Madeira River dams may spell doom for Amazon’s marathon catfish: Studies

Independent monitoring of a giant Amazon catfish population in the Madeira River, a major tributary of the Amazon, confirms that two hydroelectric dams have virtually blocked the species’ homing migration upstream — the longest known freshwater fish migration in the world.
Research completed in 2018 indicates a serious decline in catches of the gilded catfish (Brachyplatystoma rousseauxii) and other key commercial species on the Madeira, both upstream and downstream of the two dams.
New monitoring techniques show that the disruption of the migration route raises the risk of extinction for this species, for which researchers have recommended the conservation status be elevated from vulnerable to critically endangered.
If the gilded catfish and other migratory species are to survive, mechanisms to assist their migration past the dams must be improved, researchers say.

Last year, Mongabay contributor Gustavo Faleiros and filmmaker Marcio Isensee e Sá visited the unique, biodiverse Amazon forests found on the divide between the Purus and Madeira river basins, where a plan to improve the BR-319 highway, delayed by decades, is gaining momentum, bringing environmental transformation. This story is the fourth in the series.

If the Madeira River were a highway, it would certainly be a major route, a central artery, connecting important points southwest to northeast across the Amazon Basin. When its 3,380-kilometer (2,100-mile) length joins the mighty Amazon River, the two waterways link the Andes foothills, Brazilian rainforest floodplains, and the Atlantic Ocean.

This connectivity isn’t just important for human commerce. Among the Amazon’s great tributaries, the Madeira contributes the most sediments coming from the high Andes. Its nutrient-rich waters, driven by annual rainy season floods, jump riverbanks and spread out through the Amazon rainforest; those sediments are essential to floodplain fertility and to the forest ecosystem. The river’s connectivity is just as vital to fish, and to large-scale commercial and small-scale subsistence fisheries, from the Madeira’s Bolivian headwaters, downstream into Brazil, and to where the river merges into the Amazon east of the city of Manaus.

This extraordinary aquatic interconnectivity has generated tremendous evolutionary diversity. About 1,000 species of fish have been cataloged in the Madeira sub-basin, representing a third of all the ichthyofauna found in the entire Amazon Basin.

Among the travelers along this magnificent mud-brown highway are migratory fish — capable of going the distance, drifting downstream and striving upstream for thousands of miles to mate, spawn, and live out their life cycles under harsh conditions; they push through heavy rapids and navigate submerged forests, and have thrived for many centuries.

Then came the dams

Or at least that’s how things stood before Brazil built the Santo Antônio and the Jirau mega dams, operational in 2012 and 2013, respectively: man-made obstacles that the great waves of migratory fish find it difficult, if not impossible, to pass, despite the addition of fish ladders.

A decade after the start of construction of the two Madeira hydroelectric dams in Rondônia state, new scientific research indicates that the river’s fish have been negatively affected.

Investigations published in 2018 demonstrate both a reduction in fishing catches and the dangerous isolation of populations of migratory species, such as the gilded catfish (Brachyplatystoma rousseauxii), which can grow to 1.5 meters (5 feet) long, and which is considered essential to the economy and food supply of Madeira Basin residents.

The gilded catfish, or dourada, which makes the longest freshwater migration ever recorded — a round trip of some 11,000 kilometers (6,800 miles) — serves as a prime example of environmental change and species impacts. Surveys of the life cycle of individuals captured after the construction of the dams show migrations practically ceased after the closure of the floodgates — and that could ultimately have dire consequences for the catfish, including eventual extinction in some parts of the basin.

The gilded catfish, or dourada (Brachyplatystoma rousseauxii) as drawn during an 1856 Amazon expedition. The species makes the longest freshwater migration ever recorded — a round trip of some 11,000 kilometers (6,800 miles). Image by Francis de Laporte de Castelnau in the public domain

In a study done for her Ph.D. thesis, Marília Hauser, from the Federal University of Rondônia (UNIR), investigated what she calls the “black box” of the dourada. Hauser analyzed the otoliths — the deposits of calcium carbonate that build up in the inner ear cavities of all vertebrate species over their lifetime — gathered from 265 catfish captured upstream and downstream of the dams.

When strontium isotopes in the otoliths are compared with a microchemical analysis of elements found in the Madeira and Amazon rivers, it’s possible to determine the lifecycle of an individual fish and map their annual river journeys.

From such analyses, Hauser discovered that 80 percent of the catfish found in the Madeira River migrated all the way upstream to reproduce in the Andes headwaters before the hydroelectric plants were built. Now, almost all the fish analyzed are confined to the parts of the river where they’re found. There is little evidence of migration.

Hauser found in particular that the otoliths in catfish populations upstream of the dams lack some of the chemical elements found in the middle and lower sections of the Madeira. Fish older than 5 years in age showed no evidence of having arrived back upstream after a downstream journey, meaning they were born and raised in the upper Madeira, never making the journey to the Amazon estuary on the Atlantic coast.

“These results confirmed irrefutably the impacts of the dams, both on the contribution of adults in the upper reaches of the Madeira River basin, and on the migration downstream of eggs and larvae,” says the study, published in June 2018 by UNIR and titled “Migration of large catfish from the perspective of strontium isotopes in otoliths.”

Hauser told Mongabay that her research on the otoliths showed that these catfish, when allowed to migrate freely, return to spawn in the headwaters of the river where they were born.

A small part of the researcher’s sample, 16 percent, eventually reached the Amazon estuary, indicating that dourada larvae can descend through the dams’ turbines. But there’s no indication that the maturing fish ever make their way back upstream to their home territories. For Hauser, the data show conclusively that there’s been “a complete change in the migration pattern.”

One key finding came from the examination of a population of catfish captured in the Santo Antônio dam reservoir. All of these upstream individuals were adults and residents, which could indicate that even if some of the fish managed to migrate upstream into the first reservoir using a fish ladder, they weren’t able to continue upstream past the second hydroelectric plant, the Jirau dam.

The Santo Antonio mega dam seen from above. Many scientists say that the dam prevents fish migrations, though the consortium that built the dam disputes this finding. Image courtesy of Santo Antonio Energia.

Companies deny the impact

The Santo Antônio and Jirau dams generate a combined 7300 megawatts of electricity. Their environmental licensing process began in 2006, under the Brazilian presidency of Luiz Inácio Lula da Silva. Despite a great deal of opposition and concern among environmental scientists, scholars and bureaucrats about the potential impact on fishing and sediment retention, the consortia of dam builders obtained authorization for both projects. Construction began in 2008; both plants began operating at maximum capacity five years ago.

The location of Jirau and Santo Antonio on Madeira River in Brazil

The Santo Antônio Energia consortium maintains a fish species monitoring program within the dam’s area of influence. This program includes the counting of larvae that descend the river, and the capture of individual fish above and below the dam. According to biologist Marcela Velludo, who coordinates the monitoring, the findings don’t indicate the reduction reported in Hauser’s thesis.

Velludo said technical reports were regularly sent to, and approved by, IBAMA, Brazil’s environmental agency, indicating that the company’s methodology and findings have, at least for the moment, the endorsement of the federal government.

In a series of phone interviews, Velludo said the thesis, although relevant to the knowledge of the dourada lifecycle, was unable to establish a causal relationship between the dams and recorded catfish declines. She said Hauser’s data samples didn’t confirm that migrations had been interrupted, and that the presence of juveniles in the estuary was a sign of dourada health. “The count of ichthyoplankton, that is the presence of fish eggs, and the density of larvae per cubic meter, do not show any [declining] variations,” Velludo said.

Energia Sustentável do Brasil, the consortium responsible for the Jirau hydroelectric power plant, sent a note from its press office stating that ongoing monitoring hadn’t registered any change in the quality and quantity of the Madeira fish.“In the Jirau Hydroelectric Power Plant there are two Fish Transposition Systems that allow the passage of migratory species past the dam, maintaining the gene flow for health maintenance of upstream populations,” it said. “The systems are recognized by experts as efficient, the most suitable for the Jirau HPP, and meet the conditions of [environmental] licensing, avoiding serious ecological impacts on the fish community.”

The Jirau dam under construction. Image courtesy of the International Hydropower Association.

The great journey

Until the mid-2000s, visitors to the city of Porto Velho could make a side trip to the nearby Teotônio waterfalls and see an extraordinary sight. Get your timing right and the main attraction there was fishing for giant catfish as water levels began to drop, signaling the annual piracema, an indigenous word for the fish migration. Historical photos show traditional anglers walking out over the rapids on shaky bridges balanced atop improvised piers to fish for the dourada, considered a noble species by the Madeira Basin’s people.

Little was known in the past about the impressive Amazon migration made by the river’s catfish, even though its long journey upstream guaranteed the livelihoods of thousands of fishermen from Brazil to Bolivia for many decades.

Scientists only recently discovered that the fish regularly accomplishes the longest freshwater migration on Earth, a round trip of 8,000 to 11,000 kilometers (5,000 to 6,800 miles) from the headwaters in the Andes down to the Amazon estuary and back again over its 12- to 15-year life span. The upstream leg in itself exceeds the long-distance migratory record once thought to be held by salmon swimming up the Yukon River.

The giant catfish begins its lifecycle where the Andes highlands transition into areas of high hills and forest. Adult fish spawn in high-country tributaries of the Madeira. The eggs hatch and the catfish larvae drift downstream with the current for 40 days until they arrive in the Amazon estuary, where food is abundant.

There they remain until mature, a period of three to four years. After that, they begin the arduous journey upstream against river currents and through rapids, back to their home tributaries, where the cycle begins again.

Fishermen in Humaitá, an important downstream port on the Madeira saw their catches decline by 39 percent between 2002 and 2017. Image by Rangel Santos/UFMG

Upstream impacts

The NGO Faunagua, based in Cochabamba, Bolivia, monitors a portion of the dourada’s spawning grounds, looking for the presence of breeding catfish in the Madeira headwaters of the Ichilo River, a tributary of the Beni River, which, near the border with Brazil, joins the Mamoré to become the Madeira.

Faunagua monitors a section of river some 1,500 kilometers (932 miles) upstream of the two Brazilian mega dams. It collected data from 1998 to 2009, and after a pause, resumed its catfish surveys in 2015. Those two data sets provide a robust basis for comparison before and after the dams were constructed, said Faunagua researcher Paul Van Damme. The latter surveys found that recent dourada counts were only 10 percent of what existed a decade before the dams.

Van Damme said this evidence, coupled with Marília Hauser’s research, indicated that the catfish population in the upper Madeira had plummeted and could eventually be extinguished. As a result of these alarming discoveries, Van Damme, other researchers and nongovernmental organizations are requesting that the International Union for Conservation of Nature raise B. rousseaxii’s conservation status on the IUCN Red List from vulnerable to critically endangered.

But action to save the gilded catfish seems unlikely to come anytime soon. Van Damme, who participated in the bilateral commission that discussed the impacts of the Santo Antônio and Jirau dams between 2006 and 2008, says the issue is simply no longer on the agenda of the Brazilian or Bolivian governments.

He said he was even more concerned about what the decline of the dourada says about what’s going on beneath the murky surface of the Madeira and its tributaries. The dourada “is just one species we can monitor, but there are many others [about which] we do not know what is going on, which we cannot show.”

Mud-brown colored sediments that once were carried far downriver to feed the Amazon basin floodplain now pile up behind the two Madeira dams, and it is theorized, leave few rocky places where the giant catfish can lay its eggs, contributing to population declines. Image by Gustavo Faleiros/InfoAmazonia.

There is hope, but action is needed now

With the observed drastic decline of dourada catches, the Madeira’s fishermen have suffered. Fish catches recorded at Humaitá, a city 200 kilometers (120 miles) downstream from the hydroelectric dams, show a 39 percent drop in the average monthly catch between January 2002 and September 2017.

In this case, researchers led by Rangel Santos from the Federal University of Minas Gerais didn’t look just at dourada declines. Several species of commercial importance, including pacu, branquinha and jaraqui, among others, were also evaluated. In an article published in the journal Fisheries Management and Ecology, the research team identified changes in the flow of the Madeira due to the dams as a major reason for the fisheries decline.

“The river [levels] became unpredictable, and so the fisherman chooses not to hit the water because the more flooded the river is, the less abundant is the fish,” Santos said.

These sorts of fisheries impacts weren’t unexpected. When the dams were being designed, experts within the Brazilian government questioned the viability of the projects precisely because of the lack of information about the impact to the dourada and other commercially valuable migratory species. To solve any potential migration problem, the dam-building consortia proposed a solution common to hydroelectric plants in temperate countries: fish ladders.

In the case of the Santo Antônio dam, they installed a channel that tries to emulate the flow of the former rapids. Velludo, the Santo Antônio Energia biologist, said this was the first time this technology was applied in the Amazon. The channel is 15 meters (49 feet) long, 10 meters wide, and 3 meters deep.

But research by Carolina Doria, a professor at the Federal University of Rondônia, demonstrates that these fish ladders don’t work, and that they don’t mitigate the Santo Antônio and Jirau dams’ dramatic impacts on migratory routes. Doria guided the doctoral research of Maria Alice Leite Lima, who, in her 2017 thesis, recorded a decline of nearly three-quarters in dourada catches in Madeira River fishing ports since the dams were built.

Velludo disputed this finding, saying Lima’s research only considered biomass, or the total weight of fish catches in the period observed. She pointed to a record flood along the Madeira in 2014 that forced fishermen to spend less time and money fishing over the following years. In other words, their catches were smaller because they fished less, not necessarily because there were fewer fish in the river.

However, that raises yet another question: was the extent of the flooding exacerbated by the presence of the dams? There’s no clear answer yet.

Doria criticized the hydropower consortia for discontinuing their agreements with the university that allowed monitoring of the migratory species. The companies have also been at odds with the fishermen, who are often arrested for entering the no-go areas near the dams in search of fish they can no longer find. “Companies just do not want to hear,” Doria said in a phone interview.

Fabrice Duponchelle, a researcher at the France-based Institute of Research for Development, which has collaborated with researchers in the Amazon for years, is preparing an article with Marília Hauser and Carolina Doria defending their evidence showing that the dourada migration has been disrupted by the dams. Like Doria, he calls for immediate changes to be made in the Santo Antônio transposition system — a manual mechanism for separating and controlling populations of predatory species which appears not to be working — and for new dialogue with the Jirau dam management.

So where can Madeira fishermen and those thrilled by the dourada’s epic migration find hope? In those nuggets of ear stone, apparently — the otoliths that Hauser analyzed, showing that 16 percent of the dourada caught in the Amazon River estuary were born after the construction of the dams. That, said Duponchelle, presents a glimmer of light for the future: “Somehow they passed, so there is still hope.”

Fishermen sort their catch. Scientists have not only detected dourada declines, but also recorded population changes in species of commercial importance, including pacu, branquinha and jaraqui, among others. Image by Marcio Isensee e Sá/InfoAmazonia.

Citations:

Hauser, Marilia “Migration of large catfish from the perspective of strontium isotopes in otoliths.” (2018) Universidade Federal de Rondônia (UNIR), Ph.D Thesis

Santos, R. E., Pinto‐Coelho, R. M., Fonseca, R., Simões, N. R., Zanchi, F. B. The decline of fisheries on the Madeira River, Brazil: The high cost of the hydroelectric dams in the Amazon Basin, Fisheries Management and Ecology, Volume25, Issue5, October 2018 Pages 380-391. DOI: 10.1111/fme.12305

Barichivich, E., Gloor, P., Peylin, R., Brienen, J. W., Schöngart, J., Espinoza, J. C., Pattnayak, K. C.. Recent intensification of Amazon flooding extremes driven by strengthened Walker circulation. Sci. Adv. 4, eaat8785 (2018). DOI: 10.1126/sciadv.aat8785

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Banner image caption: The gilded catfish (Brachyplatystoma Rousseauxii) can grow to a length of up to 1.5 meters (5 feet). Image by Michael Goulding/WCS.

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