Abstract
The present study explored the interaction between the upriver migration of fish and the blockage of their migration routes by dam construction. Specifically, we studied (i) the capacity of migratory fish to locate alternative routes in the presence of an obstacle, and (ii) the behavior of the fish after they were artificially transferred to the reservoir. With the use of the mark-recapture technique (tagging), the study was carried out near Porto Primavera Dam (UHE Engenheiro Sérgio Motta) between 1994 and 1999, a period prior to the closure of the floodgates and the installation and operation of the fish pass facilities. The fish were caught in the dam forebay downstream, marked with LEA type tags, and released upstream (5113 individuals; 14 species) and downstream (1491; 12) from the dam. The recaptures were carried out by local professional and amateur fishermen. A total of 188 individuals (2.8%) were recaptured, mostly the curimba Prochilodus lineatus. Nearly half of the recaptures downstream occurred in tributaries, especially in the Paranapanema River, indicating that in the presence of an obstacle the fish are able to locate alternative migration routes. The remainder stayed in the main channel of the Paraná River, at a mean distance of less than 50 km from the release point. Of the fish released upriver from the dam, approximately half were recaptured downriver. Although the river was only partly dammed, the movement of the fish downriver suggests that they became disoriented after being transferred. Those that remained upriver avoided the reservoir and moved, rather rapidly, toward the lotic stretches farther upstream. From these results it is clear that, in the course of the decision process in installing fish passes, it is necessary to take into account the existence of spawning and nursery areas downriver and upriver from the reservoir.
Highlights
In the Paraná River basin, reproductive migrations of fish are relatively well-known seasonal phenomena (Godoy, 1967; Bonetto et al, 1981; Agostinho et al, 2003)
The present study explored the interaction between the upriver migration of fish and the blockage of their migration routes by dam construction
The floodplain environments have a vital role as spawning and nursery areas (Gomes & Agostinho, 1997), migratory fish still move in the direction of Porto Primavera Dam, probably toward the tributaries located upriver
Summary
In the Paraná River basin, reproductive migrations of fish are relatively well-known seasonal phenomena (Godoy, 1967; Bonetto et al, 1981; Agostinho et al, 2003). Of the more than 250 fish species catalogued in the Paraná River basin within the territory of Brazil, approximately 20 are longdistance migrators, many of them of large size (Resende, 2003; Agostinho et al, 2004). Large migratory fishes are among the most esteemed by the traditional, commercial, and sport fisheries of the region (Petrere Jr. et al, 2002). At present, this fishery is showing clear signs that the stocks are being depleted. This can be attributed to a group of factors, most prominently overfishing, occupation and incorrect use of the surrounding land, and especially the damming of the rivers (Agostinho et al, 2005; Okada et al, 2005)
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