Fish biodiversity declines with dam development in the Lower Mekong Basin

Area of Science:

• Freshwater Ecology
• Conservation Biology
• Environmental Science

Background:

• Hydropower dams provide renewable energy but pose risks to freshwater ecosystems, biodiversity, and food security.
• Dam development significantly impacts riverine environments, altering flow regimes and connectivity.

Purpose of the Study:

• To assess the impact of hydropower dam development on fish biodiversity changes from 2007 to 2014 in the Sekong, Sesan, and Srepok Basins.
• To correlate fish abundance and biodiversity trends with the cumulative number of upstream dams.

Main Methods:

• Analysis of a 7-year fish monitoring dataset.
• Regression analysis of fish abundance and biodiversity against cumulative upstream dam numbers.

Main Results:

• Hydropower dams significantly reduced fish biodiversity, including migratory and threatened species, in the Sesan and Srepok Basins.
• Fish fauna decreased in the Sesan and Srepok Basins, while increasing in the Sekong Basin, which has fewer dams.
• Fish species in Sesan decreased from 60 to 42, Srepok from 29 to 25, and Sekong increased from 33 to 56 between 2007 and 2014.

Conclusions:

• This study provides empirical evidence of reduced fish diversity linked to dam construction and river fragmentation.
• The Sekong Basin is crucial for fish biodiversity, and free-flowing sections of the Lower Mekong Basin support migratory and threatened species.
• Alternative renewable energy sources or re-operation of existing dams are recommended over new hydropower dam construction to preserve biodiversity.