- Fishers in the Amazon Basin are catching smaller species of fish than before, indicating overexploitation of the region’s aquatic biodiversity, a new study says.
- The study looked at fish catch data from six river ports (three each in Peru and Brazil) to conclude that “fisheries are losing their resilience and progressing towards possible collapse.”
- Researchers say freshwater fish stocks in the Amazon have never been a priority for conservation or monitoring, which has allowed this decline to occur over the course of decades.
- The loss of larger fish deprives communities for whom fish is a dietary staple of important nutrients, as well as impoverishes the wider river ecosystem.
Fish are an essential part of the diet for most people living in the Amazon Rainforest. But overfishing is seriously threatening biodiversity and the ecosystem’s ability to feed people, according to the first large-scale pan-Amazonian survey of fisheries.
“Amazon fisheries are showing clear signs of overexploitation, and we see indications this is threatening sustainability,” Sebastian Heilpern, presidential postdoctoral fellow at Cornell University and the study’s lead author, told Mongabay on a video call from New York.
The U.S.-led study, conducted in cooperation with several South American partners and the Wildlife Conservation Society, collected data in six main urban ports: Chachapoyas, Pucallpa and Iquitos in Peru, and Porto Velho, Manaus and Santarém in Brazil.
Fishers coming into these ports are required to report the origin, amount and species of fish they catch. This information, known as landings data, is the only type of long-term data on fish from the Amazon, spanning the previous 12 to 34 years, depending on the city.
Landings data reveal that the average size of the fish brought to port has decreased over time, meaning that the larger species are declining and being replaced by smaller species in the fishers’ catch.
Researchers also calculated the weight of each species of fish relative to the total weight of the catch in a particular time and place, a metric known as evenness. In areas with higher human populations and more developed fisheries like Manaus, Brazilian fishers are reporting a greater number of smaller and more abundant species, meaning that the evenness of fish is lower.
“One consistent trend we observed across all ports is that large species are being replaced by smaller, faster-growing species,” Heilpern said. “This is a common feature of overexploitation. In addition, we see how the biomass of the catch is changing. First, we observe an increase in ‘evenness,’ then a peak, followed by a sharp decline.”
The Amazon Basin has the highest freshwater biodiversity on the planet. Some 3,000 species navigate the rivers and flood plains, more than 80% of which are migratory fish, according to WWF.
In fish communities, as in most areas of ecology, more diversity means more resilience. The landings data point not only to overharvesting but also potential changes in the resiliency of fish communities, Heilpern said.
“Imagine a portfolio of 50 species. When the largest species is fished out, there are 49 smaller, faster-growing species to take its place. However, once they are overfished too, there is less of a bank to replace them with. This is what we are starting to see in the Amazon,” he said.
Landings data do have some strong shortcomings. For instance, they’re limited in area and scope and don’t account for subsistence fishing, Heilpern said. But “although imperfect, this [landings] data can provide a lot of information about how these fisheries are both responding as a resource and also the impact on the community.”
Heilpern gave three examples of fish facing severe declines. One of them is the gilded catfish (Brachyplatystoma rousseauxii), one of several giant catfish that migrate from the Amazon estuary to the Andes and back.
Another one is the black prochilodus (Prochilodus nigricans), a medium-distance migratory fish, which in the dry season travels in schools up the river. “In [the Peruvian department of] Loreto, the numbers were down from some 40% of the catch in the 1980s to 20% today,” Heilpern said.
He also cited the tambaqui (Colossoma macropomum), the second-heaviest scaled freshwater fish in South America. The species plays an important role in dispersing seeds up and down the river network, as it eats nuts and fruits. According to Heilpern, there’s overwhelming evidence that it’s heavily overfished.
One of the study’s co-authors, Carolina Rodrigues da Costa Doria, associate professor of biology at the Federal University of Rondônia in Brazil, has since 1996 been closely following fisheries in the basin of the Madeira River, the biggest tributary of the Amazon. Over the years, she said, she’s observed clear changes in species size and the composition of landings.
“The decline in evenness in combination with the decline in average body size signals that fisheries are losing their resilience and progressing towards possible collapse,” Doria told Mongabay in an email. “If this continues unchecked, the trend in a few years is to have fisheries based on only a few resilient species.”
She said overfishing and the lack of monitoring are major culprits in this loss in diversity, along with human-driven changes in the region, such as the construction of hydroelectric plants, deforestation and mining.
“The reason for overfishing is the same in all regions,” Doria said. “There is a demand for a certain species on which the fisherman will focus. When the stock decreases, he will move on to another, as this is his main source of income. In Madeira, I’m talking about some 2,000 fishermen earning an average of 2 minimum wages.”
In 2014, Leandro Castello, associate professor at the Department of Fish and Wildlife Conservation at Virginia Tech in the U.S., published a study on fishing of pirarucu (Arapaima spp.) across 104,000 hectares (257,000 acres) of Amazonian floodplains. It warned that populations were found to be depleted in 76% of the 81 fishing communities and overexploited in 17%.
“This timely study [by Heilpern and colleagues] documents the gradual degradation of fish stocks in the Amazon that for so long have been left at the margins of conservation,” Castello, who was not involved in this study, told Mongabay in an email.
Previous research by Heilpern and colleagues found that fishers have been catching fewer large migratory fish species and a greater number of smaller fish around the department of Loreto in Peru, where most of the region’s 800,000 people eat fish once a day or more, consuming on average about 52 kilograms (115 pounds) of fish per year.
Fish provide not only protein but also other nutrients that are not easily attainable from other sources of food in the region. And although protein levels are roughly the same per weight in large and small fish, smaller fish contain more omega-3 fatty acids but less iron and zinc overall — an issue in an area where people already have high rates of anemia and malnutrition.
“If fish decline, the quality of the diet will decline,” Shahid Naeem, director of the Earth Institute Center for Environmental Sustainability at Columbia University in the U.S., told the Columbia Climate School in a 2021 interview. “Things are definitely declining now, and they could be on the path to crashing eventually,” said Naeem, one of the co-authors of the new study.
The Amazon isn’t the only place experiencing changes in fish communities. One-third of global freshwater fish species are threatened with extinction, and 80 species are already known to be extinct, according to WWF.
Protecting fisheries, experts say, will require an investment in practices and policies that protect key freshwater habitats, maintain the connectivity of rivers and streams and enact temporary moratoriums on the capture of overharvested species.
In order to regulate overharvested or threatened fish species, we must first know what is happening in the water — information that comes from strong monitoring programs. But in the Amazon, protecting and monitoring freshwater fish populations hasn’t been a priority.
“Amazon fisheries have been widely neglected by regional governments for decades now, despite their pivotal importance to regional economy and food security,” Castello told Mongabay. “Delay in reacting to this situation is going to aggravate the trends documented.”
Many fisheries have seen success with co-monitoring programs, where the government, fishers and community share responsibility for monitoring, management and enforcement of fisheries practices. But these programs still require funding and enforcement of regulations.
For instance, the majority of fish landed in the port of Iquitos in Peru comes from Pacaya Samiria National Reserve and its buffer zone, a massive wetland that Heilpern described as “incredibly productive, beautiful, and full of fish.” Here, he said, co-management groups are allowed to fish in the reserve, but people also fish in the reserve without permission. “So regulations are important to enforce but also quite difficult and often underfunded.”
New tools and innovations that support community monitoring may also help. The database and mobile phone app Ictio allows citizens to register observations of caught fish in the Amazon Basin. This new, low-cost tool created by Cornell University in the U.S. and the Wildlife Conservation Society in collaboration with local and Indigenous people can enable users “to share their information on what they’re catching, but also own the information,” Heilpern said. “These kinds of bottom-up approaches to conservation and management have shown a lot of success.”
“Past and current efforts have shown local communities have much to contribute to fisheries conservation, and yet conservation priorities by leading organizations continue to focus on terrestrial protected areas,” Castello said.
Ultimately, it will take a suite of actions to protect the waters of the Amazon, where climate change, pollution, fires, deforestation and dams are affecting fish and all life in the world’s largest rainforest.
“Don’t get me wrong, these [other] issues have clearly affected fishes,” Heilpern said. “But overfishing is such a problem, and I often think that it gets buried … which brings us back to the why I think this work is profound. Because it is showing definitely that overfishing is a problem.”
“The trends documented in this study and the direction they point to should serve as a warning of what likely will come to pass in the future if society chooses not to do anything about it,” Castello said. “There are numerous options to prevent further declines, and they all start with paying attention to this problem.”
Heilpern, S. A., Sethi, S. A., Barthem, R. B., Batista, V. S., Doria, C. R., Duponchelle, F., … Flecker, A. S. (2022). Biodiversity underpins fisheries resilience to exploitation in the Amazon river basin. Proceedings of the Royal Society B: Biological Sciences, 289(1976), 20220726. doi:10.1098/rspb.2022.0726
Castello, L., Arantes, C. C., Mcgrath, D. G., Stewart, D. J., & Sousa, F. S. (2014). Understanding fishing-induced extinctions in the Amazon. Aquatic Conservation: Marine and Freshwater Ecosystems, 25(5), 587-598. doi:10.1002/aqc.2491
Heilpern, S. A., DeFries, R., Fiorella, K., Flecker, A. S., Sethi, S. A., Uriarte, M., Naeem, S. (2021). Declining diversity of wild-caught species puts dietary nutrient supplies at risk. Science Advances, 7(22), eabf9967. doi:10.1126/sciadv.abf9967
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