Lock and Dam Construction Changes a Large River Fish Assemblage Structure

Abstract

The Southeastern United States is rich in freshwater diversity. However, habitat alteration has a profound impact on fish assemblages across this region. The Red River, Louisiana has historically been diverse in fishes. In the 1980's and 1990's five lock and dams were constructed on the Red River to facilitate watercraft traffic. To assess assemblage changes attributable to lock and dam construction, we analyzed historical survey data from the Red River between 1966 and 2002. We compared changes in assemblages following lock and dam construction using species composition and richness, life history strategies, Rao's quadratic entropy, and functional redundancy. The results showed similar species richness across time but assemblage composition shifts after dam construction with distinct periods corresponding to pre-construction, during construction, and post-construction of lock and dams. Life history analyses were similar, with the time periods after dam construction showing a rapid decline in Periodic species and an increase in Equilibrium species. Rao's quadratic entropy also decreased in the periods after dam construction with a simultaneous increase in functional redundancy. In utilizing multiple methods, we were able to detect different aspects of assemblage change across both taxonomic and functional metrics with high duration temporal data. These results link life history theory to environmental changes and provide an empirical basis that may be used to assess or predict change of large river fish assemblages under alteration of lock and dam construction.