Amazon River freshwater fish show signs of overexploitation

The biodiversity of the Amazon's freshwater species is under strong fishing pressure, according to the first large-scale, pan-Amazonian examination, conducted by a group of international scientists and led by Cornell University researchers. Their findings -- based on examining decades of fishery landings (the places such as ports where fishers leave their catch) records from Brazil and Peru -- indicate a stress that menaces the region's ability to provide protein and other essential nutrients.

The new research was published in the Proceedings of the Royal Society B.

"We are seeing a decline in large-bodied species," said lead author Sebastian Heilpern, a Cornell Presidential Postdoctoral Fellow, who works with Peter McIntyre, associate professor, and Alex Flecker, professor, both in the College of Agriculture and Life Sciences.

"Large-body species are more vulnerable, as they are slower to develop. As they decline, we see they are also being replaced by smaller species," Heilpern said. "This pattern is consistent with overexploitation."

Heilpern explained that as fish species are replaced, harvests can be maintained. But eventually, evidence from scientific models suggest that harvests can collapse. "The continued depletion of fish biodiversity reduces the pool of compensating species," he said, "further diminishing the fishery resilience."

Effectively, overfishing is withdrawing from the natural sustainability savings account and biological security found in diversity. "There is a bank of fish species able to compensate for the loss of one species," Heilpern said. "But as the bank is depleted, we experience a loss of compensatory potential. It indicates that the sustainability is declining."

The Amazon River is one of the most productive and diverse freshwater ecosystems on the planet, according to the paper. The people living in the region have some of the highest rates of fish consumption in the world, about 110 pounds per person annually.

The percentage of freshwater fish stocks with biologically sustainable levels was 90% in 1990, according to a 2020 Food and Agricultural Organization (United Nations) report. Sustainability, however, had dropped to 65.8% by 2017.

In the Amazon, better monitoring, enforcement of regulations and governance are needed to sustain fisheries, Heilpern's paper suggests. "Additionally, expanding protected areas can maintain habitats that are critical for many fish species," he said.

The research was partially funded by the Cornell Presidential Postdoctoral Fellows. Flecker, McIntyre and Sethi are faculty fellows at the Cornell Atkinson Center for Sustainability.