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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2014年秋季ASA會議

美國聲學協會(Acoustic Society of America, ASA)每年會舉辦兩次研討會,讓各國研究聲學相關領域的研究人員們可以互相分享最新的研究成果,並洽談可能的合作機會。我也參加了201410月底在美國印第安納波里斯擧辦的會議,當然主要的興趣也是放在動物聲學(Animal bioacoustic, AB)這塊。

會議內容可以參閱ASA的連結: ASA fall meeting full program

今年的AB session討論的主題已經從過去的towed acoustic survey或是fixed platform(當然還是AB的重點項目之一),轉到autonomous mobile platform上,例如wave glider或是sea glider。這些平台可以長時間在海洋下進行海洋環境調查、環境噪音分析、魚類和海洋哺乳類聲音偵測與定位、甚至是船艦聲音偵測等任務。透過GPS的定位,這些自主式移動平台甚至在某些情形下可以替代傳統以船隻進行的調查,並且可以潛入深海進行任務。這些自主式平台甚至具備即時衛星通訊的能力,因此研究單位可以即時監測部分的調查資料、遠端改變任務規劃,或針對特殊事件即時監測,不管是在科學研究、海洋管理,甚至是國防上,潛力都是….無窮啊。

有趣的是,最近幾年參加的AB session,都是以海洋生態、尤其是鯨豚活動監測為最主要的研究主題,反而陸域的動物聲學研究主題越來越少或許這多少也反映了海洋研究對於水下聲學技術的高度需求吧。利用水下聲學獨立執行穿越線調查動物的分佈趨勢與密度也是今年會議的重點,跳脫傳統在flxed platform只能用point transect survey,這幾年mobile platform的發展讓line transect survey的未來應用更加廣泛。同時,透過多組水下麥克風組成的陣列,除了應用傳統的麥克風時間差來定位聲源,今年也有許多研究應用sound propagation modeling來協助單聲道或雙聲道水下錄音進行聲源定位或是聲源分布機率模擬。這些技術都可以大幅協助海洋動物密度調查、甚至是海洋生態環境的研究。

海洋生態環境的研究中,除了我們台灣大學研究團隊針對多種共域鯨豚的季節性活動進行調查之外,許多國外研究團隊也針對鯨豚和魚類、深海散射層等進行prey-predator relationship的探討,這些研究應用了被動與主動式聲學、訊號偵測與分類等各種技術嘗試解決長久以來的各種海洋生態問題,都獲得了不錯的成果。應用水下聲學在生態環境的研究中,又以聲境(soundscape)分析最為新穎與特別。聲境分析絕對不只是把環境噪音的頻譜能量分析一下,就說這是聲音環境的snapshot…聲境分析其實非常需要自動化事件偵測(尤其是廣義偵測器 generalized detector)、訊號分類與聲源定位這些技術的應用。最新的研究也顯示利用L型水下麥克風陣列可以觀察到水下聲境在空間與時間上的高度變異性。在未來如果搭配水下錄影或是資料庫辨識後,我相信海洋生態系研究的困難將可能可以大幅降低,並且讓大家可以有更多種方法了解海洋生態。

無論如何,可以發現海洋生態研究是多麼的需要各種不同領域的人參與合作,才能夠產出優良的科研成果。如果只是固守著自己過去學的技術、理論,而不持續學習最新的研究方向,並跨領域積極開放合作與資料分享,那在海洋研究上必定會落後別人,甚至是被遠遠抛在腦後。