A study of tambaqui, a popular table fish, in the Brazilian Amazon found that fish caught near the city of Manaus are half the size of those upriver.
Boats that buy the fish have brought the demand into the forest surrounding the city, and with holds full of ice, they’re able to travel further to bring tambaqui back to Manaus’ markets.
The fishers living in the relatively pristine forest along the Purus River reported that tambaquie are smaller and harder to catch than they were previously, a trend extended 1,000 kilometers from Manaus, the researchers found.
The sweet-tasting tambaqui (Colossoma macropomum) is a popular staple on grills and dinner tables in Manaus, Brazil. But as the human population of the Amazonian city has soared, the effects of growing demand for this fruit-eating fish have rippled through the ecosystem, affecting tambaqui living as many as 1,000 kilometers (621 miles) away.
The hunt for tambaqui has gotten more difficult and the fish have become smaller, even at that distance, a team of scientists reported Monday in the journal Proceedings of the National Academy of Sciences.
“I think anyone would expect there to be a small effect around the city,” said Daniel Tregidgo, an ecologist at Lancaster University in the U.K. and lead author of the study, in an interview. “The real thing that sticks out about the study is the distance you can travel — a thousand kilometers along a river — and still have this effect.”
Indeed, tambaqui caught around Manaus, a city of 2.1 million people, were about half the size of those snagged upriver. But, in interviews with nearly 400 fishers living in the forest along a 1,267-kilometer (787-mile), Tregidgo and his colleagues revealed a “defaunation shadow” that extends far beyond the city’s edges. Studies on bushmeat hunting in the vicinity of urban areas have shown a similar pattern in other tropical areas such as the Congo basin.
The authors of the current study postulate that the effects of the decline of these fish, especially the large ones, could spill over into the rainforest itself.
“Tambaqui can disperse seeds farther than almost any [fruit-eating] animal yet studied, and this dispersal distance increases with body size,” they write. That would limit the spread of plants that depend on tambaqui to ferry their seeds throughout the ecosystem.
The Amazon’s tambaqui could be a harbinger of the impact that urbanization is having on wildlife in some of the most biodiverse regions of our planet. Currently, some 18 million people live in the towns and cities of the Brazilian Amazon — about 75 percent of the people living in the region. That’s a major shift since 1950, when three-quarters lived in rural areas, the authors report. In Manaus, they seem to have brought their appetites for wild-caught tambaqui with them.
For this study, the Purus River served as an ideal laboratory to investigate how demand might be leading to overfishing.
“There’s no river that brings more fish to the city,” Tregidgo said.
And yet, traveling away from the city, the signs of the metropolis quickly give way to dense forest that dominates the banks of the Purus, he added. Also absent from the river are many of the signs of human impact that can “mask” the effects of fishing pressure, such as dams, mining, logging, and pollution.
“The big issue is basically fishing,” Tregidgo said. “The fact that we can separate that out is quite unique.”
The team’s conversations with rural fishers along the Purus centered on the methods they use to target tambaqui, the size of the fish they catch and how much effort it takes, as well as the changes to those aspects they’ve witnessed in their lifetimes.
It’s gotten harder to catch tambaqui, they said, and the fish are smaller than they used to be. At the same time, when fishermen and women are successful, they’re able to sell their catch more readily.
Fish buyers from Manaus, toting ice to keep the fish fresh for longer distances, make regular trips up the Purus River and become steady customers for the fishers. These boats effectively daisy-chain the city’s demand for tambaqui deeper into the rainforest than ever before.
“It really does make people go after this fish specifically,” Tregidgo said, “even though today, there is a lesser chance of getting it.”
- Tregidgo, D. J., Barlow, J., Pompeu, P. S., de Almeida Rocha, M., & Parry, L. (2017). Rainforest metropolis casts 1,000-km defaunation shadow. Proceedings of the National Academy of Sciences, 201614499.
Banner image of a tambaqui by Rufus46 (Own work) [CC BY-SA 3.0], via Wikimedia Commons.
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