[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。

New article online: Automatic classification of delphinids based on the representative frequencies of whistles

Our new article which introduce a new method of using representative frequency distribution to classify delphinid species has been published in the Journal of Acoustical Society of America. Please contact me if you are interested in the pdf copy or the algorithm.

Automatic classification of delphinids based on the representative frequencies of whistles

J. Acoust. Soc. Am. 138, 1003 (2015); http://dx.doi.org/10.1121/1.4927695

Tzu-Hao Lin, Lien-Siang Chou
Institute of Ecology and Evolutionary Biology, National Taiwan University, Number 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan

Classification of odontocete species remains a challenging task for passive acoustic monitoring. Classifiers that have been developed use spectral features extracted from echolocation clicks and whistle contours. Most of these contour-based classifiers require complete contours to reduce measurement errors. Therefore, overlapping contours and partially detected contours in an automatic detection algorithm may increase the bias for contour-based classifiers. In this study, classification was conducted on each recording section without extracting individual contours. The local-max detector was used to extract representative frequencies of delphinid whistles and each section was divided into multiple non-overlapping fragments. Three acoustical parameters were measured from the distribution of representative frequencies in each fragment. By using the statistical features of the acoustical parameters and the percentage of overlapping whistles, correct classification rate of 70.3% was reached for the recordings of seven species (Tursiops truncatus, Delphinus delphis, Delphinus capensis, Peponocephala electra, Grampus griseus, Stenella longirostris longirostris, and Stenella attenuata) archived in MobySound.org. In addition, correct classification rate was not dramatically reduced in various simulated noise conditions. This algorithm can be employed in acoustic observatories to classify different delphinid species and facilitate future studies on the community ecology of odontocetes.

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

海洋聲景與魚類的聽覺感知

如果我們是海洋裡的一隻魚,聽不見聲音會怎麼樣

這是個難以回答的問題,畢竟子非魚,怎知海洋聲音在魚聽起來是甚麼樣子甚至許多人會疑問,魚能夠聽得到聲音嗎?

對於會發出聲音的魚類,例如石首魚,這些發聲魚類會利用聲音溝通、求偶,毫無疑問的我們會認為這些發聲魚類應該也能夠敏銳地察覺聲音,否則無法和同類溝通。但對於更多不會發出聲音的魚類來說,難道聲音對牠們毫無意義嗎?

刊登在2009Integrative ZoologySoundscapes and the sense of hearing fishes一文中,作者Richard Fay彙整了近年的研究結果,認為聲音感知的能力對於海洋魚類極其重要。就像我們人類一樣,可以從聲音反射、各種設施運作的噪音分辨室內的密閉空間和室外公共場合,透過敲打物體或聆聽樂器發聲可以從其音色來了解材質構造。海洋中的聲音來自於風浪、降雨以及各種生物、人為活動,聲音就像光線一樣讓整個水下環境沉浸其中,從聲音的傳播、反射形成的音場,提供了海洋生物探測周遭環境、尋找方位以及行為反應的資訊來源。

每一種類型的海洋環境因為在其中不同的生物群聚組成、海床物理特性的差異會有著明顯不同的聲景。換句話說,在不同海洋環境所聆聽到的聲音音量、訊號特徵、出現的時間特性可能有很大的差異。可是,這對海洋魚類來說有甚麼重要的意義嗎研究發現,許多礁岩性的魚類,在較深水域生活的仔魚成長之後會回到礁岩繁殖、交配,當研究人員在新放置的礁岩中利用水下喇叭撥放出在礁岩中所錄製的槍蝦和魚類聲音時,比起沒有撥放聲音的礁岩,幼魚的數量明顯在這些利用錄音裝飾的礁岩中來得高,顯示海洋魚類確實會透過環境中的各種聲音,也就是海洋聲景來尋找其偏好的棲地環境。

 苗栗魚礁聲景
 外傘頂洲聲景

然而,海洋中的聲音極其多樣,在一個吵雜的環境之中魚類是否還可以察覺出不同類型的聲音訊號以石首魚來說,河口附近的石首魚群在傍晚過後會群體鳴唱,吵雜的程度好比夜市一樣。石首魚個體在許多同類共同大聲喧嘩的狀況下是否還能有效地透過聲音溝通、尋找交配的對象雖然目前仍無法確定魚類是否可以精確的定位聲源,但透過實驗也發現魚類似乎可以從角度的差異來察覺被噪音所遮蓋的訊號。此外,當多個聲音訊號同時出現,魚類也可以利用音頻特徵和脈衝波的重複次數來辨別不同的聲音類型,這種聽覺辨認的解析能力在兩種聲音音頻特徵差距越大時會更加提升。

石首魚群體鳴唱

雖然目前的科學研究對於魚類聽覺的了解還不是相當透徹,新的研究也可能會產生和過去相互矛盾的結果。儘管如此,越來越多研究人員皆認同聽覺感知對於海洋魚類的生存相當重要。過去大多認為只有生物發出的聲音才具有生物意義,但越來越多的證據顯示環境聲音對於生物本身也具有相當大的重要性,如同光線讓陸域動物得以透過視覺了解環境,海洋中的聲音則是魚類賴以為生的感知來源。在了解了這些之後,或許我們也應該開始注意噪音對海洋生物的影響是甚麼魚類透過感知聲景來尋找其偏好的礁岩棲地,那如果在礁岩的附近興建了大型離岸海事工程,雖然沒有破壞礁岩本身但釋放的噪音卻大幅改變了當地聲景,在這種聲景被破壞的狀況下,遷徙的魚類還能尋找到偏好的棲地嗎甚至我們的漁業資源量會不會因為海洋日益增加的人為噪音而下降為了海洋環境的永續發展,讓我們持續聆聽海洋聲音來了解這些問題的答案。

參考資料:

1. Richard Fay (2009) Soundscapes and the sense of hearing of fishes. Integrative Zoology 4: 26-32.
2. Stephen D. Simpson, Mark Meekan, John Montgomery, Rob McCauley, Andrew Jeffs (2005) Homeward sound. Science 308: 221.

International Conference on Biodiversity, Ecology and Conservation of Marine Ecosystems 2015 @ Hong Kong

1-4 June 2015

Seasonal changes in habitat use of Indo-Pacific humpback dolphins at an estuary

Tzu-Hao Lin, Chia-Yun Lee, Lien-Siang Chou

Institute of Ecology and Evolutionary Biology, National Taiwan University

Tomonari Akamatsu

National Research Institute of Fisheries Engineering, Fisheries Research Agency

River estuaries are ecotone environments where freshwater and seawater mix together. Seasonal rainfall is likely to influence the salinity, turbidity, and development of estuarine fronts, thus alter the distribution of aquatic animals at an estuary. Indo-Pacific humpback dolphin is a coastal species that use estuaries as their core habitat. According to previous studies, the distribution of humpback dolphins in their estuarine habitat moved seaward during wet seasons. In addition, circling movement associated with the hunt for epipelagic fish increased during flooding tides. However, it remains unclear how seasonal rainfall influences the estuarine habitat use of humpback dolphins. During July 2009 and October 2014, acoustic data loggers were deployed at the Xin Huwei River estuary, Taiwan to record ultrasonic pulsed sounds. Biosonar clicks of humpback dolphins were detected using an automatic detection algorithm. The temporal variations of humpback dolphin behavior were investigated in terms of detection rate, occurrence pattern within the tidal cycle, echolocation behavior. The behavior of humpback dolphins significantly varied among the four monitoring sections and two periods (wet and dry seasons). The tide related occurrence was evident at the entire monitoring area during wet seasons, however, the similar occurrence pattern was only observed at the inner and outer estuary during dry seasons. In addition, long distance biosonars were much frequently detected at the inshore and offshore sections. During drought periods, the inshore and offshore sections are less likely to be influenced by the mixtures between freshwater and seawater. Our results suggest the river runoff may play an important factor in shaping the estuarine habitat use of humpback dolphins. Therefore, it is necessary to consider the interception of river runoff in the conservation management of humpback dolphins in an estuarine habitat.

OCEANOISE 2015 @ Barcelona, Spain

2015/5/14

Spatial and temporal variations of biological sound in a shallow marine environment

Tzu-Hao Lin, Lien-Siang Chou

Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Republic of China (Taiwan)

Shane Guan

Office of Protected Resources, National Marine Fisheries Service, Silver Spring, MD, USA
Department of Mechanical Engineering, The Catholic University of America, Washington, DC, USA

The shallow marine environment exhibits different soundscape characteristics compared to that from the deep ocean. In the shallow waters, biological sound plays an important role in local soundscape. Biological sounds such as fish calls and cetacean whistles are used for communication and finding mates. In addition, odontocetes also use high-frequency biosonars to search their prey. Thus, study the spatial and temporal variations of biological sounds can help us examine the behavior and habitat use of soniferous marine animals. In shallow waters of western Taiwan, most of the biological sounds are produced by snapping shrimps, croakers, and Indo-Pacific humpback dolphins. Shallow and coastal waters are highly influenced by tidal currents, seasonal change of river runoff, and temperature. Due to the difficulty of marine ecological research using visual-based surveys in turbid waters, the temporal and spatial variations of biological activities remain unclear. In this study, underwater sound recorders, SM2M and SM2+, were used to collect long-term acoustic data. Among biological sounds, croaker chorus was identified according to the daily change of sound pressure levels within the 0.5-2.5 kHz frequency band, and whistles and echolocation clicks of humpback dolphins were detected using the local-max detector and high frequency click detector, respectively. Croaker choruses and dolphin vocalizations were frequently detected at inshore and estuarine stations during wet seasons (from April to September). Croaker choruses were evident during the nighttime, especially after sunset. Humpback dolphins were primary detected after the midnight until the next morning. During dry seasons (from October to March), the durations of croaker chorus were reduced. There were no evident differences among inshore and offshore stations. The detection rates of humpback dolphins in the estuarine station were lower compared the detection rates in wet seasons. The temporal and spatial variations of croaker chorus and dolphin vocalizations indicate that the distribution and behavior of croakers and humpback dolphins changed between wet and dry seasons. Several offshore wind farms have been planned to be built in western Taiwan waters. The construction and operation noise of these wind farms may alter the acoustic environment and influence the behavior and habitat use of marine animals. Current results can be used to evaluate the potential impacts of offshore wind farms on the local ecosystem.

2015海洋科學年會 @ 高雄

2015/3/30

竊聽海洋生態:被動式聲學監測台灣西岸淺海生物聲音的時空變化

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
Office of Protected Resources, National Marine Fisheries Service
Department of Mechanical Engineering, The Catholic University of America

了解海洋生物群聚的時空變化和海域環境變遷的關聯一直是重要的研究方向,但依賴目視或現場採樣的方法皆難以針對海洋生態系進行長期且連續的監測。然而,像是槍蝦、發聲魚類與鯨豚等海洋生物,會發出聲音來互相溝通、求偶、甚至增加覓食效率。因此,竊聽這些聲音便可以了解這些發聲動物的行為與分布範圍。本研究將SM2+長期錄音機與水下麥克風錨定在苗栗縣淺海的海床上收集長時間水下錄音,並以96 kHz的取樣頻率來收錄魚群鳴唱和中華白海豚的叫聲。透過計算0.5-2.5 kHz頻率範圍的聲壓値,可以有效辨識出石首魚群鳴唱的行為。此外,本研究也分別應用極大值偵測器和高頻脈衝偵測器自動搜尋長時間錄音中的白海豚哨叫聲與生物聲納。在春、夏等雨季,石首魚群體鳴唱和白海豚叫聲皆在離岸較近且緊鄰河口的測站被頻繁偵測。石首魚鳴唱約在日落過後開始,直到日出前才結束。此外,鳴唱時間在河口附近明顯較長,顯示石首魚可能在日落過後逐漸移動到河口海域。白海豚偵測率在夜晚至隔天早上10點之間較高,但子夜時下降的偵測率可能與吵雜的魚群鳴唱遮蓋了潛在的白海豚聲音有關。乾季時的石首魚群鳴唱長度在各測站之間沒有明顯的區分,顯示其在淺海的分布趨勢呈現明顯的季節性變化。但白海豚的偵測率在乾濕季之間沒有明顯改變,僅在河口些微降低。台灣西部海域未來將是離岸風能開發的重點區域,其施工與營運對於當地生態的影響仍屬未知。被動式水下聲學能有效監測石首魚、白海豚等發聲生物活動的時空變化,透過自動化演算法所偵測之大量資料也將能協助了解環境、氣候因子與海洋生物群聚變化的相關性,以釐清未來興建的離岸風場對海域生態的潛在影響。