江豚的一生 Life history 江豚的年齡鑑定工作，主要依靠其牙齒橫切面 的年輪分析(就像計算樹木橫切面的年輪)，而 江豚的牙齒則是從擱淺屍體取下來的。鯨豚專 家以往普遍認為所有鼠海豚壽命較短，大多不 會活超過20歲。但香港的江豚研究發現，本地 最年長的江豚達33歲，亦可能是鼠海豚科的最 老紀錄。其實，在其他地方進行有關鼠海豚的 年齡研究，由於樣本主要來自被漁網誤捕的死 亡個體，所以這些「英年早逝」的鼠海豚可能 未能活到老就已死掉，這可能令研究結果有所 偏差。當然，我們亦不能排除香港江豚較其他 鼠海豚長壽的可能性。 江豚牙齒被染色後的 橫切面 Cross-section of a finless porpoise tooth after sectioning and staining process
The estimated age of a finless porpoise is based on analysis of dentinal growth layers from a crosssection of the teeth that are retrieved from stranded specimens; this method is similar to reading the rings for growth layers observed in tree trunks. Porpoises are often thought to have short life spans, rarely reaching the age of 20. But to researchers’ surprise, the oldest finless porpoise aged thus far in Hong Kong was 33 years old, which is probably the oldest found in any porpoise species. It is possible that studies of porpoise life spans in other areas are heavily biased by examining by-caught animals only so these animals would not have been able to reach their known maximum age; or maybe finless porpoises in Hong Kong just enjoy a longer life span than other porpoises.
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