Where do the fish go in an era of hydropower development in the Lower Mekong Basin?

The Mekong River is crucial for providing populations with food and livelihoods. The Lower Mekong Basin (LMB) fishery is the world’s most productive inland fishery and provides a major source of food for people in Southeast Asia. In some Mekong countries for instance, fish supply up to 80% of protein intake requirements of the people and support the livelihoods of up to 95% of rural communities.  More than half of the annual Mekong fish catch consists of species that regularly migrate to access specific river or floodplain habitats for spawning, maturing and feeding.

However, the LMB’s fishery is currently facing serious threats from river infrastructure developments for farming and hydropower generation. The acceleration in hydropower development throughout the LMB is especially concerning. More than 160 hydropower dams are operating on the Mekong River and its tributaries, and 11 hydropower stations have been recently planned for the Lower Mekong River mainstem – with two of these already built.

Capacity building resulted in a fish tagging team that tagged and released fish in the Mekong River near Don Sahong Power Station in Southern Laos in 2022. Tagged fish were released in several locations and later detected over a range of more than 130 river kilometres.

Dams and other infrastructure developments block migratory fish from accessing crucial river and floodplain habitats to complete their lifecycles. Consequently, unless suitable conservation measures are included in the developments to maintain fish passage and access to crucial habitats, the LMB fishery will be devastated.

Basic knowledge of the migratory patterns of Mekong fishes is needed to design effective conservation measures such as fish ladders. But there is currently very limited knowledge available, and the knowledge that exists, comes mainly from surveys of fishers or from sacrificing fish to study their bone microchemistry.

The Mekong River Commission (MRC) launched the Joint Environment Monitoring (JEM) Programme for Mekong mainstream hydropower projects at two Mekong mainstream hydropower projects located at Xayaburi and in the Don Sahong area, in northern and southern Lao PDR, respectively. Charles Sturt University (CSU) partnered with the Australian Water Partnership (AWP), GIZ and the MRC, to test the MRC’s pilot fish passage monitoring guidelines and methods for the JEM Programme. Various cutting edge fish tracking technologies were trialled for using in the JEM Programme and running training sessions on the use of these technologies for regional institutions.

Surgery team inserting an acoustic and a PIT tag into a Mekong River catfish next to the Mekong River in Southern Laos. The far bank is Cambodia.

Despite beginning at the same time as the COVID-19 pandemic, the project was nonetheless able to proceed with team members from Charles Sturt University, the National University of Laos and GIZ located in-country throughout its duration. This enabled the team to carry out, in 2021, training workshops detailing several techniques for identifying individual fish, and to coordinate research with a completely independent project in Cambodia (1 km from the Don Sahong hydropower station).

The project was highly effective in informing optimal tagging and monitoring systems for monitoring fish passage at hydropower developments in the LMB. More importantly, it also built capacity within fisheries staff from Mekong countries to monitor fish passage and enabled three female Lao scientists to become the first experts in fish surgery in their home country.

In 2022, 124 tagged fish released in Laos were successfully tracked migrating up and downstream, including;

  • 4 Individual fish migrating more than 50 km upstream, bypassing the Don Sahong power station and its dam by using an engineered migration channel;
  • numerous tagged fish migrating more than 90 kms downstream into Cambodia after being released in Laos; and
  • 9 fish migrating downstream successfully passing through the turbines at Don Sahong Power Station.

With field work and data collection and analysis now completed, findings will be used to update the MRC’s Guidelines for Fish Pass Monitoring in the Lower Mekong River Basin. These will subsequently be used and actioned for future LMB hydropower developments.

Such outcomes are essential for preserving the precious LMB fishery in the face of accelerating hydropower development throughout the region.

Featured image: September 2021 was the first of two major training workshops for LMB member country fisheries staff to learn and install techniques to uniquely identify and detect fish in a river system. Credit for all images – Wayne Robinson
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