5th Joint Meeting of the Acoustical Society of America and Acoustical Society of Japan

2016/11/28-12/2 @ Honolulu, USA

Acoustic response of Indo-Pacific humpback dolphins to the variability of marine soundscape

Tzu-Hao Lin, Yu Tsao
Research Center for Information Technology Innovation, Academia Sinica

Shih-Hau Fang
Department of Electrical Engineering, Yuan Ze University

Chih-Kai Yang, Lien-Siang Chou
Institute of Ecology and Evolutionary Biology, National Taiwan University

Marine mammals can adjust their vocal behaviors when they encounter anthropogenic noise. The acoustic divergence among different populations has also been considered as the effect of ambient noise. The recent studies discover that the marine soundscape is highly dynamic; however, it remains unclear how marine mammals alter their vocal behaviors under various acoustic environments. In this study, autonomous sound recorders were deployed in western Taiwan waters between 2012 and 2015. Soundscape scenes were unsupervised classified according to acoustic features measured in each 5 min interval. Non-negative matrix factorization was used to separate different scenes and to inverse the temporal occurrence of each soundscape scene. Echolocation clicks and whistles of Indo-Pacific humpback dolphins, which represent the only marine mammal species occurred in the study area, were automatically detected and analyzed. The preliminary result indicates the soundscape scenes dominated by biological sounds are correlated with the acoustic detection rate of humpback dolphins. Besides, the dolphin whistles are much complex when the prey associated scene is prominent in the local soundscape. In the future, the soundscape information may be used to predict the occurrence and habitat use of marine mammals.

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Oceanoise Asia 2016

2016/4/20

Characterization of the marine soundscape at the core habitat of Indo-Pacific humpback dolphins

Tzu-Hao Lin, Lien-Siang Chou
Institute of Ecology and Evolutionary Biology, National Taiwan University

Shane Guan
Office of Protected Resources, National Marine Fisheries Service, Silver Spring, MD, USA

The soundscape in shallow waters displays a high level of spatial variation due to the difference in ocean environments, biological communities, and human activities. Many marine animals rely on sound for orientation; therefore, the soundscape has been hypothesized as one of the environmental indicators for marine animals. The population of Indo-Pacific humpback dolphins in western Taiwan waters is critically endangered. The anthropogenic noise might alter the marine soundscape evidently. However, the importance of soundscape for the habitat selection of cetacean remains unclear until now. In this study, underwater recorders were deployed in inshore waters to compare the difference of soundscape between the core habitat and non-core habitat of humpback dolphins. The result indicates that the composition of soundscape scene is different among our recording stations. At the core habitat, soundscape was characterized by the nighttime chorus of croakers and the quiet ambient sound in the daytime. On the contrary, snapping shrimp sounds represent the most dominated sound at the non-core habitats. The current result indicates that humpback dolphins prefer soundscape dominated by the chorus of their prey resources. The potential impacts of human activities on marine soundscape should be carefully evaluated in the future.

2016 動物行為暨生態研討會

2016/1/25-26

中華白海豚核心棲地的海洋聲景特徵以及保育經營的應用

林子皓、周蓮香

國立台灣大學生態學與演化生物學研究所

Shane Guan

美國國家海洋漁業局保護資源辦公室

海洋聲景由環境音、動物音以及人為噪音所組成,物理環境影響了聲音傳播,各地不同的動物群聚與人類活動也塑造出各種獨特的聲景。聲景中的訊息可讓海洋動物尋找適合的棲地,察知其他個體的活動位置,甚至探測獵物位置,因此可說是海洋動物生存的重要資源之一。台灣西部淺海的中華白海豚族群面臨許多威脅,水下噪音除了可能造成聽力損傷、行為干擾之外,也會改變當地的海洋聲景。但目前仍缺乏對白海豚棲地的聲景研究,也不清楚聲景的變化是否影響白海豚的棲地選擇。本研究於苗栗縣海域收集長時間水下聲音,分析時頻譜圖的時空變化,發現中港溪口的聲景與其他地區之間有明顯差異。中港溪口是中華白海豚的核心棲地,聲景以白天安靜的環境音和夜間吵雜的石首魚鳴唱為主。白海豚鮮少活動在龍鳳漁港外海的定置網區,以及外埔漁港外海的魚礁區,當地聲景則以槍蝦的寬頻脈衝聲與船隻噪音為主,石首魚的夜間鳴唱也較為低頻且不明顯。本研究結果顯示海洋聲景確實在白海豚核心與非核心棲地之間存在差異,高強度的石首魚鳴唱可能代表充足的食餌資源。未來除了可透過海洋聲景了解白海豚的潛在棲地,也可利用水下監聽站自動監測白海豚、石首魚與人為活動在各地海域的動態變化,以協助中華白海豚重要棲息環境的保育經營。

Conference presentation: 21st Biennial Conference on the Biology of Marine Mammals

13-18 Dec 2015

A noisy dinner? Passive acoustic monitoring on the predator-prey interactions between Indo-Pacific humpback dolphins and croakers

Tzu-Hao Lin, Wen-Ching Lien, Chih-Kai Yang, and Lien-Siang Chou
Institute of Ecology and Evolutionary Biology, National Taiwan University

Shane Guan
Office of Protected Resources, National Marine Fisheries Service, Silver Spring, MD, USA

The spatio-temporal dynamics of prey resources have been considered as important factors for shaping the distribution and behavior of odontocetes. Indo-Pacific humpback dolphin (Sousa chinensis) is a costal species, which primary feeds on benthic croakers. It has been hypothesized that the distribution pattern and periodic occurrence of humpback dolphins are results of their prey movement. However, the interactions between humpback dolphins and croakers remain unclear. During May 2013 and November 2014, underwater sound recordings were collected in western Taiwan waters. Croaker choruses and humpback dolphin echolocation clicks were automatically detected using custom developed algorithms. Both croaker choruses and dolphin clicks were frequently detected in shallow estuarine waters during spring and summer. In addition, shorter inter-click intervals were detected with higher frequencies in these areas, indicating more likely foraging behavior. Current results suggest that the core habitats of humpback dolphins show an agreement with the areas of prominent croaker chorus. Diurnal cycle analysis showed that croaker choruses were most evident after sunset to until approximately 4 A.M. In estuarine waters, humpback dolphin clicks were most frequently detected during the nighttime, with reduced detection rates after 8 A.M. This suggests that the diurnal behavior of humpback dolphins could be associated with the calling behavior of croakers. Although whether the position of a calling croaker could be passively localized by a dolphin remains unknown, our results indicate that the foraging probability of humpback dolphins may be elevated during the nighttime chorus of croakers. Information regarding the spatio-temporal dynamics of croaker chorus can be important for the conservation management of humpback dolphins. Further details on the predator-prey interactions between humpback dolphins and croakers can be investigated by using hydrophone arrays.

Poster (pdf)

[聲物誌] 白海豚之家

Sousa_bye

白海豚所生活的海洋是甚麼樣子的? 在混濁的海中只能仰賴聽覺了解一切,海表面下的浪花、雨聲、水流聲,透漏了所在之處的環境與位置,更聽見了各種海洋生物活動的蹤跡。聽著哨聲在旅途中尋找同伴,社交之外也合作覓食,但記得小心高速開過的船隻,不注意的話可是會命喪黃泉的。越來越頻繁的噪音,降低了聽到同伴聲音的機會,也減少了利用聲音來尋找食物的效率。這是白海豚的家園,一個正受到噪音侵蝕的海洋。

[聲物誌] 錄音機漂流記

近期颱風肆虐,連帶著海洋觀測也跟著遭殃。前一陣子就因為蓮花颱風和昌鴻颱風接連靠近台灣,造成研究團隊在苗栗外海所放置的海下錄音機因為不明原因而脫離錨錠裝置、漂流上岸。還好遇到當地的好心人通報之後,得以將錄音機尋回,今天也才有機會讓大家聽聽錄音機迷途的這段過程。 

這段漂流的時間其實不長,大約5至6個小時後錄音機就被浪打上岸。錄音機漂流的路徑根據推測應是從後龍外海約15公尺水深的礁石區一路北漂至附近的中港溪口南岸,再進入潮間帶與碎波帶。然而,在這段濃縮的3分半鐘錄音裡,卻可以聽到海洋聲景有著非常大幅度的改變。

0:00 – 1:00
礁石區內眾多的槍蝦聲音。注意1分鐘後的水花聲,顯示錄音機已經浮上水面 (痛心)。

1:00 – 1:30
脫離礁石區,槍蝦聲音明顯減少。當時已進入傍晚,可以聽見河口附近的石首魚開始發出低頻的鳴聲。

1:30 – 2:57
台灣西部河口附近著名的石首魚群體鳴唱。注意這段時間之中,石首魚聲音的音頻特徵隨錄音機漂流進入潮間帶後的改變趨勢。

2:57 – 3:39
碎波帶的浪花與水流聲。這段聲音是透過水下麥克風所錄製,和空氣中聽到的略有不同。
 

從這段錄音之中,其實我們不難發現在不同型態的海床、地區之間,可能受到當地生態系組成的不同,而造就了多樣化的海洋聲景。許多海洋動物,也可能是透過各地聲景的不同,以此來尋找其偏好的棲地位置。因此,自然的海洋聲景是否受到人為噪音的干擾,將會是海洋保育非常重要的課題,亟需我們更多的關注。

聽海洋的聲音? 從聲音訊號多樣性來探討魚類群聚的行為

生活在競爭激烈的社會中,大家都知道要去尋找『藍海』,而不是拼命地往『紅海』裡鑽。同樣的,各種動物為了減少彼此競爭資源的衝突,也在長期演化過程中發展出偏好不同資源的趨勢,在生態系統中佔據著不同區位。但大家可曾想過,『聲音空間』是否也是一種資源?

其實對於仰賴聲音求偶、競爭領域的動物來說,可供作溝通的領域、時間甚至頻率範圍都是一種另類的生存資源。如果『聲音空間』被別種動物佔據、或是被噪音干擾而無法和同種動物傳遞訊息,可能就會降低尋找同伴、交配的機會,甚至提高了和別種動物衝突的可能。就像待在一個吵鬧且缺乏光線的演唱會,台上的歌手用喇叭佔據了大部分的聲音空間。在缺乏可見度的狀況下,我們只能大聲喊叫,或是開啟假聲模式提高自己的發聲音頻,讓同伴在歌手所佔據的音頻範圍之外察覺到我們。為了避免陷入這種慘況,許多發聲昆蟲、蛙類、鳥類還有哺乳動物都會在聲音溝通中區隔出所偏好發聲的時間、音頻範圍。

但是對於共處一海域的魚類群聚來說,如何分享、利用所處的音響環境,並且能夠在吵雜的狀況下正確分辨同類聲音仍沒有明確結論。直到Ruppé等人於2013年春天,在南非Sodwana Bay外海約120公尺水深的海底峽谷收錄聲音。並將2793筆聲音訊號分為17大類,雖然沒有同步的錄影監視發聲動物,但根據聲音特徵幾乎可以確認其中有16大類屬於魚類叫聲,另一類則可能是齒鯨的脈衝聲波。

從各類聲音頻繁出現的時間,可再區分為白天和晚上出現的兩大類群。有趣的是,白天出現的聲音類群在聲學特徵上(脈衝波重複率和峰值頻率)較為相似,反而是在晚上出現的聲音類群中,各類聲音的特徵區分相當明顯。換句話說,比起白天的魚類聲音,晚上的魚類聲音多樣性較高。作者推測這是因為在白天活動的魚類主要依賴視覺展示溝通、求偶,聲音只是輔助的媒介。然而,晚上活動的魚類無法透過視覺觀察,必須仰賴聲音進行溝通。如果夜晚活動的各種魚類都使用極為相似的聲音,則可能會降低同種之間的溝通效率。這種在聲音使用上的限制,可能是夜間活動的魚類聲音具有豐富多樣性的原因。

Hastings 和Širović在2015年 PNAS 上的文章中也指出,聲學監測系統的研發在近年來大幅增加了我們對海洋聲景的了解,一旦能夠掌握各種魚類在不同行為的聲音特徵,即可透過海裡的聲音了解各種魚類的豐度與行為。即使現在還沒有辦法建立起完整的魚類聲音資料庫,也可以進行和Ruppé等人相似的研究,從水下錄音中透過聲音特徵在時間與空間上的變動趨勢,發掘出和當地魚類群聚相關的資訊。此外,在水下噪音汙染日漸增加在情況下,長期的水下錄音也可以協助我們了解魚類群聚的長期變化趨勢是否受到噪音污染的影響。

石首魚夏季鳴唱

石首魚冬季鳴唱

在台灣,雖然對於魚類群聚聲音的日夜變化還沒有詳盡的研究,但從不同季節之間的水下錄音也可以聽到石首魚在夏季和冬季之間的叫聲改變。這樣的改變是因為魚種的不同呢? 還是行為的改變? 還有待我們去發掘。

其實,透過水下錄音我們可以獲取非常大量的『聲態資訊』,生態學、海洋物理和資訊學門的跨領域合作,透過訊號偵測、大量資料分析等技術,將能夠進一步從海洋動物的聲音、海洋環境的聲景了解海洋生態與環境的變化。雖然目前這類研究在台灣學術界還非常的小眾,但在歐美已經是一個逐漸興盛的領域,並且廣泛的被應用在海洋魚類與海洋哺乳動物的生態調查、海洋工程的環境影響評估、甚至是海洋生態系的長期變遷研究之中。未來隨著台灣海洋再生能源的開發,相信這類的研究也會慢慢的在台灣擴展開來。

參考資料:

1. Philip A. Hastings and Ana Širović (2015) Soundscapes offer unique opportunities for studies of fish communities. PNAS, 112: 5866-5867.
2. Laëtitia Ruppé, Gaël Clément, Anthony Herrel, Laurent Ballesta, Thierry Décamps, Loïc Kéver, and Eric Parmentier (2015) Environmental constraints drive the partitioning of the soundscape in fishes. PNAS, 112: 6092-6097.

延伸閱讀1:【看啥小魚可以吃】有錢吃鮸,沒錢免吃!

延伸閱讀2:研究海洋生態保育魚類聲音藏玄機