Fish and fisheries in the Upper Mekong: current assessment of the fish community, threats and conservation

Abstract

The Mekong flows north to south, through six countries in south-east Asia. Many studies have concentrated on fish and fisheries in the Lower Mekong, which has been identified as one of the largest inland fisheries in the world with an incredibly rich diversity of species. In contrast, fish and fisheries in the Upper Mekong (Lancang River) have remained relatively undocumented. In this paper, we synthesized information on freshwater fish biodiversity and fisheries in the Upper Mekong and documented 173 species and subspecies (including 87 endemic species) among 7 orders, 23 families and 100 genera. We divided the Upper Mekong into 17 sub-basins based on Digital Elevation Model (DEM) and then used fish species data to cluster the sub-basins. Four parts (the headwater, the upper reach, the middle reach and the lower reach) and one lake have distinct fish species communities associated with them. There was a linear relationship between fish species (x) and endemic species (y) as y = 0.5464x -3.2926. Relationship between species number or endemic species number (y) and mean altitude (x) can be described as y = -54.352 ln(x) ? 460.79 or y = -30.381 ln(x) ? 253.85, respectively. Fisheries kept as about 6,000 t from 1989 to 1998, and then steadily increased to 10,000 t in 2004. We reviewed the overall threats to the Upper Mekong fish and fisheries, and found that hydrological alteration is the largest threat in the basin, followed by over fishing and the introduction of exotic species. In terms of specific river sections, water pollution was the most serious threat to fishes in the upper reach of the Upper Mekong, whilst migratory fishes in the lower reach of the Upper Mekong are seriously threatened by the construction of cascade dams. The Buyuan River and the Nanla River were identified as important feeding and spawning habitats for upstream migrant species and should be considered as a priority for conservation.

Influences of low-head dams on the fish assemblages in the headwater streams of the Qingyi watershed, China

“…Low-head dam buildings impact indigenous lotic fishes and create favorable conditions for lentic fishes to increasingly inhabit headwater streams. Currently, as a result of fast development in social production and economy, the freshwater ecosystems and fishes in China are being endangered from diverse anthropogenic disturbances, such as habitat degradation, water pollution, and alien species invasion (e.g., Fu et al 2004;Kang et al 2009). The results that fish assemblages in headwater streams are affected by low-head dams observed in this study will reasonably be constructive for the conservation of freshwater fishes in China, where numerous dams have been built and are being built (Liu 2004;Chen and Chen 2005).…”

Fish assemblages and diversity in three tributaries of the Irrawaddy River in China: changes, threats and conservation perspectives

“…Major threats can be classified into overexploitation, water pollution, flow modification, destruction or degradation of habitat, and invasion by exotic species (Dudgeon et al, 2006). Different areas can suffer different dominant threats, such as the considerable water pollution in specific river sections of the upper Mekong (Kang et al, 2009) and overfishing in the floodplains of the lower Mekong (Allan et al, 2005). Among the three tributaries of the Irrawaddy in China, all threats mentioned above occur in the Daying and Ruili rivers.…”

“…Exotic species can compete with native fish for food, space and other resources, leading to greatly reduced numbers of local species, and even local extinction (Kang et al, 2009). Furthermore, the shift from lotic to lentic environments after dam construction often favors generalist over specialist species, alters assemblages of taxonomic groups and puts endemic species at particular risk of extinction, leading to biotic homogenization (Liermann et al, 2012).…”

“…Such measures not only assist in the recovery of wild populations of endemic and rare fish, but also help to overcome technical bottlenecks in developing new and local aquaculture species . Current conservation policies for freshwater fish in China mainly focus on endangered species and those of economic importance (Kang et al, 2009), such as the nationally protected Acipenser sinensis, Myxocyprinus asiaticus and Sinocyclocheilus grahami, as well as major economic species such as grass, silver, bighead and black carp . Three species in the Irrawaddy River are endangered and protected species (Table 3).…”

What Do the Occurrences of Migratory Fishes in the Upper Mekong Mean?

“…Since then the local fish fauna has changed gradually, showing an increased presence of species that thrive in still water, and even the dominance of the icefish Neosalanx tangkahkeii, originally transplanted for aquaculture. In total, 48 % of the local species have disappeared in this area in 20 years from 1987 to 2007 (Kang et al 2009). Moreover, Manwan Dam trapped about 60 % of sediments into its reservoir (Fu et al 2008), and Kummu and Varis (2010) predict the sediment trapping efficiency would reach as much as 94 % for the whole cascade of eight dams, which would dramatically reduce the amount of nutrients flowing to the Lower Mekong, further affecting fish biodiversity (Osmundson et al 2002).…”