But the international
study published in the Proceedings of the National Academy of Sciences
examined the impact of building dams on dozens of the smaller branches,
known as tributaries.
Since the area is home to many species of
migratory fish, the analysis found that several dam projects could block
fish from swimming upstream and cause massive losses to diversity and
fish supply.
This could have devastating effects on the tens of
millions of rural, poor residents in the region who depend on
subsistence fishing for their main source of food, said scientists from
Cambodia's Inland Fisheries Research and Development Institute and
Stanford and Princeton University.
More than one million tonnes of freshwater fish are caught each year
in the Cambodian and Vietnamese floodplains, and the entire Mekong River
Basin is home to 65 million people, about two-thirds of whom rely on
fishing to survive.
"We find that the completion of 78 dams on
tributaries, which have not previously been subject to strategic
analysis, would have catastrophic impacts on fish productivity and
biodiversity," said the study.
"Our results argue for
reassessment of several dams planned, and call for a new regional
agreement on tributary development of the Mekong River Basin."
Specifically,
four planned dams were found to create the largest fish biomass losses,
including the Lower Se San 2 in Cambodia (9.3 per cent drop in fish
biomass basin-wide), Se Kong 3d (2.3 per cent), Se Kong 3u (0.9 per
cent), and Se Kong 4 (0.75 per cent) in Laos.
Those projects were
among 27 dams focused on by the team because they have construction
planned between 2015 and 2030 and their future remains up in the air.
In
all, the researchers identified 877 fish species in the Mekong River
Basin, 103 of which would be potentially blocked from making their
upstream migrations by hydropower development.
Tributary dams
fall under national laws and do not require international agreement,
even though building these dams could have "potentially significant
transboundary impacts" on fish in other countries' waters, said the
study.
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