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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2017年動物行為生態研討會

2017/1/23-24 @ 高雄中山大學

應用機器學習探討海洋聲景變動與中華白海豚發聲活動之關聯

林子皓、曹昱
中央研究院資訊科技創新研究中心

方士豪
元智大學電機工程學系

鯨豚的發聲行為相當多變,不同族群可能會在各種環境音改變哨聲特徵﹐也會在遭遇人為噪音時改變聲音結構。海洋聲景是由環境音、動物音與人為噪音組成,具有高度變異的特性。儘管過去已有不少針對鯨豚發聲與單一音源的研究,但是對鯨豚如何在多變的海洋聲景且多重聲源相互重疊的狀況下改變行為仍不清楚。本研究透過水下錄音機,長期收錄2014年苗栗海域的海洋錄音。首先應用自動偵測器尋找中華白海豚水下聲音,再應用非負矩陣分解法學習海洋聲景中的主要聲源特徵。透過非監督式學習器,可以有效拆解長期時頻譜圖,視覺化呈現石首魚鳴唱、槍蝦聲音、環境與人為噪音等主要聲源的相對變化。利用廣義疊加模型分析聲景與白海豚聲音後,我們發現白海豚的聲音偵測率與複雜度和各種聲源皆有不同的相關性。此結果顯示應用機器學習分離聲景中的各種聲源之後,將能夠有效瞭解動物和各種聲源的交互作用。未來,聲景中的各種訊息也可以作為預測動物活動的生態遙測資料。

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.

New article online: Seasonal Distribution of Indo-Pacific Humpback Dolphins at an Estuarine Habitat: Influences of Upstream Rainfall

Here is the new online article regarding the seasonal distribution change of coastal dolphins.

Seasonal Distribution of Indo-Pacific Humpback Dolphins at an Estuarine Habitat: Influences of Upstream Rainfall

Estuaries and Coasts (2014) doi:10.1007/s12237-014-9886-2

Tzu-Hao Lin1, Tomonari Akamatsu2, 3, Lien-Siang Chou1

1Institute of Ecology and Evolutionary Biology, National Taiwan University, Number 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan, Republic of China 
2National Research Institute of Fisheries Engineering, Fisheries Research Agency, 7620-7 Hasaki, Kamisu, Ibaraki 314-0408, Japan
3Japan Science and Technology Agency, CREST, Sanbancho, Chiyoda-ku, Tokyo, 102-0075, Japan

River estuaries are dynamic regions that are influenced by the interactions between freshwater and seawater as well as seasonal variations in river runoffs. Studies focusing on the distribution of Indo-Pacific humpback dolphins (Sousa chinensis) have indicated their general tendency toward estuarine habitats. The seasonal activities of humpback dolphins are likely to synchronize with environmental fluctuations. This study investigated the effects of seasonal changes in river runoffs on the distribution gradient of humpback dolphins by deploying acoustic data loggers along the Xin Huwei River estuary, Western Taiwan, between July 2009 and September 2012. Seasonal shifts were observed in the areas with high detected duration of humpback dolphins, which mainly stayed near the river mouth during the dry seasons but moved seaward during rainy seasons and following heavy rainfall. In addition, the gradient of ambient ultrasonic pulses, dominated by snapping shrimp sounds, exhibited regional differences following heavy rainfall. The outward movements of the humpback dolphins and the snapping shrimp sounds in the estuary indicated a temporary trophic-system shift in response to local environmental changes resulting from high volumes of river runoffs. In the future, the seasonal variation in the distribution of humpback dolphins must be considered during the conservation management of this critically endangered population.

 

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New article online: Tidal influences on the habitat use of Indo-Pacific humpback dolphins in an estuary

New article online:

Publish in Marine Biology.

Tidal influences on the habitat use of Indo-Pacific humpback dolphins in an estuary

This paper offers the first study of diurnal variations in the use of an estuarine habitat by Indo-Pacific humpback dolphins. Passive acoustic data loggers were deployed in the Xin Huwei River Estuary, Western Taiwan, from July 2009 to December 2010, to collect biosonar clicks. Acoustic encounter rates of humpback dolphins on the riverside of the estuary changed significantly over the four tidal phases, instead of the two diurnal phases based on the recordings from 268 days. Among the tidal phases, the encounter rates were lowest during ebb tides. Additionally, circling movements associated with the hunt for epipelagic fish significantly changed in temporal and spatial presence over the four tidal phases, matching the overall pattern of encounter rate changes in the focal estuary. Our findings suggest that the occurrence pattern and habitat utilization of humpback dolphins are likely to be influenced by the tidal-driven activity of their epipelagic prey.

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A coastal view of western Taiwan. The tidal difference can reach to 4 m in central western Taiwan, thus alter coastal environments and animals periodically.
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