Impacts on fisheries assessed by local ecological knowledge in a reservoir cascade in the lower São Francisco River, northeastern Brazil

Thiago D’avilla Eraldo M. Costa-Neto Marcelo F. G. Brito About the authors

Abstract

Our study assessed the fishers’ perception (local ecological knowledge, LEK) concerning environmental impacts on fisheries and fish species in the final portion of Sub-Middle and Lower São Francisco. The river was divided into four areas where 107 fishers from 22 locations (4 states) were surveyed. The dam was the most significant impact on fisheries. The loss of connectivity, changing the environmental complexity, and its secondary effects (e.g., flow control, interruption of migratory routes) were determining factors. Other impacts were pointed out, such as pollution, macrophytes, overfishing, non-native species, and aquaculture. Among migratory species, Pseudoplatystoma corruscans and Salminus franciscanus have been absent from fishery catches for decades. Prochilodus argenteus records in fisheries are likely associated with migration routes to small tributaries. The environmental disturbance favored the establishment of non-native species such as Oreochromis niloticus, Cichla monoculus, and Metynnis lippincottianus along the studied section. Over the final portion of the São Francisco River, the more significant seawater intrusion changed the target species for fisheries activities. Thus, our data validate the importance of fishers’ LEK and reinforce the adverse effects of the reservoir cascade on fishing and migratory fishes.

Keywords:
Anthropogenic impacts; Ethnoecology; Migratory fishes; Non-native species; Small-scale fisheries

Resumo

Nosso estudo avaliou a percepção dos pescadores (conhecimento ecológico local, CEL) em relação aos impactos ambientais sobre a pesca e peixes no trecho final do Submédio e Baixo São Francisco. O rio foi dividido em quatro áreas onde foram entrevistados 107 pescadores de 22 localidades (4 estados). Barragem foi o impacto mais significativo sobre a pesca. A perda da conectividade alterando a complexidade ambiental e seus efeitos secundários (e.g., controle da vazão, interrupção da rota migratória) foram fatores determinantes. Outros impactos foram apontados, como poluição, macrófitas, sobrepesca, espécies introduzidas e piscicultura. Dentre as espécies migradoras, Pseudoplatystoma corruscans e Salminus franciscanus estão ausentes da pesca há décadas. Os registros de Prochilodus argenteus nas pescarias provavelmente estão associados às rotas migratórias para pequenos tributários. A perturbação ambiental favoreceu o estabelecimento de espécies introduzidas como Oreochromis niloticus, Cichla monoculus e Metynnis lippincottianus ao longo do trecho estudado. No trecho final do rio São Francisco, a maior intrusão de água do mar mudou as espécies-alvo da pesca. Dessa forma, nossos dados validam a importância do conhecimento ecológico local dos pescadores e reforçam os efeitos adversos das cascatas de reservatórios sobre a pesca e peixes migratórios.

Palavras-chave:
Espécies não-nativas; Etnoecologia; Impactos antrópicos; Peixes migradores; Pesca em pequena escala

INTRODUCTION

Dams are responsible for alterations in morphology and hydrology of rivers (Agostinho et al., 2007Agostinho AA, Gomes LC, Pelicice FM. Ecologia e manejo de recursos pesqueiros em reservatórios do Brasil. Maringá: EDUEM; 2007.). Their effects on freshwater biodiversity are expressed by the shifts in aquatic productivity, ecosystem services, ecological process, composition and abundance of species, and even local extinction (Agostinho et al., 2007Agostinho AA, Gomes LC, Pelicice FM. Ecologia e manejo de recursos pesqueiros em reservatórios do Brasil. Maringá: EDUEM; 2007.; Santos, 2010Santos GB. A ictiofauna da bacia do Alto Paraná (rio Grande e rio Paranaíba). MG Biota. 2010; 2(6):1–56.; Hallwass et al., 2013Hallwass G, Lopes PF, Juras AA, Silvano RA. Fishers’ knowledge identifies environmental changes and fish abundance trends in impounded tropical rivers. Ecol Appl. 2013; 23(2):392–407. https://doi.org/10.1890/12-0429.1
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). The alterations caused by dams transform a dynamic system with high structural complexity into a homogeneous and less productive environment (Agostinho et al., 2007Agostinho AA, Gomes LC, Pelicice FM. Ecologia e manejo de recursos pesqueiros em reservatórios do Brasil. Maringá: EDUEM; 2007.). These changes contribute to increased sedentary, generalist, and tolerant species and the decline of migratory species (Santos, 2010Santos GB. A ictiofauna da bacia do Alto Paraná (rio Grande e rio Paranaíba). MG Biota. 2010; 2(6):1–56.; Pelicice et al., 2018Pelicice FM, Azevedo-Santos VM, Esguícero ALH, Agostinho AA, Arcifa MS. Fish diversity in the cascade of reservoirs along the Paranapanema River, southeast Brazil. Neotrop Ichthyol. 2018; 16(2):e170150. https://doi.org/10.1590/1982-0224-20170150
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). The river fragmentation process also interferes in flood pulses, reducing river connectivity and access to floodplains that correspond to fundamental nurseries and feeding grounds (Agostinho et al., 2007Agostinho AA, Gomes LC, Pelicice FM. Ecologia e manejo de recursos pesqueiros em reservatórios do Brasil. Maringá: EDUEM; 2007.). Blocking migratory routes is another impact that, combined with the previous ones, can generate failures in recruiting and maintaining viable populations (Sato, Godinho, 2003Sato Y, Godinho HP. Migratory fishes of the São Francisco River. In: Carosfeld J, Harvey B, Ross C, Baer A, editors. Migratory fishes of South America: Biology, fisheries and conservation status. Victoria: IDRC & The World Bank; 2003. p.195–232.; Pompeu et al., 2012Pompeu PS, Agostinho AA, Pelicice FM. Existing and future challenges: the concept of successful fish passage in South America. River Res Appl. 2012; 28(4):504–12. https://doi.org/10.1002/rra.1557
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).

These issues are intensified in rivers with reservoir cascades. The restructuring of fish communities in these reservoirs has shown the prevalence of small-medium-sized species (Santos, 2010Santos GB. A ictiofauna da bacia do Alto Paraná (rio Grande e rio Paranaíba). MG Biota. 2010; 2(6):1–56.; Petesse et al., 2014Petesse ML, Petrere-Jr M, Agostinho AA. Defining a fish bio-assessment tool to monitoring the biological condition of a cascade reservoirs system in tropical area. Ecol Eng. 2014; 69:139–50. http://dx.doi.org/10.1016/j.ecoleng.2014.03.070
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; Loures, Pompeu, 2018Loures RC, Pompeu PS. Long-term study of reservoir cascade in south-eastern Brazil reveals spatio-temporal gradient in fish assemblages. Mar Freshwater Res. 2018; 69(12):1983–94. https://doi.org/10.1071/MF18109
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; Pelicice et al., 2018Pelicice FM, Azevedo-Santos VM, Esguícero ALH, Agostinho AA, Arcifa MS. Fish diversity in the cascade of reservoirs along the Paranapanema River, southeast Brazil. Neotrop Ichthyol. 2018; 16(2):e170150. https://doi.org/10.1590/1982-0224-20170150
https://doi.org/10.1590/1982-0224-201701...
) with trophic plasticity to explore the new areas, using their reproductive strategies for rapid colonization (Petesse et al., 2014Petesse ML, Petrere-Jr M, Agostinho AA. Defining a fish bio-assessment tool to monitoring the biological condition of a cascade reservoirs system in tropical area. Ecol Eng. 2014; 69:139–50. http://dx.doi.org/10.1016/j.ecoleng.2014.03.070
http://dx.doi.org/10.1016/j.ecoleng.2014...
). In these new environments, non-native piscivores also find favorable conditions for their establishment (Lockwood et al., 2007Lockwood JL, Hoopes MF, Marchetti MP. Invasion Ecology. Oxford: Blackwell Publishing; 2007.) and follow the same pattern of population increase (Santos, 2010Santos GB. A ictiofauna da bacia do Alto Paraná (rio Grande e rio Paranaíba). MG Biota. 2010; 2(6):1–56.; Pelicice et al., 2018Pelicice FM, Azevedo-Santos VM, Esguícero ALH, Agostinho AA, Arcifa MS. Fish diversity in the cascade of reservoirs along the Paranapanema River, southeast Brazil. Neotrop Ichthyol. 2018; 16(2):e170150. https://doi.org/10.1590/1982-0224-20170150
https://doi.org/10.1590/1982-0224-201701...
). On the other hand, the decline in migratory fish populations is increasingly evident, mainly in the downstream direction (Santos, 2010Santos GB. A ictiofauna da bacia do Alto Paraná (rio Grande e rio Paranaíba). MG Biota. 2010; 2(6):1–56.; Petesse et al., 2014Petesse ML, Petrere-Jr M, Agostinho AA. Defining a fish bio-assessment tool to monitoring the biological condition of a cascade reservoirs system in tropical area. Ecol Eng. 2014; 69:139–50. http://dx.doi.org/10.1016/j.ecoleng.2014.03.070
http://dx.doi.org/10.1016/j.ecoleng.2014...
; Pelicice et al., 2018Pelicice FM, Azevedo-Santos VM, Esguícero ALH, Agostinho AA, Arcifa MS. Fish diversity in the cascade of reservoirs along the Paranapanema River, southeast Brazil. Neotrop Ichthyol. 2018; 16(2):e170150. https://doi.org/10.1590/1982-0224-20170150
https://doi.org/10.1590/1982-0224-201701...
), except for reservoirs with lotic stretches above the flooded area or tributary (Loures, Pompeu, 2018Loures RC, Pompeu PS. Long-term study of reservoir cascade in south-eastern Brazil reveals spatio-temporal gradient in fish assemblages. Mar Freshwater Res. 2018; 69(12):1983–94. https://doi.org/10.1071/MF18109
https://doi.org/10.1071/MF18109...
). The consequences are also observed in social and economic dimensions since small-scale fishing represents the primary source of income and food for the riverine population (Hallwass et al., 2013Hallwass G, Lopes PF, Juras AA, Silvano RA. Fishers’ knowledge identifies environmental changes and fish abundance trends in impounded tropical rivers. Ecol Appl. 2013; 23(2):392–407. https://doi.org/10.1890/12-0429.1
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; Doria et al., 2021Doria CRC, Dutka-Gianelli J, Sousa STB, Chu J, Garlock TM. Understanding impacts of dams on the small-scale fisheries of the Madeira River through the lens of the Fisheries Performance Indicators. Mar Policy. 2021; 125:104261. https://doi.org/10.1016/j.marpol.2020.104261
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).

The São Francisco River (~2,800 km in length) has large hydroelectric plants throughout its main course, and a reservoir cascade has caused numerous socio-environmental impacts in the final portion of the basin (Godinho, Godinho, 2003Godinho AL, Godinho HP. Breve visão do São Francisco. In: Godinho HP, Godinho AL, organizers. Águas, peixes e pescadores do São Francisco das Minas Gerais. Belo Horizonte: Editora PUC Minas; 2003. p.15–24.; Brito, Magalhães, 2017Brito MFG, Magalhães ALB. Brazil’s development turns river into sea. Science. 2017; 358(6360):179. https://doi.org/10.1126/science.aap9525
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). Significant water flow restrictions over the past decades (2,800 m³/s – 550 m³/s) have also favored the establishment of invasive species such as the Peacock bass Cichla monoculus Spix & Agassiz, 1831, Nile tilapia Oreochromis niloticus (Linnaeus, 1758), and Spotted silver dollar Metynnis lippincottianus (Cope, 1870) (Assis et al., 2017Assis DASD, Dias-Filho VA, Magalhães ALB, Brito MFG. Establishment of the non-native fish Metynnis lippincottianus (Cope 1870) (Characiformes: Serrasalmidae) in lower São Francisco River, northeastern Brazil. Stud Neotrop Fauna E. 2017; 52(3):228–38. https://doi.org/10.1080/01650521.2017.1348057
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; Brito, Magalhães, 2017Brito MFG, Magalhães ALB. Brazil’s development turns river into sea. Science. 2017; 358(6360):179. https://doi.org/10.1126/science.aap9525
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). The absence of flood pulses has hampered connections of lagoons and floodplains to the main river channel, with adverse effects on the subsistence agriculture (e.g., rhiziculture) and the economy of the riverine population (Sato, Godinho, 2003Sato Y, Godinho HP. Migratory fishes of the São Francisco River. In: Carosfeld J, Harvey B, Ross C, Baer A, editors. Migratory fishes of South America: Biology, fisheries and conservation status. Victoria: IDRC & The World Bank; 2003. p.195–232.; Martins et al., 2011Martins DMF, Chagas RM, Melo Neto JDO, Méllo Júnior AV. Impactos da construção da usina hidrelétrica de Sobradinho no regime de vazões no Baixo São Francisco. Rev Bras Eng Agríc Ambient. 2011; 15(10):1054–61. http://dx.doi.org/10.1590/S1415-43662011001000010
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; CBHSF, 2016Comitê da Bacia Hidrográfica do Rio São Francisco (CBHSF). Plano de Recursos Hídricos da Bacia Hidrográfica do Rio São Francisco 2016–2025. Alagoas: Comitê da Bacia Hidrográfica do São Francisco; 2016.; Santana et al., 2016Santana KNC, Torres CJF, Fontes AS, Costa AR, Peso-Aguiar MC, Santos ACA et al. Efeitos da regularização dos reservatórios na ictiofauna do baixo curso do rio São Francisco. Rev Eletrônica Gest Educ Tecnol. 2016; 4(1):95–108. http://dx.doi.org/10.9771/gesta.v4i1.15080
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; Brito, Magalhães, 2017Brito MFG, Magalhães ALB. Brazil’s development turns river into sea. Science. 2017; 358(6360):179. https://doi.org/10.1126/science.aap9525
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). The reduction of river discharge has also led to more significant seawater intrusion, increasing salinity close to the river mouth, and intensifying the problems associated with a water supply and public health issues (Brito, Magalhães, 2017Brito MFG, Magalhães ALB. Brazil’s development turns river into sea. Science. 2017; 358(6360):179. https://doi.org/10.1126/science.aap9525
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).

Implications over artisanal fisheries after the construction of reservoirs have been recurrent throughout the São Francisco River Basin (SFRB). In the Upper-Middle São Francisco, Três Marias hydroelectric power plant (HPP) construction caused changes in fishing productivity and the floodplains (Thé, 2012Thé APG. Saudades da vazante geral: um estudo etnoecológico sobre as mudanças socioambientais na pesca artesanal no Alto-Médio São Francisco, Minas Gerais. In: Costa JBA, Oliveira CL, organizers. Cerrados, Gerais, Sertão: Comunidades tradicionais nos Sertões Roseanos. São Paulo: Intermeios; 2012. p.31–46.; Lopes et al., 2019Lopes JDM, Pompeu PS, Alves CBM, Peressin A, Prado IG, Suzuki FM et al. The critical importance of an undammed river segment to the reproductive cycle of a migratory Neotropical fish. Ecol Freshw Fish. 2019; 28(2):302–16. https://doi.org/10.1111/eff.12454
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). Sobradinho dam in the Sub-Middle São Francisco (SMSF) river altered the river discharge and its original functionality and importance for fish migration (Sato, Godinho, 2003Sato Y, Godinho HP. Migratory fishes of the São Francisco River. In: Carosfeld J, Harvey B, Ross C, Baer A, editors. Migratory fishes of South America: Biology, fisheries and conservation status. Victoria: IDRC & The World Bank; 2003. p.195–232.), becoming more complex in the final portion with the construction of reservoirs from the Apolônio Sales and Luís Gonzaga HPPs. In the Lower São Francisco (LSF) portion, water control was intensified with the Paulo Afonso Hydroelectric Complex (I, II, III, IV) and the Xingó HPP (CHESF, 2020Companhia Hidrelétrica do São Francisco (CHESF). Sistema de Geração [Internet]. Recife: Companhia Hidrelétrica do São Francisco; 2020. Available from: https://www.chesf.gov.br/SistemaChesf/Pages/SistemaGeracao/SistemasGeracao.aspx
https://www.chesf.gov.br/SistemaChesf/Pa...
). The impacts over artisanal fisheries have been irreparable, causing changes in the structure of the ichthyofauna and the disappearance of important migratory and commercial species (Assis et al., 2017Assis DASD, Dias-Filho VA, Magalhães ALB, Brito MFG. Establishment of the non-native fish Metynnis lippincottianus (Cope 1870) (Characiformes: Serrasalmidae) in lower São Francisco River, northeastern Brazil. Stud Neotrop Fauna E. 2017; 52(3):228–38. https://doi.org/10.1080/01650521.2017.1348057
https://doi.org/10.1080/01650521.2017.13...
; Brito, Magalhães, 2017Brito MFG, Magalhães ALB. Brazil’s development turns river into sea. Science. 2017; 358(6360):179. https://doi.org/10.1126/science.aap9525
https://doi.org/10.1126/science.aap9525...
; D’avilla et al., 2017D’avilla T, Gomes MVT, Brito MFG. A percepção dos pescadores e a educação ambiental como subsídios para a conservação do Baixo São Francisco. Ecologias Humanas. 2017; 3(3):98–119. ).

Studies developed with artisanal fishers have provided relevant data for the management of fishing resources, making it possible to meet the demands of a given area more effectively with local ecological knowledge (LEK) (Marques, 2001Marques JGW. Pescando pescadores: Ciência e etnociência em uma perspectiva ecológica. 2nd ed. São Paulo: NUPAUB–USP; 2001. ; Thé et al., 2003Thé APG, Madi EF, Nordi N. Conhecimento local, regras informais e uso do peixe na pesca do alto-médio São Francisco. In: Godinho HP, Godinho AL, organizers. Águas, peixes e pescadores do São Francisco das Minas Gerais. Belo Horizonte: Editora PUC Minas; 2003. p.389–406.; Costa-Neto, Marques, 2008Costa-Neto EM, Marques JGW. Etnoictiologia dos pescadores artesanais de Siribinha, município de Conde (Bahia): Aspectos relacionados com a etologia dos peixes. Acta Sci Biol Sci. 2008; 22(2):553–60. https://doi.org/10.4025/actascibiolsci.v22i0.2947
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; Azevedo-Santos et al., 2010Azevedo-Santos VM, Costa-Neto EM, Lima-Stripari N. Concepção dos pescadores artesanais que utilizam o reservatório de Furnas, Estado de Minas Gerais, acerca dos recursos pesqueiros: um estudo etnoictiológico. Biotemas. 2010; 23(4):135–45. https://doi.org/10.5007/2175-7925.2010v23n4p135
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; Silvano, Begossi, 2012Silvano RAM, Begossi A. Fishermen’s local ecological knowledge on Southeastern Brazilian coastal fishes: contributions to research, conservation, and management. Neotrop Ichthyol. 2012; 10(1):133–47. https://doi.org/10.1590/S1679-62252012000100013
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; Hallwass et al., 2013Hallwass G, Lopes PF, Juras AA, Silvano RA. Fishers’ knowledge identifies environmental changes and fish abundance trends in impounded tropical rivers. Ecol Appl. 2013; 23(2):392–407. https://doi.org/10.1890/12-0429.1
https://doi.org/10.1890/12-0429.1...
; Ramires et al., 2015Ramires M, Clauzet M, Barrella W, Rotundo MM, Silvano RAM, Begossi A. Fishers’ knowledge about fish trophic interactions in the southeastern Brazilian coast. J Ethnobiol Ethnomed. 2015; 11(1):19. https://doi.org/10.1186/s13002-015-0012-8
https://doi.org/10.1186/s13002-015-0012-...
). Artisanal fishers provide theoretical and practical information, which they have observed concerning the behavior, food habits, reproduction, and ecology of fish species (Costa-Neto, 2000Costa-Neto EM. Sustainable development and traditional knowledge: a case study in a Brazilian artisanal fishermen’s community. Sust Dev. 2000; 8(2):89–95. https://doi.org/10.1002/(SICI)1099-1719(200005)8:2<89::AID-SD130>3.0.CO;2-S
https://doi.org/10.1002/(SICI)1099-1719(...
). Also, fishers are aware of the relationships between biotic and abiotic environments, understanding where, when, and why organisms are found in specific environments (Marques, 2001Marques JGW. Pescando pescadores: Ciência e etnociência em uma perspectiva ecológica. 2nd ed. São Paulo: NUPAUB–USP; 2001. ).

LEK can support the study of environmental changes caused by human actions, as these changes are perceived by the actors who carry out subsistence and recreational fishing activities in impacted environments. The survey of information from ethnoecological studies makes it possible to understand the magnitude and evolution of social and biological impacts, especially in data-deficient and dammed areas (Hallwass et al., 2013Hallwass G, Lopes PF, Juras AA, Silvano RA. Fishers’ knowledge identifies environmental changes and fish abundance trends in impounded tropical rivers. Ecol Appl. 2013; 23(2):392–407. https://doi.org/10.1890/12-0429.1
https://doi.org/10.1890/12-0429.1...
). In this sense, we address the fishers’ perception (LEK) concerning environmental impacts on fisheries and fish species in the highly modified final portion of Sub-Middle and Lower São Francisco.

MATERIAL AND METHODS

Sampling sites. The SFRB has an area of 645,000 km², and drains the states of Minas Gerais, Goiás, Bahia, Pernambuco, Sergipe, Alagoas, also including the Distrito Federal (MMA, 2006Ministério do Meio Ambiente (MMA). Caderno da Região Hidrográfica do São Francisco. Brasília: MMA; 2006.). The basin is divided into four regions: Upper, Middle, Sub-Middle, and Lower São Francisco. The SMSF and part of the LSF are inserted in the Caatinga Biome (semi-arid climate), and the final portion of the LSF is situated in the Atlantic Forest Biome (humid tropical climate). The rainfall precipitation mainly influences the regional climate of the basin (400–1500 mm/year), with an average annual temperature varying between 20–26.5 °C (Silva, Clarke, 2004Silva BC, Clarke RT. Análise estatística de chuvas intensas na bacia do rio São Francisco. Rev Bras Meteorol. 2004; 19(3):265–72.).

The study was carried out with artisanal fishing communities in the final portion of the SMSF and the LSF, between Luís Gonzaga HPP and the mouth of the São Francisco River. Four areas were defined according to river morphology and hydrology in order to assess if the impacts on fisheries would differ among areas based on their features (Fig. 1):

Area 1. Downstream of Luís Gonzaga HPP to the upstream area of Xingó HPP (~90 km). It is characterized by the reservoirs of Apolônio Sales and Paulo Afonso HPPs, and the lotic portion between the Paulo Afonso Hydroelectric Complex and the reservoir of Xingó HPP. The area is composed of remobilized massifs from the flattened soil surfaces of Paulo Afonso (BA) municipality, which expands into waterfalls and rocky beds of approximately 100 km in length (Cavalcante, 2011Cavalcante AJBD.Impactos nos processos morfológicos do baixo curso do rio São Francisco, decorrentes da construção de barragens. [PhD Thesis]. Rio de Janeiro: Universidade Federal do Rio de Janeiro; 2011. Available from: http://objdig.ufrj.br/60/teses/coppe_m/AmparoDeJesusBarrosDamascenoCavalcante.pdf
http://objdig.ufrj.br/60/teses/coppe_m/A...
). Visited communities: Glória (BA) – Nova Glória, Povoado Quixaba, Povoado Queimadas; Paulo Afonso (BA) – Paulo Afonso, Povoado Rio do Sal, and Povoado Xingozinho; Jatobá (PE) – Jatobá.

Area 2. Downstream from Xingó HPP to Poço Redondo municipality (SE) (~35 km). It is characterized by a rocky and lotic portion that runs through a narrow channel (ca. 50 m) widening as the river follows its course (600 m). Visited communities: Piranhas (AL) – Piranhas Nova, Piranhas Velha, and Povoado Entremontes; Poço Redondo (SE) – Povoado Angico, Povoado Cajueiro, Povoado Curralinho, and Povoado Bom Sucesso.

Area 3. Pão de Açúcar (AL) to Gararu (SE) (~50 km). Floodplain area, with an increase of river width (over 600 m). The margin slope is reduced with the presence of meanders, sandy banks, and sedimentary banks on the river channel (Silva, 2009Silva WF. Determinação da carga de material em suspensão no rio São Francisco: ano hidrológico 2007. [Undergraduate Monograph]. Maceió: Universidade Federal de Alagoas; 2009.; Cavalcante, 2011Cavalcante AJBD.Impactos nos processos morfológicos do baixo curso do rio São Francisco, decorrentes da construção de barragens. [PhD Thesis]. Rio de Janeiro: Universidade Federal do Rio de Janeiro; 2011. Available from: http://objdig.ufrj.br/60/teses/coppe_m/AmparoDeJesusBarrosDamascenoCavalcante.pdf
http://objdig.ufrj.br/60/teses/coppe_m/A...
). Visited communities: Pão de Açúcar (AL) – Pão de Açúcar; Porto da Folha (SE) – Povoado Niterói, and Povoado Ilha do Ouro; Gararu (SE) – Povoado Jenipatuba.

Area 4. Penedo (AL) to the mouth of the river in the Atlantic Ocean (~40 km). It is a coastal plain formed by the interaction between the river and the sea. Major influence of the sea with small islands close to its mouth. The area has flat surfaces of recent sediments, alluvial, wind, and beaches (Medeiros et al., 2007Medeiros PRP, Knoppers BA, Santos Júnior RC, Souza WFL. Aporte fluvial e dispersão de matéria particulada em suspensão na zona costeira do rio São Francisco (SE/AL). Geochim Bras. 2007; 21(2):212–31.). Visited communities: Penedo (AL) – Penedo, and Povoado Ponta Mufina; Brejo Grande (SE) – Brejo Grande; Piaçabuçu (AL) – Piaçabuçu, and Pontal do Peba.

Four expeditions (75 days) were carried out between March and August/2017. The respondents were selected using the Snowball method (Bailey, 1982Bailey KD. Methods of Social Research. New York: Free Press; 1982.), which identifies a referenced specialist recognized by the community, who, after being interviewed, recommends another specialist, and so on (Albuquerque et al., 2010aAlbuquerque UP, Lucena RFP, Neto EMFL. Seleção dos participantes da pesquisa. In: Albuquerque UP, Lucena RFP, Cunha LVFC, organizers. Métodos e técnicas na pesquisa etnobiológica e etnoecológica. Recife: NUPPEA; 2010a. p.23–37.). To survey the ethnoecological data, free and semi-structured interviews (Tab. S1), visual stimulus, and guided tours were conducted.

Free interviews consist of informal conversations with the studied population by establishing proximity and detecting relevant information to the research (Bernard, 2006Bernard HR.Research methods in anthropology: Qualitative and quantitative approaches. 4th ed. AltaMira Press; 2006.). Semi-structured interviews involve asking targeted questions with a survey, leading to an effective method for gathering specific information (Huntington, 1998Huntington HP. Observations on the utility of the semi-directive interview for documenting traditional ecological knowledge. Arctic. 1998; 51(3):237–42. ; Silvano et al., 2008Silvano RAM, Silva AL, Ceroni M, Begossi A. Contributions of ethnobiology to the conservation of tropical rivers and streams. Aquat Conserv. 2008; 18(3):241–60. https://doi.org/10.1002/aqc.825
https://doi.org/10.1002/aqc.825...
). The semi-structured interviews were recorded with a SONY ICD PX333 recorder and later transcribed for content analysis. Personal information of fishers (e.g., age, time of fishing activity, and birthplace) and the status of fishes (e.g., distribution, introduction, and disappearance) were registered in interviews. Furthermore, additional information on environmental impacts was obtained to verify if changes observed in the ichthyofauna were related to the impacts mentioned above.

Visual stimulus occurred by displaying a manual of photographs of fishes from the SFRB to identify ethno-species and obtain ethnoecological information. The guided tour is a method that relies on the help of a local guide with extensive knowledge to elucidate information in the field (Albuquerque et al., 2010bAlbuquerque UP, Lucena RFP, Alencar NL. Métodos e técnicas para coleta de dados etnobiológicos. In: Alburquerque UP, Lucena RFP, Cunha LVFC, organizers. Métodos e técnicas na pesquisa etnobiológica e etnoecológica. Recife: NUPPEA; 2010b. p.41–64.) through tours conducted with fishers during the fishery activity (Marques, 1991Marques JGW. Aspectos ecológicos na etnoictiologia dos pescadores do complexo estuarino-lagunar Mandau–Manguaba, Alagoas. [PhD Thesis]. Campinas: Universidade Estadual de Campinas; 1991. Available from: http://repositorio.unicamp.br/jspui/handle/REPOSIP/315947
http://repositorio.unicamp.br/jspui/hand...
). The specimens caught by the fishers were identified using identification keys, and taxonomical status following Fricke et al., (2020)Fricke R, Eschmeyer WN, Van der Laan R. Eschmeyer’s catalog of fishes: Genera, species, references [Internet]. San Francisco: California Academy of Sciences; 2020. Available from: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp
http://researcharchive.calacademy.org/re...
.

FIGURE 1 |
Fishers’ communities on the four areas visited on the Sub-Middle and on Lower São Francisco, Northeastern Brazil. PE = Pernambuco State; BA = Bahia State; AL = Alagoas State; SE = Sergipe State.

Statistical analyses. We analyzed all data by “Union of all individual competencies” (Hays, 1976Hays TE. An empirical method for the identification of covert categories in ethnobiology. Am Ethnol. 1976; 3(3):489–507. https://doi.org/10.1525/ae.1976.3.3.02a00070
https://doi.org/10.1525/ae.1976.3.3.02a0...
) even if containing discrepancies. Tests to verify the consistency and validity of the information were performed through interviews in synchronous and diachronic situations. The first consists of making the same question to different respondents over a short time, and the second is applied when the same question is asked to the same respondent over a longer interval (Marques, 1991Marques JGW. Aspectos ecológicos na etnoictiologia dos pescadores do complexo estuarino-lagunar Mandau–Manguaba, Alagoas. [PhD Thesis]. Campinas: Universidade Estadual de Campinas; 1991. Available from: http://repositorio.unicamp.br/jspui/handle/REPOSIP/315947
http://repositorio.unicamp.br/jspui/hand...
).

The Frequency, Word Cloud and Similitude analyses were performed with the software IRAMUTEQ version 0.7 alpha 2 (Ratinaud, 2009Ratinaud P. IRaMuTeQ: Interface de R pour les analyses multidimensionnelles de textes et de questionnaires [Internet]. 2009. Available from: http://www.iramuteq.org
http://www.iramuteq.org...
), using the R environment (R Core Team, 2019R Core Team. R: A language and environment for statistical computing. [Internet]. Vienna: R Foundation for Statistical Computing; 2019. Available from: http://www.Rproject.org
http://www.Rproject.org...
). A Frequency test demonstrated the expression of the impacts mentioned by the fishers according to the number of citations. Then, the Word Cloud analysis was performed, positioning the lexical groups according to repetitions (Camargo, Justo, 2013Camargo BV, Justo AM. IRAMUTEQ: Um software gratuito para análise de dados textuais. Temas Psicol. 2013; 21(2):513–18. http://dx.doi.org/10.9788/TP2013.2-16
http://dx.doi.org/10.9788/TP2013.2-16...
). This analysis exhibits the weight of the words mentioned by respondents, showing them in more extensive and centralized positions according to the highest frequency of citations.

To verify the relationship between the impacts mentioned by the fishers, the Similitude Analysis was carried out, which identifies co-occurrences between words and graphically demonstrates their connection through the presentation of trees — groups of words that are related to each other —, and the intensity of their connections illustrated by the line thickness (increased thickness = higher intensity) (Marchand, Ratinaud, 2012Marchand P, Ratinaud P. L’analyse de similitude appliquée aux corpus textuels: les primaires socialistes pour l’élection présidentielle française (septembre–octobre 2011). JADT. 2012; 2012:687–99. Available from: http://lexicometrica.univ-paris3.fr/jadt/jadt2012/Communications/Marchand,%20Pascal%20et%20al.%20-%20L’analyse%20de%20similitude%20appliquee%20aux%20corpus%20textuels.pdf
http://lexicometrica.univ-paris3.fr/jadt...
; Camargo, Justo, 2013Camargo BV, Justo AM. IRAMUTEQ: Um software gratuito para análise de dados textuais. Temas Psicol. 2013; 21(2):513–18. http://dx.doi.org/10.9788/TP2013.2-16
http://dx.doi.org/10.9788/TP2013.2-16...
). The difference from mentioned impacts between the surveyed areas was observed through a multivariate analysis of Non-Metric Multidimensional Scaling (NMDS) with Jaccard distribution and the Similarity Analysis (ANOSIM) using the free software Past version 21.7c (Hammer et al., 2001Hammer Ø, Harper DAT, Ryan PD. Paleontological statistics software: Package for education and data analysis. Palaeontol Electron. 2001; 4(1):1–09. Available from: https://palaeo-electronica.org/2001_1/past/past.pdf
https://palaeo-electronica.org/2001_1/pa...
). P values < 0.05 were considered significant.

The status of fishes was defined regarding the frequency of mentions and the recognition of species by fishers during interviews and visual stimulus. The categories were classified in: Frequent = most mentioned and recognized species (51–100%), with occurrence confirmed by the fishers; Rare = species with intermediate mention and identification frequency (26–50%), with occurrence related to reducing stocks or local disappearance; Imprecise = species with low mention and identification frequency (0–25%), whose status was imprecise due to insufficient data; Probably extinct = species recognized and reported for the study area, but missing.

RESULTS

A total of 107 fishers were interviewed from 22 locations over 11 municipalities in the states of Alagoas, Bahia, Pernambuco, and Sergipe. The average age was 53.2±10.44 years, and the time of experience performing the fishery activity was 40.3±11.68 years. Most of the fishers (68%) were born and have lived in the communities where they were surveyed. A portion of them (18%) reported having migrated from adjacent locations when they were younger, while 14% of respondents migrated from locations that were flooded during the construction of reservoirs of Luís Gonzaga and Xingó HPPs.

Impacts on the ichthyofauna. The surveyed fishers have pointed out 13 impacts responsible for altering the ichthyofauna and reducing fish stocks in the region. The frequency analysis of the mentioned impacts in all sampled areas showed that the dam construction (93%) was the most significant one (Fig. 2A), corroborated by its prevalence in the Word Cloud analysis (Fig. 2B).

The analysis of impacts by area also highlighted dams as the significant impact (Fig. 3). For example, at areas 1 and 2, the shift in river dynamics caused by the construction of reservoirs (Figs. 3A,B) eliminated lotic environments that included waterfalls and rapids. Fishers reported that dams also interfere on migratory routes of essential species for artisanal fisheries, such as Pseudoplatystoma corruscans (Spix & Agassiz, 1829), Salminus franciscanus Lima & Britski, 2007, Prochilodus argenteus Spix & Agassiz, 1829, and Conorhynchus conirostris (Valenciennes, 1840), claiming that after its construction there was a reduction of their populations culminating in the disappearance of some of them.

Fishers from Area 1 also mentioned impacts such as aquaculture and overgrowth of macrophytes (Egeria densa and Eichornia crassipes) (Fig. 3A). Statements made by the fishers associated these macrophytes with introduced Amazonian fish C. monoculus and Colossoma macropomum (Cuvier, 1816) after the construction of dams. Macrophyte overgrowth was associated with the formation of lakes (lentic section), low river flow (lotic section), as well as pollution from the cultivation of O. niloticus in aquaculture cages (Area 1) and domestic and industrial effluents.

Overfishing was also among the most representative impacts (Fig. 3B), with the harpoon device identified as predominantly used to capture breeding individuals. However, the target species reported were non-native primarily species, such as O. niloticus, C. monoculus, C. macropomum, and Astronotus ocellatus (Agassiz, 1831), though P. argenteus was also mentioned as a target.

FIGURE 2 |
Frequency (A) and Word Cloud (B) analyses regarding the impacts over the ichthyofauna, according to fishers from the four sampled areas on the Sub-Middle and on Lower São Francisco. a. Dam; b. Macrophytes; c. Pollution; d. Overfishing; e. Absence of rain; f. Aquaculture; g. Deforestation; h. Silting; i. Water transfer; j. Non-native species; k. Irrigation; l. Pesticide; m. Salinization.

FIGURE 3 |
List of main impacts mentioned in A. Area 1, B. Area 2, C. Area 3, and D. Area 4, according to fishers from the final portion of the Sub-Middle and Lower São Francisco. Dam: dams; Mac: macrophytes; Aqu: aquaculture; Pol: pollution; Ovf: overfishing; Abr: absence of rain; Def: deforestation; Sil: silting; Salt: salinity.

The synergy of factors such as reduced rainfall, intense water use, water flow restriction through reservoirs, and diversion was listed as responsible for the compromised flow of the São Francisco River. These factors have contributed to the increase in the salinity of Area 4 with the increased intrusion of seawater over freshwater habitats (Fig. 3D). Fishers from Brejo Grande (SE) and Piaçabuçu (AL) highlighted the reduction and disappearance of some freshwater species, the increase of marine species in the region, and problems associated with saline water capture in communities near to the river mouth.

Area 1 impacts differed significantly (Fig. 4, ANOSIM; R = 0.151; p <0.001) from the other areas, due to the more significant number of citations of the impacts from aquaculture, pollution, and macrophytes overgrowth, enhanced by the transformation from lotic to lentic waters due to the construction of dams (Fig. 4).

The maximum similarity tree exhibited three lexical islands, where “Dam” played a central role in the impacts over fisheries, which was associated with the lexical islands “Silting” and “Macrophytes” (Fig. 5). The lexical island “Macrophytes” showed greater linkage power with the central island. The relationships were associated with the proliferation of macrophytes mainly due to water pollution and aquaculture of O. niloticus in the region.

Occurrence status. Fishers recognized 82 species (Tab. S2) and stated that some migratory and economically important ones from the São Francisco River have disappeared from the study area, such as C. conirostris (±20 years), P. corruscans (±10 years), and S. franciscanus (±10 years). Other migratory species were restricted to some areas with a reduced population. Brycon orthotaenia Günther, 1864 was poorly recognized (27%) and cited as missing in areas 1 and 4. On areas 2 and 3, some fishers have recognized B. orthotaenia, stating that the species has disappeared. However, it was captured one time over recent years. During the data collection expedition, a specimen of B. orthotaenia was registered from the artisanal fisheries at Povoado Entremontes (Area 2). Megaleporinus obtusidens (Valenciennes, 1837) is restricted to the lotic sections on the canyons (Area 1), with specific capture mentions on areas 2 and 3. Despite the low catches, two Prochilodontidae (P. argenteus and Prochilodus costatus Valenciennes, 1850) seem to be the only migratory species that still occur, possibly in all areas, considering their low abundance. Fishers highlighted the increase of catches during the rainy season and associated their occurrence with the presence of tributaries around the region, such as the rivers Moxotó (Area 1), Capivara, and Ipanema (Area 3), Itiúba, and Marituba (Area 4). The remaining presence of Anostomidae populations was also associated with the tributaries.

Currently, the most common native species in catches is Serrasalmus brandtii Lütken, 1875, along with other fish considered in the past as secondary or low value as Hoplias malabaricus (Bloch, 1794), Pygocentrus piraya (Cuvier, 1819), Trachelyopterus galeatus (Linnaeus, 1766), Hypostomus sp., P. etentaculatus, and now the commercially important R. aspera (Areas 1-2). Non-native species as Plagioscion squamosissimus (Heckel, 1840) (Area 1), C. monoculus, O. niloticus, A. ocellatus, C. macropomum, and M. lippincottianus have established populations in the final section of the SMSF and LSF. Fishers informed about the increase of occurrence of the non-native species, as well as the confirmation on reproductive interactions by finding spawning sites (e.g., nests with eggs and juveniles), and description of the behavior displayed during parental care (e.g., O. niloticus and C. monoculus). The most abundant species in fisheries activity were M. lippincottianus and S. brandtii, despite having low commercial value. Catches of P. squamosissimus have also been frequent but restricted to the lentic section of the reservoirs (Area 1).

Euryhaline species such as Caranx spp., Megalops atlanticus Valenciennes, 1847, Diapterus rhombeus (Cuvier, 1829), Mugil curema Valenciennes, 1836, Centropomus parallelus Poey, 1860, and Centropomus undecimalis (Bloch, 1792) have become more frequent in catches on areas 2, 3, and 4. The higher occurrence of euryhaline species has been associated with river regulation by dams, leading to an increase of salinity in Area 4 locations.

FIGURE 4 |
Non-Metric Multidimensional Scaling (NMDS) analysis concerning impacts over the ichthyofauna in the four sampled areas on the Sub-Middle and Lower São Francisco.

FIGURE 5 |
Maximum Similitude Tree showing the expression and relationship of impacts over fisheries in the four areas sampled on the Sub-Middle and on Lower São Francisco, based on fishers’ testimonies (n = 107).

DISCUSSION

The majority of fishers pointed out the impact caused by dams on the São Francisco River as the main responsible for changes in fisheries and fish species, as observed in other large Neotropical rivers (Hallwass et al., 2013Hallwass G, Lopes PF, Juras AA, Silvano RA. Fishers’ knowledge identifies environmental changes and fish abundance trends in impounded tropical rivers. Ecol Appl. 2013; 23(2):392–407. https://doi.org/10.1890/12-0429.1
https://doi.org/10.1890/12-0429.1...
; Santos et al., 2018Santos RE, Fonseca RMPR, Simões NR, Zanchi FB. The decline of fisheries on the Madeira River, Brazil: the high cost of the hydroelectric dams in the Amazon Basin. Fish Manag Ecol. 2018; 25(5):380–91. https://doi.org/10.1111/fme.12305
https://doi.org/10.1111/fme.12305...
; Runde et al., 2020Runde A, Hallwass G, Silvano RA. Fishers’ knowledge indicates extensive socioecological impacts downstream of proposed dams in a tropical river. One Earth. 2020; 2(3):255–68. https://doi.org/10.1016/j.oneear.2020.02.012
https://doi.org/10.1016/j.oneear.2020.02...
). Dams interrupt the river connectivity, changing its environmental complexity and triggering a series of side effects that lead to environmental simplification. The formation of a lentic environment upstream, the controlled water flow downstream of the dam, changes in the morphology of the river channel (e.g., silting), limnological variations, and the interruption of migratory routes affect mainly rheophilic and migratory species (Reid et al., 2019Reid AJ, Carlson AK, Creed IF, Eliason EJ, Gell PA, Johnson PTJ et al. Emerging threats and persistent conservation challenges for freshwater biodiversity. Biol Rev. 2019; 94(3):849–73. https://doi.org/10.1111/brv.12480
https://doi.org/10.1111/brv.12480...
; Zambaldi, Pompeu, 2020Zambaldi L, Pompeu PS. Evaluation of River Fragmentation and Implications for the Conservation of Migratory Fish in Southeastern Brazil. Environ Manage. 2020; 65:702–09. https://doi.org/10.1007/s00267-020-01266-9
https://doi.org/10.1007/s00267-020-01266...
). These species depend on accessible routes to migrate and complete their life cycle (Sato, Godinho, 2003Sato Y, Godinho HP. Migratory fishes of the São Francisco River. In: Carosfeld J, Harvey B, Ross C, Baer A, editors. Migratory fishes of South America: Biology, fisheries and conservation status. Victoria: IDRC & The World Bank; 2003. p.195–232.; Godinho et al., 2007Godinho AL, Kynard B, Godinho HP. Migration and spawning of female surubim (Pseudoplatystoma corruscans, Pimelodidae) in the São Francisco River, Brazil. Environ Biol Fish. 2007; 80(4):421–33. https://doi.org/10.1007/s10641-006-9141-1
https://doi.org/10.1007/s10641-006-9141-...
; Andrade-Neto, 2008Andrade-Neto FR. Migração e conservação do dourado (Salminus franciscanus Lima & Britski, 2007) em um trecho do rio São Francisco. [MSc Dissertation]. Belo Horizonte: Universidade Federal de Minas Gerais; 2008. Available from: https://repositorio.ufmg.br/bitstream/1843/BUOS-8F6FRD/1/disserta__o_francisco_r._a._neto.pdf
https://repositorio.ufmg.br/bitstream/18...
). Thus, the construction of reservoirs may lead to consecutive recruitment failures resulting in the disappearance of migratory species, as reported in the present study for P. corruscans, C. conirostris, and S. franciscanus, and the reduction in stocks of P. argenteus, P. costatus, and M. obstusidens.

This environmental change has created an invasion window (Lockwood et al., 2007Lockwood JL, Hoopes MF, Marchetti MP. Invasion Ecology. Oxford: Blackwell Publishing; 2007.) and enabled the establishment of non-native fish, such as C. monoculus, O. niloticus, A. ocellatus, P. squamosissimus, and M. lippincottianus. Invasive species characteristics, such as rapid colonization due to reproduction occurring almost year-round (Magalhães et al., 1996Magalhães AL, Sato Y, Rizzo E, Ferreira RM, Bazzoli N. Ciclo reprodutivo do tucunaré Cichla ocellaris (Schneider, 1801) na represa de Três Marias, MG. Arq Bras Med Vet Zoo. 1996; 48(1):85–92.; Assis et al., 2017Assis DASD, Dias-Filho VA, Magalhães ALB, Brito MFG. Establishment of the non-native fish Metynnis lippincottianus (Cope 1870) (Characiformes: Serrasalmidae) in lower São Francisco River, northeastern Brazil. Stud Neotrop Fauna E. 2017; 52(3):228–38. https://doi.org/10.1080/01650521.2017.1348057
https://doi.org/10.1080/01650521.2017.13...
), parental care, and a generalist diet have enabled their establishment (Pérez et al., 2004Pérez JE, Muñoz C, Huaquín L, Nirchio M. Riesgos de la introducción de tilapias (Oreochromis sp.) (Perciformes: Cichlidae) en ecosistemas acuáticos de Chile. Rev Chil Hist Nat. 2004; 77(1):195–99. http://dx.doi.org/10.4067/S0716-078X2004000100015
http://dx.doi.org/10.4067/S0716-078X2004...
; Agostinho et al., 2007Agostinho AA, Gomes LC, Pelicice FM. Ecologia e manejo de recursos pesqueiros em reservatórios do Brasil. Maringá: EDUEM; 2007.). Besides, propagule pressure should not be ruled out since the introduction of species in Northeastern Brazil is of common practice (Brito et al., 2020Brito MFG, Daga VS, Vitule JR. Fisheries and biotic homogenization of freshwater fish in the Brazilian semi-arid region. Hydrobiologia. 2020; 847(18):3877–95. https://doi.org/10.1007/s10750-020-04236-8
https://doi.org/10.1007/s10750-020-04236...
), as well as escapes from aquaculture cages (e.g., O. niloticus) (Azevedo-Santos et al., 2010Azevedo-Santos VM, Costa-Neto EM, Lima-Stripari N. Concepção dos pescadores artesanais que utilizam o reservatório de Furnas, Estado de Minas Gerais, acerca dos recursos pesqueiros: um estudo etnoictiológico. Biotemas. 2010; 23(4):135–45. https://doi.org/10.5007/2175-7925.2010v23n4p135
https://doi.org/10.5007/2175-7925.2010v2...
; Lima Junior et al., 2018Lima Junior DP, Magalhães ALB, Pelicice FM, Vitule JRS, Azevedo-Santos VM, Orsi ML, Simberloff D, Agostinho AA. Aquaculture expansion in Brazilian freshwaters against the Aichi Biodiversity Targets. Ambio. 2018; 47:427–40. https://doi.org/10.1007/s13280-017-1001-z
https://doi.org/10.1007/s13280-017-1001-...
). The absence of an anti-predatory response from the native species to foraging strategies of introduced piscivores (prey naiveté, Cox, Lima, 2006Cox JG, Lima SL. Naiveté and an aquatic–terrestrial dichotomy in the effects of introduced predators. Trends Ecol Evol. 2006; 21(12):674–80. https://doi.org/10.1016/j.tree.2006.07.011
https://doi.org/10.1016/j.tree.2006.07.0...
), as C. monoculus, may have favored their establishment and resulted in the reduction of small-size species as reported by fishers. The decline of small-size fauna seems inevitable in these cases (Pelicice, Agostinho, 2009Pelicice FM, Agostinho AA. Fish fauna destruction after the introduction of a non-native predator (Cichla kelberi) in a Neotropical reservoir. Biol Invasions. 2009; 11(8):1789–801. https://doi.org/10.1007/s10530-008-9358-3
https://doi.org/10.1007/s10530-008-9358-...
). On the other hand, the herbivorous species M. lippincottianus was favored by the river regulation that resulted in the growth of filamentous algae (Assis et al., 2017Assis DASD, Dias-Filho VA, Magalhães ALB, Brito MFG. Establishment of the non-native fish Metynnis lippincottianus (Cope 1870) (Characiformes: Serrasalmidae) in lower São Francisco River, northeastern Brazil. Stud Neotrop Fauna E. 2017; 52(3):228–38. https://doi.org/10.1080/01650521.2017.1348057
https://doi.org/10.1080/01650521.2017.13...
), which corresponds to the main item of its diet.

The macrophytes E. densa and E. crassipes were negatively correlated to fisheries, given their impacts on navigability and equipment handling for fisheries activities. These macrophytes found favorable conditions for establishment in the reservoir lentic environment and the downstream section with controlled water flow. The overgrowth obstructed the water surface in some sections, with greater intensity on small branches of the reservoirs. At Area 1, macrophyte overgrowth was associated with residues from O. niloticus farming in aquaculture cages. This region has become one of the leading aquaculture sites for O. niloticus farming in Brazil, producing almost 33,000 tons in 2014 (Ribeiro et al., 2015Ribeiro MRF, Santos JP, Silva EM, Pereira-Júnio EA, Tenório MALS, Lino e Silva IL et al. A piscicultura nos reservatórios hidrelétricos do submédio e baixo São Francisco, região semiárida do Nordeste do Brasil. Actapesca. 2015; 3(1):91–108. https://doi.org/10.2312/ActaFish.2015.3.1.91-108
https://doi.org/10.2312/ActaFish.2015.3....
). The high solar incidence (Araújo, 2011Araújo SMS. A região semiárida do nordeste do Brasil: Questões ambientais e possibilidades de uso sustentável dos recursos. Revista Rios Eletrônica. 2011; 5(5):89–98.) and the significant incorporation of phosphorus, nitrogen, and carbon into the system (Kubitza, 1999Kubitza F. Tanques-rede, rações e impacto ambiental. Panorama da Aqüicultura. 1999; 9(51):44–50.) contributed to plant propagation. Moreover, macrophyte beds act as reproductive sites, foraging areas, and shelters for the first developmental stages (Delariva et al., 1994Delariva RL, Agostinho AA, Nakatani K, Baumgartner G. Ichthyofauna associated to aquatic macrophytes in the upper Paraná River floodplain. Rev Unimar. 1994; 16(3):41–60.), which seem to have also collaborated in the establishment of non-native species pre-adapted to lentic environments (Assis et al., 2017Assis DASD, Dias-Filho VA, Magalhães ALB, Brito MFG. Establishment of the non-native fish Metynnis lippincottianus (Cope 1870) (Characiformes: Serrasalmidae) in lower São Francisco River, northeastern Brazil. Stud Neotrop Fauna E. 2017; 52(3):228–38. https://doi.org/10.1080/01650521.2017.1348057
https://doi.org/10.1080/01650521.2017.13...
).

The absence of sewage systems and waste processing are recurrent issues over the study area and the São Francisco basin (Figueiredo et al., 2011Figueiredo AH, Rodrigues IO, Morelli JCL, Nascimento JAS, Silva JKT, Brito MA et al. Diagnóstico da socioeconomia: vetores estruturantes da dimensão socioeconômica. In: Ministério do Meio Ambiente. Diagnóstico do macrozoneamento ecológico-econômico da Bacia Hidrográfica do Rio São Francisco. Brasília: MMA; 2011. p.303–414.). In some locations, sewage is released in natura into the river channels, affecting water quality while prompting public health implications (Figueiredo et al., 2011Figueiredo AH, Rodrigues IO, Morelli JCL, Nascimento JAS, Silva JKT, Brito MA et al. Diagnóstico da socioeconomia: vetores estruturantes da dimensão socioeconômica. In: Ministério do Meio Ambiente. Diagnóstico do macrozoneamento ecológico-econômico da Bacia Hidrográfica do Rio São Francisco. Brasília: MMA; 2011. p.303–414.). The improper disposal of oil from vessels has been another concern. Over the last decade, an investment in tourism in the canyons region (Area 1), visited by ca. 46,000 people in 2008 (Braghini et al., 2009Braghini CR, Gomes LJ, Ribeiro AS. Perspectivas de sustentabilidade ecológica do turismo em Xingó, SE/AL. Rev Geogr Acad. 2009; 3(1):56–69. Available from: https://ri.ufs.br/handle/riufs/539
https://ri.ufs.br/handle/riufs/539...
), increased boat traffic in the region, possibly affecting water quality with pollution from oil by-products (Freitas et al., 2015Freitas LO, Nogueira EMS, Moura GJB. Conflitos socioambientais no território pesqueiro do cânion do rio São Francisco. In: Nogueira EMS, Sá MFP, organizers. A pesca artesanal no baixo São Francisco: Atores, recursos, conflitos. Petrolina: SABEH; 2015. p.171–98.).

The reduction in flow resulting from dams has significantly restricted the flood pulses and led to the more significant seawater intrusion over the region of the mouth of the São Francisco River (Souza, Leitão, 2000Souza MRM, Leitão SN. Conseqüências sócio-econômicas dos impactos antrópicos no estuário do rio São Francisco em Brejo Grande, Sergipe-Brasil. Trab Oceanog. 2000; 28(1):97–116.). This process was enhanced after constructing the Xingó dam on the main channel of the São Francisco River (Araújo et al., 2016Araújo SS, Netto AOA, Gomes LJ. A percepção ambiental, identidade e pertencimento dos moradores do povoado Cabeço, em Brejo Grande/SE, frente às inundações na foz do rio São Francisco. Desenvolv Meio Ambiente. 2016; 36:239–53. https://doi.org/10.5380/dma.v36i0.37818
https://doi.org/10.5380/dma.v36i0.37818...
). Also, a section of the river’s water volume on the final portion has been diverted to irrigate crops (Souza, Leitão, 2000Souza MRM, Leitão SN. Conseqüências sócio-econômicas dos impactos antrópicos no estuário do rio São Francisco em Brejo Grande, Sergipe-Brasil. Trab Oceanog. 2000; 28(1):97–116.) and shrimp farming, the latter activity having removed an essential portion of the mangrove areas (Carvalho, Fontes, 2007Carvalho MES, Fontes AL. A carcinicultura no espaço litorâneo Sergipano. Revista da Fapese. 2007; 3(1):87–112.). The circumstances worsened with the ongoing reductions of river flow reaching 550 m³/s (Brito, Magalhães, 2017Brito MFG, Magalhães ALB. Brazil’s development turns river into sea. Science. 2017; 358(6360):179. https://doi.org/10.1126/science.aap9525
https://doi.org/10.1126/science.aap9525...
). Thus, the capture of marine and euryhaline species became more frequent, with records of M. atlanticus, Mugil spp., Cynoscion spp., C. parallelus, Bagre marinus (Mitchill, 1815), Eugerres brasilianus (Cuvier, 1830), and D. rhombeus (Souza, Leitão, 2000Souza MRM, Leitão SN. Conseqüências sócio-econômicas dos impactos antrópicos no estuário do rio São Francisco em Brejo Grande, Sergipe-Brasil. Trab Oceanog. 2000; 28(1):97–116.; D’avilla et al., 2017D’avilla T, Gomes MVT, Brito MFG. A percepção dos pescadores e a educação ambiental como subsídios para a conservação do Baixo São Francisco. Ecologias Humanas. 2017; 3(3):98–119. ).

The construction of a reservoir cascade in the final portion of the São Francisco River began in the 1950s with Paulo Afonso I HPP and finished in 1994, with the start of operations of Xingó HPP (CHESF, 2020Companhia Hidrelétrica do São Francisco (CHESF). Sistema de Geração [Internet]. Recife: Companhia Hidrelétrica do São Francisco; 2020. Available from: https://www.chesf.gov.br/SistemaChesf/Pages/SistemaGeracao/SistemasGeracao.aspx
https://www.chesf.gov.br/SistemaChesf/Pa...
). As a result, populations of commercial migratory species were driven to decline, and some have disappeared. On the other hand, non-native species (e.g., C. monoculus, A. ocellatus, O. niloticus, P. squamosissimus, M. lippincottianus), and native species with higher tolerance to environmental variations (e.g., S. brandtii, L. piau, S. knerii, Hypostomus spp.) and affinity to lentic and semi-lentic environments (Santos, 2010Santos GB. A ictiofauna da bacia do Alto Paraná (rio Grande e rio Paranaíba). MG Biota. 2010; 2(6):1–56.) encountered optimal conditions to maintain their populations. The long period without records of P. corruscans and S. franciscanus attests to the harmful effect of dams on large-distance migratory species since they demand long lotic sections connected to tributaries and marginal lagoons (Godinho et al., 2007Godinho AL, Kynard B, Godinho HP. Migration and spawning of female surubim (Pseudoplatystoma corruscans, Pimelodidae) in the São Francisco River, Brazil. Environ Biol Fish. 2007; 80(4):421–33. https://doi.org/10.1007/s10641-006-9141-1
https://doi.org/10.1007/s10641-006-9141-...
; Andrade-Neto, 2008Andrade-Neto FR. Migração e conservação do dourado (Salminus franciscanus Lima & Britski, 2007) em um trecho do rio São Francisco. [MSc Dissertation]. Belo Horizonte: Universidade Federal de Minas Gerais; 2008. Available from: https://repositorio.ufmg.br/bitstream/1843/BUOS-8F6FRD/1/disserta__o_francisco_r._a._neto.pdf
https://repositorio.ufmg.br/bitstream/18...
). The living area of S. franciscanus, for example, can reach 243 km (Andrade-Neto, 2008Andrade-Neto FR. Migração e conservação do dourado (Salminus franciscanus Lima & Britski, 2007) em um trecho do rio São Francisco. [MSc Dissertation]. Belo Horizonte: Universidade Federal de Minas Gerais; 2008. Available from: https://repositorio.ufmg.br/bitstream/1843/BUOS-8F6FRD/1/disserta__o_francisco_r._a._neto.pdf
https://repositorio.ufmg.br/bitstream/18...
). Recent records of B. orthotaenia in artisanal fisheries from the present study and Brito et al., (2016)Brito MFG, Bartolette R, D’avilla T, Gomes MVT, Dias-Filho VA. Reappearance of matrinxã Brycon orthotaenia (Characiformes: Bryconidae) in the lower São Francisco River, Brazil. AACL Bioflux. 2016; 9(5):949–53. Available from: http://www.bioflux.com.ro/docs/2016.949-953.pdf
http://www.bioflux.com.ro/docs/2016.949-...
are due to the stocking actions carried out by Companhia de Desenvolvimento dos Vales do São Francisco e Parnaíba (CODEVASF) in the LSF over the last decade. Similarly, the capture of C. conirostris in May/2020 (CBHSF, 2020Comitê da Bacia Hidrográfica do Rio São Francisco (CBHSF). O Pirá, peixe-símbolo da BHSF, reaparece na região do Baixo São Francisco após quase cinco décadas de sumiço [Internet]. Belo Horizonte: Comitê da Bacia Hidrográfica do São Francisco; 2020. Available from: https://cbhsaofrancisco.org.br/noticias/novidades/o-pira-peixe-simbolo-da-bhsf-reaparece-na-regiao-do-baixo-sao-francisco-apos-quase-cinco-decadas-de-sumico/
https://cbhsaofrancisco.org.br/noticias/...
) is a direct result of fish stocking performed by CODEVASF in 2017 (MFGB, pers. obs.; Video S3).

Prochilodus argenteus has been pointed out in the study area among the native commercial species. Recent records highlight the capture of sexually mature fish (Silva et al., 2018Silva GMN, Oliveira Carvalho RMC, El-Deir ACA, Sobral MDCM, Siegmund-Schultze M. Artisanal fisheries of the Itaparica reservoir, São Francisco River, Brazil: socioeconomic profile, environmental dynamics, and management recommendations. Reg Environ Change. 2018; 18(7):1889–99. https://doi.org/10.1007/s10113-018-1293-y
https://doi.org/10.1007/s10113-018-1293-...
), suggesting that the species uses tributaries as spawning areas in the region. This migratory behavior has been observed in the upper São Francisco by species of Prochilodus (Godinho, Kynard, 2006Godinho AL, Kynard B. Migration and spawning of radio-tagged zulega Prochilodus argenteus in a dammed Brazilian river. T Am Fish Soc. 2006; 135(3):811–24. https://doi.org/10.1577/T04-176.1
https://doi.org/10.1577/T04-176.1...
; Rosa et al., 2018Rosa GR, Salvador GN, Bialetzki A, Santos GB. Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River, Brazil. River Res Appl. 2018; 34(1):69–82. https://doi.org/10.1002/rra.3225
https://doi.org/10.1002/rra.3225...
) that spawn in the tributaries and the drifting larvae reach the main river (Rosa et al., 2018Rosa GR, Salvador GN, Bialetzki A, Santos GB. Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River, Brazil. River Res Appl. 2018; 34(1):69–82. https://doi.org/10.1002/rra.3225
https://doi.org/10.1002/rra.3225...
; Lopes et al., 2019Lopes JDM, Pompeu PS, Alves CBM, Peressin A, Prado IG, Suzuki FM et al. The critical importance of an undammed river segment to the reproductive cycle of a migratory Neotropical fish. Ecol Freshw Fish. 2019; 28(2):302–16. https://doi.org/10.1111/eff.12454
https://doi.org/10.1111/eff.12454...
). We believe that tracing the migratory route of P. argenteus over this area can be a source of essential data for future investigations. Nevertheless, the population increase through artificial stocking is not ruled out, as CODEVASF conducts fish stocking with these native species (MFGB, pers. obs.). The native Loricariidae R. aspera is a secondary species that has stood out in local cuisine (Area 2) due to the collapse of medium-large commercial fishes. The increase of tourism over the region (Braghini et al., 2009Braghini CR, Gomes LJ, Ribeiro AS. Perspectivas de sustentabilidade ecológica do turismo em Xingó, SE/AL. Rev Geogr Acad. 2009; 3(1):56–69. Available from: https://ri.ufs.br/handle/riufs/539
https://ri.ufs.br/handle/riufs/539...
) may lead to higher fisheries pressure and depletion of populations of this species in the future.

Integrative planning is essential to balance the potential of electric energy and the sustainability of natural resources to minimize the loss of biodiversity and other environmental, social, and economic effects (Winemiller et al., 2016Winemiller KO, Mcintyre PB, Castello L, Fluet-Chouinard E, Giarrizzo T, Nam S et al. Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong. Science. 2016; 351(6269):128–29. https://doi.org/10.1126/science.aac7082
https://doi.org/10.1126/science.aac7082...
). An old project for constructing another dam on the main channel of Middle São Francisco has been discussed and represents a new threat (Gomes et al., 2020Gomes JPC, Salvador GN, Casarim R, Pompeu PS, Brito MFG, Andrade FR et al. Hydropower construction plans threaten the largest Brazilian national river. Aquat Conserv. 2020; 30(12):2464–65. https://doi.org/10.1002/aqc.3485
https://doi.org/10.1002/aqc.3485...
). Maintaining the longitudinal connectivity and natural flow regimes of rivers (Zambaldi, Pompeu, 2020Zambaldi L, Pompeu PS. Evaluation of River Fragmentation and Implications for the Conservation of Migratory Fish in Southeastern Brazil. Environ Manage. 2020; 65:702–09. https://doi.org/10.1007/s00267-020-01266-9
https://doi.org/10.1007/s00267-020-01266...
), combined with revitalization actions, must be effectively implemented to maintain biodiversity and ecosystem dynamics (Azevedo-Santos et al., 2021Azevedo-Santos VM, Rodrigues-Filho JL, Fearnside PM, Lovejoy TE, Brito MFG. Conservation of Brazilian freshwater biodiversity: Thinking about the next 10 years and beyond. Biodivers Conserv. 2021; 30:235–41. https://doi.org/10.1007/s10531-020-02076-5
https://doi.org/10.1007/s10531-020-02076...
).

Fishers’ LEK represents a reliable data source for investigating biological, ecological, and socio-environmental regards, especially in areas with insufficient data. Our study provides evidence that signals the incidence of anthropic impacts on artisanal fishing in the final stretch of the SFRB in areas under the influence of the reservoir cascade. The data indicate that changes in the environment caused alterations in the ichthyofauna composition, with probable local extinction of migratory species of economic importance, resulting in losses on fishing activities. The information presented here aims to collaborate with management and supervisory agencies and provide subsidies to assist in regulating measures to conserve of fishery resources. The integration of academic knowledge and fishers’ knowledge favors a contextualized analysis connected with the reality of these social actors, which can result in management practices that are appropriate to the local fishing resource (Carlsson, Berkes, 2005Carlsson L, Berkes F. Co-management: concepts and methodological implications. Journal Environ Manage. 2005; 75(1):65–76. https://doi.org/10.1016/j.jenvman.2004.11.008
https://doi.org/10.1016/j.jenvman.2004.1...
).

ACKNOWLEDGEMENTS

We want to thank the artisanal fisheries communities of the Sub-Middle and Lower São Francisco, who contributed uniquely to this study. Thanks to Carlos B. M. Alves for the availability of fish pictures used on the visual stimulus manual. To the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for granting student funding (TD), and to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the research grant (CNPq – 306851/2018-0, MFGB). We also thank the anonymous referees for various constructive comments on the earlier version of the manuscript.

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ADDITIONAL NOTES

  • HOW TO CITE THIS ARTICLE

    D’avilla T, Costa-Neto EM, Brito MFG. Impacts on fisheries assessed by local ecological knowledge in a reservoir cascade in the lower São Francisco River, northeastern Brazil. Neotrop Ichthyol. 2021; 19(3):e200156. https://doi.org/10.1590/1982-0224-2020-0156

Publication Dates

  • Publication in this collection
    08 Oct 2021
  • Date of issue
    2021

History

  • Received
    31 Dec 2020
  • Accepted
    6 July 2021
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