The Response of Nekton Communities of the Lower Brazos River Estuary, Texas to Varying Freshwater Inflow

The Brazos River, Texas functions as a Riverine estuary flowing directly into the Gulf of Mexico. The objectives of our study were to 1) characterize the freshwater inflow regime and 2) assess the influence of hydrology on water quality and nekton of the lower Brazos River. During November 2014 to March 2015 we collected data on the hydrology, water quality and nekton. This information was compared with historical data collected during January to December 2012 by Miller (2014), and during February 1973 to January 1975 by Johnson (1977).  Distinct geographical and temporal patterns in salinity, dissolved oxygen, and nekton communities were observed.  NMDS and nonlinear model results indicate that these patterns were primarily related to the timing, magnitude and duration of freshwater discharges, and the seasonality of immigrating immature estuarine nekton. The diversity and richness of nekton was generally highest at the downstream sites closest to the Gulf of Mexico where salinity and dissolved oxygen values were highest. All studies documented strong vertical and horizontal salinity gradients and bottom hypoxia during summer low flow periods when the halocline extended up to 42 km upstream.  During these periods catches of nekton were low or absent in bottom trawls.