中国澜沧江mang科鱼类种群现状及洄游原因分析
On the Population Status and Migration of Pangasiid Catfishes in Lancangjiang River Basin, China
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摘要: 我国曾经记录有mang科鱼类4种。国际上近年来对mang科鱼类的分类进行了许多重要的修订，物种数量已达3属22种。我国的mang科鱼类也因长时间没有进行及时的分类修订而存在许多疑问。基于国内自1960年以来所收集的珍贵标本和记录，确认我国记录有mang科鱼类1属3种。它们是：长丝mang(Pangasius sanitwongsei Smith)、贾巴mang(Pangasius djambal Bleeker)、短须mang(Pangasius micronemus Bleeker)。在此基础上，根据掌握的资料对我国mang科鱼类的种群现状和濒危原因、洄游的性质及洄游群体数量下降原因以及水电站建设对大型洄游鱼类的影响进行了分析。以往记录显示，捕获时间都集中于4—5月份，无冬季捕获记录。捕获季节与mang科鱼类产卵繁殖季节高度吻合，提示其上溯到我国澜沧江下游应属生殖洄游，而不是索饵洄游。被捕获记录主要出现于20世纪60—70年代，之后则数量锐减。导致这种情况发生的主要原因可能有三方面：1)下游湄公河对mang科鱼类的捕捞压力过大；2)湄公河—澜沧江航运船只对mang科鱼类有损害作用；3)由于西南季风变化的影响，澜沧江径流量发生变化，可能间接导致mang科鱼类洄游行为发生改变。分析显示，mang科鱼类的洄游与3—4月份澜沧江流量呈密切相关规律，提示适合鱼类产卵的雨季及西南夏季风比往年较早到达该地区，从而激发它们较往年提前启动生殖洄游，并且溯河的高度较高。以往的捕获记录还表明，mang科鱼类主要洄游至景洪下方的澜沧江河段及支流补远江，上述水域是其喜好的产卵场之一。景洪大桥以下的干支流不适合建设水电站，因为电站大坝必然会阻断mang科鱼类的繁殖洄游，影响其繁殖活动。而景洪大桥上方的干流电站不在mang科鱼类正常繁殖洄游通道中，大坝阻隔作用对mang科鱼类的影响相对较小。建议把补远江建设成为鱼类和水生生物保护区。Abstract: Four species of Pangasiid catfishes were once recorded in China. In recent years, several important revisions have been made to the taxonomy of the family Pangassiidae by some ichthyologists. As a result of these revisions, the original taxonomic system has changed greatly; a total of 22 valid species belonging to three genera is now recognized in the world. Because Pangasiid fishes in China have not been revised according to the new system, it is unavoidable that some confusion is present in species description. Based on specimen examinations and records in China since 1960, the present paper reconfirms that there is a total of three species of pangasiid fishes in China: Pangasius sanitwongsei Smith, Pangasius djambal Bleeker, Pangasius micronema Bleeker. Based on all the data and specimens available, the population status and threatening factors have been analyzed. According to the data, all three species of pangasiid fishes are rare critically endangered in the lower Lancangjiang River. Three specimens of P. sanitwangsei were collected in 1959 and no more have been collected since. Aside from two specimens of P. djambal collected in 1959, one more specimen has been caught from Buyuanjiang at Menglun by an ichthyologist of the Institute of Hydrobiology. Pangasius micronema is slightly more common than the above two species. One specimen was collected from Buyuanjiang River at Menglun in 1959 and five individuals have been collected since from the reach of the Lancangjiang River between Ganlanba and Jinghong in 1966. One specimen of P. micronema was also collected from the reach of Jinghong in 1967 by the Yunnan Fishery School. The most recent three specimens were caught close to the join of Buyuanjiang River to Lancangjiang River in 1978. All specimens were collected around May and June, which is recognized as the breeding season of pangasiid fishes. This suggests that pangasiid fishes migrate to the lower Lancangjiang River mainly for breeding, rather than feeding. The occurrence of pangasiid fishes in Xishuangbanna was analyzed together with the discharge records of the Lancangjiang River in March and April in Jinghong. A high correlation was demonstrated between these two factors, with 81.3% of specimens caught in years when a high discharge appeared in March and April. A high discharge in March and April may be a signal of summer monsoon, prompting the pangasiids to begin their breeding migration towards the upper MekongLancangjiang River. Populations of the three pangasiid species have been declining since 1970. The decline is not correlated to dam construction because so far no dams have been constructed in the stem rivers of the lower Lancangjiang River. Threatening factors may include overfishing and damage from boat turbines. If any dams are planned to be built in the lower Lancangjiang River, the conservation of pangasiid fishes should be carefully considered. We strongly suggest setting up the Buyuanjiang River as a nature reserve for fishes and other aquatic organisms.
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