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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 industrylogsthe 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 longlifespanand 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)
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据研究人员介绍，常在澳大利亚海岸出没的鲸鲨变得越来越小。
鲸鲨的平均长度在十年内从7米减到了5米。
鲸鲨是世界上最大的鱼。在一些东亚国家，鲸鲨被人捕食，澳大利亚的研究人员们怀疑这是导致鲸鲨体积变小的主要原因。
鲸鲨已被列为"濒危物种"，研究报告的撰写者之一说这个新发现是个"十分令人担忧的信号"。
数据资料来源于生态旅游公司，这些公司向游人提供观赏鲸鲨的探险业务，在位于西北海岸的宁格罗海洋公园，游人还有机会体验一下和鲸鲨同游的滋味。
澳大利亚海洋科学研究所的马克·米肯说，在经营业务的同时，生态旅游公司将每条陪同游人游泳的鲸鲨的位置、体积和性别都记录了下来。
他说，"我们对已经获得的数据进行了分析。而分析结果是，在过去的十年里，鲸鲨的平均身长从7米减少到了5米。"
"可以想象一下，如果鲸鲨要长到6米或7米才成熟或开始繁殖，那么这个新发现实在是个让人担忧的信号。"
在国际自然与自然资源保护联合会的濒危物种名单上，鲸鲨已被划入"濒临灭绝物种"之列。
英国约克大学的卡勒姆·罗伯特对加勒比海中的鲸鲨做了大量研究。他说，"由于鲸鲨的生命期很长，繁殖率又低，因此和很多其他的鲸类一样，鲸鲨正面临着被过度捕猎的危险。"
同时也有迹象表明"光临"澳大利亚海域的鲸鲨数量正在减少，这也进一步说明过度渔猎是鲸鲨体积不断变小的罪魁祸首。
(中国日报网站编译)
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Updated: 2006-01-19 08:50
