Harumi Irene Suzuki

Effects of the hydrological regime on the ichthyofauna of riverine environments of the Upper Paraná River floodplain

In this work, spatial and temporal variations in the diversity (species richness and Simpsons Diversity Index) and abundance (indexed by the capture per unit effort--CPUE; total and for reproductive groups) of fish from three rivers (Baía, Ivinheima and Paraná) located in a floodplain of the Upper Paraná River basin were analyzed over a period of 20 years (1987-2007). In addition, we evaluated the relationships of these ecological attributes with variations in the hydrologic regime, considering the possible effects of natural (climatic events) and artificial (discharge control by dams) disturbances. Annual variations in hydrometric attributes were calculated using PULSO software and daily water level data. We applied analysis of covariance to determine the relationships between ecological and hydrometric attributes, the latter summarized in axes of a principal component analysis. Lower values of the fish assemblage attributes (diversity and abundance) were registered in the Paraná River. Species richness, total CPUE and CPUE of long-distance migratory species were positively related to the duration of the floods and the connectivity of the area. Variations in the annual hydrological cycle and their effects on fish assemblage appear to be affected by extreme natural (ENSO) and artificial (discharge control by dams) events.

Molecular biogeography of the Neotropical fish Hoplias malabaricus (Erythrinidae:Characiformes) in the Iguaçu, Tibagi, and Paraná Rivers

Hoplias malabaricus, the common trahira, extended its range into the Iguacu River sometime in the last decades. To determine levels of genetic differentiation in neighboring basins of this nominal taxon, as well as to unveil the source of the invading population, we analyzed patterns of similarity of RAPD-PCR genomic markers of samples from Parana, Iguacu and Tibagi Rivers. The high genetic diversity of samples from the Parana and Tibagi Rivers suggested strong population structuring or even the occurrence of undescribed species. All alleles of the sample from the headwaters of Tibagi River were present in the sample from the Iguacu River, which suggests that the former population or another population with similar genetic makeup, may be the source of the trahiras of the Iguacu River.

Inter-annual variations in the abundance of young-of-the-year of migratory fishes in the Upper Paraná River floodplain: relations with hydrographic attributes

In this study, we identified and characterized the hydrographic attributes related to the success of recruitment of migratory fishes in the Upper Paraná River floodplain. To achieve our objectives, we analyzed inter-annual variations in the abundance of young-of-the-year (YOY; index of recruitment) of six migratory species and their relations with hydrographic attributes. Recruitment was related to the intensity, duration (in different fluviometrical levels), elasticity, number of pulses, greater uninterrupted overflow and delay of the floods (all obtained using the PULSO software). Collections of fish were conducted in the period between January 1987 and November 2007 in distinct environments (river channels, secondary channels and connected and disconnected floodplain lakes) distributed along three subsystems (Paraná, Baía and Ivinheima). Relations between recruitment and the attributes of interest were determined through analysis of covariance. In the studied period, the highest abundances of YOY were registered in 2007, followed by 1992, 1993, 2005 and 1988. The abundance of YOY was positively correlated with an intensity of high water levels (potamophase) and the duration of potamophase 1 and negatively with the duration of low water levels (limnophase) and a delay of flood. Higher hydrometric levels (540 and 610 cm for Paraná and 325 and 450 cm for Ivinheima) and greatest uninterrupted overflow presented different relations (significant interactions) among subsystems, but all with positive effects on recruitment. Results evidenced that recruitment responded better when floods started in January with potamophase intensities above 610 cm and water levels above 450 cm over a period of 50 days and repeated every two years (or > 610 cm for 38 days and repeated every two or three years). Therefore, artificial control of the floods at intervals of two or three years by manipulating the discharge of dams located upstream from the floodplain in a way that promotes potamophases with the potential to ensure recruitment of migratory species may become an important tool for conservation of migratory fish species in the floodplain.

Colonization of the Corumbá Reservoir (Corumbá River, Paraná River Basin, Goiás State, Brazil) by the "lambari" Astyanax altiparanae (Tetragonopterinae; Characidae)

This work aimed to determine which population features were important to the colonization process of Astyanax altiparanae in the Corumba Reservoir. The species presented wide spatial-temporal distribution, caught in all months and sites. Higher CPE values were recorded upstream from the reservoir during the filling phase. In this phase, reproductive activity was intense upstream and moderate in the tributaries. However, a fall in abundance of juveniles was observed after the formation of the reservoir. Among the most relevant population features to grant a successful colonization were wide geographic distribution, ability to occupy and spawn in lentic habitats and feeding flexibility.

Interspecific variation in migratory fish recruitment in the Upper Paraná River: effects of the duration and timing of floods

This study evaluated the relationship between the young of year (YOY) abundance of migratory fish species and the interannual variations in the duration and delay of floods in the Upper Paraná River floodplain. YOY of the most abundant migratory species Brycon orbignyanus, Hemisorubim platyrhynchos, Leporinus elongatus, Leporinus macrocephalus, Leporinus obtusidens, Pseudoplatystoma corruscans, Pterodoras granulosus, Prochilodus lineatus, Salminus brasiliensis and Sorubim lima were studied in a stretch of the Paraná river influenced by dams. Multiple regression analyses were performed with flood duration and delay as predictors for YOY abundances. There were differences among the species in the responses to flood duration and delay. The species B. orbignyanus, L. elongatus, L. macrocephalus, L. obtusidens, and P. lineatus exhibited an exponential increase in YOY abundance with flood duration. An exponential decrease in YOY abundance with flood delay was found for most of the studied species. Nevertheless, flood delay and flood duration were significant predictors of YOY abundance for L. elongatus, L. obtusidens, P. corruscans and P. lineatus. For these species, flood delays may result in failure of recruitment because these species migrate early in the season to adjust their energy reserves and their swimming patterns. Therefore, any efforts to preserve migratory fish should consider discharge manipulation from reservoirs upstream of the study areas. It is crucial that reservoirs are operated in such a way that the quantity, duration and timing of water release are compatible with the viability of spawning and the survival of early life stages of migratory fish.