Bonner, TimothyKollaus, Kristy A.2020-06-122020-06-122009-08Kollaus, K. A. (2009). Fish assemblage structure and associations with environmental conditions in a Texas spring-fed river (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.https://hdl.handle.net/10877/11625Numerous spring systems in the Edwards Plateau and Trans-Pecos regions of Texas support parapatric fish assemblages, spring-associated species and riverine species. Previous studies have identified constant water temperature as the segregating factor but have lacked the ability to effectively distinguish temperature from headwater influence. Multiple spring sources along a 64 km course of the Devils River, Texas allowed an opportunity to assess the influence of temperature and other variables (i.e., current velocity, depth, and substrate) on spatial and temporal patterns in the fish assemblage Physical parameters (10.6%), site (4.9%), and season (1.6%) explained 19.6% (CCA, P<0.01) of the Devils River fish assemblage. Current velocity, depth, and vegetation were among the strongest factors explaining fish segregation. Astyanax mexicanus and Cyprinella proserpina were generally found in riffle habitats, Etheostoma grahami, and Notropis amabilis were found in runs with moderate current velocities and depths, and, Micropterus salmoides, Lepomis macrochirus, and Dionda diaboli were more associated with deeper, vegetated pools. Water temperature influenced seasonal movement of spring associated species (i.e., A. mexicanus, N. amabilis, C. Proserpina, Dionda argentosa, and E. graham) into spring outflow habitats during summer and winter and resulted in a segregated assemblage. Surprisingly, the abundance and distribution of the federally threatened Dionda diaboli, a species listed as a spring-associate, did not correlate with spring outflows and was present throughout the Devils River. This study suggests spring flow (i.e., current velocity and depth) and constant water temperature are segregating factors and important for maintaining parapatric assemblages.Text43 pages1 file (.pdf)enfish communitiesenvironmental aspectsfishesgeographical distributionhabitatsDevils RiverThesis