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Water quality and quantity within the upper San Antonio River (Bexar County, Texas) were supported historically from spring flows of the Edwards Aquifer. Since the 1700s, water quality, quantity, physical aquatic habitats, and presumably fish communities have been altered in the upper San Antonio River, including loss of spring flow and replacement of base flow by treated wastewater. The upper San Antonio river fish community provides a unique opportunity to fill a gap in knowledge on spring-associated fish responses to spring flow loss. The purpose of our study was to describe temporal changes in the upper San Antonio River fish community in relation to increased anthropogenic alterations from reported fish collections and infer from reference conditions. Comparisons with reference conditions were necessary since anthropogenic alterations occurred before the first fish collections within the basin. We found the upper San Antonio River fish community changed through time with increases in native and introduced fishes and decreases in spring-associated fish richness and relative abundances. Decreases in spring-associated fish richness and relative abundances were attributed to decreases in spring flow and to changes in water quality; however, specific mechanisms between loss of spring flow and spring-associated fishes are unknown at this time. Quantifying historical fish community changes through time in systems with a long history of urbanization is difficult, but our assessment provides a greater understanding of how spring flow loss due to increasing water demand in highly urbanized areas can alter communities with spring-associated species.

Pelagic broadcast spawning cyprinids are a mobile group of fishes commonly found within semi-arid areas of the Great Plains of North America. In several species, upstream movements of 50 to 200 km have been reported and associated with reproductive migration. Long distance migrations also are associated with finding food and refuge. Goals of this study were to detect synchronous movement of Prairie Chub at specific life stages and relate movement to functions associated with migration (i.e., reproduction, feeding, and refuge). Movement was inferred by quantifying monthly occurrences of age groups using length frequency distributions among five sites in two rivers and supported with range-wide assessment of genetic structuring. Monthly occurrences of age groups among sites were related to reproductive season (i.e., gonadosomatic indices, ovarian condition) for assessing reproductive migration, to food consumption (i.e., gut content assessments) for assessing feeding migration, and to habitat associations (e.g., specific conductance) for assessing refuge migration. Spatial and temporal patterns in age-0, age-1 and age-2 fish occurrences and abundances suggested movement within only one river. Non-synchronized movements were more consistently associated with specific conductance following a high flow event, which was more consistent with a refuge function than reproductive season or food consumption. Our findings suggest that Prairie Chubs are capable of moving long distances, but movement was inconsistently associated with reproductive efforts as previously described. Without synchronized movements, we question whether movement is migration or dispersal and provide a contrasting narrative to the drift compensation theory used to describe broadcast spawning cyprinid migrations.

Purposes of this study were to assess population status and life history attributes of the Texas Shiner Notropis amabilis, a minnow endemic to the Edwards Plateau region in Texas and the Rio Grande drainage of U.S.A. and Mexico. Despite possible extirpation from three stream reaches, populations of Texas Shiners persist with abundances categorized as occasional and frequent among multiple and independent stream reaches, streams, and drainages. Therefore, Texas Shiner population is considered stable. Quantification of life history traits suggest Texas Shiner has a protracted reproductive season (i.e., 9 mo), a life span of 2 y, and feeds on primarily aquatic invertebrates. Protracted spawning seasons are consistent with Texas Shiner's reported associations with spring systems of the Edwards Plateau. Current and future conservation of N. amabilis and other spring-associated fishes are explicitly linked to spring complexes, although exact mechanisms of association are unknown.

We report the occurrence of a single population of Etheostoma parvipinne (Goldstripe Darter) in a small, acidic, spring-fed stream within the Colorado River drainage following an extended period of below-average precipitation (January–September 2011), a wildland fire (September 2011), and subsequent debris and sediment flows (November 2011–May 2012). Goldstripe Darters were taken from Alum Creek (Bastrop County, TX) along with a cyprinid, a poeciliid, and several species of centrarchids in June 2012. Occurrence of Goldstripe Darters in Alum Creek provides a regional example of fish-community responses to wildland fires. In additio n, understanding the mechanism of long-term persistence in a single tributary on the periphery of a species range might offer insight into the origin of endemic fishes and persistence of disjunct fish populations within aquatic evolutionary refugia of central Texas.

Within its southwestern native range, Ameiurus nebulosus (Brown Bullhead) had been found in the Red River drainage within Oklahoma, Arkansas, and Louisiana but not Texas. We report for the first time the occurrence of Brown Bullhead within the Cypress River system of Texas, a tributary of the Red River. We tentatively conclude that the Cypress River system of Texas is within the natural range of Brown Bullhead, but we cannot exclude human introduction as a possible mechanism for its occurrence, given that Brown Bullhead are introduced worldwide.

Aquifers and spring complexes within the arid and semi-arid karst Edwards Plateau region of Texas are evolutionary refugia supporting a large number of endemic flora and fauna. Spring fishes, many of which are endemic, are associated with the spring complexes, whereas river fishes generally avoid spring complexes. Purposes of this study were to experimentally test affinities of spring fishes and river fishes for spring complexes and rivers among six independent spring-river systems of the Edwards Plateau and to quantitate relationship among spring fishes, river fishes and spring flow magnitude within spring complexes. We found that spring fishes did not exclusively use spring complexes but were more abundant in spring complexes than rivers and that species richness, relative abundance, and density of spring fishes were directly related to spring flow magnitude. Patterns in affinities for river fishes were less distinct. Quantitation of fish–habitat relationships will assist efforts in conserving aquatic resources within the Edwards Plateau and provides predictive models to assess biological integrity of other spring complexes. In addition, consistency in distributional patterns of spring and river fishes provides a framework for testing underlying processes of species segregation and diversification, establishes boundaries of aquatic evolutionary refugia, and expands the value of evolutionary refugia from historical refugia to contemporary and future refugia for Edwards Plateau aquatic biota.

Freshwater fish communities segregate along water temperature gradients attributed in part to temperature-mediated physiological processes that affect species fitness. In spring complexes of southwest USA, spring complexes with narrow range of water temperatures are dominated by a community of fishes (i.e., spring-associated fishes), whereas riverine habitats with wide-range of water temperatures are dominated by a different community of fishes (i.e., riverine-associated fishes). The purpose of this study was to test a prediction of the concept that temperature-mediated species performance is a mechanism in maintaining community segregation. We predicted that a spring-associated fish (Largespring Gambusia Gambusia geiseri) would feed first and more often in a pairing with a riverine-associated fish (Western Mosquitofish G. affinis) at an average spring temperature (23 °C) and that the riverine-associated fish would feed first and more often in a pairing with the spring-associated fish at a warm riverine temperature (30 °C). Among four trails consisting of 30 pairings, at the spring complex temperature (23 °C), Largespring Gambusia had a greater number of first feeds (mean ± 1 SD, 5.0 ± 0.82) than Western Mosquitofish (2.5 ± 1.73) and had greater mean number of total feeds (1.9 ± 0.31) than Western Mosquitofish (0.81 ± 0.70). At the riverine environment temperature (30 °C), Western Mosquitofish had a greater number of first feeds (5.25 ± 1.71) than Largespring Gambusia (2.5 ± 1.73) and had greater mean number of total feeds (2.78 ± 1.05) than Largespring Gambusia (0.94 ± 0.68). Our findings suggest that temperature-mediated species performance could be maintaining segregation between the two fish communities. This study benefits our understanding of distributional patterns and improves threat assessments of stenothermal aquatic organisms.