Fragmentation of a Neotropical migratory fish population by a century-old dam

Abstract

Loss of connectivity in impounded rivers is among the impacts imposed by dams, and mitigation measures such as fish passages might not accomplish their purpose of reestablishing an efficient bi-directional gene flow in the fish populations affected. As a consequence, fish populations remain fragmented, and a new interpopulational structure may develop, with increased risk of reduced genetic diversity and stochastic extinction. In order to evaluate the effects of the Gavião Peixoto Dam, which was constructed almost a century ago on the Jacaré-Guaçu River in the Upper Paraná River basin, Brazil, a comparative morphometric study was undertaken on the populations of the Neotropical migratory characid fish Salminus hilarii living up-and downstream of this dam. Population dynamics, spatial segregation, and habitat use by different age classes were monitored for 2 years. We found that segregation caused by the dam and long periods with no efficient connection by fish passages have led to fragmentation and interpopulational structuring of S. hilarii, as revealed by canonical variable analysis of morphometric features. The fish populations occupying the up-and downstream sections have succeeded in performing short-distance reproductive migrations in the main river and tributaries, have found suitable habitats for completing their life cycle, and have been able to maintain distinct small-sized populations so far.

Genetic diversity of pacu for restocking programs in the Tietê and Grande rivers, Brazil

“…Thus, subpopulations may have been clustered into new groups of different genetic pools in every water reservoir. Contextually, Esguícero and Arcifa (2010) analyzed the morphologic characteristics of Salminus hilarii up-and downstream of the Gavião Peixoto dam (built in 1913) on the Jacaré-Guaçu River in Brazil and reported interpolated fragmentation and structures similar to the results of the current study. Similarly, Yamamoto et al (2004) evaluated the genetic differences of eleven WPs of Salvelinus leucomaenis in Japanese rivers, also affected by dams.…”

The fish fauna of the Jacaré-Guaçu River basin, Upper Paraná River basin

“…According to some authors (Peres Neto et al 1995, Uieda & Barreto 1999, Súarez 2008, several ecological factors, such as food availability and habitat structure, can be responsible for the fish fauna composition and diversity. The existence of a higher floodplain area downstream the Gavião Peixoto Dam (Esguícero & Arcifa 2010b), and the free section downstream the Jacaré-Guaçu River confluence with the Tietê River (downstream the Ibitinga Dam), could support a higher number of fish species in that stretch. Another factor is that depth of the water body can positively influence the population size and the number of fish species (Súarez 2008), what was also observed in this study.…”

Phenotypic differentiation of Barilius bendelisis (Cypriniformes: Cyprinidae) in four rivers from Central Indian Himalaya

“…It has been suggested that the morphometric differentiation of a fish can be influenced by genetic, environment and the interaction between them (Mir et al, 2013). Apparently, the fragmentation of river impoundments can lead to an enhancement of pre-existing genetic differences, providing a high interpopulational structuring (Esguicero, & Arcifa, 2010). The influences of environmental parameters on morphometric characters have been well discussed by several authors in the course of fish population segregation (Swain, & Foote, 1999).…”