Deforestation in the Amazon is lowering fish yields

When tropical forests are converted to land for agricultural use, the result is less rain, more droughts, and deteriorating freshwater ecosystems. And now, surprising new research reveals that the clearing of tropical forests can also lead to negative changes in fish production.

Study lead author Leandro Castello is an assistant professor of Fisheries at Virginia Tech‘s College of Natural Resources and Environment. The researchers set out to investigate how deforestation along the Amazon River impacts fish yields.

“The conflict between raising cattle and managing fisheries is a concern that is shared with floodplain residents, but there had been no rigorous studies of how loss of forest affects the productivity of floodplain fisheries,” explained study co-author David McGrath.

Approximately one-third of the world’s wild-caught fish yield comes from tropical regions, and fisheries are critical to this production. The conditions of the area of land adjacent to a river, known as a floodplain, have a major impact on the success of fisheries.

“Floodplain forests can provide structures that protect fish and their offspring, and provide habitat for insects that many fish rely on for food,” said Castello. “Those forests also produce plant material on which fish may also feed.”

Using a study area of 1,000 square kilometers, the researchers collected data on fisheries yields over a 12-year time period. The team also created a map of the region’s 1,500 lakes and interviewed local fishermen about fish caught in different areas. By combining this data, the experts determined which areas yielded the most fish.

“We collected roughly 36,000 separate data points that were plotted in order to make a map of where the fish were coming from,” said Castello.

Satellite images from NASA allowed the researchers to collect a second data set on habitat features in the study region to examine whether the presence of floodplain forests impacted fish yields.

“Essentially, we wanted to know if fish yields in areas with forested floodplains are greater, the same, or less than areas where forests have been cut down,” explained Castello.

“Our results indicated that lakes with floodplain forests provided fishers with greater fish yields,” he said. “This allows us to infer that if you cut down the forests, fish yields in those lakes would decrease. Tropical deforestation is not only a terrestrial issue – it can also decrease the number of fish available to some of the world’s poorest populations.”

The researchers will continue to investigate what other factors affect fisheries yields, but the indications of this particular study are clear.

“You have to protect these habitats if you want to maintain the food production and the income that rivers provide,” said Castello. “If we don’t protect these areas, we lose the rivers and we lose the fish.”

The study is published online in the journal Fish and Fisheries.

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By Chrissy Sexton, Earth.com Staff Writer