Fish community structure of Juramento reservoir, São Francisco River basin, Minas Gerais, Brazil André R. M. Silva 1, 2; Gilmar B. Santos 1 & Thiago Ratton 2 1 Programa de Pós-graduação em Zoologia de Vertebrados, Universidade Católica de Minas Gerais. Rua Dom José Gaspar 500, prédio 41, 30535-610 Belo Horizonte, Minas Gerais, Brasil. E-mail: [email protected] 2 Centro Universitário UNA. Rua José Cláudio Resende 80, 30455-590 Belo Horizonte, Minas Gerais, Brasil. ABSTRACT. Many rivers in Brazil as the São Francisco (SFR) have been impounded for reservoirs construction purposes. However, there is a lack of knowledge on their fish fauna in many areas, including headwaters. The present study aimed to describe the fish community structure from Juramento reservoir, located on Juramento River, a branch of SFR basin. Six bimonthly samplings were made in four different sites. Gill and cast nets, beach seines and sieves were used to collect fish. Ecological indexes as well as the relationship between fish abundance and some limnological variables were determined. 3288 fish belonging to 33 species (16.5% of the total de- scribed for SFR basin) were captured, being 75.7% Characiformes, 18.1% Siluriformes, 3% Cyprinodontiformes and 3% Gymnotiformes. Only two non-native species, ‘tamboatá’ – Hoplosternum littorale (Hancock, 1828) and ‘trairão’ – Hoplias lacerdae Ribeiro, 1908 were found. The highest catches in number occurred in the dry period (March-October) and the lowest one in the wet season (November-February). Diversity was higher at Barragem station and richness did not vary between reservoir zones. Five migratory species were found downstream of the dam (four exclusively there), whereas only the ‘curimbatá-pioa’ – Prochilodus costatus Valenciennes, 1850 occurred in the reservoir. The low observed correlations between fish abundance and the limnological variables utilized suggest that the local fish fauna is not strongly affected by their variation. KEY WORDS. Fish diversity. RESUMO. Estrutura da comunidade de peixes do reservatório de Juramentoamento, bacia do Rio São Franciscoancisco, Minas Geraisais, Brasil. No Brasil, vários rios, como os da bacia do São Francisco (RSF), são barrados para a formação de reservatórios. Entretanto, o estudo desta ictiofauna, especialmente a dos rios de cabeceira, ainda deixa a desejar. O presente estudo descreveu a estrutura da ictiofauna do reservatório de Juramento, Rio Juramento, bacia do RSF. Foram realizadas seis coletas bimestrais em quatro locais empregando-se redes de emalhar, tarrafas, arrastões e peneiras. Foram determinados índices ecológicos e a relação entre abundância da ictiofauna e algumas variáveis limnológicas do reservatório. Foram capturados 3288 exemplares, pertencentes a 33 espécies (16,5% das descritas para a bacia do RSF), sendo 75,7% Characiformes, 18,1% Siluriformes, 3% Cyprinodontiformes e 3% Gymnotiformes. Apenas 2 espécies exóticas, tamboatá – Hoplosternum littorale (Hancock, 1828) – e trairão – Hoplias lacerdae Ribeiro, 1908 – foram capturadas. As maiores capturas em número ocorreram no período seco (março-outubro) e a menor durante a estação chuvosa (novembro-fevereiro). A diversidade foi maior em Barragem e a riqueza específica não variou entre as regiões do reservatório. Cinco espécies migradoras ocorreram a jusante (quatro exclusivamente ali), e apenas uma – Prochilodus costatus Valenciennes, 1850 – a montante. As baixas correlações entre a abundância de peixes e as variáveis limnológicas utilizadas, sugerem estar a ictiofauna local menos sujeita às alterações relacionadas a estas variáveis. PALAVRAS-CHAVE. Diversidade de peixes. Among the Brazilian rivers, the São Francisco (SFR) is Gerais, Bahia, Pernambuco, Sergipe and Alagoas) and three distinguished for its extension, volume, economic and envi- important biomas (‘Cerrado’, ‘Caatinga’ and Atlantic Forest) ronmental importance. Its basin covers an area of 631,133 km2 (COPASA 2001). Its central segment, from Pirapora city (Minas (PLANVASF 1989) representing 7.5% of Brazilian territory. Dur- Gerais State) to Sobradinho reservoir (Bahia), comprises an area ing its course of nearly 3,000 km from Espinhaço range toward of 1,090 km plenty of marginal lagoons and floodplains, and the Atlantic Ocean, the SFR crosses through five States (Minas produces overflows that can spread out to 84 km (average of 9 Revista Brasileira de Zoologia 23 (3): 832–840, setembro 2006 Fish community structure of Juramento reservoir, São Francisco River basin... 833 km) from its margins, as occurs at Xique-Xique (Bahia). The SFR gill nets with mesh sizes from 3 to 16 cm (opposite knots length) floodplains areas are very important for fish recruitment, espe- soaked for 15 hours per station (from 16:00 PM to 7:00 AM). cially for migratory species nursery habitat (POMPEU & GODINHO After this period, the nets were removed of water and all the fish 2003, SATO & GODINHO 2003). These species are among the more captured were gathered by mesh size. Beach seines (2 mm diam- important ones to commercial fisheries, and allow the SFR to eter), sieves (2 mm) and cast nets (7 cm) were also utilized. support an expressive fishery activity. Besides, mineral substances In Jusante station it was not possible to apply the same as lead, zinc, gold, silver, cadmium, chromium, quartz and sul- sampling effort utilized upstream due to local limitations. Thus, fur have been extracted from that basin (COPASA 2001). just qualitative sampling was made there, using cast nets (7 cm Studies involving SFR basin fish fauna are gradually in- between opposite knots), gill nets (7-8 cm), beach seines and creasing, calling attention, among other, some papers on in- sieves (2 mm diameter). ventory (BRITSKI et al. 1986, SATO & GODINHO 1999), community In the field, specimens were identified, labeled and stored structure (ALVES & VONO 1997, ALVES & POMPEU 2001), food hab- in 10% formaldehyde solution. In laboratory, from each speci- its (POMPEU 1999, POMPEU & GODINHO 2003, OLIVEIRA et al. 2004) men was obtained the standard length (cm) and body weight and fisheries (GODINHO et al. 2003, SATO & GODINHO 2003). (g). A small representative fraction of sampled fish has been However, information concerning the fish fauna of the deposited at Pontifícia Universidade Católica de Minas Gerais SFR upper drainages, especially related to impounded areas, is (PUCMinas). Few specimens were sent to Museu de Zoologia, poorly available yet. This is the current status of the Juramento Pontifícia Universidade Católica do Rio Grande do Sul, (PUC- reservoir, located in the headwaters of the Verde Grande river, RS) for taxonomic confirmations. where just one preliminary inventory (DABÉS et al. 2001) had Data on water temperature, conductivity, pH, transpar- been made. As the main water supplier for Montes Claros city ency, and dissolved oxygen from the stations upstream the dam (Minas Gerais), Southeastern Brazil, the study of its fish fauna were also collected by COPASA staff, from 9:15 to 10:55 AM at is important to support the future management plan and the 0.5 m deep, from February 2002 to February 2003. species conservation of that area. Catches in number and biomass The aims of the present study were to describe the struc- For the species captured by gill nets, fish abundance was ture of reservoir fish community. The species composition, determined through the capture per unit of effort (CPUE), de- spatial and temporal variations on the species abundance (in fined as the sum of the number (CPUEn) or biomass (CPUEb) number and biomass), the assemblage constancy, richness, di- of captured fish by 100 m2 of nets soaked for 12 hours. This versity and similarity between the sampled sites were deter- procedure allowed quantitative comparisons between species, mined. This study also intended to relate the reservoir fish abun- stations and dry (March to October) and wet seasons (Novem- dance with some limnological variables. ber to February). Before the analyses, two normality tests MATERIAL AND METHODS (Kolmogorov-Smirnov and Lillifors & Shapiro-Wilks) were per- formed on abundance data. A one-way ANOVA was carried out Study area to verify eventual significant abundance differences between The Juramento reservoir (16º46’20”S e 43º39’56”W) is the sampled stations, and a Tukey test was also applied when owned by COPASA (Companhia de Saneamento de Minas appropriated. A student t-test for independent samples was Gerais). It was formed in 1981 by the Juramento river impound- performed to verify significant differences in the abundance ment and has two tributaries (Saracura and Canoas rivers). between dry and wet seasons. A 0.05 significance level was es- Located 5 km far from Verde Grande river, it has a flooded area tablished for all tests utilized. 2 of 7.63 km , 9.1 m of mean depth and a total volume of 45 Ecological parameters billions of liters. The reservoir was built in 1981 for supplying The cumulative curve of the species captured with gill nets Montes Claros city, 27 km away. Currently, it is responsible for was drawing along the sampling period to verify the influence 70% of the total water supplied to that city. Juramento has a of the number of samples on the species richness, following perimeter of 52 km at 640.3 m, surrounded by 31 km2 of pro- BOSCHUNG & O’NEIL (1981), among other. The species constancy tected woody area. Its basin vegetation is characterized mainly was calculated according to DAJOZ (1973), for all the sampled by ‘Cerrado’ formations and pastures (DABÉS et al. 2001). stations including all species captured. The following categories Sampling were established: constant (equal or more than 50%), accessory Four sampling locals were defined in the study area: (1) (equal or more than 25% and less than 50%) and accidental Barragem, which represents the reservoir lentic zone; (2) Canoas, (less than 25%). The total number of species captured with gill the transition region; (3) Juramento, the lotic area, and (4) Jusan- nets was used as a richness index for each sampled station. Di- te, downstream the reservoir in front of the dam (Fig. 1).