation. A-tag can be attached on a rope towed from a boat, or on a pipe fixed beside a waterbreak, or on an animal using a suction cup.  Application for passive acoustic monitoring, see this pdf file (ASA 2009, Portland, USA) .

A-tag can be used to count the number of animals acoustically. Two ultrasonic hydrophones of  A-tag enables to record sound pressure at each hydrophones as well as the sound source direction calculated by the sound arrival time difference between two hydrophone. Identification of each sound source can be used to descriminate each phonating animal individually. 

A-tag is a small and stand-alone system. The water registant body of A-tag sizes 21 mm in diameter and 108 mm in length + external stereo hydrophones. All of the data is stored in the flash memory of A-tag and is downloaded after you retrieve it. A-tag works up to 40 hours by CR2 lithium battery (standard type)and one month by two D cells for long-life stationed type (optional).

A-tag offers open source. For data analysis, Igor (Wavemetrics, AZ, USA) has been used. Source code of the noise reduction and identification of biosonar clicks is archived in this web page. You can download and modify the parameters to fit your animals and noise conditions.

A-tag does not record sound waveform. It is event recorder of each pulse with received sound pressure level over the pre-set detection threshold level. Although the 70 kHz high-pass filter in A-tag reject the low frequency noise due to engine operation and water flow, heavy snapping shrimp noise in warm waters could reduce the detection performance of A-tag.


A-tag fixed on a rope towed from a boat (left). Long life A-tag for stationary observation in the Yangtze River, China

Manual is available here ver.4.35

RESEARCH EXAMPLES

1.Tagging on the animal

Acoustical inspection ahead in advance monotired an animal-mounted A-tag on free ranging finless porpoise. Free-ranging finless porpoises scan ahead by their sonar in advance before swimming silently. The inspection distance reached several tens meters that provide long enough ‘safety margin’ for the animal before facing to real risks or rewards. Once the porpoise detect a potential prey, it keeps focusing sonar to the target during approaching. When we are driving a car with listening music, we should check ahead in advance before changing a compact disk, otherwise we can crash easily. Detecting objects in their path is a fundamental perceptional function of moving organisms. Source: Biosonar behaviour of free-ranging porpoises, Proc. R. Soc. Lond. B, 272, 797-801.


2.Towing from a ship

Quantitative acoustic strip transect to count porpoises monitored by towed A-tag from a vessel. Yangtze finless porpoises were surveyed by using simultaneous visual and acoustical methods from 6 November to 13 December 2006. Two research vessels towed stereo acoustic data loggers, which were used to store the intensity and sound source direction of the high frequency sonar signals produced by finless porpoises at detection ranges up to 300 m on each side of the vessel. Simple stereo beam forming allowed the separation of distinct biosonar sound source, which enabled us to count the number of vocalizing porpoises. Acoustically, 204 porpoises were detected from one vessel and 199 from the other vessel in the same section of the Yangtze River. Visually, 163 and 162 porpoises were detected from two vessels within 300 m of the vessel track. The calculated detection probability using acoustic method was approximately twice that for visual detection for each vessel. The difference in detection probabilities between the two methods was caused by the large number of single individuals that were missed by visual observers. However, the sizes of large groups were underestimated by using the acoustic methods. Acoustic and visual observations complemented each other in the accurate detection of porpoises. The use of simple, relatively inexpensive acoustic monitoring systems should enhance population surveys of free-ranging, echolocating odontocetes. Source: Estimation of the detection probability for Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) with a passive acoustic method. J. Acoust. Soc. Am. 123(6), 4403-4411.

3. Stationed longterm monitoring

Attendance and swimming directions could be measured using stationed A-tag on a seabed or a buoy.  From March 2005 to March 2006, the presence of the finless porpoise Neophocaena phocaenoides in the Kanmon Strait, Japan was monitored using a stationary acoustic event recording device. A stereo acoustic event recorder (A-tag) recorded biosonar signals as well as sound source directions, which can be used to count the number of echolocating porpoises within a distance of 126 m. During 75 days of effective observation, 37 porpoises were detected acoustically. On average, one individual was detected every two days. Most of the finless porpoises appeared at night, and no porpoises were observed from 12:00 to 18:00 hours. Shipping traffic observed using the same acoustic system showed trends opposite to that of finless porpoise during the daytime. The tidal current did not affect the presence of the animals (up to 5.2 knots). However, porpoises were suggested to swim along the current direction. Finless porpoises appeared to be isolated and used relatively long-range sonar during the observations, suggesting that the porpoises passed through the Kanmon Strait rather than searched for prey.  Source: Evidence of nighttime movement of finless porpoises through Kanmon Strait monitored using a stationary acoustic recording device, Fisheries Science 74, 970-976. Seasonal and diurnal presence of finless porpoises at a corridor to the ocean from their habitat, Marine Biology 157, 1879-1887.

COLLABORATION

Why not to to collaborate with us? If you will provoide platforms or animals, we are happy to bring some of our A-tags to your research field, as long as the collaboration will be fruitful for both of us. Feel free to contact

SPECIFICATIONS

Sensor
Stereo hydrophone MHP-140-140 or MHP-140-070.

Frequency response of  MHP-140 (left) and MHP-70 (right).

MHP-140 is most sensitive at 130kHz (-200.0dB re 1V/uPa). MHP-70 is most sensitive at 70 kHz (-200.2 dB re 1V/uPa).

Recording parameters
1. Sound pressure level
 Minimum detection threshold level: 130 dB p-p re 1uPa @ 100kHz
 maximum input for the circuit 3.22 Vp-p
 amplification +60dB
 resolution 10 bits
 band pass filter 55kHz - 235 kHz
 sampling interval 0.5ms, 1ms, 2ms
2. Time difference
 Range +/- 139us, +/-278us, +/-556us (sampling interval 0.5 ms, 1ms and 2ms)
 Resolution 271.265ns, 542.53ns, 1085.06ns
 Trigger ch A level (ch B is slaver)

Start mode
1. Timer mode
 Delay timer to start (0-255hours)
2. Clock mode
 Start at specific time up to 30 days
3. Interval mode
 Interval recording (interval 1-255 minute>recording 1-255 minute, 1min step)

Data size
 42,500,000 data (1Gbit flash memory)

Interface
 Interface box (MIF-200) and cable (MIFC-1) is used to communicate with A-tag
 Logger Tools vr.4.34 is the software to set up and data loading by PC

Size (A-tag short term version without hydrophone)
 Material aluminum
 Diameter 21 mm
 Length 112 mm
 Weight 72 g (with hydrophone and CR2 battery for short term version)

Battery
 CR2 (commercial lithium battery) x 1 for short term use
 D cell x 2 for for long term use (note that long term housing is necessary)