Fish assemblages and habitat conditions of oxbow lakes and the main channel of the middle-lower Brazos River, a meandering lowland river in east central Texas, were investigated during summer 1994. All oxbows were eutrophic, with chlorophyll-a levels of up to 640 μg/L. Assemblage structure showed large between-lake variation that was explained by both physical and biotic variables, with combinations of water depth, dissolved oxygen, dissolved nutrients, turbidity, and plankton densities accounting for 45–59% of the variation in abundance of the dominant species. Water depth and dissolved nutrient concentrations were the best predictors of species diversity and fish abundance. Periodic desiccation of shallow, vegetated oxbows created harsh conditions that favored small fishes that are efficient colonizers. The two youngest oxbows were relatively deep and contained a high diversity and biomass of fishes. Of the 42 fish species collected, several were largely restricted to oxbow lakes, and others were either entirely restricted to or common only in the river channel. The flood dynamics of Brazos River floodplain habitats are less predictable (both intra- and interannually) than are those of large temperate rivers that receive runoff from snowmelt or predictable spring rainfall. As a result, Brazos River oxbow lakes remain separated from the river channel for many months or years, such that faunal exchange between oxbows to the channel should be pulselike and irregular.
|Original language||English (US)|
|Number of pages||18|
|Journal||Transactions of the American Fisheries Society|
|State||Published - Mar 2000|
Bibliographical noteFunding Information:
We thank the following landowners for sharing historical information and for granting us access to study sites: D. Lightsey, J. T. Lyons, T. Arho-pulos, J. R. Siegert, B. Look, R. B. Woodley, D. Matthews, J. C. Jones, G. Brandt, E. Malin, and U. Diemer. We are grateful to the following individuals for their valuable assistance during field sampling: A. Adite, D. Jepsen, L. Moriarty, N. Valdes, B. Blackwell, H. Elder, B. R. Murphy, E. Moeller, Z. Homsley, E. Porter, B. Heyer, L. McCallum, and T. Tucker. We thank B. R. Murphy for funding our first reconnaissance flight. We also thank M. Stellbauer of the Soil Conservation Service for assistance in identifying landowners. Collections were made under TPWD permit SPR-0193-580. Funding was provided by a research enhancement program grant from the Texas Agriculture Experiment Station. This research was conducted under TAES Project 8258.