Fish or hydropower? New research eases choices in one of world’s most important rivers

Managing the dams water release could make the difference between these baskets being full of fish or empty during the annual drought. (© Vittoria Elliott)

In few places on Earth do so many depend on one river for so much.

The Mekong River basin is the lifeblood of 300 million people across Southeast Asia, and communities from China to Cambodia rely on 2 million tons of fish per year that the river provides.

But amid the appetite for fish is the struggle for power — electrical power, that is.

The dams that provide crucial hydropower to those same communities pose a threat to the river’s fisheries — leading to a fiendishly difficult balancing act between keeping the lights on or keeping people fed. In a new paper published in the journal Science, researchers explain a data-driven approach to find the “sweet spot” between the two.

Human Nature sat down with Vittoria Elliott, director of the Mekong Science Program at Conservation International and a co-author of the paper, to get the full story.

The fishery provides food security and revenue for the poorest communities. (© Vittoria Elliott)

Question: Why is this region so important?

Answer: The Mekong River, and in particular, the Tonle Sap Lake, is the most productive freshwater system in the world. It’s incredibly important for biodiversity, food security and people’s livelihoods. There’s an urgent need to understand how energy and food security affect one another. Regional communities obtain 50 to 70 percent of their animal protein from fish. For these communities to develop, they also need energy availability, and hydropower is preferable to non-renewable energy. Finding the balance where both sectors can be sustained was a critical goal for us as researchers and for the region’s governments.

Q: Why are dams potentially bad for fish?

A: One of the reasons that hydropower has a big impact on fisheries is because it blocks access for migratory species to their spawning grounds. There are many spawning grounds around some of the proposed dam sites in Cambodia. These are species that we find down in the delta and into the lake farther downstream. To maintain these populations, you need to keep open access between the sites where they’re spawning and the sites where they’re recruiting (surviving and growing up). If you stick a dam in between the spawning sites and the flood plains, then you’re not going to get any fish surviving for any period of time, regardless of whether you maintain flows.

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This process can only work in certain dams where there’s enough water storage to rescue downstream flows. There’s only certain circumstances that it would work under if you had extreme climate conditions that would create a massive drought. If you had other dams operating that were blocking the water, then it wouldn’t work. The starting point is to look at your baseline flows and identify potential sites.

Q: Tell us more about those flows.

A: River flows are influenced by water runoff from mountains, monsoon intensity and rising waters in the delta. In our research, we found key flow factors that affect fish more than others. For example, we see that how far the water spreads across the landscape is linked strongly to fish availability, because that water provides access to important feeding grounds and habitats for species. But, perhaps counter-intuitively, the dry period also increases the productivity of the fishery. If you have a long dry season — a drought — it provides a longer time period for nutrients from dead plants and the animals to sink into the soil. If this is followed by a rapid spike in water coming in, then the fisheries manage to capture the nutrients quickly, which also helps the fish population grow.

A boat load of fish from the Dai fishery in the Tonle Sap lake provides a vital source of annual protein for the fishing communities of Cambodia. (© Vittoria Elliott)

Q: What were the key takeaways from your research?

A: We were unsure if we could find the balance — the “sweet spot” — that would allow for healthy fisheries and dams, so it’s great that our results gave us key insights about sustainably managing fish and hydropower. Ultimately, our results suggest that we don’t have to consider dams versus fisheries as an all-or-nothing outcome. There’s potential to manage hydrology for food security. Tracy Farrell, the director of CI’s Greater Mekong Program, calls it a “win-win” scenario that keeps the fish  —  and the energy  —  flowing. What does that look like in reality? In some cases, dams that can actually be used to rescue fisheries from drought.

Q: What could this research mean for other places facing similar issues?

A: This approach is very adaptable. John Sabo, an eco-hydrologist and the paper’s lead author, has been working with other teams on many of these same hydro-fish interactions in other watersheds. Members of our team are exploring opportunities to apply something similar in other developing-country basins where fish support food security. There are certainly other landscapes where hydropower is a threat to inland fisheries and food security, such as the Amazon, Africa and even in the U.S.

If you tell an operator, or a government official working on hydropower that you want to talk about fish, then the door closes. This research can be used to address those concerns, and to show positive opportunities for both fisheries and dams.

Vittoria Elliott is the director of the Mekong Science Program at CI.

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