Fishing yields in the Upper Paraná River, on the border between the Brazilian states of São Paulo, Paraná, and Mato Grosso do Sul, have fallen by around 50% in two decades. According to a study published in the journal Nature Ecology & Evolution, the decline is an effect of the invasion of exotic species and human occupation in the region.
The authors analyzed data collected from 2002 to 2022 by the Long-Term Ecological Program for the Upper Paraná River Floodplain ( PELD-PIAP ), which has been investigating and cataloguing biodiversity and environmental conditions in the area since 2000. During the period analyzed, the average size of commercially exploited fish decreased. At the same time, economic gains from fishing fell by half.
"As environmental degradation has increased due to human occupation, native species such as the spotted sorubim [Pseudoplatystoma corruscans] have been caught less by fishermen and in the monitoring carried out by the PELD-PIAP, with the individuals found becoming smaller and smaller," explains Dieison Moi . The study was conducted during his postdoctoral fellowship, funded by a scholarship from FAPESP , at the Institute of Biology of the State University of Campinas (IB-UNICAMP) in the state of São Paulo. "At the same time, invaders such as the tucunaré [Cichla sp.], native to the Amazon basin, have increased in body size and become more abundant," he adds.
In addition to the well-known ecological damage caused by the replacement of native species by invasive ones, such as loss of biodiversity, this exchange is harmful to fishermen in economic terms. On average in the region, native fish have a market value that is 80% higher than that of invasive species. For example, while the increasingly rare native spotted sorubim could cost around BRL 47 (USD 8.26) per kilogram at the time the study was published, the same quantity of the abundant invasive tucunarés was worth around BRL 9 (USD 1.65).
"The replacement of native species by invasive ones is a phenomenon that's been observed worldwide, with serious impacts on biodiversity and the lives of human populations that depend on fishing. However, few studies have a continuous sample like the one we used, which quite clearly demonstrates the size of the problem," comments Gustavo Quevedo Romero , a professor at IB-UNICAMP and the senior author of the paper.
Romero currently coordinates three projects supported by FAPESP, including one under the FAPESP Research Program on the Characterization, Conservation, Restoration, and Sustainable Use of Biodiversity ( BIOTA ) and another under the FAPESP Research Program on Global Climate Change ( RPGCC ) ( 23/01589-0 , 22/10765-3 and 19/08474-8 ).
Big river, small fish
At 5,695 kilometers long, the Paraná River is the second largest river in South America and the fourth largest in the world in terms of drainage area. Despite occupying only 10% of Brazil's territory, its basin has the highest population density in the country, with 32% of Brazil's population living there. In 1984, the upper portion of the river received the Itaipu Binacional hydroelectric power plant, which profoundly altered the local ecosystems.
For the study, eight environments were analyzed: five lakes and three rivers along the Upper Paraná River floodplain. Each environment was sampled four times a year, once in each season. Fishing nets were placed in the same locations in each environment and remained there for 24 hours. Fish of different sizes were collected three times daily.
To analyze human occupation in the region between 2002 and 2022, the researchers used satellite-generated maps from MapBiomas that classified areas as either natural (forests, wetlands, and bodies of water) or human (agricultural areas and cities). MapBiomas is a collaborative network formed by non-governmental organizations, universities, and technology startups that maps land cover and land use in Brazil.
The authors observed a correlation between the loss of native species and the intensification of human occupation. Thirty-one native species (36.9%) exhibited a direct link between phenomena such as deforestation and urbanization and a decrease in biomass, whether in number or size of individuals. Only three species (3.5%) benefited.
The opposite occurred with invasive species: 20 species (37%) benefited from intensified land use, while only two (3.7%) were harmed when the same criteria were analyzed. Meanwhile, an increase in the body size of native species was positively associated with the region's fishing potential. Conversely, an increase in the body size of invasive species reduced the region's fishing potential.
"The presence of non-native species erodes the supply of ecosystem services in this region. There's a cascade effect in which human occupation reduces the coverage of natural areas, harming native species and favoring invasive ones. As a result, native species decrease in size and presence, causing a decline in fishing," says Moi.
From an ecosystem services perspective, the results of the study show that developing conservation and management strategies for natural resources is much more effective than introducing non-native species. However, public policies that aim to solve the problem often do the opposite by facilitating or encouraging the introduction of fish from other environments.
"We need resources for long-term studies like the PELD-PIAP, which in turn can provide the scientific evidence needed to support public policies in this field and benefit the species and the human population," says the researcher.
In addition to UNICAMP, the study involved researchers from four other Brazilian universities – the State University of Maringá (UEM), the State University of Santa Catarina (UDESC), the Federal University of São Carlos (UFSCar), and the Federal University of Santa Catarina (UFSC) – as well as universities in Uruguay and the United Kingdom.
The work was also supported by FAPESP through a project that is part of the BIOTA program coordinated by Victor Saito , a professor at UFSCar.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
