Assessment of Mussel and Fish Communities in a Northern Chihuahua Desert Stream with Recommendations on Biomonitoring
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The Delaware River, located in the northern Chihuahua Desert of Texas and New Mexico, is a moderately saline tributary of the middle Pecos River and provides habitat for state-listed and federally-listed aquatic organisms. Oil and gas extraction has increased within the northern Chihuahua Desert with over 51,000 oil and gas wells drilled within and near the Delaware River basin since 2012. Purposes of this study were to document existing mussel and fish communities within the Delaware River -Texas Reach, a reach of the river poorly documented in the past because of limited access, and to develop a biomonitoring plan for future assessment of stream health within the river. Study objectives were to quantity riverine habitats, mussels, and fishes within the Delaware River across multiple sites and years and to validate the appropriateness of using regionalized Indices of Biotic Integrity (IBI) for biomonitoring. Three reaches were sampled across seasons between 2016 and 2020. Live freshwater mussels were not detected among the nine sites, but multiple long-dead valves of the Texas Hornshell Popenaias popeii were found. Fish communities shifted from upstream to downstream, attributed to a longitudinal specific conductance gradient with fresher water upstream and more saline water downstream. A total of 16,027 fishes was collected and 13 species were identified among 143 mesohabitats. Fish communities shifted from upstream to downstream, attributed to a longitudinal specific conductance gradient with fresher water upstream and more saline water downstream. The most abundant species was Mexican Tetra Astyanax mexicanus in the Spring season and Cyprinella lutrensis in the Summer season. Notable fishes included populations of the state-listed Headwater Catfish Ictalurus lupus but was hybridized with the Channel Catfish Ictalurus punctatus, and Gray Redhorse Moxostoma congestum. Gray Redhorse was recently introduced into the Delaware River to serve as the host fish for Texas Hornshell (Bivalvia). Two regionalized IBIs metrics (i.e., Desert Ecoregion, Western High Plains and Southwestern Tablelands Plains ecoregions) were assessed on the Delaware River mainstem communities. Delaware River fish communities were more similar (mean Renkonen Similarity Indices among metrics: 43%) to the Western High Plains and Southwestern Tablelands Plains ecoregions metrics than to the Desert Ecoregion metrics (10%). Consequently, I recommend the use of the Western High Plains and Southwestern Tablelands Plains ecoregions metrics for future biomonitoring of the Delaware River.