Evaluating Effects of Drought and Anthropogenic Influences on the Growth of Stream Fishes on the Edwards Plateau, Central Texas

Home , Blanco River (Texas)

Evaluating effects of drought and anthropogenic influences on the growth of stream fishes on the Edwards Plateau, Central Texas

Wade A. Massure

A Thesis

Wildlife, Aquatic, and Wildlands Science and Management

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE

Approved

Dr. Timothy Grabowski Chair of Committee

Dr. Tom Arsuffi

Dr. Nathan Smith

Dr. Mark Sheridan Dean of the Graduate School

August, 2016

Texas Tech University, Wade A. Massure, August 2016

ACKNOWLEDGEMENTS

This project was made possible by funding from Texas Tech University Llano

River Field Station, Texas Tech University Graduate School, Texas Cooperative

Fisheries and Wildlife Research Unit and the Department of Natural Resources

Management. This work was conducted under the auspices of the TTU Animal Care and

Use (AUP #14020-03). I thank my committee chair and major advisor, Dr. Timothy

Grabowski, for helping me improve not only as a student but as a biologist and for always being available to provide assistance and guide me through my master’s project. I also thank my other committee members, Drs. Tom Arsuffi and Nate Smith, who were always available to help and provide support throughout my project. I am grateful to the amazing staff at Texas Tech University-Junction Campus for their hospitality during my sampling events in the Texas Hill Country and the staff at Texas Parks and Wildlife Heart of the Hills Research Fisheries Science Center for their support.

The completion of this project would not have been possible without the assistance and willingness to help of all the other members of the Grabowski Lab, especially Matthew Acre, Preston Bean, Heather Williams and Scott Hill. I want to especially thank Jessica Pease, who was always there to provide support and power through those long sleepless nights removing fish otoliths, and Jessica East whose support and guidance helped me get through some difficult points throughout the duration of my thesis. Lastly, I am grateful for my amazing and supportive family and friends who were always there for me when I needed them.

Texas Tech University, Wade A. Massure, August 2016

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ...... ii ABSTRACT ...... v LIST OF TABLES ...... vi LIST OF FIGURES ...... ix LIST OF APPENDICES ...... xi I. INTRODUCTION ...... 1 II. METHODS ...... 7 Study Area...... 7 Fish Collection...... 8 Otolith Preparation and Interpretation...... 10 Acquisition and Analysis of Discharge Data...... 11 Fish Growth...... 12 Data Analysis...... 12 III. RESULTS ...... 17 Annual Stream Flow Metrics...... 17 Species Abundance...... 17 Species-Specific Growth ...... 18 Lepomis Species ...... 18 Micropterus Species ...... 19 Other Species ...... 20 Feeding Guild ...... 21 Reproductive Guild ...... 22 IV. DISCUSSION ...... 42 Lepomis species ...... 44 Micropterus species ...... 47 Other Species ...... 51 Feeding Guild ...... 56 Reproductive Guild ...... 58 Management Implications ...... 59 LITERATURE CITED ...... 61

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APPENDICES ...... 77

Texas Tech University, Wade A. Massure, August 2016

ABSTRACT

Drought and flow regime alteration have the potential to affect fish growth through numerous ecological and physiological mechanisms, and in so doing, can greatly influence demographic processes, such as recruitment and mortality. Changing climate patterns and increasing water demands from a rapidly growing human population has made understanding these effects critical to the conservation and management of stream fishes on the Edwards Plateau in central Texas. My objective was to evaluate the influence of annual flow regime on the growth rates of a suite of stream fishes within a paired river system in central Texas. The North Llano River (NLR) and South Llano

River (SLR) are adjacent low-order, spring-fed streams of similar size that differ greatly in their flow regimes due to differences in spring inflows and anthropogenic water withdrawals. I extracted otoliths from eleven stream fish species common to both the

NLR and the SLR and used them to back-calculate lengths at age. I used mixed-effect models to evaluate the influence of annual flow metrics on growth. Response to annual flow metrics, particularly during drought conditions, was species-specific, and varied between the two river systems. In general, the North Llano River was influenced by the extent and duration of flow events, and the South Llano River was influenced by monthly flows and can be seen in species such as Redbreast Sunfish and Guadalupe Bass. My results will provide a better understanding of how drought, coupled with anthropogenic alterations, affects the growth rate of stream fishes. Results from this study can provide guidance for the management and conservation of stream fishes relative to water use and instream flows.

Texas Tech University, Wade A. Massure, August 2016

LIST OF TABLES 1. Feeding and reproductive guilds, overall number of individuals, mean age in years (±SD), age range, mean total length (TL) (±SD), length range, and generated growth curve parameter estimates for eleven of the dominant large-bodied fish species captured in the North Llano River and South Llano River in central Texas from 2014-2015...... 15 2. List of Index of Hydrological Alteration discharge metrics (Richter et al. 1996) with associated eigenvectors from a principle components analysis describing the annual flow regimes of the North Llano River from 1916- 1977 and 2001-2015 and South Llano River from 1960-1977 and 2001- 2015 in central Texas. Eigenvector values of principle component 1 and 2 arranged by major hydrological grouping where values ≥ 0.15 were used in axis interpretations. Principle component 1 largely separated the two rivers, and drought, flood and “normal” years. Principle component 2 separated out the variability of magnitude, duration and of flow between each river...... 23 3. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river, fish age and PC scores of annual flow metrics and their influence on growth rate residuals for all ages of five sunfishes (Lepomis spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Bluegill and Warmouth models incorporated the effect of the interaction between PC scores and each river as it was found to be significant for these species. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 24 4. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river, fish age, and PC scores of annual flow metrics and their influence on growth rate residuals for all ages of two black bass (Micropterus spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 25 5. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river, fish age, and PC scores of annual flow metrics and their influence on growth rate residuals for all ages of Gray Redhorse, Rio Grande Cichlid, Channel and Flathead Catfish captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 26 6. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river and PC scores of annual flow metrics and

Texas Tech University, Wade A. Massure, August 2016

their influence on growth rate residuals during the first year of growth of five sunfishes (Lepomis spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Bluegill model incorporated the significant effect of the interaction between PC scores and each river. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 27 7. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth of two black basses (Micropterus spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 28 8. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth for Gray Redhorse, Rio Grande Cichlid, Channel and Flathead Catfish captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 29 9. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age, and PC scores of annual discharge metrics and their influence on standard growth of all ages of the representatives of two feeding guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Carnivorous guild consists of Largemouth Bass, Guadalupe Bass, Green Sunfish and Warmouth and incorporated the effect of the interaction between PC scores and each river as it was significant to this guild model. Piscivorous guild consists of three Lepomis spp. (Bluegill, Longear Sunfish and Redbreast Sunfish) and incorporated the effect of the interaction between age and each individual species as it was significant to this model. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 30 10. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age, and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth of two reproductive guilds captured from the North Llano and South Llano Rivers in central Texas during 2014- 2015. Polyphilic guild consists of both Mictropterus spp. and four Lepomis spp. (Green Sunfish, Warmouth, Bluegill, and Longear Sunfish) and incorporated the effect of the interaction between PC scores and each river as it was significant to this guild model. Lithophilic guild

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Texas Tech University, Wade A. Massure, August 2016 consists of Gray Redhorse, Redbreast Sunfish, and Rio Grande Cichlid. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 31

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LIST OF FIGURES

1. Map of the locations that stream fishes were sampled in the North Llano River watershed and South Llano River watershed on the Edwards Plateau in central Texas during 2014-2015. Inset map shows location of study area in Texas...... 14 2. Median daily discharge rates taken from two USGS gaging stations (m- 3s-1) during 1916-1977 and 2001-2015 for the North Llano River (A) and 1960-1977 and 2001-2015 for the South Llano River (B), central Texas...... 32 3. Scatterplot of the two primary PC scores for flow years based on Indices of Hydrological Alteration variables (Richter et al. 1996; see Table 2) for the North Llano River (blue circles) from 1916-1977 and 2001-2015 and South Llano River (red circles) from 1960-1977 and 2001-2015 in central Texas. Years with associated fish age data collected in this study are labeled within the plot. Principle component 1 which explained 46% of the variance is on the X axis. It explains the separation of the two rivers and also separates drought, flood, and “normal” years for each river. Principle component 2 which explained 18% of the variance is on the Y axis. It explains the magnitude, duration, and frequency of flow between these rivers...... 33 4. Influence of annual stream discharge metrics on the standardized growth for all ages of Redbreast Sunfish (A), Green Sunfish (B), Warmouth (C), Bluegill (D), and Longear Sunfish (E) captured on the North Llano River and South Llano River in central Texas during 2014-2015...... 34 5. Influence of annual stream discharge metrics on the standardized growth during the first year of growth for Redbreast Sunfish (A), Green Sunfish (B), Warmouth (C), Bluegill (D), and Longear Sunfish (E) captured on the North Llano River and South Llano River in central Texas during 2014-2015...... 35 6. Influence of annual stream discharge metrics on the standardized growth for all ages of Largemouth Bass (A) and Guadalupe Bass (B) captured on the North Llano River and South Llano River in central Texas during 2014-2015...... 36 7. Influence of annual stream discharge metrics on the standardized growth during the first year of growth for Largemouth Bass (A) and Guadalupe Bass (B) captured on the North Llano River and South Llano River in central Texas during 2014-2015...... 37 8. Influence of annual stream discharge metrics on the standardized growth for all ages of Gray Redhorse (A), Rio Grande Cichlid (B), Channel Catfish (C), and Flathead Catfish (D) captured on the North Llano River and South Llano River in central Texas during 2014-2015...... 38

Texas Tech University, Wade A. Massure, August 2016

9. Influence of annual stream discharge metrics on the standardized growth during the first year of growth for Gray Redhorse (A), Rio Grande Cichlid (B), Channel Catfish (C), and Flathead Catfish (D) captured on the North Llano River and South Llano River in central Texas during 2014-2015...... 39 10. Influence of annual stream discharge metrics on the standardized growth of all ages of fishes in carnivorous (A) and piscivorous (B) feeding guilds captured from the North Llano River and South Llano River in central Texas during 2014-2015. The carnivorous guild consists of Guadalupe Bass, Largemouth Bass, Green Sunfish and Warmouth. The piscivorous guild consists of Bluegill, Longear Sunfish, and Redbreast Sunfish...... 40 11. Influence of annual stream discharge metrics on the standardized growth during the first year of growth of fishes in the polyphilic (A) and lithophilic (B) reproductive guilds captured from the North Llano River and South Llano River in central Texas during 2015-2016. The polyphilic guild consists of Guadalupe Bass, Largemouth Bass, Green Sunfish, Warmouth, Bluegill, and Longear Sunfish. The lithophilic guild consists of Gray Redhorse, Redbreast Sunfish, and Rio Grande Cichlid...... 41

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LIST OF APPENDICES 1. Pooled Von Bertalanffy growth curves based on back-calculated total length-at-age of Redbreast Sunfish (A), Green Sunfish (B), Warmouth (C), Bluegill (D), and Longear Sunfish (E) captured in the North and South Llano Rivers, Texas from March 2014 ─ November 2015. Green Sunfish growth curve is based on parameters taken from Rypel (2011) as there was not sufficient data to provide curve parameters for this species...... 77 2. Pooled Von Bertalanffy growth curves based on back-calculated total length-at-age of Largemouth Bass (A) and Guadalupe Bass (B) captured in the North and South Llano Rivers, central Texas from March 2014 ─ November 2015...... 78 3. Pooled Von Bertalanffy growth curves based on back-calculated total length-at-age of Gray Redhorse (A), Rio Grande Cichlid (B), Channel Catfish (C), and Flathead Catfish (D) captured in the North and South Llano Rivers, central Texas from March 2014 ─ November 2015...... 79 4. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age, and PC score describing annual flow metrics and their influence on standardized growth of all ages for the representatives of two reproductive guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The polyphilic guild consisted of Largemouth Bass, Guadalupe Bass, Green Sunfish, Warmouth, Bluegill, and Longear Sunfish. Lithophilic included Gray Redhorse, Redbreast Sunfish, and Rio Grande Cichlid...... 80 5. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age and PC score describing annual flow metrics and their influence on standardized growth during the first year of life of fishes from two feeding guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The carnivorous guild consisted of Largemouth Bass, Guadalupe Bass, Green Sunfish and Warmouth. The piscivorous guild consisted of Bluegill, Longear Sunfish and Redbreast Sunfish. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant...... 81

CHAPTER I INTRODUCTION

Drought, climate change, and anthropogenic flow alterations have all become recent issues in regards to how they affect stream fish populations and species assemblages (Ficke et al. 2007; Nelson et al. 2009; Palmer et al. 2009; Brander 2010).

Several anthropogenic influences have been shown to influence growth rates of fishes, such as nutrient loading (Schindler et al. 2000), altered temperature and siltation (Lotrich

1973; Berkman and Rabeni 1987; Nelson et al. 2009), and physical habitat alteration

(Schindler et al. 2000; Gilliers et al. 2006; Finstad et al. 2007). However, evaluations of the impact of drought and flow alteration together on fish growth are underrepresented in fisheries literature (Lake 2000; Matthews and Marsh-Matthews 2003). This area of study should be of increasing concern to biologists as drought is predicted to increase in both frequency and magnitude across many parts of the world in response to climate change

(Dai 2011). The impacts of more frequent and/or severe droughts on riverine fish populations is likely to be exacerbated by the anthropogenic flow alterations which have already occurred throughout a large proportion of the world’s rivers and streams

(Xenopoulos et al. 2005; Ficke et al. 2007). However, the precise nature of the interaction between flow alteration and drought is not well understood. Therefore, the purpose of this study was to assess how drought and anthropogenic flow alterations effect stream fish populations using growth as a proxy for many of the processes occurring in fish populations. Growth can provide an overall assessment of habitat suitability which can be used to evaluate management techniques, because it integrates the effects of water chemistry, food availability, and physiological conditions on individual fish (Murphy and

1 Texas Tech University, Wade A. Massure, August 2016

Willis 1996). However, studies of the relationships between anthropogenic flow alterations, environmental conditions, and fish growth in streams have been scarce

(Putman 1995).

Drought is a prolonged period during which precipitation is deficient relative to long-term climatic norms (National Weather Service 2008) and can vary greatly in spatial extent, temporal duration and degree of aberration from the long-term average. While a period of lower than normal precipitation totals has to persist for at least a season to be considered a drought (National Weather Service 2008), drought conditions can persist for years. Extreme drought can persist several years, even decades or centuries for so-called mega-droughts (Thornthwaite 1948; Dai 2011; Coats et al. 2013; Ault et al. 2014).

Drought is a recurring climate factor that has affected North America, types and definitions of drought have been assigned by the American Meteorological Society

(1997) into four different categories which include: meteorological or climatological, agricultural, hydrological, and socio-economical. All categories of drought affect stream and riverine ecosystems in some form. Of particular note is hydrological drought, which in arid and/or semi-arid regions and warmer conditions has a greater effect on surface and subsurface water supplies (Matthews and Marsh-Matthews 2003; CDWR 2012; Folger and Cody 2014), reducing stream flows, groundwater, reservoir, and lake levels and limiting habitat availability and altering habitat quality for many fish species (Heim Jr

2002). Recently, portions of western and southwestern North America have experienced historic drought conditions, but anthropogenic climate change is predicted to increase drought severity even further in the coming decades (Trenberth et al. 2004; Strzepek et al.

2010; Dai 2013) and lead to many changes in aquatic ecosystems, including increased

Texas Tech University, Wade A. Massure, August 2016 water temperatures, lower groundwater levels, and changes in stream flows (Lake 2003).

These changes are likely to cause interruptions in the flow regime of rivers and streams.

The flow regime of a river or stream is a defining characteristic and influences everything from stream geomorphology to fish assemblage structure to riparian corridors

(Gordon et al. 1992; Marchetti and Moyle 2001; Stromberg 2001; Poff et al. 2006). A flow regime is defined by five components: magnitude of flows, frequency of high and low flow events, duration of high and low flow events, timing of high and low flow events, and rate of change of stream flows (Richter et al. 1996; Poff et al. 1997). Natural flow regimes of rivers and streams worldwide are becoming increasingly modified due to many factors. Drought, anthropogenic climate change, and other more direct anthropogenic disturbances, such as agricultural withdrawals and diversions of surface flow have caused an increase in demand for water (e.g. dams being built to store water for economic development, and groundwater withdrawal for municipal and agricultural purposes) and have all contributed to altered flow regimes in varying degrees.

Modification of flow regimes through these processes directly affects aquatic species in streams and rivers worldwide (Poff et al. 1997; Milly et al. 2005). For example, the effects of urbanization can severely degrade these ecosystems by altering temperature, inputs (i.e. nutrients, contaminants, and sediment loads), and flashiness of discharge

(Wang et al. 2000, 2001; Paul and Meyer 2001; Morgan and Cushman 2005). Water withdrawals affect these ecosystems by reducing discharge which has been shown to impact fish size (Walters and Post 2008). Furthermore, water withdrawals have the potential to reduce stream connectivity, cause a loss of habitat volume (Labbe and Fausch

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2000), and influence the availability of food resources and water quality (Richter et al.

1996; Lake 2003).

Aquatic ecosystems in the southern and southwestern United States have been particularly impacted by drought, climate change, and anthropogenic impacts (Larimore et al. 1959; Fisher et al. 1982). In the past decade, this region has been in moderate to exceptional stages of drought (NOAA 2011), and is vulnerable to extensive

“megadroughts” whose frequency and severity may be increasing due to anthropogenic climate change (Ault et al. 2014). For example, a majority of Texas entered into drought conditions in 2010, with the most severe, extreme, and exceptional drought conditions occurring in 2011 and persisting through 2014 (Nielsen-Gammon 2012). Climate model projections indicate that Texas is susceptible to future climate variability leading to stresses on water resources (Banner et al. 2010). Combining the impacts of increased water demands due to population growth and current climate change projections, first- order water budget calculations indicate that under drought conditions Texas’ surface water supply will fail to meet the state’s water-use demands by 2050 (Ward 2010). These projected outcomes of future weather and climate trends throughout Texas and the southern and southwestern regions of the United States have the potential to negatively impact fisheries resources and the aquatic ecosystems in which they thrive.

Drought coupled with anthropogenic alterations to the landscape such as modification of stream channels, flow alterations, fragmentation, and habitat degradation have the potential to impact fish growth. Impacts, such as loss of connectivity, decreases in surface area/volume, and increases in extremes of physiochemical parameters will likely affect various feeding guilds differently. One possibility is that growth will be

Texas Tech University, Wade A. Massure, August 2016 hindered in more specialized species and conditions may shift to favor more generalist species in rivers where flows are diminished (Poff and Allan 1995; Bunn and Arthington

2002; Magoulick and Kobza 2003). As flows decline, riffle and run habitats can become dewatered isolating fish, which in turn can cause an increase in predator-prey interactions due to a lack of site mobility (Dobbs et al. 2004). If conditions persist, overall pool surface area and volume can diminish resulting in potential loss of riparian habitat that is critical to smaller prey species (Capone and Kushlan 1991; Lake 2011). Decreased flows may also cause a decline in macroinvertebrate community and overall density as downstream drift of these organisms could be halted or greatly diminished (Acuña et al.

2005; Lake 2011).

Changing water temperatures may also affect both fish and macroinvertebrate communities within these systems. River systems with stable flows may not experience the extreme changes in water temperatures that low flow systems and isolated pools may incur (Poole and Berman 2001). Higher water temperatures can cause stress in more specialized vertebrate species disrupting growth, while generalist species may be unaffected (Poff et al. 1997; Lessard and Hayes 2003). Macroinvertebrate diversity has been shown to decline with higher water temperatures in southwestern systems (Lessard and Hayes 2003).

Fish growth was chosen as a metric to assess these factors because it can provide long-term datasets which is useful in understanding past environmental disturbances.

Otoliths were used to assess these factors, as they can provide persistent data from before, throughout and after a drought event. Growth is one of three primary functions that regulate fisheries population dynamics (Ricker 1975). In fisheries, growth can indicate

Texas Tech University, Wade A. Massure, August 2016 both direct and indirect responses to trophic interactions, mortality, and recruitment dynamics (Birkeland and Dayton 2005; Winemiller 2005). Fish growth information provides a thorough evaluation of environmental conditions and alterations which can be crucial in managing fisheries effectively (Quist et al. 2012). I hypothesized that fish growth would be negatively impacted on the North Llano River because it is heavily influenced by the effects of drought and anthropogenic alterations. Alternatively, I expected to see normal or increased fish growth on the South Llano River because of consistent year round flows.

The primary objective of this study was to evaluate the influence of drought and other anthropogenic factors on the growth of 11 stream fish species in a paired river system in central Texas. The acquisition and analysis of discharge data of these two rivers was used to differentiate between the effects of drought and flow alteration. My first specific objective, was to describe growth patterns of eleven stream fish species inhabiting a paired river system (NLR and SLR). While both streams in this paired system experienced a historic drought during 2009-2014, they differ with respect to the degree of anthropogenic alteration of their flow regimes and riparian areas (Broad 2012).

Secondly, I examined differences between the components of this paired river system to determine if they explained differences in fish growth.

Texas Tech University, Wade A. Massure, August 2016

CHAPTER II

METHODS

Study Area

The North Llano River (NLR) and South Llano River (SLR) are spring-fed, second order streams that join near Junction, Texas to form the Llano River, a major tributary of the Colorado River, approximately 180 km west of San Antonio (Figure 1).

Due to their close spatial proximity and confluence, the NLR and SLR share a common pool of species (Hendrickson and Cohen 2015), as well as similar geology and climate.

Furthermore, the NLR and SLR have watersheds of approximately equal size (about

2,400km²) and the two streams are similar in length (NLR= 93 km; SLR= 88 km). The upper 50-60 km of both the NLR and SLR experience intermittent flows before reaching their more consistently flowing, spring-influenced portions. These rivers are representative of those found throughout the Edwards Plateau ecoregion of central Texas.

Both are characterized as pool and drop rivers with substrates consisting primarily of karst bedrock in the upstream reaches transitioning to coarse gravel and cobble substrates further downstream (Broad 2012; SLWA 2012; Cheek et al. 2016).

Although the NLR and SLR rivers are similar across most geomorphological, physicochemical, and climatic attributes, they exhibit different hydrologic characteristics and degree of anthropogenic disturbance (Edwards et al. 2004; Broad 2012). On average, the NLR has a typical discharge rate that is about 25% of that of the SLR. The NLR runs dry most years and averages 21-22 zero-flow days per year. During the summer the NLR is typically reduced to a series of isolated pools. In contrast, the SLR has not experienced a zero-flow day in recorded history (TPWD 2005; Broad 2008; 2012; U.S. Geological

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Survey gage 08148500 and gage 08150000) and maintains longitudinal connectivity throughout the year. While both rivers have similar types of anthropogenic disturbances, permanent and primitive road crossings, riparian alterations, dams, agricultural water withdrawals, and mining operations are more prevalent on the NLR (SLWA 2012).

Overall, these rivers are still considered relatively pristine and of great conservation value, in part due to their support of robust populations of Guadalupe Bass Micropterus treculii (Hubbs et al. 1991; Curtis et al. 2015; Hendrickson and Cohen 2015).

Fish Collection

Eleven fish species representing four families were included in this study (Table

1). These species represented the dominant large-bodied fish species in the SLR and NLR

(Cheek et al. 2016; T.B. Grabowski pers. comm) and encompassed a range of life history traits including three feeding guilds and three reproductive guilds (Balon 1975; Thomas et al. 2007; Frimpong and Angermeier 2009; Table 1). Seven of the eleven species examined in this study were classified into two feeding guilds following Frimpong and

Angermeier (2009): carnivores (Guadalupe Bass Micropterus treculii, Largemouth Bass

Micropterus salmoides, Green Sunfish Lepomis cyanellus, and Warmouth Lepomis gulosus), which fish but also other terrestrial organisms and piscivores (Bluegill Lepomis macrochirus, Longear Sunfish Lepomis megalotis, and Redbreast Sunfish Lepomis auritus; Table 1), which eat only fishes. Exclusion of ictalurid catfishes from the carnivore guild was due to low sample size from the NLR. Gray Redhorse Moxostoma congestun is classified as a benthic invertivore and was the only species to represent this specific guild in my samples. Similarly, Rio Grande Cichlid Herichthys cyanoguttatus was classified as omnivorous (Table 1) and thus was also excluded due to being the sole

Texas Tech University, Wade A. Massure, August 2016 representative of that feeding guild. Two reproductive guilds: polyphilic species

(Guadalupe Bass, Largemouth Bass, Green Sunfish, Warmouth, Bluegill, and Longear

Sunfish; Table 1) and lithophilic species (Gray Redhorse, Redbreast Sunfish, and Rio

Grande Cichlid; Table 1) were defined according to Frimpong and Angermeier (2009).

Lithophilic fish prefer to spawn and nest over hard substrates such as rock, gravel and sand, while polyphilic fish are not particular in selection of nest building materials and spawn and nest over miscellaneous substrate and materials (Balon 1975; Simon 1999).

Ictalurid catfishes encompassed a separate reproductive guild and low sample size from the NLR precluded them from this analysis. Representatives of the family Cyprinidae, which included the dominant small-bodied species in these rivers, were excluded because they are generally short-lived species (one to three yrs), whose lifespan would not encompass a sufficient range of flow conditions for analysis.

Sampling was conducted at sites dispersed throughout the middle and lower sections of each river (Figure 1) and were chosen either haphazardly or opportunistically to take advantage of other ongoing sampling efforts (SLWA 2012). Fishes were collected using a combination of rod and reel, gill nets, trot lines, backpack electrofishing, and barge/boat mounted electrofishing. All available size classes for each targeted species were included for this study; however, larger, presumably older individuals were targeted to encompass the largest number of water years as possible. Sampling for individual specimens was non-specific with regards to habitat types (riffles, runs and pools) within a sampling section. Specimens collected for this study were euthanized upon capture by immersion in a >250 mg/L aqueous solution of buffered tricaine methanesulfonate (MS-

Texas Tech University, Wade A. Massure, August 2016

222; Leary et al. 2013), and were subsequently stored on ice or frozen until otoliths were removed.

Otolith Preparation and Interpretation

Each fish was measured to the nearest mm total length (mm TL) and its sagittal otoliths, or lapillar otoliths in the case of Gray Redhorse, Channel Catfish Ictalurus punctatus, and Flathead Catfish Pylodictis olivaris, were removed and stored dry in labeled coin envelopes. Otolith preparation followed the protocol of Buckmeier et al.

(2002) and Quist et al. (2007). One otolith from each pair was individually mounted in epoxy and cross sectioned along the transverse plane through the nucleus using a low speed isometric saw (South Bay Technologies, San Clemente, CA) equipped with two

10cm x 0.3cm x 1.27cm precision diamond metal bond high concentration saw blades

(UKAM Industrial Superhard Tools, Valencia, CA; Quist et al. 2012). Otolith sections were then digitally photographed using an Olympus SZX16 stereo microscope (Olympus

Corporation, Tokyo, Japan) equipped with Infinity 1-5C 5.0MP digital camera

(Lumenera Corporation, Ottawa, Ontario). Images were digitally manipulated to enhance the visibility and clarity of annuli (Campana 2001), using ImageJ v. 1.48 imaging software (Abramoff et al. 2004). Annuli were counted and the otolith radius and increment widths of each annulus measured using ImageJ v. 1.48. The direct proportion method, which assumes otolith and body growth are proportional, was used to back calculate the total length at each annulus using the following equation; Li = Lc (Si / Sc), where Li is the back-calculated length of the fish when the ith increment was formed, Lc is fish length at time of capture, Si is the radius of the hard structure at the ith increment, and Sc is the otolith radius at capture (Ricker 1975; Campana 1990; Schramm et al. 1992;

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Quist et al. 2012). A birthdate of 01 January was assumed and assigned to all aged fish.

Fish ages were estimated by a second reader to evaluate the reproducibility of the age estimates of the first reader.

Acquisition and Analysis of Discharge Data

Discharge data for the NLR and SLR were acquired from the gaging stations on the NLR near Junction, TX (U.S. Geological Survey gage 08148500; Figure 1) and the

Llano River approximately 4.5 km downstream of the confluence of the NLR and SLR

(U.S. Geological Survey gage 08150000; Figure 1). SLR discharge was estimated by subtracting NLR gaging station discharge data from that of the Llano River gage as the

NLR and SLR are the only tributaries which contribute to the discharge rates encountered at the Llano River gaging station (Figure 1). Annual discharge metrics were calculated separately for the NLR and SLR using the Indicators of Hydrologic Alteration (IHA) v.

7.1 software package (Richter et al. 1996). A suite of 31 hydrologic attributes (IHA

Statistics) were calculated for each year of data. These attributes encompassed four groupings: 1) magnitude of monthly flow conditions (mean for each month), 2) magnitude and duration of annual extreme flow events, 3) frequency and duration of high- and low-flow pulses, and 4) rate and frequency of changes in water conditions

(Richter et al. 1996). The level of variation around hydrologic variables produced from the IHA allowed for comparison between these systems. Principal component analysis

(PCA) was used to assign possibly correlated variables into two linearly uncorrelated components to reduce dimensionality of the data (Jacquemin et al. 2014). These two principle components differentiated the influence of either drought or flow alteration.

Texas Tech University, Wade A. Massure, August 2016

Fish Growth

Back-calculated length-at-age data were used to construct a single growth curve

-k (t-t ) for each species using the Von Bertalanffy growth model, Lt = L∞ (1 – e o ), where Lt estimates length at time t, L∞ is the asymptotic or theoretical maximum length, k is a growth coefficient, and to is the theoretical age when length equals zero (Von Bertalanffy

1939). Back-calculated length-at-age data growth curves were similar to curves derived from length data (Morales Nin 1988; Campana 2001; Pardo et al. 2013). Green Sunfish growth was estimated using the parameter values of L∞= 199.6, k= 0.41 and t0= 0.31 published by Rypel 2011 as there were insufficient data to generate reliable curve parameters for this species. Residuals for each observation were standardized as a percent deviation from the predicted value to allow comparisons among ages and species.

Departure from the size-at-age as predicted by species-specific Von Bertalanffy growth curves in a given year, are hereafter referred to as standardized growth.

Data Analysis

I used mixed-model repeated-measures analysis of covariance (ANCOVA) to test whether fish age, river, or flow metrics (i.e. principle component scores of annual flow metrics) influenced standardized growth. This hypothesis was tested for several species groupings, including each individual species, guild groupings, and individual species first year of growth. Fixed effects for all models consisted of a specific grouping, i.e. each individual species, guild groupings, individual species first year of growth, and river.

Covariates included in each model were fish age and the two primary flow regime principle components scores generated for each year from analysis of the IHA annual flow metrics. Individuals were used as a subject effect as the linear model assumed equal

Texas Tech University, Wade A. Massure, August 2016 slopes for individuals from predicted size at age growth curves. However, this model assumption can be violated due to variability among individuals within multiple cohorts that were grouped together. To avoid violating the model, individuals were treated as a repeated factor to account for this variability and were modeled with first order autoregressive correlation matrix to account for repeated measures on the individual, and thus avoiding temporal pseudoreplication by assuming that back-calculated lengths from the same fish are not independent. This first order autoregressive correlation matrix allowed each paired observation of back-calculated lengths from age one to age two or age one to age five to correspond with the correlation decreasing with the farther apart age. Significant effects from the ANCOVA were then analyzed using a Tukey HSD post- hoc test. I plotted residuals and used either a Kolmogorov-Smirnov or Shapiro-Wilk test, depending on sample size, to determine if species models violated normality assumptions. Small sample sizes may have resulted in residuals that were not normally distributed in certain species. All analyses were performed using SAS 9.4 (SAS Institute,

Inc., Cary, North Carolina).

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Figure 1. Map of the locations that stream fishes were sampled in the North Llano River watershed and South Llano River watershed on the Edwards Plateau in central Texas during 2014-2015. Inset map shows location of study area in Texas.

Texas Tech University, Wade A. Massure, August 2016

Table 1. Feeding and reproductive guilds, overall number of individuals, mean age in years (±SD), age range, mean total length (TL) (±SD), length range, and generated growth curve parameter estimates for eleven of the dominant large-bodied fish species captured in the North Llano River and South Llano River in central Texas from 2014-2015. Guild North Llano River South Llano River Growth curve parameters Age Mean Mean Age Mean Mean (± SD) range (± SD) TL Range (± SD) age range (± SD) TL Range TL Family Species Feeding Reproductive n age (yrs) (yrs) (mm) TL (mm) n (yrs) (yrs) (mm) (mm) L∞(± SE) k(± SE) t0(± SE) Catostomidae Gray Redhorse Benthic Lithophilic (Moxostoma Invertivore 3 1.3 ± 0.6 1-2 264 ± 15 246-274 22 2.5 ± 2.2 1-7 277 ± 101 172-472 557.0 ± 74.7 0.19 ± 0.05 -0.43 ± 0.21 congestum) Ictaluridae Channel Invertivore/ Speleophilic, Catfish Carnivore 4 3.0 ± 2.5 1-6 334 ± 207 169-813 38 3.6 ± 1.8 1-7 419 ± 144 121-576 925.1 ± 179.4 0.13 ± 0.04 -0.43 ± 0.19 (Ictalurus punctatus) Flathead Invertivore/ Speleophilic Catfish Carnivore 3 1.0 ± 0.0 1 194 ± 48 145-241 15 2.3 ± 3.0 1-13 344 ± 205 200-1018 1421.0 ± 206.5 0.08 ± 0.02 -0.36 ± 0.18 (Pylodictis olivaris) Cichlidae Rio Grande Omnivore Lithophilic Cichlid 6 1.7 ± 0.8 1-3 106 ± 41 60-157 50 2.5 ± 1.2 1-6 139 ± 30 87-196 219.8 ± 27.1 0.29 ± 0.07 -0.22 ± 0.17 ( Herichthys cyanoguttatus) Centrarchidae Redbreast Invertivore/ Lithophilic Sunfish Piscivore 50 2.0 ± 0.9 1-5 136 ± 28 75-191 46 1.9 ± 0.9 1-4 122 ± 28 67-184 203.6 ± 20.0 0.36 ± 0.07 -0.10 ± 0.11 (Lepomis auritus) Green Sunfish Invertivore/ Polyphilic 17 1.4 ± 0.5 1-2 103 ± 32 63-167 11 1.6 ± 0.5 1-2 103 ± 24 78-156 199.61 0.411 0.311 (L. cyanellus) Carnivore Warmouth Invertivore/ Polyphilic 28 1.9 ± 1.1 1-4 127 ± 33 76-187 40 2.2 ± 0.8 1-5 147 ± 31 92-205 167.1 ± 12.0 0.67 ± 0.15 0.17 ± 0.13 (L. gulosus) Carnivore Bluegill Invertivore/ Polyphilic (L. Piscivore 45 1.3 ± 0.5 1-3 101 ± 16 70-134 28 1.4 ± 0.6 1-3 104 ± 19 80-154 173.9 ± 75.9 0.34 ± 0.30 -0.41 ± 0.47 macrochirus)

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Table 1 Continued.

Guild North Llano River South Llano River Growth curve parameters Age Mean Mean Age Mean Mean (± SD) range (± SD) TL Range (± SD) age range (± SD) TL Range TL Family Species Feeding Reproductive n age (yrs) (yrs) (mm) TL (mm) n (yrs) (yrs) (mm) (mm) L∞(± SE) k(± SE) t0(± SE) Centrarchidae Longear Invertivore/ Polyphilic Sunfish Piscivore 59 1.3 ± 0.6 1-3 97 ± 15 73-131 37 1.8 ± 0.7 1-3 96 ± 19 67-131 220.7 ± 131.7 0.19 ± 0.18 -0.70 ± 0.43 (L. megalotis) Largemouth Invertivore/ Polyphilic Bass Carnivore 34 1.9 ± 1.1 1-6 188 ± 87 101-441 46 2.9 ± 1.8 1-9 276 ± 77 130-447 505.5 ± 64.8 0.18 ± 0.04 -0.22 ± 0.16 (Micropterus salmoides) Guadalupe Invertivore/ Polyphilic Bass Carnivore 73 2.1 ± 1.3 1-6 171 ± 69 74-365 46 2.4 ± 1.6 1-8 191 ± 85 78-461 818.7 ± 170.9 0.09 ± 0.02 -0.02 ± 0.08 (M. treculii) 1Green sunfish standardized growth was estimated using length-at-age parameters published by Rypel (2011) as there was not sufficient data to provide curve parameters for this specie

Texas Tech University, Wade A. Massure, August 2016

CHAPTER III RESULTS

Annual Stream Flow Metrics

The NLR and SLR had minimal overlap in annual stream flow metrics during the period for which records were available (Figure 2). In general, the SLR maintained a more stable flow regime year to year as evidenced by the relatively limited range of principle component scores, while the NLR showed a greater level of interannual variation. The first principle component, hereafter referred to as PC1, largely separated out the two rivers, but also separated low flow, high flow and “normal” flow years within each river (eigenvector: 14.3; proportion of variation: 0.46). PC1 was primarily defined by monthly mean flows, daily minimum flows, baseflow, number of reversals, and fall rate (Table 2; Figure 3). The second principle component, hereafter referred to as PC2, separated out variability within the two rivers systems by assessing the extent of maximum flow events, when and how long maximal flows occurred, and average flow condition for each river (eigenvector: 5.5; proportion of variation: 0.18). Daily maximum flows, baseflow, and fall rate were the IHA metrics that were most influential on PC2

(Table 2; Figure 3).

Species Abundance

A total of 701 fishes (NLR= 322; SLR= 379) from eleven species were collected and included in analyses. Individuals ranged from 1-13 years of age and 60-1,018 mm TL

(Table 1). Fishes from the genera Lepomis and Micropterus were the most commonly captured species from both rivers. While Green Sunfish was the least represented sunfish in my samples, it was encountered more frequently in the NLR than in the SLR. In

Texas Tech University, Wade A. Massure, August 2016 contrast, both catfish species, Gray Redhorse, Longear Sunfish, both Micropterus spp., and Rio Grande Cichlid were more frequently encountered in the SLR than in the NLR.

Furthermore, individuals of these species taken from the NLR tended to be younger and smaller for their age than counterparts from the SLR. Redbreast Sunfish, Green Sunfish,

Warmouth, and Bluegill were captured at approximately the same rate between the two rivers.

Species-Specific Growth

Lepomis species— The standardized growth of most Lepomis species was related to flow conditions represented by PC1 and PC2 (Table 3). The standardized growth of

Redbreast Sunfish and Warmouth were positively correlated to PC2, but independent of

PC1 (Table 3; Figure 4). PC1 and PC2 influenced the standardized growth of Bluegill differently depending on the river of origin (Table 3; Figure 4). The standardized growth of Bluegill from the NLR exhibited a positive correlation to PC1 and PC2, while standardized growth exhibited a negative correlation to PC1 and PC2 in the SLR (Table

3). There was evidence that the standardized growth of Longear Sunfish might be lower in years with higher scores for PC1, but this factor exceeded my a priori threshold for statistical significance (Table 3). Bluegill and Warmouth exhibited differences in standardized growth between the two rivers. However, river of origin had no influence in the other species (Table 3). Longear Sunfish was the only species for which age was a factor influencing standardized growth (Table 3), but this was likely due to the relatively large proportion of the sample consisting of age-1 individuals. No significant correlations were found for Green Sunfish.

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The response of Lepomis species to PC1 and PC2 during their first year of life tended to be similar to that when all ages were considered. Standardized growth of

Bluegill and Longear Sunfish were influenced by PC1 and PC2 during the first year of life (Table 6; Figure 5), which was consistent with the patterns observed across all ages.

Similarly, the standardized growth of Green Sunfish during their first year was the same as all ages and exhibited no relationship to PC1 and PC2 (Table 6; Figure 5). In contrast,

Redbreast Sunfish standardized growth was independent of all factors during their first year (Table 6) despite exhibiting a relationship when all ages were included. Further, there was evidence that the standardized growth of Warmouth might be influenced by

PC1, but the factor exceeded my a priori threshold for statistical significance (Table 6).

Both PC1 and PC2 influenced the standardized growth of Bluegill through their first year, but did so differently depending on the river of origin (Table 6; Figure 5), similar to what was observed when all ages were considered. Standardized growth of individuals from the SLR exhibited a negative correlation to PC1 and PC2, while a positive correlation existed between standardized growth and PC1 and PC2 in Bluegill from the

NLR. During their first year, standardized growth of Longear Sunfish was positively correlated to PC2 (Table 6) and lacked the relationship with PC1 observed with all age classes. Warmouth standardized growth during their first year was independent of PC1 and PC2, however, the SLR on average produced larger individuals at this age compared to the NLR (Table 6).

Micropterus species— The standardized growth of the two Micropterus species were influenced by different factors (Table 4; Figure 6). Standardized growth of

Guadalupe Bass was positively correlated to PC1 and PC2 independent of river of origin.

Texas Tech University, Wade A. Massure, August 2016

In contrast, Largemouth Bass standardized growth varied by river of origin independent of annual flow conditions and was greater in the SLR than in the NLR (Table 4).

In general, the factors influencing the standardized growth of both Micropterus species during the first year of life were comparable to those affecting standardized growth for all ages. Standardized growth of young of year Largemouth Bass in the SLR was independent of PC1 and PC2. The NLR did not have a sufficient sample size to evaluate whether standardized growth during the first year followed the same pattern as that for all ages (Table 1 and 7; Figure 7). Guadalupe Bass had greater variability in their standardized growth in both rivers during their first year of life compared to that for all ages during the same period (Figure 7). However, Guadalupe Bass standardized growth during the first year of life was positively correlated to PC1 and independent of all other factors (Table 8), similar to the pattern seen across all ages.

Other species— The remaining four species, Gray Redhorse, Channel Catfish,

Flathead Catfish, and Rio Grande Cichlid, share few ecological, behavioral, or taxonomic commonalities with the Lepomis and Micropterus species described above. Capture rates for these species were relatively low throughout the NLR compared to those in the SLR

(Table 1), making comparisons between the two rivers difficult. However, in general, these four species exhibited similar variability in the factors influencing standardized growth (Table 5; Figure 8).

Gray Redhorse standardized growth in the SLR tended to be higher as values of

PC1 decreased, but this was not a particularly strong relationship and there was no evidence of a similar relationship between standardized growth and PC1 and PC2 in the

NLR (Table 5; Figure 8). In general, Gray Redhorse from the SLR tended to have higher

Texas Tech University, Wade A. Massure, August 2016 standardized growth than their counterparts from the NLR independent of age or PC1 and

PC2 (Table 3). In contrast, the standardized growth of Gray Redhorse during the first year of life was influenced by the PC1 and independent of other factors, including river of origin (Table 7).

Standardized growth of Rio Grande Cichlid was positively correlated to PC1 and

PC2 (Table 5; Figure 8). Furthermore, Rio Grande Cichlid from the NLR exhibited lower standardized growth compared to individuals from the SLR (Table 5; Figure 8), independent of PC1, PC2, and age. Likewise, their first year, Rio Grande Cichlid from the NLR exhibited lower standardized growth compared to individuals from the SLR

(Table 8; Figure 9), independent of PC1 and PC2 or age. Standardized growth of Rio

Grande Cichlid through their first year tended to be lower in years with higher scores for

PC1 (Table 8), similar to what was observed when all ages were considered.

Standardized growth at all ages (Table 5; Figure 6), including young of year

(Table 8; Figure 9), of both catfish species were independent of all factors considered in the models. However, I did not have a sufficient sample size to adequately represent and evaluate standardized growth of these species across the two rivers and therefore, these species were not included in any further analyses (Table 1).

Feeding Guild— Both PC1 and PC2 were the most important factors influencing the growth of fishes within the carnivorous and piscivorous feeding guilds (Table 9;

Figure 10). As a group, carnivores exhibited greater standardized growth in the NLR compared to that in the SLR independent of age or PC1 and PC2. In contrast, piscivores exhibited greater standardized growth in the SLR compared to the NLR (Table 9; Figure

10). While PC1 and PC2 influenced the standardized growth of the carnivorous guild

Texas Tech University, Wade A. Massure, August 2016 independent of species and age, the relationship differed between the two rivers (Table 9;

Figure 10). Standardized growth for fishes in the carnivorous guild increased with increasing values of PC1 and PC2 in the NLR, while in the SLR, standardized growth of carnivores was negatively correlated with PC1 but positively correlated with PC2 (Table

9). In contrast to carnivorous guild species, standardized growth for piscivorous guild increased with increasing values of PC2 (Table 9), but was independent of species and

PC1. Furthermore, standardized growth for fishes in the piscivorous guild increased with increasing values of age and its interaction with species within this guild (Table 9).

Reproductive Guild— River of origin and PC1 and PC2 were all correlated with the standardized growth of fishes through their first year within the polyphilic and lithophilic reproductive guilds (Table 10; Figure 11). As a group, polyphilic guild through their first year exhibited greater standardized growth in the NLR compared to that in the SLR independent of species or PC1 and PC2. Standardized growth of polyphilic guild through their first year was correlated with the interaction of PC2 and river of origin, exhibiting a positive correlation on the NLR and a negative correlation on the SLR (Table 10), but independent of species and PC1. In contrast to polyphilic guild, lithophilic guild through their first year exhibited greater standardized growth in the SLR compared to the NLR (Table 10; Figure 11) independent of species or PC1 and PC2.

Lithophilc guild standardized growth through their first year was correlated with PC1 and tended to be lower in years with higher values of PC1 (Table 10; Figure 11).

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Table 2. List of Index of Hydrological Alteration discharge metrics (Richter et al. 1996) with associated eigenvectors from a principle components analysis describing the annual flow regimes of the North Llano River from 1916-1977 and 2001-2015 and South Llano River from 1960-1977 and 2001-2015 in central Texas. Eigenvector values of principle component 1 and 2 arranged by major hydrological grouping where values ≥ 0.15 were used in axis interpretations. Principle component 1 largely separated the two rivers, and drought, flood and “normal” years. Principle component 2 separated out the variability of magnitude, duration and of flow between each river.

IHA Type IHA Attribute PC1 Eigenvector PC2 Eigenvector Magnitude of monthly October 0.22 -0.05 flow conditions November 0.22 0.04 (mean for each month) December 0.24 0.00 January 0.25 -0.01 February 0.25 -0.02 March 0.24 -0.02 April 0.22 -0.03 May 0.19 0.03 June 0.20 0.07 July 0.22 0.01 August 0.19 0.04 September 0.16 0.14 Magnitude and duration of 1-day minimum 0.22 -0.06 annual extremes 3-day minimum 0.25 -0.06 7-day minimum 0.25 -0.07 30-day minimum 0.26 -0.06 90-day minimum 0.26 -0.04 1-day maximum 0.01 0.40 3-day maximum 0.01 0.41 7-day maximum 0.02 0.41 30-day maximum 0.03 0.42 90-day maximum 0.06 0.41 Frequency and duration of Zero flow days -0.11 -0.02 high- and low-flow pulses Base flow 0.21 -0.15 Date of minimum -0.07 0.07 Date of maximum 0.05 0.05 Number of low pulses -0.01 -0.12 Number of high pulses 0.03 0.11 Rate and frequency of Rise rate 0.04 0.10 changes in water Fall rate -0.15 -0.17 conditions Reversals 0.17 -0.11

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Table 3. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river, fish age and PC scores of annual flow metrics and their influence on growth rate residuals for all ages of five sunfishes (Lepomis spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Bluegill and Warmouth models incorporated the effect of the interaction between PC scores and each river as it was found to be significant for these species. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Redbreast Sunfish Intercept 0.01 ± 0.04 ─ ─ ─ ─ River -0.01 ± 0.06 0.01 1 94 0.93 BC Age 0.01 ± 0.01 0.82 1 87 0.37 PC1 -0.02 ± 0.04 0.15 1 87 0.70 PC2 0.04 ± 0.02 5.53 1 87 0.02 Green Sunfish Intercept 0.06 ± 0.15 ─ ─ ─ ─ River 0.04 ± 0.43 0.01 1 26 0.92 BC Age -0.03 ± 0.04 0.67 1 10 0.43 PC1 0.07 ± 0.34 0.04 1 10 0.85 PC2 0.05 ± 0.05 1.06 1 10 0.33 Warmouth Intercept 0.64 ± 0.21 ─ ─ 66 ─ River -0.57 ± 0.22 6.66 1 66 0.01 BC Age 0.01 ± 0.01 1.31 1 69 0.26 PC1*River ─ 2.68 2 69 0.08 PC1(NLR) 0.09 ± 0.07 PC1(SLR) -0.13 ± 0.08 PC2*River ─ 7.55 2 69 < 0.01 PC2(NLR) 0.07 ± 0.03 PC2(SLR) 0.67 ± 0.22 Bluegill Intercept -0.98 ± 0.44 ─ ─ ─ ─ River 2.79 ± 0.72 14.78 1 71 < 0.01 BC Age -0.04 ± 0.03 1.97 1 20 0.18 PC1*River ─ 8.99 2 20 < 0.01 PC1(NLR) 1.70 ± 0.49 PC1(SLR) -0.78 ± 0.22 PC2*River ─ 9.51 2 20 < 0.01 PC2(NLR) 0.48 ± 0.12 PC2(SLR) -1.46 ± 0.53 Longear Sunfish Intercept -0.01 ± 0.05 ─ ─ ─ ─ River -0.28 ± 0.19 2.24 1 93 0.14 BC Age 0.05 ± 0.01 21.36 1 46 < 0.01 PC1 -0.29 ± 0.15 3.77 1 46 0.06 PC2 0.01 ± 0.04 0.11 1 46 0.74

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Table 4. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river, fish age, and PC scores of annual flow metrics and their influence on growth rate residuals for all ages of two black bass (Micropterus spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Largemouth Bass Intercept 0.05 ± 0.05 ─ ─ 78 ─ River -0.18 ± 0.08 5.18 1 78 0.03 BC Age 0.02 ± 0.01 4.80 1 117 0.03 PC1 -0.03 ± 0.03 0.92 1 117 0.34 PC2 0.00 ± 0.02 0.01 1 117 0.92 Guadalupe Bass Intercept 0.02 ± 0.03 ─ ─ 117 ─ River 0.03 ± 0.05 0.52 1 117 0.47 BC Age 0.00 ± 0.01 0.23 1 145 0.63 PC1 0.06 ± 0.02 6.68 1 145 0.01 PC2 0.05 ± 0.02 9.90 1 145 < 0.01

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Table 5. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river, fish age, and PC scores of annual flow metrics and their influence on growth rate residuals for all ages of Gray Redhorse, Rio Grande Cichlid, Channel and Flathead Catfish captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Gray Redhorse Intercept -0.07 ± 0.04 ─ ─ 23 ─ River 0.07 ± 0.09 0.48 1 23 0.50 BC Age 0.04 ± 0.01 17.14 1 30 < 0.01 PC1 -0.01 ± 0.02 0.08 1 30 0.78 PC2 -0.03 ± 0.02 1.66 1 30 0.21 Flathead Catfish Intercept -0.03 ± 0.06 ─ ─ 16 ─ River -0.14 ± 0.13 1.11 1 16 0.31 BC Age 0.01 ± 0.01 0.94 1 16 0.35 PC1 0.01 ± 0.03 0.03 1 16 0.86 PC2 0.01 ± 0.02 0.05 1 16 0.82 Channel Catfish Intercept 0.01 ± 0.04 ─ ─ 40 ─ River -0.04 ± 0.09 0.21 1 40 0.65 BC Age -0.01 ± 0.01 0.63 1 105 0.43 PC1 0.01 ± 0.02 0.10 1 105 0.76 PC2 0.01 ± 0.03 0.11 1 105 0.74 Rio Grande Cichlid Intercept 0.27 ± 0.07 ─ ─ 54 ─ River -0.56 ± 0.12 20.54 1 54 < 0.01 BC Age 0.00 ± 0.01 0.06 1 77 0.81 PC1 -0.14 ± 0.04 13.15 1 77 < 0.01 PC2 0.20 ± 0.05 13.98 1 77 < 0.01

Texas Tech University, Wade A. Massure, August 2016

Table 6. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth of five sunfishes (Lepomis spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Bluegill model incorporated the significant effect of the interaction between PC scores and each river. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Redbreast Sunfish Intercept 0.08 ± 0.06 ─ ─ 93 ─ River -0.18 ± 0.13 2.10 1 93 0.15 PC1 -0.13 ± 0.08 2.38 1 93 0.13 PC2 0.05 ± 0.05 0.73 1 93 0.39 Green Sunfish Intercept 0.06 ± 0.14 ─ ─ 25 ─ River -0.97 ± 0.65 2.19 1 25 0.15 PC1 -0.85 ± 0.54 2.45 1 25 0.13 PC2 -0.34 ± 0.17 3.77 1 25 0.06 Warmouth Intercept 0.13 ± 0.06 ─ ─ 65 ─ River -0.31 ± 0.13 5.30 1 65 0.02 PC1 -0.19 ± 0.09 3.80 1 65 0.06 PC2 0.06 ± 0.06 0.84 1 65 0.36 Bluegill Intercept -1.16 ± 1.05 ─ ─ 68 ─ River 3.17 ± 1.26 6.30 1 68 0.01 PC1*River ─ 5.55 2 68 0.01 PC1(NLR) 1.93 ± 0.68 ─ ─ ─ ─ PC1(SLR) -0.65 ± 0.37 ─ ─ ─ ─ PC2*River ─ 6.83 2 68 < 0.01 PC2(NLR) 0.52 ± 0.15 ─ ─ ─ ─ PC2(SLR) -1.56 ± 1.14 ─ ─ ─ ─ Longear Sunfish Intercept 0.04 ± 0.08 ─ ─ 92 ─ River 0.11 ± 0.38 0.08 1 92 0.77 PC1 0.09 ± 0.30 0.09 1 92 0.77 PC2 0.20 ± 0.08 6.28 1 92 0.01

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Table 7. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth of two black basses (Micropterus spp.) captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Largemouth Bass Intercept 0.13 ± 0.13 ─ ─ 77 ─ River -0.41 ± 0.22 3.55 1 77 0.06 PC1 -0.19 ± 0.11 3.12 1 77 0.08 PC2 -0.06 ± 0.09 0.37 1 77 0.54 Guadalupe Bass Intercept -0.01 ± 0.04 ─ ─ 116 ─ River 0.12 ± 0.08 2.40 1 116 0.12 PC1 0.12 ± 0.05 6.11 1 116 0.01 PC2 0.06 ± 0.04 2.41 1 116 0.12

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Table 8. Summary of species-specific mixed-model repeated-measures ANCOVA evaluating the effect of river and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth for Gray Redhorse, Rio Grande Cichlid, Channel and Flathead Catfish captured from the North Llano and South Llano Rivers in central Texas during 2014- 2015. The symbol “─” indicates that no value is associated with the model term. Effects with a P- value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Gray Redhorse Intercept 0.18 ± 0.12 ─ ─ 22 ─ River -0.40 ± 0.23 2.96 1 22 0.10 PC1 -0.23 ± 0.09 6.29 1 22 0.02 PC2 0.06 ± 0.09 0.47 1 22 0.50 Flathead Catfish Intercept 1.13 ± 1.51 ─ ─ 15 ─ River -0.46 ± 0.65 0.51 1 15 0.49 PC1 -0.00 ± 0.22 0.00 1 15 0.99 PC2 1.35 ± 1.67 0.65 1 15 0.43 Channel Catfish Intercept -0.15 ± 0.10 ─ ─ 39 ─ River 0.23 ± 0.18 1.62 1 39 0.21 PC1 0.12 ± 0.06 3.77 1 39 0.06 PC2 -0.07 ± 0.08 0.73 1 39 0.40 Rio Grande Cichlid Intercept 0.16 ± 0.16 ─ ─ 53 ─ River -0.69 ± 0.23 9.33 1 53 < 0.01 PC1 -0.33 ± 0.09 12.39 1 53 < 0.01 PC2 -0.04 ± 0.17 0.06 1 53 0.81

Texas Tech University, Wade A. Massure, August 2016

Table 9. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age, and PC scores of annual discharge metrics and their influence on standard growth of all ages of the representatives of two feeding guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Carnivorous guild consists of Largemouth Bass, Guadalupe Bass, Green Sunfish and Warmouth and incorporated the effect of the interaction between PC scores and each river as it was significant to this guild model. Piscivorous guild consists of three Lepomis spp. (Bluegill, Longear Sunfish and Redbreast Sunfish) and incorporated the effect of the interaction between age and each individual species as it was significant to this model. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant. Species Effect Value (±SE) F DF1 DF2 P Carnivorous Guild Intercept 0.05 ± 0.04 ─ ─ 290 ─ Species ─ 0.10 3 290 0.96 Species(GB) -0.01 ± 0.03 ─ ─ ─ ─ Species(LMB) 0.00 ± 0.03 ─ ─ ─ ─ Species(GS) -0.01 ± 0.04 ─ ─ ─ ─ Species(WM) 0 ─ ─ ─ ─ River 0.03 ± 0.05 0.30 1 290 0.58 BC Age 0.01 ± 0.01 3.31 1 350 0.07 PC1*River ─ 5.96 2 350 < 0.01 PC1(NLR) 0.10 ± 0.03 ─ ─ ─ ─ PC1(SLR) -0.02 ± 0.02 ─ ─ ─ ─ PC2*River ─ 6.37 2 350 < 0.01 PC2(NLR) 0.04 ± 0.01 ─ ─ ─ ─ PC2(SLR) 0.02 ± 0.02 ─ ─ ─ ─ Piscivorous Guild Intercept 0.01 ± 0.03 ─ ─ 260 ─ Species ─ 4.10 2 260 0.96 Species(BG) -0.06 ± 0.03 ─ ─ ─ ─ Species(LE) -0.07 ± 0.03 ─ ─ ─ ─ Species(RB) 0 ─ ─ ─ ─ River -0.01 ± 0.05 0.05 1 260 0.82 BC Age 0.00 ± 0.01 25.15 1 159 < 0.01 BC Age*Species ─ 9.56 2 159 < 0.01 BC Age(BG) 0.05 ± 0.02 ─ ─ ─ ─ BC Age(LE) 0.05 ± 0.01 ─ ─ ─ ─ BC Age(RB) 0 ─ ─ ─ ─ PC1 -0.04 ± 0.03 1.28 1 159 0.26 PC2 0.04 ± 0.01 14.32 1 159 < 0.01

Texas Tech University, Wade A. Massure, August 2016

Table 10. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age, and PC scores of annual flow metrics and their influence on growth rate residuals during the first year of growth of two reproductive guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. Polyphilic guild consists of both Mictropterus spp. and four Lepomis spp. (Green Sunfish, Warmouth, Bluegill, and Longear Sunfish) and incorporated the effect of the interaction between PC scores and each river as it was significant to this guild model. Lithophilic guild consists of Gray Redhorse, Redbreast Sunfish, and Rio Grande Cichlid. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant.

Species Effect Value (±SE) F DF1 DF2 P Polyphilic Guild Intercept 0.00 ± 0.11 ─ ─ 452 ─ Age 1 Species ─ 0.23 5 452 0.95 Species(GB) 0.00 ± 0.03 ─ ─ ─ ─ Species(LMB) 0.02 ± 0.03 ─ ─ ─ ─ Species(GS) 0.01 ± 0.04 ─ ─ ─ ─ Species(WM) 0 ─ ─ ─ ─ Species(BG) -0.01 ± 0.03 ─ ─ ─ ─ Species(LE) -0.01 ± 0.03 ─ ─ ─ ─ River 0.15 ± 0.14 1.17 1 452 0.28 PC1*(River) ─ 2.85 2 452 0.06 PC1(NLR) 0.14 ± 0.08 ─ ─ ─ ─ PC1(SLR) -0.10 ± 0.06 ─ ─ ─ ─ PC2*(River) ─ 6.42 2 452 < 0.01 PC2(NLR) 0.10 ± 0.03 ─ ─ ─ ─ PC2(SLR) -0.04 ± 0.10 ─ ─ ─ ─ Lithophilic Guild Intercept 0.14 ± 0.06 ─ ─ 172 ─ Age 1 Species ─ 0.02 2 172 0.98 Species(GR) 0.01 ± 0.04 ─ ─ ─ ─ Species(RB) 0.01 ± 0.03 ─ ─ ─ ─ Species(RGC) 0 ─ ─ ─ ─ River -0.35 ± 0.09 15.09 1 172 < 0.01 PC1 -0.22 ± 0.05 21.68 1 172 < 0.01 PC2 0.03 ± 0.04 0.37 1 172 0.54

Texas Tech University, Wade A. Massure, August 2016

Figure 2. Median daily discharge rates taken from two USGS gaging stations (m-3s-1) during 1916-1977 and 2001-2015 for the North Llano River (A) and 1960-1977 and 2001-2015 for the South Llano River (B), central Texas.

Texas Tech University, Wade A. Massure, August 2016

Figure 3. Scatterplot of the two primary PC scores for flow years based on Indices of Hydrological Alteration variables (Richter et al. 1996; see Table 2) for the North Llano River (blue circles) from 1916-1977 and 2001-2015 and South Llano River (red circles) from 1960- 1977 and 2001-2015 in central Texas. Years with associated fish age data collected in this study are labeled within the plot. Principle component 1 which explained 46% of the variance is on the X axis. It explains the separation of the two rivers and also separates drought, flood, and “normal” years for each river. Principle component 2 which explained 18% of the variance is on the Y axis. It explains the magnitude, duration, and frequency of flow between these rivers.

Texas Tech University, Wade A. Massure, August 2016

Figure 4. Influence of annual stream discharge metrics on the standardized growth for all ages of Redbreast Sunfish (A), Green Sunfish (B), Warmouth (C), Bluegill (D), and Longear Sunfish (E) captured on the North Llano River and South Llano River in central Texas during 2014-2015.

Texas Tech University, Wade A. Massure, August 2016

Figure 5. Influence of annual stream discharge metrics on the standardized growth during the first year of growth for Redbreast Sunfish (A), Green Sunfish (B), Warmouth (C), Bluegill (D), and Longear Sunfish (E) captured on the North Llano River and South Llano River in central Texas during 2014-2015.

Texas Tech University, Wade A. Massure, August 2016

Figure 6. Influence of annual stream discharge metrics on the standardized growth for all ages of Largemouth Bass (A) and Guadalupe Bass (B) captured on the North Llano River and South Llano River in central Texas during 2014-2015.

Texas Tech University, Wade A. Massure, August 2016

Figure 7. Influence of annual stream discharge metrics on the standardized growth during the first year of growth for Largemouth Bass (A) and Guadalupe Bass (B) captured on the North Llano River and South Llano River in central Texas during 2014-2015.

Texas Tech University, Wade A. Massure, August 2016

Figure 8. Influence of annual stream discharge metrics on the standardized growth for all ages of Gray Redhorse (A), Rio Grande Cichlid (B), Channel Catfish (C), and Flathead Catfish (D) captured on the North Llano River and South Llano River in central Texas during 2014-2015.

Texas Tech University, Wade A. Massure, August 2016

Figure 9. Influence of annual stream discharge metrics on the standardized growth during the first year of growth for Gray Redhorse (A), Rio Grande Cichlid (B), Channel Catfish (C), and Flathead Catfish (D) captured on the North Llano River and South Llano River in central Texas during 2014-2015.

Texas Tech University, Wade A. Massure, August 2016

Figure 10. Influence of annual stream discharge metrics on the standardized growth of all ages of fishes in carnivorous (A) and piscivorous (B) feeding guilds captured from the North Llano River and South Llano River in central Texas during 2014-2015. The carnivorous guild consists of Guadalupe Bass, Largemouth Bass, Green Sunfish and Warmouth. The piscivorous guild consists of Bluegill, Longear Sunfish, and Redbreast Sunfish.

Texas Tech University, Wade A. Massure, August 2016

Figure 11. Influence of annual stream discharge metrics on the standardized growth during the first year of growth of fishes in the polyphilic (A) and lithophilic (B) reproductive guilds captured from the North Llano River and South Llano River in central Texas during 2015-2016. The polyphilic guild consists of Guadalupe Bass, Largemouth Bass, Green Sunfish, Warmouth, Bluegill, and Longear Sunfish. The lithophilic guild consists of Gray Redhorse, Redbreast Sunfish, and Rio Grande Cichlid.

Texas Tech University, Wade A. Massure, August 2016

CHAPTER IV DISCUSSION

Major changes in aquatic ecosystems due to flow regime alteration have been documented in the majority of lotic systems worldwide (Pringle et al. 2000) and the effects of altered flow regimes can be exacerbated by the onset of drought conditions

(Lake 2003). Even river systems characterized by relatively stable flow regimes are influenced by drought (Wood et al. 1999). However, the effects of drought in ecosystems that are impacted by prolonged drying due to river diversions and groundwater abstraction (Agnew et al. 2000) are likely to experience greater disturbance and have highly altered species assemblages relative to less altered systems (Boulton 2003).

Effects of drought were similar across the two basins in this study; however, the impacts of drought differed with varying degrees of flow alteration between the North and South

Llano Rivers. While the community-level impacts of flow alteration and disturbance are relatively well-documented, the responses at the individual level that drive community responses are not well understood. My results show that the growth of species comprising a riverine fish assemblage exhibited differential responses to annual flow conditions, which were influenced by the ecological niche, habitat preferences, and in some cases, river of origin. Furthermore, my results suggest that members of different feeding or reproductive guilds exhibit similar responses to annual flow conditions irrespective of phylogenetic relationships.

The North and South Llano Rivers are representative of typical Edwards Plateau streams and share many similarities, however the influence of flow alteration varies between the systems (Edwards et al. 2004). The SLR which is a relatively pristine and

Texas Tech University, Wade A. Massure, August 2016 unaltered system is typically less effected by drought, as it maintains a consistent flow year round due to higher spring inputs resulting in consistently higher base, minimum, and monthly flows compared to the NLR (Figure 3). In contrast, the addition of increased anthropogenic influences in the NLR compounds influences of drought conditions on flows as seen by the consistent decreased values across a large proportion of years along both the PC1 and PC2 axis. With the onset of drought and altered flows, reduced water levels in rivers can limit the amount of suitable habitat and resources available for fish inhabiting these waters (Stanley et al. 1997). Shallow sections of rivers characterized by riffles and runs are the first to dissipate causing sections of river to become a series of fragmented pools (Stanley et al. 1997; Matthews 1998; Magoulick and Kobza 2003).

Schlosser (1982) found that habitats such as riffles and temporally variable areas are of particular importance to the growth of specific age classes of species primarily young of year, which I found to be true in several of the species I tested. The inability to use or access these preferred habitats during drought and low flows in the first year of life can cause poor growth and ultimately poor survival (Schlosser 1982). Other direct and indirect impacts of drought in rivers with altered flow regimes can considerably reduce population densities, species richness and composition, type and influence of biotic interactions (predation and competition), food resources, ecosystem processes, and trophic structure (Lake 2000; Boulton 2003; Lake 2003; Matthews and Marsh-Matthews

2003). Drought and reduced stream discharge tend to increase the intensity of predation and competition within a river system (Schlosser et al. 2000), more so in rivers with altered flow regimes such as the NLR. Food resource availability in systems much like the NLR which consists primarily of isolated pools can dwindle rapidly causing a decline

Texas Tech University, Wade A. Massure, August 2016 in younger smaller fish and in turn favor growth of larger fish inhabiting these areas.

Another factor affecting growth in fish includes invertebrate drift which can be reduced by lower stream discharge and drought, thus reducing foraging opportunities for fish

(Harvey et al. 2006). Species regarded as generalists are typically better adapted to altered conditions and can outcompete specialized species in these systems causing a reduction in their growth. Therefore, the ecological differences between the species tested may provide a better insight to how growth of these species during periods of drought differed between rivers that have either a consistently stable flow regime or that of a heavily altered flow regime.

Lepomis species— The Von Bertalanffy growth parameter estimates of three

(Bluegill, Green Sunfish and Warmouth) Lepomis species used in this study were lower than estimates found in previously published studies of riverine populations at similar latitudes (Jenkins et al. 1955; Houser and Bross 1963; Carlander 1977). Differences observed in my parameter estimates for these species may be due to zoogeography as they are on the western edge of their native distribution and may not have the optimal instream conditions needed for growth (Lee 1980b, c, d; Delp et al. 2000). Growth parameter estimates for Longear Sunfish were consistent with previously published studies. I found that flow metrics and river of origin were the primary drivers in variations of growth found at all ages for these four Lepomis species. However, the relationships of Green and Longear Sunfish to flow and river metrics may have been disproportionately influenced by the small sample size of these species from this system.

My results indicated that these species growth was positively correlated with periods characterized by low to normal flows and negatively correlated with periods

Texas Tech University, Wade A. Massure, August 2016 characterized by higher flows in the SLR. In contrast, growth in the NLR tended to increase during periods of higher flows.

Ecological similarities between these four native species can provide better insight as to how the effects of hydrologic alterations to flow regimes compounded by the effects of drought may influence their growth. Typically, Bluegill, Green Sunfish,

Warmouth, and Longear Sunfish are characterized as fluvial and habitat generalist species (Lee 1980b, c, d; Page and Burr 1991; Glenn 1999; Ross 2001; Robison and

Buchanan 1988) and are native to Texas. My hypothesis was that reductions in water quantity caused by drought and altered flow regimes would have either a neutral or positive effect on growth in these species. An explanation for this may be that native centrarchid species are better adapted to these periods of drought and low flow conditions. These periods of extended low flows compounded by drought conditions tend to be highly variable from year to year, however, timing (seasonality) of these events is largely predictable (Power et al. 2008). Studies have shown that native generalist fish species have evolved life history strategies and traits to tolerate and thrive in changing hydrologic conditions (Power et al. 2008; Yarnell et al. 2010). Adaptation to low flow conditions and drought may explain increased growth of these four sunfish species as they may be outcompeting other riverine species for available food sources and habitats

(Grossman et al. 1998). Another explanation for increased growth during periods of low flows and drought may be explained by density dependent factors such as a differential dilution of predators and prey with declining water levels. A reduction in fish density has been found to correspond to increases in invertebrate production which may benefit and increase native and generalist species growth (Bartels 1995). Lastly, the habitats in which

Texas Tech University, Wade A. Massure, August 2016 these species are generally found consists of woody structure, vegetated backwaters, pools, and sluggish, slow moving waters of streams (Page and Burr 1991; Etnier and

Starnes 1993). During periods of low flows and drought these areas can become the prominent habitat types in this system, thereby potentially increasing the availability of optimal habitats for growth in these species.

In contrast to native, generalist sunfish species, Redbreast Sunfish growth parameter estimates were higher than estimates from other published studies (Mantini et al. 1992; Ashley and Rachels 2000). I found that the standardized growth of Redbreast

Sunfish at all ages, including age one, were correlated with stream flow metrics. Growth in the first year increased during periods of low flows and drought, conversely, individuals age two and older had growth increase during years characterized as high flow years. This variation in growth between ages is likely due to the difference in habitat types occupied by juveniles compared to older, larger individuals (Freeman 1995). Life history traits and ecological differences for Redbreast Sunfish were generally different than that of the other four Lepomis species and may provide a better explanation as to how flow alterations and drought effect growth in this species. Aho et al. (1986) found that current velocity, gradient, and proportion of mesohabitats available were the major factors influencing this species. Redbreast Sunfish are characterized as a fluvial specialist species (Lee 1980a), that is nonnative in Texas. Compared to the other Lepomis species which inhabit more slack water type habitats, Redbreast Sunfish typically inhabit riverine systems in areas with flowing water over rocky and sandy substrates (Lee 1980a; Page and Burr 1991). It has been shown that nonnative species often lack biological and behavioral mechanisms to cope with region-specific flow regimes and are often

Texas Tech University, Wade A. Massure, August 2016 disproportionately vulnerable to altered stream flow conditions (Kiernan et al. 2012). I hypothesized that low flows and drought would have an overall negative effect on growth in this nonnative species. Sammons and Maceina (2009) found that growth of Redbreast

Sunfish was positively related to flow in Georgia Rivers. It is likely that high flows benefited growth for this species in the NLR and SLR by connecting current habitats with newly inundated riparian habitat and shallow floodplain habitat which resulted in increased availability of preferred habitats, a refuge from flows, increased invertebrate drift, and greater terrestrial invertebrate food resources (Schlosser 1998). This species was found to be an opportunistic feeder in other river systems eating both aquatic and terrestrial invertebrates (Sandow et al. 1975). My results support the conclusion that

Redbreast Sunfish may be better adapted to high flow conditions by taking advantage of newly inundated habitats and food resources that become available after prolonged periods of low flows and drought.

Micropterus species— The Von Bertalanffy growth parameter estimates for black basses from my study were generally comparable to those from other published studies.

Guadalupe Bass standardized growth in the NLR and SLR was consistent with that described throughout the range of the species in the late 1970s (Edwards 1980) and within the SLR during 2006-2013 (Groeschel 2013). In contrast, growth parameter estimates for Largemouth Bass from the NLR and SLR were somewhat lower compared to estimates from similar latitudes (see Carlander 1977 for compilation). However, the majority of Largemouth Bass age and growth studies in Texas and the southeastern

United States are focused on reservoir populations, which likely have different growth profiles from riverine populations (Hoyer and Canfield 1994; Johnson 1997; Hill and

Texas Tech University, Wade A. Massure, August 2016

Cichra 2005). Riverine populations of Largemouth Bass generally exhibit lower growth rates than counterparts residing in reservoirs (Scott and Crossman 1973; Stuber et al.

1982).

I found that Guadalupe Bass growth exhibited a strong positive correlation to annual stream discharge metrics associated with monthly mean flows (i.e. PC1) independent of whether the fish was living in the NLR or SLR. This species is characterizated as a fluvial specialist (Edwards 1980), typically associated with higher current velocities found within riffle and run habitat types (Boyer et al. 1977; Edwards

1980; Perkin et al.. 2010). However, the species is relatively plastic in its habitat use, capable of inhabiting a range of habitat types depending on season (Cheek and

Grabowski 2015) and age (Groeschel 2013). Growth in this species tended to be higher in the SLR than the NLR, which was due to the underlying differences in annual flow regimes between the two rivers and shown along the PC1 axis. Growth was lower than expected during years experiencing drought; however, this reduction in growth during drought seemed to be greater in the NLR than the SLR. My results are consistent with those of Groeschel (2013), who found that growth rates of Guadalupe Bass in the SLR were negatively correlated with the proportion of stream discharge observations characterized as extreme low flows, i.e., Q90, in a year. The sensitivity of Guadalupe Bass growth to changes in stream discharge could be due to many factors, but I hypothesize that it is primarily being driven by the response of prey species to prevailing flow conditions. Guadalupe Bass feed primarily on riffle-dwelling macroinvertebrates, including crayfish (Edwards 1980; Farquhar 1995). Reduction in stream discharge, whether through anthropogenic water withdrawals or drought, will reduce the

Texas Tech University, Wade A. Massure, August 2016 accessibility and availability of riffle habitats (Jowett et al. 2005; Bradford and Heinonen

2008). Loss of connectivity with these preferred habitats has been shown to cause changes in available prey items such as: fish and invertebrate abundance, production, and species composition (Cushman 1985). Changes in prey item community structure and abundance increases the potential for competition between Guadalupe Bass and other riverine species (Hurst et al. 1975), especially Largemouth Bass (Lasenby and Kerr

2000), which can lead to the depletion of specific prey items which in turn may hinder growth. In addition to a reduction of preferable habitats used for foraging, increased water temperatures associated with lower stream discharge can increase physiological stress of individuals and inhibit growth (Coutant 1985; Petty and Grossman 2004; Ficke et al. 2007).

Guadalupe Bass inhabiting the NLR can experience a large reduction in the availability and accessibility of riffle habitats every year, but individuals in the SLR experience only relatively modest changes in the availability and accessibility of these habitats, except during periods of extreme drought. Furthermore, growth of Guadalupe

Bass during their first year seemed to be even more responsive to changes in annual streamflow metrics. While it is difficult to fully evaluate explanations for this observation without information on recruitment levels, I hypothesize that this sensitivity may be due to the reliance of young-of-year Guadalupe Bass on insect drift, a potentially a key component of their diet (Edwards 1980; Edwards 1997). Although the SLR has never ceased flowing, the growth of individuals during their first year seemed much more responsive to streamflow than that of older individuals. However, the potential influence of the Texas Parks and Wildlife stocking program for Guadalupe Bass that began in 2011

Texas Tech University, Wade A. Massure, August 2016 in the SLR should also be considered. As this large influx of young individuals into the

SLR may have caused a reduction in forage materials needed for growth in this species at this young age. Stocking events, however, may have benefited other species growth as it lead to a large influx of prey species into this system.

In contrast to Guadalupe Bass, the growth of Largemouth Bass did not seem to be influenced by flow conditions. Instead, the river of origin and age of the individual had the greatest influence on relative growth for this species. My results indicated that growth in the NLR was highly variable across years, with growth in a given year either much higher or much lower than values predicted by the Von Bertalanffy growth curve. In contrast, growth was greater and less variable in the SLR. Growth rates for Largemouth

Bass are typically higher in southern portions of the species range and in systems with reduced flows due to longer periods of warmer water temperatures (Clugston 1964;

Coutant and Deangelis 1983). Keith (1975) found that reduced water levels due to alterations in flow regimes and compounded by the effects of drought during warm weather months can enhance Largemouth Bass growth. The difference in response of growth of these species to changes in flow metrics and drought may be better explained by the life history of each species.

Largemouth Bass is a generalist species which prefer habitats characterized by clear, wide and slow moving waters with pools, backwaters and aquatic vegetation

(Trautman 1981; Scott and Corssman 1973; Stuber et al. 1982). These habitat types, specifically, clear, slow moving water, pools and aquatic vegetation are the dominant types found in the NLR compared to the SLR (TPWD 2005). Possible explanation for this variation in growth between rivers of origin may be that growth for this species is

Texas Tech University, Wade A. Massure, August 2016 related to an interaction between flow and stream morphology. However, variation in stream morphology over time was not included in my study. Furthermore, this variation in growth may be caused by flow conditions in which pool habitats formed by low water years may have had optimal temperature or prey availability (Welcomme 1979). This annual variation in quality of available habitat may be the next step in understanding the influence of flow alteration and drought on fish growth. Like other Micropterus species,

Largemouth Bass prey on a wide range of items which can benefit this species during these low water events as loss of connectivity in streams tends to concentrate prey in isolated pools and other habitats therefore increasing prey availability at all ages for this species (Lewis 1967; Carlander 1977). However, depending on overall water conditions these ideal isolated pool conditions may be intermittent throughout the years which may be a possible explanation as to why growth is so variable within the NLR. Lastly, age had a positive influence on standardized growth for largemouth bass which is typically expected as fish get older they get larger. However, a possible explanation for this is that individuals sampled from the SLR were on average two years older and 100+ mm larger than individuals from the NLR therefore driving that relationship with growth between the two rivers in the model.

Other species–– The Von Bertalanffy growth parameter estimates for Gray

Redhorse and both ictalurid catfishes from my study were generally similar to those from other published studies. In the case of Rio Grande Cichlid, growth parameter estimates from my study represent the first detailed description of growth rates for this species.

Gray Redhorse standardized growth in the NLR and SLR was consistent with a previous study described in its native range (Zymonas and Propst 2007) and within the SLR during

Texas Tech University, Wade A. Massure, August 2016

2012-2013 (Bean and Grabowski 2015). Standardized growth of Flathead Catfish in the

NLR and SLR was consistent with that described throughout its native and introduced ranges (Grabowski et al. 2004; Kwak et al. 2006; Jackson et al. 2008; Kaeser et al. 2011).

Growth parameter estimates for Channel Catfish from the NLR and SLR were consistent with a previous study from a similar latitude (Halls and Jenkins 1952) and somewhat higher compared to other riverine populations throughout its native range (Quist and Guy

1998; Arterburn 2001; Nelson 2015). Growth of riverine Channel Catfish in Texas may be higher than other populations as they may have a different growth profile than those found in other states. Previous studies have shown evidence that length of growing season specifically in more southern latitudes may improve growth in Channel Catfish

(Carlander 1969; Durham et al. 2005). It should be noted that results for these species are preliminary and should be interpreted with caution due to low sample sizes of these species from the NLR.

Standardized growth of Gray Redhorse in their first year of growth was found to be negatively correlated with flow metrics. Growth of Gray Redhorse tended to be higher in years characterized as low flow years. Similar to results from other species in this study, Gray Redhorse from the SLR tended to be larger and older compared to the few individuals captured from the NLR, which to was likely due to the underlying differences in annual flow regimes between the two rivers. Results from my study are consistent with those of Bean and Grabowski (2015), who found that growth rates of Gray Redhorse tended to be higher in years characterized by lower flows. A possible explanation for this could be that lower flows may not have as great of an impact on the habitats that Gray

Redhorse are primarily found in the SLR. In contrast, lower flows in the NLR may

Texas Tech University, Wade A. Massure, August 2016 greatly reduce available food resources and connectivity to optimal habitat that Gray

Redhorse need to persist there. Previous studies have found that Gray Redhorse are typically associated with deep, higher current velocity and low turbidity habitats in rivers and streams (Zymonas and Propst 2007; Bean and Grabowski 2015). The response of growth of Gray Redhorse to changes in flow metrics and drought may be better explained by this species diet and habitat use.

Gray Redhorse are typically found in upland and lowland rivers and streams

(Conner and Sutkus 1986), and generally inhabits areas characterized with aquatic vegetation, firm substrates and deep pools and runs (Edwards 1997). Likewise, a study found that young of year and juvenile Gray Redhorse were commonly found in areas that consist of shallow, vegetated runs (Cheek at al 2016). I hypothesized that growth of individuals in the SLR may be optimal for this species during periods characterized by lower flows, in contrast, lower flows in the NLR may cause a reduction in growth. Gray

Redhorse are considered an opportunistic benthic invertivore/detritivore. Both adults and young of year have been found to forage in runs and other shallow water environments

(Edwards 1997). These type of habitats are often much more prevalent in the SLR during lower flows and may provide an optimal forage base for this species. In contrast, these habitats may be the first to disappear in the NLR due to reduction in stream discharge due to anthropogenic water withdrawals or drought, therefore causing increased competition within the species. Gray Redhorse are also a very mobile species, during periods of lower flows it is likely that they are able to move greater distances in search of forage material

Similar to Largemouth Bass and the generalist sunfish species, Rio Grande

Cichlid growth rates were influenced by river of origin and flow metrics. During periods

Texas Tech University, Wade A. Massure, August 2016 characterized by lower flows growth rates of Rio Grande Cichlid tended to be higher in the SLR. Life history and habitat requirements for the Rio Grande Cichlid are similar to that of other generalist species (Hubbs et al. 1991; Martin 2000), and can explain the species resilience to low flow and drought conditions.

Similar to generalist sunfish species, I hypothesized that the effects of drought and altered flow regimes would have either a neutral or positive effect of growth in Rio

Grande Cichlid. This species is ecologically very similar to generalist sunfish species in this study. Rio Grande Cichlid typically inhabit rivers, streams, springs, ponds and lagoons, and within those areas are associated with riffles, pools, backwaters, or other areas with some degree of water flow (Robertson and Winemiller 2003; Miller et al.

2005). During periods of low flows these habitat types may become more prominent in this system, therefore providing optimal habitat for growth in this species. During periods of lower flows Rio Grande Cichlid was found to thrive in slight to strong currents and clear to turbid waters (Miller et al. 2005), which is indicative of the SLR during low flow conditions. Another explanation for increased growth during periods of low flows may be due to shifts in diet due to competition with other centrarchid species. Rio Grande

Cichlid in central Texas were found to be almost exclusively herbivorous while individuals in south Texas were omnivorous and other populations were found to be carnivorous (Buchanan 1971; Tomerelli and Eberle 1990). Buchanan (1971) speculated that these shifts in diet may be caused in response to competition from ecologically equivalent centrarchids.

Low sample sizes for Channel and Flathead Catfish, particularly in the NLR likely led to a lack of significance in ANCOVA models for these species. Alternatively,

Texas Tech University, Wade A. Massure, August 2016 growth of these species may be resilient to drought effects and variation in flows. Results for these species were from small sample sizes, but suggest that these species growth responded to flow regime alterations and drought in similar manners. I found that these species did exhibit a relationship with flow metrics, however, these relationships may have been disproportionately influenced by the presence of a small number of older individuals in the samples. Response of standardized growth to lower flows may be better understood by ecological traits and habitat associations of these species.

Channel and Flathead Catfish are considered habitat generalists and found to be tolerant of a broad range of environmental conditions (Minkley and Deacon 1959; Layher and Maughan 1985). They typically inhabit medium to large size rivers, but also persist in ponds, lakes and reservoirs (Glodek 1980; Etnier and Starnes 1993). A possible explanation for growth in older individuals may be that lower flows increased optimal habitat and prey availability for these species, while young of year and juveniles growth may decline due to lowered prey availability and loss of preferred habitats. Most commonly adult Channel and Flathead Catfish are typically found in medium to deep pool habitats with some degree of structure, while young of year and juveniles are found more often in riffle type habitats (Hubbs et al. 1953; Cowley and Sublette 1987; Kelsch and Wendel 2004). Diets of adult fish primarily consist of fish, crayfish and freshwater mussels (Busbee 1968; Jackson 1999), while younger fish feed primarily on insect larvae and riffle-dwelling macroinvertebrates (Etnier and Starnes 1993). The result of lower flows in the SLR and especially the NLR can increase the amount of pool habitat available to larger fish which in turn can provide optimal habitats for these species. The result of low water events can also cause a loss of connectivity in streams which tends to

Texas Tech University, Wade A. Massure, August 2016 concentrate prey in pools and other habitats therefore increasing prey availability for larger predatory adults (Lewis 1967). In contrast low flow events will reduce the accessibility and availability of riffle habitats (Jowett et al. 2005; Bradford and Heinonen

2008) that younger individuals are typically found in forcing them into less favorable habitats. The loss of riffle habitats may result in a decline of prey availability leading to decreased growth in younger individuals of these species (Bailey and Harrison 1948;

Irwin et al.. 1999). In conclusion, additional research on population structure is needed as capture of these species was difficult especially for Flathead Catfish, as my sampling gears didn’t effectively sample this species in this system, particularly in the NLR.

Further research is needed to fully assess the compounding impacts of hydrologic alterations and drought on the growth rates of Gray Redhorse, Rio Grande Cichlid,

Channel, and Flathead Catfish.

Feeding Guild–– With the groupings of fish used in my project it was difficult to make a clear distinction between carnivorous and piscivorous guild groupings as the fish that were used share the same diet items and many of the same ecological and feeding traits. Fish in these two guild groupings tend to occur in most habitats and generally occupy the top of most aquatic food webs (Juanes et al. 2002). However, fish were characterized as carnivores if they were able to feed on not only fish but other terrestrial items, whereas, fish in the piscivorous guild feed primarily on fish (Juanes et al. 2002;

Warren Jr 2009). One of the main distinctions used to separate the two guild species is the difference in mouth size. Fish placed in the carnivorous guild have relatively large mouths for their body size, while fish placed in the piscivorous guild have relatively small mouth sizes (Thomas et al. 2007; Hubbs et al. 2008). Since the two guilds are

Texas Tech University, Wade A. Massure, August 2016 ecologically so similar, they exhibited very similar trends in relation to changes in flow and will be discussed together as a whole

Fish in the carnivorous and piscivorous guilds typically occur in a wide range of habitats, but prefer areas of streams and rivers with slow moving water, pools and backwaters (Robison and Buchanan 1988; Etnier and Starnes 1993; Ross 2001). During periods of lower flows these types of habitats are readily available in the NLR and SLR

(TPWD 2005). My results indicated that standardized growth of these guilds increased in both rivers during periods characterized by lower flows. However, growth for carnivorous guild was higher in the NLR compared to the SLR. A possible explanation for this difference in growth between rivers may be better explained by available habitats and abundances of prey during low flow periods. Variation in growth for this guild may be caused by flow conditions in which pool and backwater habitats are formed by low water years may have increased the availability of prey (Welcomme 1979). With the ability of these fish to prey on a wide variety of fishes and other terrestrial organisms the occurrence of low water events may cause a loss of connectivity within a stream and therefore concentrating prey in isolated pools and other habitats increasing chances of predator prey interaction which may increase growth of this guild (Lewis 1967; Heman et al. 1969; Schlosser and Ebel 1989). This interaction of lower flows causing decrease in habitat thus increasing prey availability has the potential to be increase growth of these guilds under these lower flow conditions. However, further studies may want to consider combining carnivorous and piscivorous guilds into one guild as fish from these guilds exhibit many of the same ecological traits and feeding characteristics.

Texas Tech University, Wade A. Massure, August 2016

Reproductive Guild–– Using classifications designated by Frimpong and

Angermeier (2009), species were assigned to either lithophilic or polyphilic guild groupings. There have been relatively few studies on how standardized growth of fish in these guilds are effected by changing flow conditions as diets of these species at older ages can vary greatly, whereas, fish at younger ages typically share the same habitat and diet (Warren 2009). Availability of suitable habitat and forage items at this early life stage, along with density dependent effects related to reproductive success may better explain the effects of low flow conditions on these guilds.

Both lithophilic and polyphilic fishes are characterized as nest spawners and guard their nests until young have hatched (Balon 1975). Upon hatching young fish from both guilds tend to take cover in rocky habitat or vegetation. During periods of low flows, increases in aquatic vegetation can provide greater habitat and protection for microinvertebrates in which young fish feed on and reduced flows may reduce the amount of energy expelled while foraging which may increase growth (Dibble et al.

1996). Results for both reproductive guilds indicated that standardized growth increased during periods of low flows and decreased during periods of high flows. A possible explanation for this could be due to the loss of reproductive habitat which may lead to lower recruitment. Density dependent effects due to lower recruitment may be a possible explanation for increased growth in this guild, as a lower abundance of fish may lead to a higher influx of food in these systems leading to increased growth in individuals left in the system. Reduced flows may also create pools and backwater habitats that are preferred by these young fish and may act as a refugia by reducing the risk of predation and increasing time spent foraging on prey (Larimore et al. 1959). In general young fish

Texas Tech University, Wade A. Massure, August 2016 from these guilds may have increased growth during periods of low flows as prey resource availability and suitable habitats may increase, thus increasing growth. In contrast studies have shown that periods of high flows has the ability to displace organisms and modify habitats due to scouring during these events (Franssen et al. 2006).

In turn high flow events can severely reduce the availability of prey items to species in these guilds and may also cause a reduction in available habitats that these young fish need to survive.

Management Implications–– This study provides a better understanding of the complex relationships between natural and human induced changes in the aquatic environment and their effects on fish growth. My results show that fish respond to drought conditions as in the South Llano River and compounding flow alterations found in the North Llano indicating that during drought conditions it is imperative to maintain consistent flows and strive to maintain natural flow regimes. Further research to include shorter lived species, such as the cyprinid family, would highlight the short term impacts of drought and flow alterations. Populations of short lived species show a more rapid response to a few years of poor growth and recruitment than longer lived species, leading to these species tending to be imperiled, increasing the need for management consideration. Results from this study highlighting the impact of drought and flow regime alterations on the growth of stream fishes provides a better understanding of the impacts these environmental changes have on Hill Country ecosystems and can provide insight to similarly impacted systems. The use of growth rates of fishes to assess the ecological influence of drought and flow alteration on aquatic ecosystems may be an

Texas Tech University, Wade A. Massure, August 2016 additional tool in the management toolbox and can guide policy makers in critical allocation of flow decisions essential to riverine ecosystems.

Texas Tech University, Wade A. Massure, August 2016

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APPENDICES

Appendix 1. Pooled Von Bertalanffy growth curves based on back-calculated total length-at-age of Redbreast Sunfish (A), Green Sunfish (B), Warmouth (C), Bluegill (D), and Longear Sunfish (E) captured in the North and South Llano Rivers, Texas from March 2014 ─ November 2015. Green Sunfish growth curve is based on parameters taken from Rypel (2011) as there was not sufficient data to provide curve parameters for this species.

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Appendix 2. Pooled Von Bertalanffy growth curves based on back-calculated total length-at-age of Largemouth Bass (A) and Guadalupe Bass (B) captured in the North and South Llano Rivers, central Texas from March 2014 ─ November 2015.

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Appendix 3. Pooled Von Bertalanffy growth curves based on back-calculated total length-at-age of Gray Redhorse (A), Rio Grande Cichlid (B), Channel Catfish (C), and Flathead Catfish (D) captured in the North and South Llano Rivers, central Texas from March 2014 ─ November 2015.

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Appendix 4. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age, and PC score describing annual flow metrics and their influence on standardized growth of all ages for the representatives of two reproductive guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The polyphilic guild consisted of Largemouth Bass, Guadalupe Bass, Green Sunfish, Warmouth, Bluegill, and Longear Sunfish. Lithophilic included Gray Redhorse, Redbreast Sunfish, and Rio Grande Cichlid. Species Effect Value (±SE) F DF1 DF2 P Polyphilic Guild Intercept -0.00 ± 0.03 ─ ─ 456 ─ Species ─ 1.74 5 456 0.12 Species(GB) 0.04 ± 0.03 ─ ─ ─ ─ Species(LMB) 0.01 ± 0.04 ─ ─ ─ ─ Species(GS) 0.06 ± 0.05 ─ ─ ─ ─ Species(WM) 0 ─ ─ ─ ─ Species(BG) -0.03 ± 0.04 ─ ─ ─ ─ Species(LE) -0.04 ± 0.04 ─ ─ ─ ─ River -0.01 ± 0.03 0.20 1 456 0.66 BC Age 0.00 ± 0.01 12.88 1 421 < 0.01 BC Age*Species ─ 7.87 5 421 < 0.01 BC Age(GB) -0.04 ± 0.01 ─ ─ ─ ─ BC Age(LMB) -0.01 ± 0.01 ─ ─ ─ ─ BC Age(GS) -0.06 ± 0.03 ─ ─ ─ ─ BC Age(WM) 0 ─ ─ ─ ─ BC Age(BG) 0.03 ± 0.02 ─ ─ ─ ─ BC Age(LE) 0.03 ± 0.02 ─ ─ ─ ─ PC1 0.01 ± 0.02 0.19 1 421 0.66 PC2 0.03 ± 0.01 16.57 1 421 < 0.01 Lithophilic Guild Intercept 0.04 ± 0.03 ─ ─ 173 ─ Species ─ 0.10 2 173 0.90 Species(GR) -0.00 ± 0.04 ─ ─ ─ ─ Species(RB) -0.01 ±0.03 ─ ─ ─ ─ Species(RGC) 0 ─ ─ ─ ─ River -0.09 ± 0.04 3.94 1 173 0.05 BC Age 0.02 ± 0.01 7.04 1 200 0.01 PC1 -0.05 ± 0.02 7.16 1 200 0.01 PC2 0.03 ± 0.01 3.68 1 200 0.06

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Appendix 5. Summary of combined species-specific mixed-model repeated-measures ANCOVA evaluating the effect of species, river, fish age and PC score describing annual flow metrics and their influence on standardized growth during the first year of life of fishes from two feeding guilds captured from the North Llano and South Llano Rivers in central Texas during 2014-2015. The carnivorous guild consisted of Largemouth Bass, Guadalupe Bass, Green Sunfish and Warmouth. The piscivorous guild consisted of Bluegill, Longear Sunfish and Redbreast Sunfish. The symbol “─” indicates that no value is associated with the model term. Effects with a P-value ≤ 0.05 were considered significant.

Species Effect Value (±SE) F DF1 DF2 P Carnivorous Guild Age 1 Intercept 0.05 ± 0.13 ─ ─ 287 ─ Species ─ 0.12 3 287 0.95 Species(GB) 0.01 ± 0.03 ─ ─ ─ ─ Species(LMB) 0.02 ± 0.03 ─ ─ ─ ─ Species(GS) 0.01 ± 0.05 ─ ─ ─ ─ Species(WM) 0 ─ ─ ─ ─ River 0.09 ± 0.16 0.32 1 287 0.57 PC1*River ─ 3.36 2 287 0.04 PC1(NLR) 0.18 ± 0.09 ─ ─ ─ ─ PC1(SLR) -0.12 ± 0.07 ─ ─ ─ ─ PC2*River ─ 0.59 2 287 0.55 PC2(NLR) 0.04 ± 0.04 ─ ─ ─ ─ PC2(SLR) -0.03 ± 0.11 ─ ─ ─ ─ Piscivorous Guild Intercept 0.12 ± 0.04 ─ ─ 258 ─ Age 1 Species ─ 1.58 2 258 0.21 Species(BG) -0.04 ± 0.02 ─ ─ ─ ─ Species(LE) -0.03 ± 0.02 ─ ─ ─ ─ Species(RB) 0 ─ ─ ─ ─ River -0.20 ± 0.10 4.42 1 258 0.04 PC1 -0.14 ± 0.07 4.09 1 258 0.04 PC2 0.10 ± 0.03 11.84 1 258 < 0.01