- The Madeira Basin has the most diverse fish life in the Amazon River Basin with 1,406 species catalogued, but human interference and the climate crisis are provoking a significant decline in fish stocks.
- According to scientists, the Madeira hydropower plants have affected the hydrological cycle downstream due to irregular pulses, impacting the migratory patterns of fish.
- These disturbances have reduced the annual catch of fishers by 39% in the municipality of Humaitá.
- In the Madeira River, fishing became more costly and demanding, with fishers needing to spend more days and travel farther to spots to maintain decent productivity, which led many riverines to illegal activities.
HUMAITÁ, Brazil — At dawn, 20 fishers received a tip that matrinxãs were swimming down the Aripuanã River toward the Madeira, the Amazon Basin’s largest tributary. It was their opportunity to interrupt a week of unproductive fishing in Novo Aripuanã, a municipality in southern Amazonas state, in the Brazilian Amazon. So, they divided themselves among three wooden canoes and went to the river. It was just a matter of waiting for the shoal, which swims on the surface, and throwing the net.
At 11 a.m., with no sign of the matrinxãs (Brycon melanopterus), half of them gave up and, in the larger canoe, returned to the city. A fisher observed everything from a tip of land at that meeting of white and black waters in the Middle Madeira, while just ahead several pink river dolphins (Inia geoffrensis) and tucuxis (Sotalia fluviatilis) emerged to breathe while fish hunting. “Maybe the school doesn’t even get here, because the river is very dry,” Raimundo Dias told Mongabay.
At the end of April, the Madeira Basin was transitioning from the wet to the ebb season. With the water level still high, fish group into schools and migrate from lakes, tributaries and igarapés (small streams) to feed on fruits, seeds and terrestrial invertebrates that fall into igapós (flooded forests) and in the Madeira flood plains.
But for a decade, abrupt and frequent changes in river levels have disoriented migratory patterns. Scientists and fishers attribute these irregular pulses to the Madeira hydropower plants, two large facilities installed in the neighboring state of Rondônia. “In this month, the flood-and-dry has already happened about four times. The level was high yesterday. It’s very difficult for the fish,” Dias said.
Born and raised in Novo Aripuanã, Dias is 50 years old and has always survived on fishing, but making a living from this activity has been increasingly difficult due to the reduction in captures in the Madeira, the most diverse in the Amazon, with 1,406 species of fish catalogued. “There was a lot of abundance, there was no way not to catch fish here. For 10 years now, fishing has declined. This hydroelectric plant ruined us,” the fisher said.
The Santo Antônio plant, in Porto Velho, went into operation in March 2012 and has Brazil’s fifth-highest power capacity, and Jirau, installed 115 kilometers (71.4 miles) upstream, has been operating since September 2013 and is the fourth largest in the country.
According to Dias, the most affected species by the plants are the most consumed locally: pacu (Mylossoma), aracu (Leporinus fasciatus), sardinha (Triportheus auritus, T. angulatus), matrinxã (Brycon) and jaraqui (Semaprochilodus insignis, S. taeniurus). High-value fish species sold to large cities, such as the migratory catfishes dourada (Brachyplatystoma rousseauxii) and piramutaba (B. vaillantii), have also disappeared.
This scarcity has an impact not only on trade but on the diet of the Novo Aripuanã citizens. Fish, the main protein source for the Amazonian riverine population, has become pricier in markets and restaurants. “We used to sell a handful of matrinxãs for 5 reais [$0.89]. Now, it costs up to 40 [$7],” Dias said.
An unpredictable river
In Humaitá, a municipality on the border with Rondônia, fishing productivity is strongly influenced by seasonality. As the river dries up, many species come from the Lower Amazon, enter Madeira through the mouth and swim upstream to the whitewater river, where they breed.
However, 58-year-old fisher José Pessoa says this migration was impaired because the river lost its currents after the dams. “The fish requires rapids to make the piracema,” he said, referring to the breeding period. “If it doesn’t find it in the Madeira, it takes the Amazon, swims to the Solimões River and goes away. Here, we end up with nothing.”
“Nowadays, the fish we get around here is when the water level gets a little higher, so the fish comes out of the lakes, travels to another one and goes up [the Madeira],” said Pessoa, who has been fishing since the age of 13. “This year, with little flood, there won’t be as much, because there’s no water for them to travel.”
Artisanal fishing is also affected by the climate crisis, which intensifies meteorological phenomena. In October 2023, the Madeira suffered its worst drought in history, when it reached 1.10 meters (3.6 feet) of depth, influenced by El Niño (the warming of the equatorial Pacific) and the tropical North Atlantic Ocean. The Madeira lowered almost 3 m (9.8 ft) in 15 days in June 2024, and Rondônia decreed a state of alert for drought.
In the community of Paraisinho, 10 km (6.2 mi) upstream from Humaitá, fishing has become “almost nonexistent,” according to João Mendonça, president of the local farmers’ association, which also represents fishers. The community is sustaining itself thanks to floodplain agriculture, whose production is acquired by governmental food programs.
“The period that’s supposed to be drying is flooding,” Mendonça told Mongabay. “When it’s supposed to be flooding, it’s drying. The fish gets out of control. They don’t do their piracema at the right time. … Today, people come to buy chicken [in the city] because it is difficult to catch the fish in the community, both on the lake and the riverbanks.”
The dams adopt the run-of-river model, which retains less water in its reservoir but still affects the hydrology of the Madeira. After analyzing discharge data from three hydrological stations, scientists found that the “dam operations significantly increased day-to-day and sub-daily flow variability.”
Scientists measured this by monitoring sudden changes in river flow — or “reversal” events, the sudden shifts from a period of rising to a period of falling levels, or vice versa, on two consecutive days. This event almost doubled (94%) at the Porto Velho station, 5 km (3.1 mi) downstream of the Santo Antônio Dam. In Humaitá, 255 km (158.4 mi) from this plant, the increase was attenuated (13%), but still significant, according to researchers, who attribute the numbers to fluctuations in energy demand.
“The daily hydropeaking events are very frequent due to the hydroelectric plant because it controls the amount of water it retains and releases,” biologist Carolina Doria told Mongabay. She is co-author and coordinator of the Ichthyology and Fisheries Laboratory, of the Federal University of Rondônia. “This abrupt variation on the same day has a very big impact on the fish.”
The fish knows that it needs to get out of the flood plains, flooded forests and lakes and swim to the main river when the water level begins to rise daily and gradually, Doria said. “If this flood-and-dry happens, the fish doesn’t even leave the tributary. It gets lost. Physiologically, there is a lack of control.”
Barriers to healthy fish
Humaitá locals were used to well-defined periods for fishing. “The fish we expected the most in the flood were the jaraqui and the matrinxã. In the drought, it was the pintado, the pacu and the curimatã,” Mendonça said. “We used to catch them in large amounts. Today, you can’t count on that.”
The fish dynamics is closely linked to the availability of water in the basin, according to Marcelo dos Anjos, coordinator at the Laboratory of Ichthyology and Fisheries Planning of the Madeira River Valley, at Amazonas Federal University (UFAM).
“These species did not cease to occur there due to an environmental preference, but because they no longer have access,” Anjos told Mongabay. “The fragmentation of habitats has led to the decline of fish populations.” He said this loss of connectivity is linked to a set of factors: hydroelectric dams, deforestation, river silting, gold mining, settlements and agribusiness expansion.
Samuel de Moraes, president of the fishers’ association in Humaitá, observed that the riverine people of the Madeira can no longer plan according to the environment’s natural dynamics. “If the river is drying on the new moon we can have a good production because the fish leave the lakes to reproduce,” Moraes told Mongabay. “Now we have the new moon. It was supposed to be drying, but it’s flooding.” He also noticed changes in the behavior of the fish that live in the tributaries and lakes of the Madeira Basin.
Besides changes in the river flow, fish also suffer from poor water quality, which has been dropping in the Madeira, according to Adriano Nobre, a biologist from Amazonas State University (UEA). “Anthropic [human made] alterations directly affect water quality,” Nobre told Mongabay. “The changes in the hydrological regime made by hydroelectric dams, the presence of mining, deforestation, among other factors, have influence over the maintenance of aquatic life.”
In April, UEA researchers began to develop the first Water Quality Index (WQI) for a whitewater river in the Amazon, to understand the Madeira’s health. In March, the group launched the first WQI for the Amazon Basin, developed for blackwater rivers.
Researchers from UEA navigated almost 800 km (497 mi) on the Madeira to assess its WQI; results were not released yet.
Fishing in crisis
In Humaitá’s local market, Osvaldo de Araújo cleaned branquinhas in his stand while recalling the time when he fished in Três Casas Lake, 45 km (27.9 mi) downstream. “It was so much fish we couldn’t handle it,” Araújo, a 63-year-old fishmonger, told Mongabay. “We would catch any species we wanted.”
Araújo used to catch up to half a ton of fish in five days in his canoe, but he said today, a fisher can take at least 10 days to get 100 kilos (220.4 pounds). “In this market, if it wasn’t for the nursery fish, these stands would be empty,” he said.
There was a 39% reduction, from 267 to 163 tons, in the annual average of the fish landings in Humaitá, according to a UFAM study, comparing the periods before (2002-10) and after (2012-16) the dams. The most impacted species were branquinha, pirapitinga (Piaractus brachypomus), tucunaré (Cichia), curimatã (Prochilodus lineatus), jaraqui and pacu (Serrasalmidae). “These species are widely used in local cuisine, especially among riverine dwellers, and also represent a large part of the fishing effort of this population for regional trade,” said biologist Rogério Fonseca, co-author of the article and coordinator of UFAM’s Fauna and Forest Interactions Laboratory.
In the period analyzed, the most productive years took place before the hydroelectric plants came into operation: 2002 (294 tons), 2006 (350) and 2011 (407). The worst in fish landings happened after the dams: 2014 (158), 2015 (94) and 2017 (101). “Today, we are not reaching 100 tons anymore,” Moraes said.
The Humaitá association has around 3,700 fishers. The dams’ impact “represents a loss of approximately $342,000 per annum for fishing activity in Humaitá,” according to the researchers.
Another recent study found that five traditional fishing points became unproductive. There are also places with a strong decline in captures. In the Beem Stream, previously the most productive, capture dropped 99%, from 164 tons to 1.3. In the Lake Três Casas, it was reduced by a third, from 4.2 to 2.8 tons. Fishers needed to seek more distant places and started fishing in 25 new sites, according to the researchers. On each fishing trip, the riverine dwellers acquire fuel, ice, hire staff and buy food for the time in the river. “It’s not worth going far away,” Araújo said. “Today, the expense of a canoe to go to a lake is 500, 600 reais [$89, $107]. If you don’t bring in enough fish to cover the costs, you cannot afford to go again”, Araújo said.
In 2013, more than 1,500 fishers from Humaitá went to court against the companies that owned the plants, based on studies that attributed to the dams’ impacts on fisheries and fishing. The lawsuits claimed moral and property damages.
However, the judge of Humaitá considered that the disturbances to the fishers began during the construction of the plants in 2007, so he decided that the lawsuits were prescribed because the time limit had already passed.
The fishers appealed the sentence, and the cases are now in the Amazonas Court of Justice.
A tradition at risk
On a Friday afternoon, many boxes filled with jaraquis arrived at Manicoré’s local market, a municipality 355 km (220.5 mi) downstream of Humaitá. “This year, we expected a better production, but just now this fish is coming,” said Ancelmo de Menezes, a 59-year-old fisher. Before the dams, he said he used to capture fish in a higher amount and diversity. “It was matrinxã, it was everything. Now, as you can see, there’s only this fish here.”
“The most abundant fish species became very scarce,” said Antônio Veiga, president of the fishers’ association in Manicoré. In his opinion, the decline was not greater because Manicoré is surrounded by five large tributaries of the Madeira River, where the lakes have good productivity.
According to Veiga, who has been head of the association for 25 years, there was no public hearing or consultation regarding the hydropower plants in the region. “We had no knowledge of anything good or bad that it could bring to our municipality. They were installed in Rondônia, but the impact came down to Amazonas,” he said.
“Nobody has control of the situation. The fisherman no longer knows when the water comes, when it goes, how the riverbanks will be,” he said.
In Manicoré, the disturbances in the river and fish caused many fishers to give up and move to other activities. Some began gold mining in the Madeira’s main course, which also causes a lot of damage to the river, Veiga added, but this illegal activity is declining after Federal Police raids. In September 2023, agents destroyed 302 mining rafts and dredges scattered from Manicoré to Autazes. In May 2023, 86 vessels were disabled in the Humaitá region.
“Generations of fishermen are being forced to change their jobs. The mining and deforestation are at their door. Illegal activities are being pushed to these people, who are seeing themselves without opportunity,” Fonseca said.
A critical future
By the end of June, Novo Aripuanã fishers were still surprised by the absence of matrinxã schools. “So far, they haven’t come down,” said Allan de Barros, president of the city’s fishers’ association. This is an example of the uncertainty of fishing activity caused by the Madeira’s imbalance.
“We consumed a range of 100-150 tons of fish per year in the municipality, and exported more than 500 tons to Porto Velho and Manaus,” Barros said. “Today, we don’t even catch enough to meet the city’s demand. It’s something unusual.”
In Novo Aripuanã, the piramutaba used to climb the Madeira up to three times a year, but since the installation of the dams, “we have never seen a school in our river again,” Barros said. He also notes that the catfish species have decreased in size: the filhote (Brachyplatystoma filamentosum) used to reach 80 kg (176.3 pounds) and the dourada, 40 kg (88 lbs), but today they do not exceed, respectively, 10 kg (22 lbs) and 6 kg (13.2 lbs).
Amid this context, the number of active fishers in the association nearly halved. “The fish are far away and the expense is huge,” Barros said. “The city has no ice factory or diesel and gasoline subsidies. We do not have a cold room to store the fish, so we could sell it cheaper in the off-season. How will the fisherman go that far to catch this fish and sell it for a fair price?”
The fishers of Novo Aripuanã have not yet gone to court to be recognized as affected by the dams. But Barros said the best compensation would be a continuous transfer of resources, for example, via royalties or a support fund, so the city could invest in small-scale fish farming, in order to meet the citizens’ demands and have emergency resources to mitigate extreme events
At the meeting of the Madeira and Aripuanã rivers, Raimundo Dias told Mongabay that the 2023 historic drought also contributed to the unproductive fishing year in the Madeira Basin. As a result, other types of food prices also had risen. With the river drying fast again, he expects another rough season. “If it keeps drying like that until August or September, we will have a very big crisis here.”
Kevin Damasio and Bruno Kelly joined the Medeira River expedition with the support of Mongabay and Ambiental Media.
Study to benchmark water quality finds key Amazon tributary in good shape
Citations:
Almeida, R. M., Hamilton, S. K., Rosi, E. J., Barros, N., Doria, C. R., Flecker, A. S., … Roland, F. (2020). Hydropeaking operations of two run-of-River mega-dams alter downstream hydrology of the largest Amazon tributary. Frontiers in Environmental Science, 8. doi:10.3389/fenvs.2020.00120
Santos, R. E., Pinto‐Coelho, R. M., Fonseca, R., Simões, N. R., & Zanchi, F. B. (2018). The decline of fisheries on the Madeira river, Brazil: The high cost of the hydroelectric dams in the Amazon basin. Fisheries Management and Ecology, 25(5), 380-391. doi:10.1111/fme.12305
Lourenço, I. H., Doria, C. R., & Anjos, M. R. (2023). Spatial–temporal analysis of the effects of hydropower plants over the artisanal fishing in the middle Madeira region, Southwest Amazon. Fisheries Science, 90(1), 1-14. doi:10.1007/s12562-023-01730-5
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