Flow regulation by dams affecting ichthyoplankton: the case of the Porto Primavera Dam, Paraná River, Brazil

Abstract

The effects of a dam closure (Porto Primavera Dam) on reproduction of the main species that use the floodplain located below a nursery area were determined. Specifically, we examined, before and after the closure of the dam, the spatial distribution of larvae and the differences in density according to life strategy (migratory and non-migratory species). Fifteen points distributed along the channels of the Paraná, Ivinheima and Paranapanema rivers were sampled, between 1997 and 2001, (October 1997 to December 1998 and between January 1999 to March 2001-post closure), during the spawning period of most fish species found in the region (October to March). Samplings were always conducted at night, using a conical-cylindrical plankton net (0.5 mm mesh) with a flowmeter attached. There were significant differences in larvae densities between pre and post dam closure for several species. Also, there were significant differences between the pre and post-closure periods for densities of migratory and non-migratory species, and between sampling sites. These findings indicate decline in densities and number of taxa caught after the closure of the dam. Larvae of migratory species, formerly common in the entire study area, were registered only in points influenced by the non dammed rivers (such as the Ivinheima River), indicating that the closure of Porto Primavera caused negative impacts on fish reproduction downstream of the dam.

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

“…This event seemed to be neutralized by the filling of Porto Primavera Reservoir (December 1998 to January 2000; 225,000 ha). Studies on the distribution of eggs and larvae of long-distance migratory fish conducted below Porto Primavera Dam revealed high densities in this period, especially in tributaries (Sanches et al, 2006). However, the absence of connectivity between the river channels and the adjacent floodplain (nurseries) did not allow their development, negatively affecting recruitment of these species (Agostinho et al, 2004a).…”

“…The increase in larvae density of long-distance migratory species in the Ivinheima River demonstrates the importance of this river to spawning in the upper Paraná River floodplain Nakatani et al, 1997;Sanches et al, 2006). In this sense, the creation of conservation units such as the "Parque Estadual do Ivinheima" (Ivinheima State Park) favors the integrity of the ecosystem and the maintenance of regional diversity.…”

Fish larvae assemblages in two floodplain lakes with different degrees of connection to the Paraná River, Brazil

“…The park is located along a stretch of the Paraná River that was free of dams and, until mid-1998, had a flood regime that dependent only upon the hydrological cycle. Presently, the river flow is managed by the Sérgio Motta Power Plant (Porto Primavera Dam), and the previously frequent floods are now unable to reach the floodplain lakes (Sanches et al, 2006;Gubiani et al, 2007).…”

“…Without the overflow of the river and consequent flooding of the floodplain, fish eggs and larvae do not reach the lagoons. They instead remain in the main river channel, where they are more susceptible to predation by fish and other aquatic organisms (Sanches et al, 2006). This may reduce diversity and cause the disappearance of species in the area, mainly large migratory fishes that have a life cycle intimately linked to the elevation of the fluviometric level (Agostinho et al, , 2004.…”

Impact of the Three Gorges Dam on reproduction of four major Chinese carps species in the middle reaches of the Changjiang River

“…These eff ects have been reported on many rivers around the world, including the Parana River in Brazil (Sanches et al, 2006), the Sinnamary River in France (de Mérona et al, 2005), and the Colorado River Basin in the USA (Clarkson and Childs, 2000). These results have lead to proposed conservation measures, such as releasing more water to maintain minimal ecological fl ow (Agostinho et al, 2004) or creating artifi cial fl oods (King et al, 2010).…”