How to keep fishing in the Amazon: Texas A&M scientists study what keeps freshwater fish abundant

By: Olga Kuchment

On a recent plane trip to Santarem, Brazil, Kirk Winemiller gazed at a vast mosaic of lakes and waterways of the Amazon region. One huge muddy river split into multiple channels, each as wide as the Mississippi river.

The waters house over a thousand species of fish, which Winemiller, a professor in the Department of Wildlife and Fisheries Sciences, studies. The fish are an indispensable food resource and an essential part of the economy in this part of Brazil.

Each winter the rivers and lakes flood and water levels can rise by more than 30 feet, flooding forests and meadows. Researchers have known that fish migrate to flooded areas to feed on fruits, nuts, and seeds, but nobody has yet estimated how access to these resources influences fish production.

Amazon fish populations have decreased in recent decades, and the landscape has changed. Roughly 56 percent of the Amazon forest has been cut between 1970 and 2008.

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Dr. Leslie Winemiller (left) and Carol Arantes (right) process fish samples during a field survey on the river.

To quantify the effect of deforestation on fish, Winemiller is working with a team of Texas A&M and Brazilian researchers. Leading the project is Winemiller’s doctoral student Carol Arantes. She is spending the 2013-2014 academic year examining fish specimens and conducting workshops with villagers on sustainable fishing. Once completed, the project will inform the work of government agencies and conservation groups in Brazil.

“The project is looking at the patterns of fish abundance in relation to vegetation in the floodplains, particularly whether or not there are more fish species and more fish biomass in areas where the forest is more intact,” Winemiller says.

“People in the Amazon depend so much on the fisheries,” he adds. “My lab conducts research on rivers in Texas, but we can also take our expertise to other countries to help people confronted with serious natural resource issues.”

Travel and living

Arantes has been renting a houseboat and hiring local fishermen to help catch and catalog fish. She stays at different locations for several days, collects environmental data, surveys fish stocks, processes fish samples, and preserves some samples for later study.

Winemiller and his wife, Leslie, traveled to Brazil during January and February to participate in the final field survey for the project.

“It’s a long day of travel,” Winemiller says. “We first arrived in the Manaus airport, right smack dab in the middle of the Amazon. One is surprised to learn that Manaus is a modern city of nearly 2 million people. From there we flew to Santarem where we headed out on the boat with Carol and her field team.”

They lived on a houseboat with 16 others, including the boat’s crew, local fishermen, student volunteers, and a cook. They slept in hammocks that swayed with the waves on windy, rainy nights.

“The cook was excellent,” Winemiller says. “The fish were delicious, and there were so many different kinds.”

Boating around the river afforded the team a close-up look at scattered villages and farms where people support themselves by fishing and raising livestock.

“There are seasonally flooded pastures that somehow support cows,” Winemiller says. “That was surprising to see along the shore of the Amazon River.”

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Typical houses on stilts along the Amazon.

When the river floods, big barges carry the livestock up and down the river to other pastures or to markets.

Houses in the floodplains are built on tall stilts. Despite the stilts, some houses are flooded with up to a foot of water during the rainy season. One woman said that she found a big lungfish swimming in her living room one year, Winemiller recounted.

Catching fish 

Arantes and Winemiller are comparing fish communities from regions that have been deforested with those where the forest remains intact, and they also will analyze the structure of fish communities during the different periods of the flood cycle.

By some counts, 1500 to 3000 species of fish can be found along the main channel of the Amazon. It would take years to survey all the species even in one location, Winemiller says. Arantes aims to focus her analyses on the fishes that are most common within each location.

“It would be a lot easier in a place like the Brazos River, where we only have maybe 40 fish species that are fairly common,” Winemiller says. “But we don’t need large samples. We try to get a few individuals of each species at each location during four different phases of the annual flood cycle.”

By April, Arantes had completed the last of four planned surveys. Now she needs to identify the remaining samples and bring fish samples back to be analyzed in the lab at Texas A&M.

In the lab, the preserved samples will be analyzed for stable isotopes: Ratios of carbon and nitrogen in fish tissues allow researchers to analyze the structure and dynamics of food webs, for example by determining whether a fish is a top predator or an herbivore.

Promoting conservation

The research Winemiller and Arantes are conducting will help Brazilian natural resource agencies and nongovernmental organizations in promoting conservation. Findings may help them promote the conservation of forests and the sustainable use of other natural resources, including fisheries.

Brazil

Aerial view of the Amazon region near Santarem, Brazil.

Arantes is also conducting workshops to encourage community-based conservation. The strategies she teaches are aimed at allowing fish to survive long enough to grow and reproduce, which ultimately increases fishery yields. So far, at least two communities have embraced these strategies, and fish stocks are rebounding.

“They have monitored and limited their fishing effort and had a lot more fish and bigger fish,” Winemiller says. “That’s a preliminary finding without formal data analysis, but that’s encouraging. It means you really can manage more effectively. Hopefully this will convince people living on the Amazon floodplains to adopt better management practices.”

“I told you how huge the Amazon system is,” Winemiller says. “You wouldn’t believe that humans with small boats and nets could make an impact, but they really can.”

The project is funded by Brazil’s Conselho Nacional de Desenvolvimento Científico e Tecnológico.

 

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