Fish communities are often used as indicators of environmental quality, and may be especially useful assessors of climate change impacts on environmental flows associated with drought and flood. We used a paired spring-fed river system in the Texas Hill Country to assess drought and intermittent flows effects on fish assemblages in the North (NLR) and South Llano (SLR) rivers. Although both rivers are spring fed, the discharge from the North is much lower that the South and the NLR becomes intermittent in summers. Superimposed on these natural flow regimes, Texas experienced a severe drought in 2011 that continued through May 2015. To determine if drought and intermittency patterns were related to patterns of fish community structure, we measured flow and conducted 3, 10-day summer sampling events at 4 sites in each river using seine hauls (6) and backpack shocking to collect fish. Our specific objectives were to: 1) compare fish diversity, trophic structure, mesohabitats and IBI characteristics of the NRL and SLR, 2) effect of temporal flow changes and 3) management considerations.
SLR had an average discharge of 61 cfs compared to the NLR’s 7.5 cfs. Mesohabitat characteristics of sample sites for the 2 streams were comparable - SLR: 25% Riffles 65% Runs and 10% pools and NLR: 25% riffles, 49% Runs and 26% pools. Both streams were similar in species richness (SLR – 22, NLR – 21), dominant species (in order, Cyprinella venusta, Notropis amabilis and Dionda nigrotaeniata) and IBI measures of water quality showing exceptional aquatic life use (score of 52). Green Throat darters more prevalent in NLR (104 to 19) (3.15% of community to 9%). Channel catfish were more prevalent in the NLR (49 to 8) (1.5% of community to .4%). Orange throated darters are more prevalent in SLR (21 to 5) (1% of community to .2%). Invertivores were the dominant trophic group. surprisingly, the two rivers were similar in assemblage structure even in response to the differences in discharge. This suggests refugia play an important role in maintaining community structure to recurring short term summer intermittency episodes in the NLR and indicates fish communities in Texas Hill Country rivers have some resiliency capacity to drought.