The rise and fall of fish diversity in a neotropical river after impoundment

Abstract

In contrast to the fast-paced dam construc- tion and river ecosystem alteration which is taking place in the neotropics, ecological knowledge about the effects on fish fauna are still scarce. To contribute with knowledge on the effects of damming on fish fauna, we assessed the response of fish assemblages to the construction of a run-of-the-river dam in an Amazonian river by selecting eight sampling sites along a longitudinal gradient in the vicinity of a new hydroelectric dam. Sites were sampled monthly through a 1-year period before dam closure (2004-2005), 1 year after closure (2006-2007), and 5 years after closure (2011-2012). Following dam closure, there was an initial overall increase in fish abundance and richness across sites. However, despite the initial upsurge, after 5 years, populations were reduced and communities contracted to a level of diversity below that observed prior to dam closure. Respective sites demonstrated distinct ecological responses that were related to the environmental characteristics of their transformed habitats. Important changes in fish assemblages were visible in a short- term period of 5 years after dam closure. Therefore, monitoringfishspecies assemblagesina longertermis important to assess the consequences of a decrease in diversity.