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| The new finding has been described as "very
worrying". |
Whale sharks spotted off the coast of Australia are getting smaller,
researchers have said.
In a decade the average size has shrunk from seven metres to five
metres.
Whale sharks, the world's largest fish, are caught for food in some
east Asian countries and Australian researchers suspect this is causing a
decline.
The fish is listed as "vulnerable", and one of the authors of the new
study has described the new finding as "a very worrying sign".
The data comes from ecotourism companies which run expeditions to watch
whale sharks and swim with them in Ningaloo Marine Park off the north-west
coast.
"The eco-tourism industry logs the position
and size and sex of every shark it swims with," said Mark Meekan of the
Australian Institute of Marine Science (Aims).
"We have obtained those datasets and analysed them over time," he said,
"and essentially what we have seen in the last decade is a decline in
average size of shark from seven metres to five metres.
"Now if you consider that the sharks probably aren't sexually
reproductive or mature until they're six or seven metres long - that's a
very worrying sign."
Under the IUCN Red List of threatened species, they are categorised as
"vulnerable" to extinction.
"Whale sharks, like many other shark species, are highly vulnerable to
over-exploitation due to their long lifespan
and low reproductive rate," commented Callum Roberts of York University in
the UK, who has researched whale sharks extensively in the Caribbean.
There are also indications that the number of sharks visiting
Australian waters may be decreasing, which would be additional evidence
for a decline prompted by over-fishing.
(Agencies) |
據研究人員介紹，常在澳大利亞海岸出沒的鯨鯊變得越來越小。
鯨鯊的平均長度在十年內從7米減到了5米。
鯨鯊是世界上最大的魚。在一些東亞國家，鯨鯊被人捕食，澳大利亞的研究人員們懷疑這是導致鯨鯊體積變小的主要原因。
鯨鯊已被列為"瀕危物種"，研究報告的撰寫者之一說這個新發(fā)現是個"十分令人擔憂的信號"。
數據資料來源于生態(tài)旅游公司，這些公司向游人提供觀賞鯨鯊的探險業(yè)務，在位于西北海岸的寧格羅海洋公園，游人還有機會體驗一下和鯨鯊同游的滋味。
澳大利亞海洋科學研究所的馬克·米肯說，在經營業(yè)務的同時，生態(tài)旅游公司將每條陪同游人游泳的鯨鯊的位置、體積和性別都記錄了下來。
他說，"我們對已經獲得的數據進行了分析。而分析結果是，在過去的十年里，鯨鯊的平均身長從7米減少到了5米。"
"可以想象一下，如果鯨鯊要長到6米或7米才成熟或開始繁殖，那么這個新發(fā)現實在是個讓人擔憂的信號。"
在國際自然與自然資源保護聯(lián)合會的瀕危物種名單上，鯨鯊已被劃入"瀕臨滅絕物種"之列。
英國約克大學的卡勒姆·羅伯特對加勒比海中的鯨鯊做了大量研究。他說，"由于鯨鯊的生命期很長，繁殖率又低，因此和很多其他的鯨類一樣，鯨鯊正面臨著被過度捕獵的危險。"
同時也有跡象表明"光臨"澳大利亞海域的鯨鯊數量正在減少，這也進一步說明過度漁獵是鯨鯊體積不斷變小的罪魁禍首。
(中國日報網站編譯) |
Updated: 2006-01-19 08:50
