Sea turtles have existed for millions of years. International Union for Conservation of Nature (IUCN) has reported that the Hawksbill Turtle (Eretmochelys imbricata) is classified as critically endangered. Turtle excluder device (TED) deployment on shrimpnet fisheries is needed for turtle conservation.TED using sound technique is challenge method in fisheries development.The knowledge on turtle hearing capability is limited. The auditory brainstem response (ABR) assessment is method to determine turtle hearing capability. Turtle hearing assessment is basis to design TED. The objective of this paper is to determine turtle hearing cability by analyze its ABR spectral.The subject is Hawksbill turtle with number 2 turtles ie: 3 and 2 years. The measurement was taken at Pusat Pengurusan Penyu (Turtle Management Centre) Padang Kemunting Masjid Tanah Melaka Malaysia. The results shows that turtle 3 years have peak power frequencies 50.78, 101.6, 152.3, 304.7, 355.5, 457, and 507.8Hz respectively whereas the spectral amplitude is ranging 0.03-32.44% spectral. Turtle 2 years has peak power at 457Hz in whole stimulus frequencies while the spectral amplitude is ranging 0.01-2.5% spectral

Abdullah, Syed

Din, Jafri

Hassan, Raja Bidin Raja

Sunardi, Sunardi

Yudhana, Anton

English

TELKOMNIKA (Telecommunication Computing Electronics and Control)

ISSN: 1693-6930 Terakreditasi DIKTI, SK No: 51/DIKTI/Kep/2010      187 
  
Turtle Hearing Capability Based on ABR Signal Assesment (Anton Yudhana) 
TURTLE HEARING CAPABILITY 
BASED ON ABR SIGNAL ASSESMENT 
 
 
Anton Yudhana1,2 , Sunardi1,2, Jafri Din2, Syed Abdullah3, Raja Bidin Raja Hassan4 
1Electrical Engineering Department, Universitas Ahmad Dahlan 
Jl. Prof. Dr.Soepomo Janturan UH, Yogyakarta 55164 Indonesia, Phone. +62 274 379418 
2Electrical Engineering Faculty, Universiti Teknologi Malaysia 
3TUMEC (Turtle and Marine Ecosystem Center) Rantau Abang, Dungun, Terengganu, Malaysia 
4Marine Fishery Resources Development and Management Department Terengganu, Malaysia 
e-mail: antony@uad.ac.id 
 
 
Abstrak 
Penyu telah ada di bumi selama jutaan tahun. Telah dilaporkan oleh International Union 
for Conservation of Nature (IUCN) bahwa Hawksbill Turtle (Eretmochelys imbricata) 
diklasifikasikan ke dalam penyu yang terancam punah. Penggunaan turtle excluder device 
(TED) pada nelayan udang diperlukan untuk menjaga kelestarian penyu. TED menggunakan 
suara merupakan alternatif teknologi yang dapat digunakan dalam teknik penangkapan ikan. 
Pengetahuan tentang kapasitas pendengaran penyu masih terbatas. Pengamatan terhadap 
sinyal auditory brainstem response (ABR) adalah metode untuk penentuan pendengaran penyu 
Hasil penilaian kapasitas pendengaran penyu menjadi dasar bagi perencanaan TED Tujuan 
dari makalah ini adalah menentukan kapasitas pendengaran penyu dengan analisis spectrum 
ABR-nya. Subjek dalam penelitian ini adalah penyu Hawksbill berjumlah 2 ekor dengan umur 3 
dan 2 tahun.. Pengukuran dilakukan di Pusat Pengurusan Penyu Padang Kemunting Masjid 
Tanah Melaka Malaysia. Hasil pengukuran telah diperoleh bahwa penyu 3 tahun memberikan 
respons tertinggi pada frekuensi 50,78, 101,6, 152,3, 304,7, 355,5, 457, dan 507,8 Hz dengan 
amplitude dalam kisaran 0.03-32.44% spektrum. Penyu 2 tahun memberikan respons tertinggi 
pada frekuensi 457Hz dengan amplitudo dalam kisaran 0,01-2,5% spektrum.  
 
Kata kunci: ABR, kapasitas pendengaran, power spektrum, TED 
 
 
Abstract 
Sea turtles have existed for millions of years. International Union for Conservation of 
Nature (IUCN) has reported that the Hawksbill Turtle (Eretmochelys imbricata) is classified as 
critically endangered. Turtle excluder device (TED) deployment on shrimpnet fisheries is 
needed for turtle conservation.TED using sound technique is challenge method in fisheries 
development.The knowledge on turtle hearing capability is limited. The auditory brainstem 
response (ABR) assessment is method to determine turtle hearing capability. Turtle hearing 
assessment is basis to design TED. The objective of this paper is to determine turtle hearing 
cability by analyze its ABR spectral.The subject is Hawksbill turtle with number 2 turtles ie: 3 
and 2 years. The measurement was taken at Pusat Pengurusan Penyu (Turtle Management 
Centre) Padang Kemunting Masjid Tanah Melaka Malaysia. The results shows that turtle 3 
years have peak power frequencies 50.78, 101.6, 152.3, 304.7, 355.5, 457, and 507.8Hz 
respectively whereas the spectral amplitude is ranging 0.03-32.44% spectral. Turtle 2 years has 
peak power at 457Hz in whole stimulus frequencies while the spectral amplitude is ranging 
0.01-2.5% spectral. 
 
Keywords: ABR, hearing capability, power spectral, TED 
 
 
1. INTRODUCTION  
  Sea turtles have existed for millions of years. International Union for Conservation of 
Nature (IUCN) has reported that the hawksbill turtle (Eretmochelys imbricata) is classified as 
critically endangered in 2004 [1]. Fishermen to catch fish and shrimp in accordance with the 
rules must be equipped with a TED. TED that is equipped in the nets and trawls will be able to 
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reduce the number of turtle bycatch but the recent TED used is still mechanical [2]. Sound 
deployment on TED is one of challenge method in fisheries development. The knowledge on 
turtle hearing capability is limited for previous study so the improvement on turtle hearing 
measurement is needed as basis on designing TED using sound technique [3].  
 One method to asses the subject hearing capability is by analysis ABR signal. ABR 
signals are traditionally occurs during the first 11 ms after the stimulus, followed by a Mid-
Latency cortical Response (MLR) which is typically confined to the next 70ms, followed by a 
slow cortical response which starts at about 80 ms after the stimulus. ABR signals have a 
waveform morphology which typically exhibits five waves (peaks) in the 1.5 to 6 ms post-
stimulus interval [4], [5]. Works described techniques for extracting the human ABR from the 
EEG by deployed new algorithm of adaptive filtering in the time-frequency domain using a 
specific Wavelet Transform and compare it to traditional ABR extraction are given in [4].  
 The ABR signals are acquired from the animals and humans subject in order to asses 
and determine the cranial auditory nerve function, to asses the viability of cochlear implantation, 
or the existence of any physical conditions that may prevent successful implantation [6]. The 
ABR technique is a noninvasive and rapid method to measure the hearing range of animals. It is 
a method that requires no training of the subject and is used also to asses hearing response in 
human infants [7]. ABR models classification by generated using time, frequency and cross-
correlation measures. Classification employed both artificial neural networks (NNs) and the C5.0 
decision tree algorithm [8].  
 ABR analysis deployed on animals ie: dolphin [9], fishes clupeid species [10], tuna 
(Thunnus albacores), turle (C.mydas and L.Kempi) [11], prawn [12]. The collective knowledge of 
marine hearing and sound detection capabilities is very limited because limited knowledge of 
true hearing thresholds of such animals and their sensitivity to various sound levels, frequencies 
and durations [13]. 
 This research is aimed to identify turtle hearing capability focoused on Hawksbill 
species by analyze its ABR signal. This study is expected to increase knowledge on marine 
turtle hearing capability, especially the hawksbill turtle.  
 
 
2. RESEARCH METHOD  
2.1. Subject and Facility 
Two Hawksbill Turtles were used in the ABR measurement. The turtle’s profile is stated 
in Table 1.The research was conducted at Pusat Pengurusan Penyu (Turtle Management 
Centre) Padang Kemunting Masjid Tanah Melaka Malaysia in December 24, 2008. The turtle 
brought out from the pool and put it into the research box as shown in Figure 1. The turtle 
dimension measurement was done previously before established ABR recording.  
 
 
 
 
Figure 1. Length Measurement of Karah 
 
 
 
Figure 2. Weigth Measurement of Karah 
 
 
First stage of measurement is dimension measurement. The turtle length divided into 3 
categories, ie: total length (TL), length of neck-head (NH), and width. The weight of turtle has 
been measured. The turtles dimension measurement procedure is shown in Figure 1 and 2.    
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Table1. Species is used in ABR measurement 
No Age 
(year) 
Sex TL 
(cm) 
NH 
(cm) 
Width 
(cm) 
Weight 
(Kg) 
1. 3 NA 55 15 34 7,4 
2. 2 NA 37 12 33 5,1 
 
Note: 
TL : total length 
NH : length of neck-head. 
 
   
Both of length and weight measurement is taken in dried condition. The aimed of this 
procedure is to get the correlation between the turtle age and its dimension. The second stage 
was ABR recording. The Measurement used ABR hardware that was supported with the 
SmartEP software.   
 
 
2.2. ABR Recording and measurement 
 ABR system was installed to turtle for one hour as shown in Figure 3. In this 
measurement click stimulus is used. The frequency of ABR analyzer is ranging between 0 to 5 
kHz. During the ABR measurement, turtles were stated in the research box and. Turtles were 
equipped with ABR system and hold in stable position. The subject becomes relaxed in resting 
position. During a sound presentation, the turtle was stationed. The measured data is analyzed 
using SmartEp software and compared with Matlab program. IHS system stimulus was set on 
parameters as follows:  
a. Sweeps =  1000 
b. Time =  25.0 us, 
c. Intensity = 58 dB nHL 
d. Ear = right 
e. Rate = 70.00/s 
f. Rej. Artefact = 31.00uV 
g. Rej. Time = 1.0-10.0 ms 
 
 
 
 
Figure 3. ABR recording in the box 
 
 
 
Figure 4. ABR Measurement team 
 
 
The transducer that produced the stimulus is placed 0.5 m from the box. It is depicted in 
Figure 3 and Figure 4.The Turtle were equipped with ear electrode (earphones). Earphones are 
small stimulating transducer that delivers the stimulus to the turtle’s ear. Four earphones were 
used to measured turtle hearing response. The amount of collected data indicated the respond 
of the turtle. 
The click stimulus divided into 15 durations. The durations were set up from 100 µs-
1500 µs. The recorded data saved into three modes ie: time domain, ASCII code, and data 
reported (.rpt).Furthermore, data in time domain were converted in frequency domain using 
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SmartEP software and Matlab.Both SmartEP dan Matlab deployed Fast Fourier Transform 
(FFT).   
 
 
3. RESULTS AND DISCUSSION  
3.1. Turtle 3 years 
The click stimulus was transmitted started in 100 µs duration time. It was obtained 
response signal ABR of turtle in the time domain signal. The result of ABR signal for 300µs 
duration is plotted in Figure 5.  
 
 
 
 
Figure 5. Turtle 3 years ABR signal in time domain, 300µs stimulus duration 
 
 
 
 
Figure 6. Turtle 3 years ABR spectral, 300µs stimulus duration 
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Figure 7. Turtle 3 years ABR signal, stimulus duration 300 µs. 
 
 
Then the signal in the time domain converted into frequency domain with SmartEp. The 
resulted signal is called frequency spectral as seen in Figure 6. Figure 6 indicated frequency 
spectral was obtained with a stimulus duration 300 µs has maximum power at frequency more 
300 Hz.The frequency spectral has the harmonisa at a frequency of more 900 Hz.  
  
 
Table 2. The Response of 3 years turtle 
Sample 
Number 
Stimulus 
Duration  
(µs) 
Peak power in 
freq Spectral 
(Hz) 
Spectral 
Amplitude 
(%) 
1.  100 355,5 0,064 
2.  200 304,7 0,034 
3.  300 507,8 1,193 
4.  400 507,8 0,92 
5.  500 50,78 4,72 
6.  600 152,3 1,27 
7.  700 101,6 25,34 
8.  800 NA NA 
9.  900 457 32,44 
10.  1000 NA NA 
11.  1100 NA NA 
12.  1200 NA NA 
13.  1300 NA NA 
14.  1400 NA NA 
15.  1500 NA NA 
 
 
Conversion of ABR signals to its spectral using SmartEP still unclear. To get better 
results Matlab is deployed as a comparison. To get the ABR signals in time and spectralnya 
area in Matlab, ASCII data from the ABR processed first in Excel. Artifact information in numeric 
data is removed. ABR value is selected start from 0 ms-12.8 ms. 
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Results of ABR signal processing using Matlab is more accurate. Signals have obtained clearly 
in numerical values of the spectral signal as in Figure 7. The figure shows that ABR signal in 
time domain selected for 0ms-12.8 ms with the amplitude in µV. Turtles 3 years respond to 
stimulus at 507.8 Hz and the amplitude 1.193%. 
Later in the same manner by increased 100 µs duration time until 1500 µs would be 
obtained the frequency spectral of 3 years turtle as shown in Table 2. Turtle 3 years response 
could be analyzed if failed to respond when the stimulus set on 1000µs-1500 µs. While the 
stimulus 100 µs -700 µs and 900 µs turtle responded obviously. The event of peak power 
occurs in varying frequencies ie: 50.78 Hz, 101.6 Hz, 152.3 Hz, 304.7 Hz, 355.5 Hz, 457 Hz, 
and 507.8 Hz. The spectral amplitude is not uniform in some stimulus. The spectral amplitude is 
ranging 0.03%-32.44% power spectrum. 
 
3.2. Turtle 2 years 
The click stimulus was deployed for 2 years turtle. It was transmitted started in 100 µs 
duration. Measurement has been obtained signal ABR of turtle in the time domain signal that 
coud be seen in Figure 8. Turtle still not in relaxed yet in stimulus 100 µs as of the ABR signal 
failed to measure. Futher, stimulus duration was increased to 200 µs. The subject responds to 
stimulus. Plotted data in the figure is processed in SmartEP.  
 
 
 
 
Figure 8. Turtle 2 years ABR signal in time domain, 300µs stimulus duration 
 
 
ABR signal then converted into spectralnya. Frequency spectral was obtained with a 
stimulus duration 200 µs has maximum power at frequency more 300 Hz is depicted in Figure 9.  
The result has the harmonisa at other frequency.  
Conversion of ABR signals to its spectral using SmartEP still unclear. The frequency on 
maximum power not exact yet. Matlab is deployed as a comparison to complement the lack of 
information. ABR signals in ASCII form is extracted in Excell. Numeric value is easier to analyze 
in excell form. By reject artifact value ABR signal is selected start from 0-12.8 ms as shown in 
Figure 10. 
The Figure 10 shows that ABR signal in time domain selected for 0-12.8 ms with the 
amplitude in µV. Turtles 2 years respond to stimulus at 457 Hz and the amplitude is 0.043 %. 
Turtle response could be analyzed if failed to respond when the stimulus set on 100 µs. 
While the stimulus 200-1500 µs turtle responded clearly. The occurance of peak power is at 457 
Hz in whole stimulus frequencies. The spectral amplitude is not uniform in some stimulus. The 
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spectral amplitude is ranging 0.01-2.502% power spectrum. Later in the same manner with 3 
years turtle the ABR signal of 2 years turtle could be seen in Table 3. 
 
 
 
 
Figure 9. Turtle 2 years ABR spectral, 300(s stimulus duration 
 
 
 
 
Figure 10.Turtle 2 years ABR signal, stimulus duration 300 µs. 
 
Table 3. The Response of 2 years turtle 
Sample 
Number 
Stimulus 
Duration  
((s) 
Peak power in 
freq Spectral 
(Hz) 
Spectral 
Amplitude 
(%) 
1.  100 NA NA 
2.  200 457 0,043 
3.  300 457 0,071 
4.  400 457 0,011 
5.  500 457 0,019 
6.  600 457 0,161 
7.  700 457 0,203 
8.  800 457 1,605 
9.  900 457 0,028 
10.  1000 457 4,73 
11.  1100 457 0,016 
12.  1200 457 0,119 
13.  1300 457 2,502 
14.  1400 457 0,116 
15.  1500 457 0,074 
 
  
 
4. CONCLUSION  
 The measurement of Hawksbill Turtle ABR signal has been conducted in the turtle 
research box. Turtles hearing capability has been determined. ABR signal assesment has been 
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done by converted recorded data into frequency domain by deployed FFT method. The results 
show that turtle 3 years responds to the transmitted stimulus wider than turtle 2 years in 
frequency range and amplitude response.   
 
 
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[9]. Mooney TA, Tachtigall PE, Yuen ML. Temporal resolution of the Risso’s Dolphin, Grampus 
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