船舶噪音對台灣西海岸中華白海豚之潛在影響

Abstract

台灣西部海域的中華白海豚主要棲息在離岸3公里內之淺海區域，飽受人類活動威脅，在2008年被IUCN Red List列為「極度瀕危」族群。水下噪音是中華白海豚面臨的眾多威脅之一，其中船隻交通是常見的水下噪音。中華白海豚屬於中頻類群鯨豚種類，主要利用3-5 kHz的哨叫聲溝通，並會發出高於10kHz的寬頻聲音進行回聲定位。為了解中華白海豚之聲音行為與溝通是否受船隻噪音干擾，本研究於2012年夏季及秋季，於雲林新虎尾溪口及外傘頂洲海域各放置一組SM2M水下錄音機，分別收集1817小時及1824小時的資料，分析船隻噪音的出現頻率及頻譜特性，並分析白海豚哨叫聲呼叫率、聲音結構與使用的哨叫聲曲譜種類來評估船隻噪音對白海豚的影響。本論文內容分為兩部分：(1)瞭解船隻噪音對中華白海豚聲音行為的影響，(2)利用聲音的傳遞損失(transmission loss)估算中華白海豚在船隻噪音影響下損失的溝通範圍(communication space)。 結果發現雲林海域在白天平均每日可偵測到6次貨輪與4次漁船噪音，每日噪音暴露的時間比例平均為12%與7%，而外傘頂洲海域在白天平均每日可偵測到12次漁船噪音，平均約有11%的時間受到噪音干擾。當有船隻噪音干擾時，白海豚的哨叫聲呼叫率顯著高於平時，且使用的哨叫聲類型較少，僅使用11種 (佔17種哨叫聲類型的65%)。另外船隻噪音對海豚溝通距離的遮蔽影響方面，低頻噪音的遮蔽距離較短較強(貨輪與漁船的影響分別在多於30公里與15公里內可以遮蔽50%以上的溝通範圍)，而高頻噪音的遮蔽距離可延伸較遠，但遮蔽效應較弱(最多僅遮蔽40%的溝通範圍)。且在白天，貨輪平均可以遮蔽12%的溝通範圍，但漁船噪音平均僅遮蔽不到1%的溝通範圍。 此為第一篇有關船隻噪音對台灣西岸中華白海豚之影響的論文，總結來說，白海豚受到船隻噪音干擾時，會改變其聲音行為以彌補被遮蔽的溝通範圍，其中又以貨輪噪音的影響範圍較漁船大。本論文所得之結果可做為未來擬定減輕船隻噪音對於白海豚之影響的政策之參考。

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.