Estudo da alça de vazão reduzida da UHE Passo São João - RS como possível área de reprodução da ictiofauna migratória

Abstract

Ecological corridors play a key role in the ecosystem. The fragmentation of these systems often causes environmental destabilization, provoking direct impacts on associated biodiversity. One of the main reasons of fragmentation of such ecological corridors in water resources is the construction of dams that alter the natural water flow regime caused by the diversion of natural flow range thus emerging altered flow passages known as stretch of reduced flow (SRF). Fish that have migratory behavior use these corridors in spawning seasons for ecological succession. Thus, the understanding of this ecological succession is important for the conservation of the species. The Passo São João Hydroeletric Plant (UHE PSJ), constructed in the town of Roque Gonzales - RS by the Ijuí river, possesses a dam of 21 meters, which in the context is considered a potential fragmenting of the natural ecological corridor of the river. The present study aimed at assessing whether the SRF, which is 4 km long and emerged from the installation of this plant, presents any value as breeding or nursery area of the migratory fish. For this, monthly samples were collected in the spawning period between October 2013 and March 2014. In addition, a one-off collection of 24 h was performed in October 2014. Embarked and disembarked surface collections lasting 20 min each were carried out with support from a bongo net measuring 0.5 / 1.3 m x 0.5 mm of mesh. Shortly thereafter, a replica with the same duration and greater depth was conducted. A flow meter was coupled to the network in order to calculate the amount of water filtered. In all sampling points, measurements of pH, water temperature and the ambience, transparency of the water column, depth of collection and dissolved oxygen were taken. After collecting over 13 thousand m³ of filtered water, 25 larvae were registered. One larva of the species Prochilodus lineatus, one Pimelodus maculatus and one Leporinus sp. Still seven individuals classified at the level of order, four Siluriformes and three larvae of order Characiformes. All samples were preserved with formaldehyde 4%. Once the sample success of this study is characterized by periods of peak rainfall occurring in the months of October and November, extreme events such as long periods of rain and high temperatures may probably be directly influencing the reproductive cycle of fish. Given the present results, we can conclude that the SRF has value as a passage and migration area for both upstream and downstream migratory fish and their larvae. However, in view of the great buoyancy of this environment, the abiotic conditions, and the monthly samplings of this study, it was not possible to determine whether the SRF has been serving as a nursery or local for the spawn of the ichthyofauna.