The Influence of Record Discharge on the Small-Bodied Fish Community in a Portion of the Missouri River

During the summer of 2011, the Missouri River system experienced the largest ever recorded discharge since the closing of its mainstem dams in the 1960’s (i.e., an approximate four-fold increase above normal). Extensive floodplain inundation occurred, providing important shallow-water habitats for small-bodied fishes. The objective of this study was to compare the relative abundance (CPUE) of small-bodied fishes captured with mini-fyke nets (n = 72) in 2011 to CPUE during years (2005–2010) of normal discharge between Fort Randall and Gavins Point dams in the Missouri River. The overall mean CPUE (n per net night) was larger (0.685) in 2011 compared to previous years (< 0.523). Black bullhead Ameiurus melas and gizzard shad Dorosoma cepedianum CPUE increased 4,074% and 1,244%, respectively. Large numbers of rainbow smelt Osmerus mordax were sampled in 2011 (CPUE = 1.429) compared to previous years (< 0.075) due to entrainment from upstream reservoirs. In 2011, mean CPUE for black crappies Pomoxis nigromaculatus, bluegills Lepomis macrochirus, freshwater drum Aplodinotus grunniens, and yellow perch Perca flavescens were the largest recorded. Conversely, mean CPUE for johnny darters Etheostoma nigrum, saugers Sander canadense, and white crappies P. annularis were the lowest ever observed. Overall, the large discharge in 2011 was associated with a general abundance increase in many small-bodied fish species in the Missouri River downstream of Fort Randall Dam. However, relative abundance of some species remained unchanged or decreased, possibly a result of export or mortality of pelagic eggs or fry by sustained high discharge.