Larval Fish Assemblages of Three Eastern South Dakota Rivers

Frequent disturbances and extreme environments make prairie streams, such as those in eastern South Dakota, highly unpredictable. Fishes in these streams have adopted reproductive strategies that allow for rapid recolonization after frequent and sometimes intense floods and droughts. New stresses, such as the recent introduction of the invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix, may affect the ability of native fishes to exploit favorable conditions for recolonization after major disturbances. Evaluating the reproductive success of fish in eastern South Dakota rivers can provide insight into how native populations respond to disturbances. Our first objective was to characterize the larval fish assemblage in the lower James River, South Dakota in four disparate hydrological years: pre-flood drought (2003 and 2004), flood (2010), and post-flood drought conditions (2012). We compared diversity across years using a variety of methods and found that hydrology played an important role in both taxa richness and abundance. There was high taxa richness but low abundances of larval fish in pre-flood drought years (2003 and 2004), low richness and abundances in the flood year (2010), and low richness but high abundances in the postflood drought year (2012). Our results suggest that fish increased reproduction following a major flood event, allowing for recolonization. Our second objective was to characterize drifting larval fish assemblages in three major tributaries to the Missouri River in eastern South Dakota from 2010 through 2012. We used both alpha and beta diversity measures to compare within rivers or sample sites across years and found that fish assemblages in our study rivers are comprised mainly of opportunist-like species. The use of protracted spawning and spawning cues such as water temperature and decreasing discharge allowed fishes to concentrate reproductive efforts and maximize the potential for successful recruitment. Recolonization processes will become increasingly important for sustainability of fish species in Great Plains streams as new stressors such as invasive species, global climate change, and land use changes threaten these already-endangered biomes