Potential Effects of Hydroelectric Dam Development in the Mekong River Basin on the Migration of Siamese Mud Carp (Henicorhynchus siamensis and H. lobatus) Elucidated by Otolith Microchemistry

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409–0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed.

本研究以耳石微化学技术为手段，对湄公河两种经济价值极高的鱼类——暹罗泥鲤（学名：Henicorhynchus siamensis与H. lobatus）的洄游行为展开了研究。在为期4年的研究周期内，研究团队于泰国、老挝、柬埔寨境内的湄公河流域全域7个区域采集了鱼类与河水样本。环境水体与耳石表面的元素组成具有显著一致性，其中锶（Sr）与钡（Ba）的相关性最为突出。锶的分配系数区间为0.409~0.496，钡的分配系数为0.055。耳石锶-钡剖面分析结果显示，同一区域内的个体洄游模式高度同步，且均起源于相似的产卵场。在一处建有多座灌溉大坝的支流水系中，H. siamensis的洄游行为已受到严重阻断。在湄公河干流孔恩瀑布上下游采集的H. lobatus样本，其耳石表面元素特征存在统计学意义上的显著差异，但耳石核心元素特征却高度相似。该结果表明，这群个体起源于单一产卵场，但通过一处可通行的旁道绕过了孔恩瀑布，而该旁道区域正规划建设一座大型水电站大坝。本研究最后讨论了湄公河流域大坝建设的潜在生态影响。