台灣西海岸中華白海豚時空分布與棲地利用

The spatiotemporal and habitat utilization of Sousa chinensis off the western coast of Taiwan

林圻鴻(Chi-Hung Lin)

指導教授 ： 周蓮香

國立臺灣大學/生命科學院/生態學與演化生物學研究所/博士(2021年)

https://doi.org/10.6342/NTU202103753

摘要

台灣的中華白海豚族群(或亞種)棲息於台灣西部沿海，因其棲地飽受大量的人為利用與沿海工業發展衝擊而面臨極度瀕危。為了解此族群在雲林海域(族群分佈熱區之一)的空間分佈年間變異以及與環境因子的關係，本論文的研究目的有兩大方向: (1)白海豚在雲林海域的分佈動態：於2008-2018年期間，執行海上目視調查242趟天，紀錄中華白海豚目擊群次數量及行為，並採樣固定的19測站及白海豚目擊位置當時的環境因子(水溫、鹽度、水深、pH及濁度)。(2)中華白海豚活動與河口環境因子的關係：於2017-2018年間在台灣西岸新虎尾溪口以及另外7個河口區域調查淨基礎生產力、葉綠素a、水溫、鹽度、濁度、pH值，以及蒐集雨量與逕流量等環境資料，最後與河口區的中華白海豚活動進行四季的相關分析。
本論文的主要結果: (1)中華白海豚在雲林海域的分佈動態：11年調查結果顯示，白海豚的空間分布在東西向(水深)梯度穩定，而南北向(緯度)梯度的年間變化大。中華白海豚群次目擊率的分佈或覓食行為頻率皆與穿越線測站的濁度(正相關)及pH值（負相關）的相關最為顯著。當這兩個因子劇烈變化下可能會迫使中華白海豚暫時放棄了它們原本的棲息地。(2)中華白海豚與河口環境因子的關係：本研究發現白海豚與河口環境因子的關係會因地理尺度不同結果有異。若以八個河口區的比較分析顯示，不同的河口區的環境因子以及白海豚活動變異頗大，兩者之間的關係也不明朗。不過整體而言，河口區域的白海豚目擊率與雨量及逕流量呈顯著正相關。但是單就白海豚分佈的熱點新虎尾溪口來分析，中華白海豚的目擊率與行為指標主要是與與葉綠素a以及濁度有顯著相關。另外，在新虎尾溪河口區的環境有明顯年週期變化，明顯為三個季節（秋冬合併）循環，推論其與白海豚的相關動態可能是：春季時升高的淨基礎生產量應該可支持更豐富的食物網，於是會吸引白海豚進來。但是夏末的颱風豪雨致使河口的濁度顯著升高，白海豚的目擊率與覓食行為就顯著減少了。
總結來說，環境因子的變化會牽引中華白海豚的分佈，各個河口區的棲地環境特性不同，或者同一個河口環境的季節變化，都會影響白海豚的棲地利用模式。未來保育白海豚的重要棲地的環境指標上，本文指出其關鍵的因子至少要包括河口雨量/逕流量以及濁度。

關鍵字

中華白海豚 ； 時空分佈 ； 棲地利用 ； 河口環境因子

並列摘要

Indo-Pacific humpback dolphins inhabit the western coastal waters off Taiwan. This population is critically endangered due to the overlap of their habitat with human activity and coastal industrial development. In order to understand the spatial-temporal variation of dolphins occurred in the coastal waters off Yunlin county, and their association with environmental variables, this dissertation includes two parts: (1) the dynamic change in spatial-temporal distribution of dolphins: Two hundred and forty-two visual surveys were carried out from the year 2008 to 2018 to record sightings and behaviors of humpback dolphins. Measurements of environmental factors (water temperature, salinity, water depth, pH, and turbidity) were collected at 19 stations on transect lines and at dolphin-sighting positions, and (2) Correlation between humpback dolphin activity and environmental factors of the Hsinhuwei as well as other 7 estuaries: environmental measurements including primary productivity, chlorophyll a, water temperature, salinity, pH, turbidity rainfall, and runoff during were collected during the year 2017–2018, and the relationship between environmental factors and dolphin activities at estuary area were analyzed by season.
Two major findings were: (1) the dynamic change in spatial-temporal distribution of dolphins: the decade-long survey data revealed that the spatial gradient of dolphin distribution was steady in the eastern-western direction (water depth variation), but not in the northern-southern direction (latitude variation). Either dolphin sighting rates or foraging-behavioral index showed significant correlated with turbidity (positively) and pH (negatively). Dramatic changes in these variables may push dolphins to temporarily abandon their preferred habitat. (2) Correlation between Sousa chinensis activity and environmental factors: this study found that the association between dolphin activity and estuary environment varied with different geographic scale. From the aspect of 8 estuaries, the sighting rate of humpback dolphins as well as the environmental conditions varied greatly among 8 estuaries, and their relationships cannot be clearly defined. In the whole, the dolphin sighting rates at estuary was significantly positive-correlated with rainfall and runoff only. However, from the aspect of single site, the Hsinhuwei estuary, the dolphin sighting rate and behavioral index was significantly correlated with chlorophyll a and turbidity. In addition, this study has revealed an obvious cyclic change among 3 environmental clusters, Spring, Summer and Autumn-winter clusters. The scenario for seasonal change in dolphin activity can be deducted as: in spring, the dolphin activity increased at estuary area could be attracted by the increased food abundance supported by high chlorophyll a and primary production, but dolphin sighting rate and foraging-behavioral index drop in late summer when the turbidity increased due to heavy rainfall accompanied by typhoons.
In concluding, the distribution of humpback dolphin can be affected by environmental changes. The habitat utilization of dolphins at the estuary area varied with each estuary environmental condition, or with its seasonal change. The study recommends the key index for essential habitat conservation of this critically endangered population of Sousa chinensis in Taiwan should include rainfall and turbidity as the key ones.

並列關鍵字

Sousa chinensis ； spatiotemporal ； utilization of habitat ； estuarine environment

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