Studies on two migratory fish from lower Tocantins River before closure of Tucurui dam

Migratory fish species are generally the most important species for the fishing industry as well as for artesanal fishing. In the lower Tocantins, two species of migratory fish dominate the captures: the mapará (Hypophthalmus marginatus) and the curimatã (Prochilodus nigricans). These two species were studied before the daming of this river by the Tucuri hydroelectric dam as part of a larger study of commercial fisheries encompassing the Tocantins basin from the mouth to Marabá (Pará). Based principally on landing records, this study describes the migration cycles of the two species. A classical and simple pattern of migration can be recognized: an upstream movement of immature and adults in the upper part of the distribution area, and then, the reverse or downstream movement of larvae and adults in a dispersion phase. The main difference between these two species lies in the size of distribution area. The mapará is limited to part of the river downstream from the hydroelectric dam of Tucurui, and so, would not be affected by its presence. The curimatã has a much larger geographic range in the Tocantins basin. The part of population living downsteam will probably be profundly pertubed by the dam due to the blockage of its migratory route

Colonização ictiofaunística do Reservatório de Itaipu e áreas adjacentes Ichthyofaunistic colonization of the Itaipu Reservoir and vicinity áreas

<abstract language="eng">Samples were taken from November 1983 to October 1989 in sites along the main body of the Itaipu reservoir and its area of influence to evaluate the impacts of this reservoir on ichthyofauna and to provide information about the colonization process in the dammed area. The ichthyofaunistic similarity between the sites was analysed during the studied period. Spatial and temporal variations of the ichthyofaunistic diversity were also done, using Shannon-Winer Index of Diversity, eveness and species richness, comparing the results with those obtained before the damming. After Itaipu Reservoir formation, it was observed significative alteration in specific abundance and ichthyofauna structure of the Paraná River, with an increase in species number in ali tributaries of the reservoir, and a high replacement in species. Diversity and species richness were higher in the dammed stretch of the Paraná river and in its tributaries of the left side after the Itaipu reservoir formation. Among the sampled sites, the highest values of the diversity index were registered in Paraná River upstream and downstream the reservoir, Iguatemi river and Arroio Guaçu. Based on information of similarity in species composition and abundance in the sampled area, five site groups could be identified