Abstract
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.
Highlights
Migratory behaviors are extremely common in fisheries, and understanding fish migrations is vital to sustainable management and conservation of fisheries resources
Blocked by mainstream dams only in the uppermost Chinese territory, the Mekong River has 11 more dam proposals on the mainstream and more than 100 in tributary systems in the lower basin, all of which are scheduled to be installed within the decade [15]
The Linear discriminant analyses (LDA) of the two-element model classified 68.4% of the data correctly to the regions of sampling, whereas a full model based on the five elements classified 86.7% of the data (Table 1)
Summary
Migratory behaviors are extremely common in fisheries, and understanding fish migrations is vital to sustainable management and conservation of fisheries resources. A significant proportion of Mekong fishes are migratory, potamodromous (i.e., migratory wholly in freshwater) [8], and, more importantly, this enormous fisheries production relies heavily on the migratory habit of these species [9], [10] They are harvested mostly with gears and techniques developed to capture fishes during their seasonal migrations [11,12,13,14]. Blocked by mainstream dams only in the uppermost Chinese territory, the Mekong River has 11 more dam proposals on the mainstream and more than 100 in tributary systems in the lower basin, all of which are scheduled to be installed within the decade [15] These dams will impact fishes directly as a barrier to their migrations or indirectly through creation of huge impoundments and alterations to the natural flow regime, leading to a substantial loss of fish species and their habitats [10], [16,17,18]
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