a noisy dinner? passive acoustic monitoring on the ... · • croakers, anchovies, and sardines are...
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Indo-Pacific humpback dolphin (Sousa chinensis) • Coastal and estuarine species • Croakers, anchovies, and sardines are the most
important prey families (Barros et al. 2004)
Croaker • Benthic species in shallow coastal waters • At least 20 species in Taiwanese waters • Nighttime chorus (Mok et al. 2011)
Do humpback dolphins alter their distribution and behavior according to the calling behavior of croakers?
Echolocation clicks • Automatic detection based on signal-to-noise
ratios in two frequency bands: <8 kHz & >20 kHz • Time resolution: 1 ms
Figure 2. (A) Spectrogram (B) SNRs of <8 kHz (black) and >20 kHz (red) (C) SNRs of detected clicks (D) Inter-click intervals
Croaker chorus • Identify the chorusing period based on the
threshold of median(SPL) + 3 dB
Figure 3. (A) Long-term spectral average of one day recordings (B) Diurnal change of sound pressure level in 0.5 – 2.5 kHz, the red line indicates the detection threshold
A noisy dinner? Passive acoustic monitoring on the predator-prey interactions between Indo-Pacific humpback dolphins and croakers
Tzu-Hao Lin1*, Shane Guan2, Wen-Ching Lien1, Chih-Kai Yang1, Lien-Siang Chou1 1 Institute of Ecology and Evolutionary Biology, National Taiwan University 2 Office of Protected Resources, National Marine Fisheries Service
INTRODUCTION
SM2+ recorders & HTI-96-MIN hydrophone • Sensitivity: -165 dB re 1 V/lμPa • Sampling rate: 96 kHz • Data collection: 2013 – 2014 (>1000 hours) • Bottom mounted by anchors
PASSIVE ACOUSTIC MONITORING
ANALYSIS OF ACOUSTIC DATA PREDATOR-PREY INTERACTIONS
Spatial variations of detection results • More echolocation clicks and short-range biosonars at stations B, C • Longer duration of croaker chorus at stations B, C, D
Figure 4. (A) Detection rates of click train (B) Probability distributions of ICI (C) Duration of croaker chorus
A B C D E
(A) (B) (C)
Echolocation clicks Croaker chorus
A B C D E
Diurnal variations of detection results • Croaker choruses were most evident between 6 P.M. and 4 A.M. • More clicks were detected between 9 P.M. and 12 P.M.
Conclusion and outlook • Humpback dolphins prefer shallow waters with prominent croaker calls • The diurnal behavior of humpback dolphins could be associated with the
croakers, but was not completely matched • Further investigations by using hydrophone arrays are necessary References Barros, N. B., Jefferson, T. A., and Parsons, E. C. M. (2004). “Feeding hab-its of Indo-Pacific humpback dolphins (Sousa chinensis) stranded in Hong Kong,”
Aquat. Mamm.30, 179 – 188. Mok, H.-K., Lin, S.-Y., and Tsai, K.-E. (2011 ). “Underwater ambient biological noise in the waters on the west coast of Taiwan,” Kuroshio Sci. 5, 51–57.
Acknowledgements This work was part of the project “The investigation of physiological and ecological effects of offshore wind farm on Sousa chinensis (II)” supported by Ministry of Science and Technology (MOST 104-3113-E-002-012-). Field works were supported by the Swancor company. The authors thank Mei Li-Ching, Chang Mu-Hsin, and members from NTU cetacean lab for their support in field works.
Recording stations Proposed offshore wind mills
Zhonggang River
Taiwan Taiwan Strait
5 m
Miaoli County
10 m 15 m 20 m
A
B
C D
E
STUDY AREA
Figure 1. Map of study area. Humpback dolphins were frequently encountered near the stations B & C according to visual observations
Figure 5. (A) Detection rate of echolocation clicks (B) Probability distribution of ICI (C) SNR of croaker chorus
0.5 – 2.5 kHz
Echolocation clicks (station C) Croaker chorus (C)
(A) (B) (C)