Potential Effects of Vessel Noise on Indo-Pacific Humpback Dolphins (Sousa chinensis) off Western Taiwan

• Main Authors: Chih-Kai Yang, 楊志凱
• Other Authors: 周蓮香
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/7r2ar6

碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 105 === The habitat of Indo-Pacific humpback dolphins (Sousa chinensis) off western Taiwan primarily distributes in shallow and estuarine waters where the distance to shore is less than 3 kilometers. Due to the intensive development at coastal zone with various human activities, this population has been recognized as a “critically endangered” population by the IUCN Red List since 2008. Underwater noise has been one of the major threats to dolphins, and vessel noise is a common type of underwater noise. Humpback dolphins use whistles ranging from 3-5 kHz to communicate with conspecifics and use bio-sonar clicks higher than 10 kHz to search for preys. To investigate the impacts of vessel noise on the acoustic behaviors of humpback dolphins, two sets of underwater acoustic recorders, SM2M, were deployed at Yunlin and Waisanding waters during summer and fall of the year 2012. The recording time is 1,817 hours and 1,824 hours, respectively. I used whistling rate, whistle character, and whistle repertoire to assess the impacts of vessel noise on humpback dolphins. This thesis contains two parts: (1) investigating the influences of vessel noise on the acoustic behaviors of Indo-Pacific humpback dolphins and (2) assessing the loss of communication space of Indo-Pacific humpback dolphins due to the masking effect of vessel noise by using transmission loss of sound underwater. The results showed that 6 cargo ships and 4 fishing boats in average were detected daily during day time in Yunlin waters, and vessel noise occupied 12% and 7% in time duration, respectively. In Waisanding, 12 fishing boats were detected per day, and vessel noise occupied only 11% of time. When vessel noise occurred, whistling rate increased, whistle repertoires were less diverse, and only 11 types of whistles were used (65% of all the 17 whistle types). For the communication space loss, results showed that the low-frequency sounds of cargo ships and fishing boats can mask more than 50% of the communication space within more than 30 km and 15 km, respectively. However, the communication space can be masked by only 40% at most at high frequency ranges. In addition, the loss of communication space is about 12% in average during day time for cargo ship noise, but less than 1% for fishing boats. This is the first thesis to investigate the effects of vessel noise on humpback dolphins in Taiwan. Conclusively, when humpback dolphins encounter vessel noise, they changed their acoustic behaviors to compensate for the loss of communication space, and the impact was higher by cargo ships than that by fishing boats. This study can provide valuable information for the future decision making on the conservation of this critically endangered population of Indo-Pacific humpback dolphins in Taiwan.