Role of water availability on fish assemblage structure: effects of agricultural land use and spawning mode

Abstract

The availability of water has been changing as human demands increase, weather patterns change, and land use is altered. This is a common trend throughout the world as well as in the tributaries of the Middle Chattahoochee River Drainage. While many studies have examined the effects of drought on fish assemblages, few have studied long-term decreases in water availability and associated fish assemblage changes. The aim of this study was to examine the effects long- and short-term effects of water availability on fish assemblages. Stream discharge has steadily decreased in the study area over the last 50 years, leading to fish assemblage homogenization over time. Species that prefer or tolerate low flow conditions such as Cyprinella venusta, Lepomis auritus, and Percina nigrofasciata are becoming dominant and replacing historically dominant species such as Notropis hypsilepis, Lythrurus atrapiculus, and Notropis cummingsae. When looking at short term changes between a dry year and a wet year, some species preferring higher flows, such as Notropis hypsilepis, have recovered when water returns after a drought, suggesting that the amount of water is important for the persistence of some species. Land use changes in relation to water availability have also been observed to play a role in fish assemblage homogenization. We believe these changes are occurring based on differential spawning modes. Species that can reproduce successfully in low flow conditions are thriving and expanding their native ranges while species that require higher flows for successful reproduction however are declining overall, despite temporary recovery during wet years.