The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Analysis of echolocation click signals of Indo-Pacific bottlenose dolphin (Tursiops aduncus) in Jeju Island

제주 남방큰돌고래 반향정위 클릭음 특성 분석

  • 최강훈 (한양대학교 해양융합공학과) ;
  • 윤영글 (국립수산과학원 고래연구센터) ;
  • 김선효 (한양대학교 해양융합공학과) ;
  • 김현수 (한양대학교 해양융합공학과) ;
  • 최지웅 (한양대학교 해양융합공학과) ;
  • 배호석 (국방과학연구소) ;
  • 박경주 (해군사관학교)
  • Received : 2018.08.31
  • Accepted : 2019.01.25
  • Published : 2019.01.31
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Abstract

The Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a toothed whale using echolocation clicks and have been studied continuously abroad. However, most studies on this whale's clicks were performed about captive animals and, in Korea, only the studies of the whistle sounds of this animal were done. In this paper, acoustic characteristics of clicks were analyzed about the free-ranging Indo-Pacific bottlenose dolphins living in the coast of the Jeju Island. Acoustic parameters such as signal duration, 1st and 2nd peak frequency, 3 dB and 10 dB bandwidth for acoustic characteristics were calculated and compared with those of Australian species. As a result, the signal durations had average of $38{\mu}s$ and most clicks were within range of $20{\mu}s-60{\mu}s$. The two types of bandwidths showed both narrowband and broadband characteristics, and bimodal signal characteristics were confirmed through the 1st peak frequencies(average of $96kHz{\pm}18kHz$) and the 2nd peak frequencies(average of $69kHz{\pm}19kHz$).

남방큰돌고래(Tursiops aduncus)는 클릭음을 사용하는 이빨고래로써 국외에서 지속적인 연구가 수행되어 왔다. 그러나 남방큰돌고래의 클릭음에 대한 연구는 대부분 사육중인 개체에 대해 이루어졌으며 국내에서는 휘슬음에 관한 연구만 수행되었다. 본 논문에서는 제주 연안에 서식하는 야생개체의 남방큰돌고래 클릭음에 대한 음향특성을 분석하였다. 음향특성을 분석하기 위해 음향 파라미터인 신호 길이, 첫 번째 피크 주파수, 두 번째 피크 주파수, 3 dB 대역폭 및 10 dB 대역폭을 산출하였으며 호주 서식 종의 클릭음 음향특성과 비교하였다. 결과적으로, 신호 길이는 평균 $38{\mu}s$를 나타냈고 대부분의 클릭음이 $20{\mu}s-60{\mu}s$ 범위 내에 속하였다. 2종류의 대역폭의 경우 협대역과 광대역의 주파수 특성 모두 나타냈으며, 첫 번째 피크 주파수(평균 $96kHz{\pm}18kHz$)와 두 번째 피크 주파수(평균 $69kHz{\pm}19kHz$)를 통해 바이모달 신호 특성을 확인하였다.

Keywords

GOHHBH_2019_v38n1_56_f0001.png 이미지

Fig. 1 Experimental site of the south-western part of Jeju Island (33°15'8.58"N, 126°11'35.94"E).

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Fig. 2. Spectrogram of signal recorded in the south-western part of Jeju Island on 14 June 2017, (a) full data, (b) whistle signals (FFT size : 1024, overlap size : 512, frequency resolution : 375 Hz, window : hanning).

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Fig. 3. Comparison of power spectral density between echolocation click signal of Indo-Pacific bottlenose dolphin (solid line) and ambient noise (dotted line) (a) spectrogram, (b) power spectral density (FFT size: 1024, frequency resolution: 375 Hz, window: hanning).

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Fig. 4. Waveforms and energy spectral densities of 8 types of echolocation clicks emitted by Indo-Pacific bottlenose dolphin and acoustic parameters [signal duration (ΔT), 1st peak frequency (Fp1), 2nd peak frequency (Fp2), 3 dB bandwidth (ΔF3dB), 10 dB bandwidth (ΔF10dB)], (a) - (d) click signals with 1st peak frequency of ~ 100 kHz,(e) - (h) click signals with 1st peak frequency of ~ 60 kHz.

GOHHBH_2019_v38n1_56_f0005.png 이미지

Fig. 5. Distribution of acoustic parameters of echolocation clicks emitted by Indo-Pacific bottlenose dolphin (N = 1597) (a) signal duration (ΔT), (b) 1st peak frequency (Fp1), (c) 2nd peak frequency (Fp2), (d) 3 dB bandwidth (ΔF3dB) , (e) 10 dB bandwidth (ΔF10dB).

GOHHBH_2019_v38n1_56_f0006.png 이미지

Fig. 6. Scatter plots of (a) signal duration (ΔT) versus 1st peak frequency (Fp1), (b) 3 dB bandwidth (F3dB) versus 1st peak frequency (Fp1), and (c) 3 dB bandwidth (ΔF3dB) versus signal duration (ΔT).

GOHHBH_2019_v38n1_56_f0007.png 이미지

Fig. 7. Scatter plots of (a) signal duration (ΔT) versus 1st peak frequency (Fp1) [Fp1 < 75 kHz], (b) 3 dB bandwidth (ΔF3dB) versus 1st peak frequency (Fp1) [Fp1 < 75 kHz], (c) signal duration (ΔT) versus 1st peak frequency (Fp1) [Fp1 > 75 kHz], and (d) 3 dB bandwidth (ΔF3dB) versus 1st peak frequency (Fp1) [Fp1 > 75 kHz]. The equation of the least square linear regression line through the data, its correlation coefficient are indicated in the upper of each plot.

Table 1. Comparisons of acoustic parameters of echolocation clicks emitted by Indo-Pacific bottlenose dolphin by habitat (Jeju Island of South Korea and Exmouth Gulf North West Cape of Australia).

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