Chronological Distribution Pattern of Finless Porpoises along Coastal Matzu Islands Based on Stranding, Bycaught and Landbased Sighting Surveys
|露脊鼠海豚分佈於亞洲近岸淺海與中國長江流域，是馬祖水域最常見的海豚，IUCN紅皮書將本種列為脆弱等級，牠們正面臨族群下降問題。我們自2003- 2009年在馬祖蒐集露脊鼠海豚擱淺或漁業致死個體資料，也於2005-2008年期間從事陸上鯨豚目擊調查，以了解其出現在馬祖的時間特性。結果共記錄56隻死亡個體，除7- 9月份未發現紀錄，其他月份的累積數為1-13 隻，牠們大多在馬祖列島北岸被發現，體長介於71-170公分，涵蓋新生兒至性成熟個體，前者佔總數14%。陸上鯨豚目擊調查共407時次努力量，資料以季風期、四季、每日潮汐與日周期變化等因子進行統計分析，發現東北季風與西南季風期之目擊指數(以下稱SI，Sighting Index, 目擊群數/小時）與每時海豚出現總數（以下稱TRPP，Total Recorded Porpoise Presence ，海豚總出現隻數/小時）有顯著差異；夏季SI與TRPP亦與春、秋、冬季各有顯著差異；而每日不同潮汐時段與日周期變化期間之SI與TRPP無差異。從標本與活體記錄顯示，每年十月到隔年五月是露脊鼠海豚在馬祖近岸出現較頻繁之時節，建議未來就季節性差異做適當的保育及漁業管理，並持續監測其族群動態。
Finless porpoises are small-sized toothed-whales inhabiting both in marine and freshwater areas. Their distribution is limited to Asian shallow coastal areas, river mouths, around some islands and the Yangtz River basin in China. They are the most commonly seen cetaceans in Matzu waters. During the years of 2003 - 2009, we collected the specimens of finless porpoises which had died due to stranding or fishing incident. Starting from the year 2005, we conducted a three-year landbased surveys to monitor finless porpoises' occurrences near the coast of Matzu. Our survey results indicate that from October to the following April are the months when finless porpoises most frequently die due to stranding or fishing incident. The majority of the carcasses of the porpoises, with the body length ranging from 71 to 170 centimeters, were found in the northward shore. Some of them were young while others had reached sexual maturity, and 14% were neonatal calves. Two southward locations on Nan-Gang Island where the environments were favorable to proceed the investigation were selected for the landbased observation. Sighting Index (hereafter SI, sighting/hour) and Total Recoded Porpoise Presence (hereafter TRPP，total porpoise presence /hour）were significantly higher in the period of north-east monsoon season than in the period of south-west monsoon. In addition, SI and TRPP for summer were lower than those of spring, fall and winter. In the Redlist issued by IUCN in 2011, finless porpoises were ranked as vulnerable. Consequently, appropriate conservational management will be an important task in the future. Both the records of the dead samples and the sighting of the live finless porpoises suggest that from autumn to the following spring are the seasons when finless porpoises constantly appear. Hence we propose that the conservation of finless porpoises in Matsu waters should be adjusted based on the seasonal differences. We also suggest that some measures on fishery control should be taken. Furthermore, continuous monitoring of the activities of finless propoises is essential.
Keywords - finless porpoise, Matsu Islands, seasonal distribution