Expedition on the Lower São Francisco: An X-ray of fisheries and agriculture, pollution, silting and saline intrusion

Abstract

The São Francisco River represents 2/3 of the Northeast Region freshwater availability. Its basin is divided into Upper São Francisco, Middle São Francisco, Sub-Middle São Francisco, and Lower São Francisco. The Lower São Francisco is one of the most impacted regions of the Northeast, considering factors related to fishing, electric power generation and city sewage pollution. The first Scientific Expedition of the Lower São Francisco aimed at evaluating the water quality, pollution, silting, deforestation of the ciliary forest, socioeconomic survey, environmental education, ictiofaunal composition, analysis of metals in fish, fishing and catching and salt intrusion. The samples were collected in seven coastal municipalities in the states of Alagoas and Sergipe. The results indicate that all the municipalities studied have water pollution problems from household and diffuse sewages, pesticides, and organic matter deposited in the sediment. Much of the crops are dependent on the use of agrochemical in crops on the banks of the river, with a prevailing environmental degradation scenario. There was a decrease in the number of native fish species and predominance of exotic and invasive marine species. In addition, it was possible to detect the occurrence of catch methods with high impact on the fishes. The saline wedge is already 16 km from the river mouth, replacing agricultural activities by shrimp farming. Fish show metal content, but a large part of them are within acceptable limits and a georeferenced database with the results of the expedition was made available for consultation.

Pesca artesanal e ictiofauna no baixo São Francisco, após sete anos de redução de vazões na hidroelétrica de Xingó

“…Among the marine species, the authors highlighted the robalos and carapebas. In our survey, fishers mentioned all these species, especially robalo and carapeba, as the most prominent occurrences in addition to the xira, which currently is uncommon (Soares et al 2016;Soares et al 2020c). Soares et al (2011; and Rodrigues et al, (2017) also reported that robalos and carapebas were among the most captured species around Penedo and Igreja Nova, 40 km from the São Francisco mouth, corroborating the perceptions of artisanal fishers.…”

“…Soares et al (2011; and Rodrigues et al, (2017) also reported that robalos and carapebas were among the most captured species around Penedo and Igreja Nova, 40 km from the São Francisco mouth, corroborating the perceptions of artisanal fishers. Soares et al (2020b;2020c) noted an impoverishment of native and freshwater species in fishers catches in the years 2018 and 2019, during which they report the disappearance of xiras, pilombetas (Anchoviella sp., Lophiosilurus alexandrii), and pacamãs and piabas (Astyanax sp. )…”

“…The flow from the Xingó Hydroelectric Power Plant is governed by reservoirs in the upper and middle São Francisco River regions (Três Marias and Sobradinho dams). There are problems caused by changes in the hydrological regime, such as lower water flow and volume in the lower course of the river, with a consequent increase of salinity in the region (Soares et al, 2020c). Near the municipality of Piaçabuçu, Cruz et al, (2020) measured a mean surface salinity of 3.55 ± 1.35 ‰ to 2.71 ± 1.54 ‰; both surface and bottom waters were defined as brackish.…”

“…Thus, marine and estuarine species are currently found in areas where freshwater species previously dominated (Soares et al, 2016;2020b). Salt water currently reaches approximately 10-16 km up the lower São Francisco River, expanding its estuary by 4 km (Soares et al, 2020a;2020c). Salinity is most important for governing the distribution of estuarine fish (Blaber, 2000).…”