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

*schonkopf@gmail.com

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)