The Role of Thermal Regime on Interspecific Competition Between Largemouth Bass and Smallmouth Bass in the Ozark National Scenic Riverways

A shift in species distribution and displacement caused by anthropogenic disturbance and climate change may affect how agencies manage and conserve fish populations. The Ozark National Scenic Riverways, in southeast Missouri, USA, has populations of both Smallmouth Bass Micropterus dolomieu (SMB) and Largemouth bass Micropterus salmoides (LMB) with SMB historically dominating. The Riverways are influenced by several large springs distributed longitudinally through the park which greatly influence its thermal regime. However, with warming temperatures LMB and piscivore species may become more abundant, displacing the dominating SMB. We used fish community samples from seven sites sampled seven times from 2005-2013 to determine if abundance, size structure, and condition of SMB are influenced by LMB or piscivore (LMB, chain pickerel, shadow bass, spotted bass, and yellow bullhead) abundance.  Additionally, water temperature, discharge, and wetted width were compared to SMB, LMB, and piscivore abundances. Our results reveal that SMB abundance increased with discharge and decreased with temperature whereas LMB and piscivores abundance decreased with discharge and increased with temperature. Our results suggest that increased temperatures within the range of tolerability to a given species may create an increase in competitive interactions thereby causing their displacement.