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

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.


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.

Article published by Glenn Scherer

This story first appeared on Mongabay

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