Persistence of fish populations in the upper Paraná River: effects of water regulation by dams

Abstract

– River–floodplain systems present intense temporal variations in physical, chemical and biological factors. These variations are closely related to alterations in water levels, which have been attributed to the flood pulse. As several species are strictly related to the flood pulse to fulfil their life cycle, the pulse may be seen as a dispersal mechanism of species onto a floodplain. In this study, we determine how dam construction influenced the persistence of Prochilodus lineatus population, a large migratory fish species from the upper Paraná River floodplain. Data used were collected in two distinct periods, from April 1992 to March 1993 and from January 1999 to December 2001. Fish were collected using seining nets in six (monthly in the first period) and seven (quarterly in the second period) isolated lagoons. The fraction of occupied lagoons was high in the first period (higher than 0.65), when flood was intense. However, in the second period, when the flood pulse did not happen or was short, the fraction of occupied lagoons sharply decreased over time (from 0.85 to 0.22). For the first period, no model fitted to data, but for the second period, a negative linear model (named drought‐dependent model) presented good fit (r2 = 0.97). Therefore, it is possible to infer that long and intense flood pulses are important to maintain the persistence of P. lineatus populations in the floodplain. The artificial control of water levels prompted by dams disrupts this dynamic, reducing persistence to critical levels.

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

“…The reduction of the stress period linked to dry conditions when floods are long also favors juveniles. Additionally, long-lasting floods result in increased dispersion of migratory species, and the increase in connectivity allows colonization of more patches, favoring persistence through metapopulation dynamics (Gubiani et al, 2007).…”

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).…”

Temporal and Spatial Patterns of Fish Distribution and Diversity in the Noxubee River, Mississippi and Alabama

“…The construction of dams for the purpose of creating a navigation corridor has created a chain of sluggish reservoirs, canals, and cutoff bendways along the length of the TTW, potentially creating a barrier to fish dispersal (Pringle et al 2000). The fragmentation of river systems, disruption of natural hydrologic regimes, and creation of barriers to fish dispersal can lead to declining fish populations and the loss of aquatic diversity (Zwick 1992, Pringle et al 2000, Gubiani et al 2007, Taylor et al 2008). Hubbard (1987) sampled 79 locations during 1982 and 1983 in the Noxubee River drainage with rotenone and block nets.…”