臺灣西部近岸海域水下聲景研究

Abstract

我國為應對全球暖化趨勢，正努力進行能源轉型，大力發展再生能源，以達成2050年「淨零排放」（Net Zero）之目標，然而其中離岸風場之開發將有可能影響廣大的西部海域生態環境，近岸海域人類活動頻繁，鄰近保護礁、河口區有較豐富的生物多樣性，有可能受到較大的影響，為需要優先進行調查研究之區域。 水下聲景可被利用於生物多樣性調查及海域環境影響評估，本研究利用水下被動式監測技術蒐集長期水下聲訊，建構彰化、雲林近岸海域之水下聲景，結果顯示受地理景觀、季節差異、人為及海洋生物活動而有所不同，在10 Hz－20 kHz頻段的每小時平均聲壓位準(SPL)之中位數介於114－123 dB(re 1µPa2)，彰化近岸海域之聲壓位準中位數較高；第5百分率位準(L5)約在125－133 dB，5－8月份為聲壓位準較低的季節，峰值主要由各點位之聲學事件所主導。 在彰化海域離岸風場施工期間，打樁、船舶機械等持續人為噪音事件造成鄰近點位500 Hz以下頻段能量顯著上升，距風場15 km亦有導致魚類鳴音減弱3－5 dB的負面影響，可能為施工期間增長的船舶噪音所導致。船舶噪音會對鯨豚產生行為干擾或聲學遮蔽作用，在苗栗海域的研究顯示，船舶通過期間中華白海豚減少了發聲行為，其口哨聲和喀答聲次數顯著下降，並且口哨聲的持續時間明顯縮短，船隻通過前的口哨聲持續時間中位數為0.3秒，通過期間降為0.22秒，通過後更降為0.15秒，在離岸風場大規模開發之際，海洋生物受到的行為影響是亟需探索的課題。 「全球海洋公約」（Global Ocean Treaty）對海洋生物多樣性的保育和永續利用，訂立在2030年前保護至少30%海洋的目標，水下聲景調查與監測可協助獲得海域生態基線資料，調查成果可供溝通、教育、促進公眾參與，以實現良好永續的海洋環境並保護生物多樣性的目標。

Taiwan is making efforts to transform its energy system in response to the global trend of climate change, vigorously developing renewable energy to achieve the goal of "Net Zero" emissions by 2050. However, the development of offshore wind farms may have an impact on the ecological environment of the vast western waters. The coastal waters are heavily used for human activities, and the adjacent protected reefs and estuary areas have abundant biodiversity, which may be greatly affected and require priority investigation. Underwater soundscapes can be used for biodiversity surveys and assessments of marine environmental impacts. This study used underwater passive acoustic monitoring technology to collect long-term underwater acoustic data and constructed soundscapes of Changhua and Yunlin coastal waters. The results showed that the soundscapes varied due to geographic landscape, seasonal differences, human activities, and marine biological activity. The median of the hourly average sound pressure level (SPL) in the frequency range of 10 Hz－20 kHz ranged from 114 to 123 dB (re 1µPa²). The median SPL in the coastal waters of Changhua was relatively higher. The 5th percentile (L5) was about 125－133 dB. May to August was the season with lower levels, and the peak was mainly dominated by the acoustic events at each location. During the construction period of the offshore wind farm in the Changhua area, continuous anthropogenic noise events such as pile driving and vessel machinery caused a significant increase in energy below 500 Hz at nearby locations. At a distance of 15 km from the wind farm, there was also a negative impact causing a reduction of fish vocalizations by 3－5 dB, which may be attributed to the increased shipping noise during the construction period. Shipping noise can interfere with cetacean behavior or have acoustic masking effects. Studies in the Miaoli waters showed that during the ship passage, the Taiwanese humpback dolphin reduced its vocalizations, with the number of whistles and clicks significantly decreased, and the duration of whistles significantly shortened. The median duration of whistles before the ship passage was 0.3 seconds, reduced to 0.22 seconds during the passage, and further reduced to 0.15 seconds after passage. With the large-scale development of offshore wind farms, the impact on marine life behavior needs to be explored as an urgent issue. The "Global Ocean Treaty" sets a target to protect at least 30% of the ocean by 2030 for the conservation of marine biodiversity and sustainable use. Underwater soundscape surveys and monitoring can help obtain baseline ecological data in marine areas. The results of the investigation can be used for communication, education, promoting public participation, and achieving a sustainable marine environment and the goal of biodiversity conservation.