[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。

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OCEANS’14 MTS/IEEE Conference on April 7-10, 2014, in Taipei, Taiwan

The OCEANS’14 MTS/IEEE conference will be hosted in Taipei, Taiwan. There will be a special session for UNDERWATER ACOUSTICS AND ACOUSTICAL OCEANOGRAPHY. This special session will focus on the application of using underwater acoustics to explore the ecology, meteorology, and underwater communication.

In 2010, there was a marine cable hosted observatory (MACHO) established off the northeastern Taiwan. This is the first long-term marine observatory in eastern Taiwan waters. The continuous transmission of underwater recordings can help us to monitor the weather, biological noise, and anthropogenic noise. Weather events, such as rain and wind, produce unique acoustic features. In other words, people can use underwater recordings to understand the local weather without the surface monitoring buoy. Biological noise, such as cetacean vocalizations, are very prominent in that area. Our team can detect cetacean tonal sounds (whistles) every day, especially during nighttime. The northeastern Taiwan waters is a very good place for dolphin watching with at least seven sympatric odontocete species. However, the current technology is still difficult to distinguish between different cetacean species based on the acoustic characteristics of tonal sounds.

Our team will have one presentation in the bioacoustic session. The issue of using tonal sounds to distinguish cetacean species will be studied, and applied on the underwater recordings collected from the long-term marine observatory. In the future, we hope that the marine observatory can be a biodiversity monitoring station for marine mammals!