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生活在大西洋海域、尾巴成圓形槳狀的是海牛 (manatee),而生活在印度太平洋、尾巴成鯨豚式三角狀的是儒艮 (dugong)。無論是海牛還是儒艮,都是屬於海牛目 (Sirenia) 的動物,以水草為食,外表看起來相當善良溫吞。介紹如何由外型和生活史特徵來區別海牛和儒艮的科普文章很多(譬如說這篇,雖然文章裡把生活在美洲的「西印度海牛」 West Indian manatee 誤解為「西印度洋海牛」有點 NG,不過大致上沒有太大的問題),所以在此請讀者們原諒一心一意想省話的作者,就不再贅述。
好吧,那我們就直接切入正題:所以說儒艮到底有幾種?
儒艮在印度太平洋海域的分佈範圍,從非洲的莫三比克、馬達加斯加,到澳洲、南太平洋的新克里多尼亞 (New Caledonia) 之間,包括阿拉伯紅海、印度、馬來西亞和印尼等等地區近岸海域。儒艮是海牛目裡現生的四種海牛之中,分佈範圍最為廣泛的一種。但是因為儒艮所在地周遭的國家,大多不是很熱衷生態學研究,而且相較於其他蹦蹦跳跳的野生動物,生性害羞低調的儒艮又特別難以觀察。所以除了有長期調查觀察記錄的澳洲海域以外,科學界對於其他海域的儒艮所知少之又少。
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為了尋找更關鍵的證據,一個由美國、巴哈馬和英國科學家所組成的研究團隊,於 2009–2015 年間,在巴哈馬附近、美國海軍的測試基地 Atlantic Undersea Test and Evaluation Center (AUTEC) 海域,在七隻柏氏中喙鯨身上裝了衛星發報器,記錄這些喙鯨們在演習前後的活動路徑、所在海水溫度,以及其中兩隻喙鯨的潛水水深的資料。
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