Spatial and temporal variation in fish assemblage of the Lower Pecos River, TX

Most river systems have been heavily impacted by human alterations that have long-term ecological consequences. The lower Pecos River in the Trans-Pecos region of Texas has undergone anthropogenic changes that include decreased flow, elevated salinity, species loss, and species invasion. Comparative studies are important to determine the long-term effects of these changes on fish assemblages. I compared historical and contemporary fish assemblages from the Pecos River at local (site-specific) and regional (Trans-Pecos region) scales across 24 years. Fish assemblage data were collected during two time periods, October 1987 and 2011, by seining at 15 sites spanning 430 km of the river in Texas. Additionally, I examined contemporary environmental conditions to determine species-environment relationships. I found that fish assemblages were significantly different between time periods, likely due to increased salinization caused by irrigation and oil field pollution. Decreased species richness, species replacement, and increases in tolerant species were documented in the upstream sites. Freshwater springs lower the salinity in the downstream reach which allows for higher species diversity. Better management of regional aquifers, changes to irrigation practices, mitigation of petroleum waste water, and proper flow regulation are necessary for protecting biodiversity in the lower Pecos River.