RIO DE JANEIRO – Fish biodiversity in the Amazon, the world’s largest river basin, is threatened by overfishing.
This is shown by an investigation, based on data from the inventories of fish landed in six of the largest ports in the Brazilian and Peruvian Amazon in the last 30 years.
Published in the Proceedings of Royal Society B, the study indicates that uncontrolled fishing threatens not only the biodiversity of the Amazon ecosystem, but also the sustainability of fishing itself, which is the main source of protein and essential nutrients for local populations.
“We have seen changes consistent with superexploitation in all databases and in all households analyzed; no matter when,” she noted via zoom to SciDev.Net Sebastian Heilpernen, lead author of the research and ecologist at Cornell University, United States, who has been studying the aquatic systems of the Amazon for 15 years.
The signs of overfishing emerged when the researchers analyzed the proportion and size of fish species brought to ports in the Peruvian departments of Loreto, Ucayali and Madre de Dios, and in the Brazilian cities of Porto Velho, Manaus and Santarém.
The data was collected by different state agencies in time series that vary between 34 and 10 years depending on the region.
They found that, in general, the larger species were disappearing from the catches, while the smaller species dominated the majority of the loads. According to them, this is a clear sign of overfishing.
The logic is as follows, Heilpernen points out: Large fish, which are the most sought after because of their mass and because they are easier to catch, are also slower to grow and reproduce than smaller fish. If large fish are overharvested, their population cannot reproduce fast enough to recover and the species begins to die out.
When large fish are no longer available, fishermen redirect their catch to smaller species, which are more abundant because they grow and reproduce faster. And this trend is exactly what the fish landing records showed.
The large migratory fish that were common in the region, such as the Brachyplatystoma filamentosum (known as saltón or valentón in Spanish and filhote in Portuguese) and the Colossoma macropomum (gamitana or cherna in Spanish and tamabaqui in Portuguese) are disappearing.
Even the medium sized fish Prochilodus nigricans (boquichico in Spanish and curimatã in Portuguese), which is one of the most caught species by weight in the Brazilian Amazon, is becoming less common. Landings of this fish decreased from 45 to 25 percent between 1984 and 2016 in the Peruvian port of Loreto, and from 21 to 8 percent between 1994 and 2009 in the Brazilian Porto Velho.
“We have the impression that some species are already collapsing,” he told SciDev.Net another author of the study, the biologist Ronaldo Barthem, from the Museu Paraense Emilio Goeldi, in Pará, Brazil.
According to Barthem, previous studies show that the tambaqui It is no longer found in the central Amazon region. “We are waiting for the bomb to explode, for the tipping point to arrive when production no longer recovers and fishing for the species is no longer sustainable,” he warns.
However, it is still unknown when that moment will come, adds the scientist. This is because there is a lack of data, since there is no systematic policy for monitoring fishing in the region.
In Peru, the government does some monitoring, but in Brazil, which is the Amazonian country with the highest consumption of fish in absolute numbers, the last monitoring of landings financed by the state was carried out more than ten years ago. In addition, there is also no data on artisanal fishing in local communities.
“We are in the dark,” says Barthem. “Meanwhile, fishing does not stop: the production chain is increasingly efficient, fishermen are incorporating new techniques and organizing themselves, putting together teams and we are not following that.”
The reason for overfishing, he explained to SciDev.Net Another author of the study, biologist Carolina Doria, from the Federal University of Rondônia, Brazil, is the increase in demand, driven by the growing urbanization in the region.
The study authors also used mathematical models to simulate the resistance of commercial fish species to different overfishing scenarios. They observed that as the variety of species caught decreases, so does the ability of fish populations to sustain themselves.
“The study is important because it shows that even with the diversity of fish that exists in the Amazon, fishing can be depleted,” says ecologist and fish specialist Jean Vitule, from the Federal University of Paraná, Brazil.
But the scientist, who was not involved in the study, points out that it is risky to extrapolate the finding to the entire Amazon because the study sample is small compared to the size of the basin and the diversity of the fishing industry in the region (which goes from small fishermen to large companies).
More than 3,000 species of fish live in the 6,300,000 km² of the Amazon basin, but only about 120 are consumed commercially.
Furthermore, the threat to biodiversity is not limited to fishing, notes Vitule.
Other factors already present in the basin, such as the introduction of exotic species, mercury contamination from illegal mining, the construction of hydroelectric plants that prevent the migration of species, and climate change add to the pressure on fisheries.
“The basin is a single system,” he says. “A dam built in Brazil can impact Peru or Bolivia. The river is like the root of a plant, if you kill the root, the tree cannot grow”, he stresses.
This article was originally published on SciDevNet Latin America.