A hydroelectric dam impacting Brazil’s Amazonas and Rondônia states have slashed fished populations by as much as 90% in some locations, according to a new a study based on on-the-ground research in partnership with riverine communities.
The 2008 construction of the Santo Antônio hydroelectric dam dramatically reduced the natural flow of the Madeira River, which runs through the states in the northwestern Brazilian Amazon.
As a result, species including pirarucu (Arapaima gigas), tambaqui (Colossoma macropomum) and pirapitinga (Piaractus brachypomus) have largely disappeared from traditional fishing communities.
“Fish need currents to navigate. They don’t need still water, they need moving water. And the Madeira River stopped flowing,” fisher Raimundo Nonato dos Santos, from the Lago Puruzinho community in Amazonas state, told Mongabay reporter Karla Mendes. “The impact was huge for us: the decline in fish stocks, the [milky] water remaining for many months within [the lake in] the community. It affected us a lot.”
Dos Santos was one of more than a hundred fishers who collaborated with researchers from the Federal University of Amazonas on the 2023 study. They analyzed daily catch data between 2009 and 2010, before the dam was completed, and again between 2018 and 2019, after it was finished. They found a dramatic drop in the number of fish caught in the region following the dam.
“The results show that the installation of the hydropower plants negatively affected the capture dynamics of several fish species by changing the capture periods and spots previously recorded,” the study’s authors wrote.
In the Sossego, Trapicho, Lago do Caiarí and Santa Júlia communities along the Madeira River, a reduction in fish stocks has forced fishers to travel longer distances, to more varied locations, to find fish.
“After the power plants, the fish disappeared,” smallholder Maria Delci Barros de Morais told Mongabay from the Paraíso Grande community in Rondônia. “My sons spend money on fishing nets, on Styrofoam, on ice, and sometimes they don’t even make enough for subsistence, let alone to sell and to cover their costs.”
Similar impacts are also reported from Indigenous territories farther away from the dam. Indigenous leader Adriano Karipuna told Mendes that 10 years ago, it was possible to catch half a metric ton of fish in half an hour. “Today, we spend six hours fishing, and if we catch four fish, that’s a lot. And it’s not the right size of fish,” he said.
Igor Lourenço, lead author of the study, told Mongabay the situation has likely changed since the data were collected between 2018 and 2019. He is setting up an ongoing data collection system to track fish stocks in the region in collaboration with local communities.
Read the full story by Karla Mendes here.
Banner image: Hydroelectric dams built in the Amazon caused up to a 90% reduction in fish stocks in some locations. Image by Kelvily Santos de Souza for Mongabay.
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