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.

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)

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.

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。

New article online: Passive acoustic monitoring of the temporal variability of odontocete tonal sounds from a long-term marine observatory

A new article regarding the usage of long-term marine observatory to monitor the odontocete behavior was published on PLOS One.

Passive acoustic monitoring of the temporal variability of odontocete tonal sounds from a long-term marine observatory

PLOS One (2015). DOI: 10.1371/journal.pone.0123943

Tzu-Hao Lin, Hsin-Yi Yu, Lien-Siang Chou

Institute of Ecology and Evolutionary Biology, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.)

Chi-Fang Chen

Department of Engineering Science and Ocean Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.)

The developments of marine observatories and automatic sound detection algorithms have facilitated the long-term monitoring of multiple species of odontocetes. Although classification remains difficult, information on tonal sound in odontocetes (i.e., toothed whales, including dolphins and porpoises) can provide insights into the species composition and group behavior of these species. However, the approach to measure whistle contour parameters for detecting the variability of odontocete vocal behavior may be biased when the signal-to-noise ratio is low. Thus, methods for analyzing the whistle usage of an entire group are necessary. In this study, a local-max detector was used to detect burst pulses and representative frequencies of whistles within 4.5–48 kHz. Whistle contours were extracted and classified using an unsupervised method. Whistle characteristics and usage pattern were quantified based on the distribution of representative frequencies and the composition of whistle repertoires. Based on the one year recordings collected from the Marine Cable Hosted Observatory off northeastern Taiwan, odontocete burst pulses and whistles were primarily detected during the nighttime, especially after sunset. Whistle usage during the nighttime was more complex, and whistles with higher frequency were mainly detected during summer and fall. According to the multivariate analysis, the diurnal variation of whistle usage was primarily related to the change of mode frequency, diversity of representative frequency, and sequence complexity. The seasonal variation of whistle usage involved the previous three parameters, in addition to the diversity of whistle clusters. Our results indicated that the species and behavioral composition of the local odontocete community may vary among seasonal and diurnal cycles. The current monitoring platform facilitates the evaluation of whistle usage based on group behavior and provides feature vectors for species and behavioral classification in future studies.

台灣東部海域鯨豚群聚生態之自動化監測平台

最近台大生命科學院舉辦了三分鐘口說論文比賽,又稱生命科學懶人包比賽。這次參加僥倖得了觀眾之選獎,不管在結果或是參與過程中,收穫真的是很多。但是除了結果之外,我更希望這些生態的研究成果,能夠真正地走入台灣社會中,讓更多台灣人了解學術圈為台灣的生態環境作的努力和貢獻,也期許未來能夠和民間結合激盪出更多的可能性。

3min

東部海域自動化鯨豚哨叫生監測平台懶人包

這個監測平台囊括了水下工程技術(長期海洋觀測站)、自動化訊號偵測(鯨豚哨叫聲偵測)、自動化分類(訊號特徵分析與鯨豚種類辨識)以及生態資料分析四層面的工作,缺一不可。如果沒有中央氣象局在宜蘭外海建置臺灣東部海域海纜觀測系統、蘭陽博物館與台大鯨豚研究室的工作人員協助建立台灣東部海域鯨豚聲音資料庫、科技部對於部分研究經費的支持,這整個監測平台就不可能建立。

Life Science 3 Minute Thesis Competition from Lin on Vimeo.

在臺灣東部海域海纜觀測系統從海底傳回水下錄音資料後,這個平台透過將鯨豚聲音視覺化的呈現在頻譜圖(spectrogram)上,並偵測這些像線條一般的鯨豚哨叫聲,分析鯨豚聲音的音頻位置,作為種類辨識的特徵之用。不同鯨豚種類的聲音使用習性都有不同之處,體型大的偽虎鯨通常使用的音頻較低,但體型較小的飛旋海豚通常使用的音頻則較高。透過類似的音頻分析,可以發現在蘇澳外海的這個海脊附近,常吃花枝、透抽的花紋海豚最為活躍,偽虎鯨則似乎在冬、春兩季較為頻繁的進入此海域,小型海豚的活動則在夏季較為頻繁。

這個監測平台才剛完成沒多久,還需要很長的路來改良裡面的演算法、擴大種類辨識的資料庫、甚至建立一個完善的使用者介面來讓公眾使用。但是我們相信透過這些平台,能夠讓更多人了解我們所不熟悉的海域生態,尤其是台灣周遭海域的鯨豚生態。

如果大家有興趣閱讀更進一步的學術論文資料,可以參考發表在水下技術研討會的論文全文(中文):

水下技術研討會暨國科會成果發表會