Copyright 2013, Jillian Groeschel · Texas Tech University, Jillian Groeschel, December 2013 iv...

EVALUATIONS OF GROWTH AND HABITAT USE BY GUADALUPE BASS AT A

RIVERSCAPE SCALE IN THE SOUTH LLANO RIVER, TEXAS

by

Jillian Groeschel, B.S.

A Thesis

In

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

Timothy B. Grabowski, Ph.D.

Chair of Committee

Shannon K. Brewer, Ph.D.

Gary P. Garrett, Ph.D.

Dr. Dominick Joseph Casadonte, Jr.

Interim Dean of the Graduate School

December, 2013

Texas Tech University, Jillian Groeschel, December 2013

ii

ACKNOWLEDGMENTS

I thank the entire staff and faculty of the Department of Natural Resources

Management and the Texas Cooperative Fish and Wildlife Research Unit at Texas Tech

University for their guidance and support during my time as a graduate student.

Specifically, I thank my major advisor, Dr. Timothy Grabowski, for providing project

funds as well as constantly being available to support, guide, and direct me throughout

my master’s project. I am also grateful for my committee members, Drs. Shannon Brewer

and Gary Garrett. Without their support and helpful advice, this project would not have

been possible. I thank the staff, and especially Karen Lopez and Robert Stubblefield at

the Texas Tech University-Junction Campus for their kind words, flexibility, and

hospitality during my stays in Junction, Texas. I thank Dr. Tom Arsuffi, Scott

Richardson, and those from the South Llano Watershed Alliance for their knowledge of

the area and people, support, and assistance. I am grateful for Carl Kittel and the staff at

the A.E. Wood State Fish Hatchery for donating Guadalupe bass fingerlings for this

project as well as the entire staff at the Heart of the Hills Fisheries Science Center,

specifically Bobby Wienecke and Bob Betsill, for caring for those fingerlings until I was

ready to tag and release them. I also thank Tim Birdsong for his involvement and

knowledge as well as allowing funding for this project.

The completion of this thesis would not have been possible without the assistance

of several volunteers. I thank P. Bean, B. Cheek, Q. Chen, C. Craig, C. Holmes, K.

Linner, J. Mueller, B. Perkins, B. Skipper, M. Vanlandeghem, and the TTU Bass Club for

helping collect Guadalupe bass. I thank the South Llano River landowners for their

support and allowance of access during sample collections. I am also thankful to Dijar

Lutz-Carrillo at the A.E. Wood State Fish Hatchery for teaching and assisting me in my

genetic analysis. Lastly, I am grateful for the support from my family and friends. God

has blessed me on this great journey, and your support, motivation, and advice has

always helped. Funding was provided by a U.S. Fish and Wildlife Service State Wildlife

Grant administered by Texas Parks and Wildlife Department (contract number 415385)

and the U.S. Geological Survey (cooperative agreement number G11AC20436).


iii

TABLE OF CONTENTS

ACKNOWLEDGMENTS............................................................................................... ii

ABSTRACT.................................................................................................................... iv

LIST OF TABLES........................................................................................................... v

LIST OF FIGURES......................................................................................................... vii

I. INTRODUCTION........................................................................................................ 1

II. METHODS.................................................................................................................. 7

Study Area............................................................................................................ 7

Habitat mapping of the South Llano River, Texas............................................... 8

Guadalupe bass PIT-tag telemetry...................................................................... 9

Guadalupe bass age and growth......................................................................... 10

Guadalupe bass genetics...................................................................................... 12

Data Analysis....................................................................................................... 13

III. RESULTS.................................................................................................................. 21

Instream habitat types and composition of the South Llano River, Texas........... 21


Guadalupe bass population demographics-age and growth............................... 22


Relation between habitat and Guadalupe bass growth....................................... 24

Guadalupe bass age-specific habitat associations.............................................. 24

Influence of discharge rate and fragment on Guadalupe bass growth rates....... 27

IV. DISCUSSION........................................................................................................... 44

Habitat mapping of the South Llano River, Texas............................................... 44


Guadalupe bass population demographics-age and growth............................... 48


Relation between habitat and Guadalupe bass growth....................................... 50

Guadalupe bass age-specific habitat associations.............................................. 52

Influence of discharge rate and fragment on Guadalupe bass growth rates....... 54

Conclusions.......................................................................................................... 56

REFERENCES................................................................................................................ 58


iv

ABSTRACT

Guadalupe bass Micropterus treculii is a black bass species endemic to central

Texas. Its dependence on undisturbed pool and run habitats with sufficient flow and

cover renders it sensitive to habitat alteration. The decline of the species due to habitat

alteration/loss and introgressive hybridization with introduced smallmouth bass

Micropterus dolomieu has prompted efforts to restore Guadalupe bass habitats. However,

detailed data on how the species may respond to these efforts are lacking. I assessed age-

specific Guadalupe bass habitat associations and habitat specific growth rates at three

different scales (fine, intermediate, and coarse) in the South Llano River. Substrates were

classified using side-scan sonar. Scales and otoliths were extracted from Guadalupe bass

to determine age and growth. Over 65% of captured Guadalupe bass were age-2 or age-3,

but individuals ranged from 0-7 years of age. Overlap in habitat associations was

exhibited between age classes 1-3+. Age-0 Guadalupe bass tended to associate with

greater proportions of pool and run mesohabitats with submerged aquatic substrates.

Finally, low discharge rates appeared to have the greatest influence on Guadalupe bass

growth rates with growth exhibiting a negative correlation with the proportion of

discharge observations falling in the Q90 range in a given year. My results suggest age-

specific Guadalupe bass habitat associations that may increase the effectiveness of

restoration efforts directed at the species. Further application of these results may allow

the use of the Guadalupe bass population trajectories and habitat occupation rates as an

indicator of stream health in Edwards Plateau streams or as a predictor of changes in

stream condition.


v

LIST OF TABLES

1. Classification of substrate type and instream cover (Cummins & Lauff 1969;

Minshall 1984; Quinn & Hickey 1990, Snedden 1999, Perkin et al.

2010) used to classify substrates of the South Llano River, Texas

based on side scan sonar imagery collected in October 2011.................. 16

2. List of six multiplex polymerase chain reactions (PCRs) used for Guadalupe

bass fin clips captured from the South Llano River, Texas in spring

2012 – fall 2012....................................................................................... 17

3. Relocated and recaptured PIT-tagged Guadalupe bass and associated habitat

type in the South Llano River, TX from May – August 2012,

November 2012, and July........................................................................ 29

4. Mean (±SE) back-calculated total length (TL) at each annulus of Guadalupe

bass captured in the South Llano River, Texas from April –

November 2012........................................................................................ 30

5. Age-length key based on the total length (TL) at age and age at capture of

Guadalupe bass captured in the South Llano River, Texas from

April 2012 – November 2012. Numbers in rows give the

probability (%) that a Guadalupe bass within the 20-mm length

interval is a certain age............................................................................ 31

6. Discriminant analysis of hybrids versus pure strain Guadalupe bass at the

stream unit and 50-m buffer scale. No clusters were identified at

the 250-m scale (F1,284<3.42, P>0.07)..................................................... 32

7. Results from the ANCOVA of habitat variables influencing the most recent

year of growth (2012) of Guadalupe bass younger than age-6 at

(A) stream unit, (B) 250-m, and (C) 50-m scales captured in the

South Llano River, Texas from April 2012 – November

2012......................................................................................................... 33

8. Most informative habitat variables selected from the discriminant analysis

that best discriminated among age classes (Age-0, Age-1, Age-2,

Age-3+) of Guadalupe bass captured in the South Llano River, TX

from April 2012 – November 2012......................................................... 34


vi

9. Description of variables by scale and correlation coefficients between

habitat variables and the first and second canonical axes. Bolded

values indicate the most correlated variables for that

axis........................................................................................................... 35

10. Percent of observations classified into each age class and error rates by scale

from crossvalidation of the discriminant analysis of Guadalupe

bass captured in the South Llano River, Texas from April 2012 –

November 2012........................................................................................ 36


vii

LIST OF FIGURES

1. The 48-km study area of the South Llano River located on the Edwards

Plateau and part of the Colorado River Drainage basin in Kimble

County, Texas. The upper limit was approximately 840 m

upstream of its confluence with Big Paint Creek (30.29798°N,

99.90688°W) and extended downstream to the dam at Lake

Junction. Red areas delineate road crossings and natural

barriers..................................................................................................... 18

2. Release sites of PIT tagged juvenile Guadalupe bass released in the South

Llano River, Texas, and area surveyed with a LF HDX RFID

portable backpack antenna (Oregon RFID, Portland, Oregon) from

May 2012 – September 2012................................................................... 19

3. Survey locations of Guadalupe bass caught from the South Llano River,

Texas in spring 2012 – fall 2012 based on gear type and month.

(A) April angling, (B) May angling, (C) June angling, (D) July

angling, (E) August angling, (F) September angling, (G) October

angling, (H) April and October electrofishing, (I) August

electrofishing, (J) November electrofishing, (K) Seine sites................... 20

4. Mesohabitat and substrate type proportions within the eight fragments of the

South Llano River, Texas, surveyed October 2011. (A) Fragment I,

(B) Fragment II, (C) Fragment III, (D) Fragment IV, (E) Fragment

V, (F) Fragment VI, (G) Fragment VII, (H) Fragment VIII, (I)

amount of boulders and large woody debris (LWD) in each

fragment................................................................................................... 37

5. Images of age-2 scales and their associated otoliths from Guadalupe bass

caught in the South Llano River, Texas. (A) An example of a bass

with discernible annuli in scales but not otoliths, (B) an example of

a bass with discernible annuli in both scales and otoliths........................ 38

6. Age frequency distribution of Guadalupe bass captured in the South Llano

River, Texas in spring 2012 – fall 2012................................................... 39

7. Von Bertalanffy growth curve based on back calculated total length at age

of Guadalupe bass captured in the South Llano River, Texas from

April 2012 – November 2012. Black circles represent back

calculated total lengths (TL) at age, green circles represent actual

lengths at age, and yellow circles represent at capture total lengths....... 40


viii

8. Canonical correlation biplot of age-specific habitat associations of

Guadalupe bass captured in the South Llano River, Texas from

April 2012 – November 2012 at the (A) stream unit scale,

(B) 250-m scale, and (C) 50-m scale....................................................... 41

9. Proportions of discharge rates (m-3

s-1

) observed in the South Llano River,

Texas from 2004 to 2012......................................................................... 42

10. Guadalupe bass residuals from the von Bertalanffy model were negatively

correlated to the proportion of Q90 discharge rates observed during

a particular year over the first three years of growth (F3,542=10.62,

P<0.0001) of Guadalupe bass captured in the South Llano River,

Texas from April 2012 – November 2012. (A) back-calculated

age-1 (n=209), (B) back-calculated age-2 (n=195), (C) back-

calculated age-3 (n=142)......................................................................... 43


1

CHAPTER I

INTRODUCTION

Human-induced habitat degradation and alteration of flow regimes have been

established as major stressors to the ecological integrity of rivers and streams (Poff et al.

1997, Poff and Zimmerman 2010) as well as major factors driving the decline of

freshwater fish diversity in North America (Warren et al. 2000, Cooke et al. 2005).

Stream management depends on a solid understanding of biota-habitat relationships and,

as such, specific habitat classifications and associations are critical components of stream

science and management. For example, managers often rely on empirical descriptions of

habitat use to infer factors that limit the growth, survival, and abundance of a species

(Hawkins 1993). The quantification of habitat as well as a species’ associations with that

habitat at different ontogenetic stages provides a basis for predicting response to changes

in habitat availability. Considerable evidence suggests that both the quality and quantity

of available habitat for use affect the structure and composition of resident biological

communities and populations (Ward and Stanford 1979, Meffe and Sheldon 1988, Calow

and Petts 1994, Maddock 1999). Because biological communities are sensitive to changes

in a wide array of environmental factors, they will reflect watershed conditions and

alterations (Karr 1981). Therefore, understanding the interaction of life-history

characteristics with environmental factors may help predict how a species will respond to

disturbance or degradation and furthermore, assist in determining appropriate

conservation actions and evaluating restoration projects.

The concern that anthropogenic activities have reduced the biological integrity of

rivers and streams has led to the development of biological indicators to assess the status

and trends of these ecosystems (Norris and Thoms 1999, Karr and Chu 2000, Butler et al.

2012). Biological species are widely seen as good indicators of habitat quality because

their habitats relate them to aspects of the surrounding physical, chemical, and biological

environment (Milner et al. 1985, McDowall and Taylor 2000). It is important to clearly

describe the ecological characteristics or features with which an indicator species is

associated, and to be able to demonstrate empirically that there is a consistent and


2

persistent relationship in order for that species to serve as a useful indicator of ecosystem

health (Dale and Beyeler 2001). Thus, an indicator species emerges from a complete

comprehension of a large amount of data; it cannot be safely selected a priori. This

research will help to develop the knowledge base necessary to determine the suitability of

a predatory fish species, Guadalupe bass Micropterus treculii, as an indicator of stream

health in the Edwards Plateau, Texas.

The Edwards Plateau roughly extends from the Pecos River on the west to the

Balcones Escarpment (Austin to San Antonio to Del Rio) on the east and south (Figure

1). The region contains 62,160 km2 of land characterized by asymmetric mountains and

wide, intervening basins (Bates and Jackson 1984, Edwards et al. 2004). It overlays a

foundation of Cretaceous limestone, and is considered to be the largest continuous karst

area in the United States (Kastning 1983, Fowler and Dunlap 1986, Anaya 2004). Twelve

aquifers are the source of the water for the springs that supply stable river and stream

systems which are home to most of the region’s biodiversity (Edwards et al. 2004, TPWD

2005). All aquatic-dependent plants and wildlife in the Edwards Plateau rely on these

aquifers to support essential components of their habitats, from the fish that occur directly

in the spring outlets or those found downstream that indirectly depend on the

groundwater (Edwards et al. 2004). However, these aquatic systems are at risk due to the

region’s anticipation of a 20-25% population increase over the next 10 years (Murdock et

al. 2002). Edwards et al. (2004) reported that while the Edwards Plateau contains many

aquifers, its annual precipitation is highly variable, and it is susceptible to prolonged,

frequent, and unpredictable drought. The growing human population of the Edwards

Plateau will use groundwater sources to help meet current and future water needs as

surface-water resources are limited (Edwards et al. 2004). This withdrawal of

groundwater is expected to result in decreased flows in the rivers and streams of this

region, exacerbating the predicted increased temperatures, decreased dissolved oxygen,

and an increased risk of introduction and establishment of nonnative species (Bezanson

and Wolfe 2001, TPWD 2005). Responsible management of the waters from the aquifers

of the Edwards Plateau will conserve regional spring flows that maintain flowing rivers

and allow healthy fish populations to persist. Thus an indicator species that is dependent


3

upon aquifer discharges would be a direct indicator of the overall health of the

ecosystem.

The official Texas state fish, Guadalupe bass is endemic to the streams and rivers

of the northern and eastern Edwards Plateau in central Texas, including portions of the

Brazos, Colorado, Guadalupe, and San Antonio basins (Hubbs 1957b, Edwards et al.

2004, Broad 2008, Hubbs et al. 2008) as well as portions of the lower Colorado River off

the Edwards Plateau downstream of Austin. It is currently listed as a species of greatest

conservation need by the state of Texas due to hydrological alteration, habitat

degradation, and, especially, introgression with introduced smallmouth bass (Edwards

1980, Hubbs et al. 2008). Habitat degradation is thought to have resulted in declines in

their abundance; however, detailed habitat use data are lacking, i.e. the influence of

discharge rate and habitat type on growth rate as well as age-specific habitat associations.

In particular, the habitat associations of juveniles are poorly understood (Riley et al.

2003, Perkin et al. 2010).

Guadalupe bass has the potential to be an effective indicator species of stream

health in its native range because of its position near the top of the aquatic food web and

its demonstrated habitat requirements (Edwards 1980, 1997, Perkin et al 2010). Perkin et

al. (2010) found that a population of adult Guadalupe bass associated with eddy

mesohabitats created by instream cover within or near run mesohabitats. Habitats also

included small to medium-size substrates, current velocities less than 0.1 m s1, and

depths of 1.0 m. They generally avoided open water and associated more with woody

debris, boulders, and ledges (Perkin et al. 2010). Daily movements increased more than

200% as spring approached due to foraging activities and reproduction (Edwards 1980).

They also tended to associate with pools of greater depths during periods of extreme low

flow in the summer (Perkin et al. 2010). These specific associations as well as the

endemism to the streams and rivers of, and just outside the Edwards Plateau could render

Guadalupe bass sensitive to habitat alteration. However, while these are established

associations, previous studies on Guadalupe bass habitat associations are mostly

qualitative and based on small sample sizes (Edwards 1980, 1997, Perkin et al. 2010).


4

Furthermore, the potential of a top-level predatory fish as an indicator species has not

been thoroughly investigated.

Indicator species of ecosystem health used in past studies have included diatoms

(Patrick 1975), benthic macroinvertebrates (Gaufin and Tarzwell 1952, Mason 1978,

Muenz 2006), amphibians (Muenz 20063), and insects (Peck et al. 1998). However,

fishes also have numerous advantages as indicator organisms of stream health such as,

there is extensive knowledge of the life history for most fish species, their positions at the

top of, and throughout the aquatic food chain in relation to diatoms and invertebrates

helps to provide an integrative view of the watershed environment, and the general public

can relate to statements about conditions of the fish assemblage. Additionally, they are

typically present in all but the most polluted waters, and they are fairly easy to identify

(Karr 1981). However, it must also be recognized that there are several disadvantages in

using fish as indicator organisms. For instance, because they are highly mobile and may

be migratory, they can avoid exposure to unfavorable environmental conditions, and

ethical problems exist with any destructive sampling of fish (Cranston et al. 1996).

Additionally, because fish typically have long generation times relative to diatoms,

macroinvertebrates, amphibians, and insects, it may take longer to observe responses to a

disturbance. Perhaps one of the biggest obstacles to using predatory fishes as indicators

of stream health is that a large proportion of them are ubiquitous and tolerant of a wide

range of conditions (Schiemer 2000). Nonetheless, based on the advantages, measuring

the condition of a fish population and understanding its habitat associations may help

draw conclusions about the overall health of a river system.

The South Llano River located in the Edwards Plateau is one of the few places

where genetically pure, naturally-occurring populations of Guadalupe bass still exist

(Koppelman and Garrett 2002, Broad 2008). However, human disturbances have caused

habitat degradation and fragmentation along an upstream-downstream gradient (Edwards

et al. 2004). The upper reaches are mainly undisturbed, whereas the lower reaches

become increasingly degraded due to land use and fragmentation from road crossings,

thus having the potential to limit fish passage and sediment transport. Conservation

efforts dedicated to restoring habitat for Guadalupe bass are already underway in the


5

South Llano River (Birdsong et al. 2010). The Texas Guadalupe Bass Restoration

Initiative, beginning in 2010, is committed to conserving Guadalupe bass populations by

involving willing landowners in landscape conservation activities at watershed scales.

These types of activities include reducing or eliminating actions that degrade riparian

systems and water quality, reduce water quantity, favor nonnative species, and fragment

the river (TPWD 2010). However, there are no agreed upon benchmarks by which to

determine whether these restoration activities are successful as there is no data on what

characteristics represent a healthy Guadalupe bass population.

Similar studies on other black bass species have been completed to assess their

population characteristics and habitat associations in response to a changing environment.

For example, Kanehl et al. (1997) evaluated the response of smallmouth bass to the

removal of the Woolen Mills Dam from the Milwaukee River. They demonstrated that

before dam removal, smallmouth bass populations were low; however, after dam

removal, habitat quality improved and smallmouth bass abundance increased

substantially (Kanehl et al. 1997). Additionally, Peterson and Kwak (1999) suggested that

land-use changes may be a greater detriment to smallmouth bass populations than

projected climate change, and that the combined effects of both may lead to local species

extirpation. Brewer (2011) examined how human activities in a catchment influenced

habitat conditions and use by smallmouth bass and concluded that young-of-the-year

smallmouth bass mostly used low-velocity, deeper-water habitats when streams were

impacted by pasture land use in comparison to forest land use. These studies all

demonstrate the importance of establishing baseline data in order to understand a species’

population and whether restoration efforts focused on that population will be successful.

Before habitat restoration actions can be addressed, it is important to first

understand how an organism is associated with its physical environment under a variety

of natural and altered landscape conditions. The objectives of my study were to examine

the influence of discharge and habitat on Guadalupe bass growth rates, and determine

Guadalupe bass age-specific habitat associations at three different spatial scales. Overall,

the results of this study will help to develop a better understanding of Guadalupe bass


6

habitat associations and patterns in order to assist in the assessment of restoration efforts

targeting this species.


7

CHAPTER II

METHODS

Study Area.—The South Llano River is a second order stream and tributary of the Llano

River within the Colorado River Basin, approximately 200 km west of San Antonio

(Figure 1). It is approximately 175 km in length, but only the lower 53 km maintains

year-round discharge due to the numerous springs that supply water to this portion of the

river. The remainder of the river is ephemeral, and contains flowing water only after

heavy precipitation events. The South Llano River provides continuous flow downstream

to the Llano and Colorado rivers, especially during times of drought, and has not ceased

flow in recorded history (TPWD 2005, Broad 2008). It is considered to be a relatively

pristine river with minimal human disturbance due to its hydrological regime, good water

quality, and diverse benthic macroinvertebrate and fish assemblages that are

representative of the Edwards Plateau (Bayer et al. 1992). While the South Llano River

may seem pristine relative to other streams on the Edwards Plateau (Broad 2008, Broad

2012), there is a fair amount of anthropogenic disturbance within the watershed. For

example, the river is fragmented by seven road crossings of varying design (Figure 1)

that have the potential to limit the connectivity of riverine populations and alter sediment

transport. The overgrowth of Ashe juniper Juniperus ashei on upland habitats has the

potential to decrease the water quantity of the river (Bolton et al. 1991, Thurow and

Hester 1997), while overgrazing and other land-use practices on some properties

bordering the river have resulted in erosional banks and the potential for elevated

sediment loads and altered channel morphology (Edwards et al. 2004, Broad 2012).

However, the primary threat to the river is the reduction or loss of spring discharge due to

the increasing water demands on the Edwards-Trinity Plateau Aquifer associated with

increasing urban development of Austin, San Antonio, San Marcos, and other

neighboring metropolitan areas (Murdock et al. 2002, Edwards et al. 2004).

My research focused on a 48-km reach of the South Llano River with its upper

limit approximately 840 m upstream of its confluence with Big Paint Creek (30.29798°N,

99.90688°W) and extending downstream to the dam at Lake Junction (Figure 1). This


8

area was chosen due to ease of access, the upstream-downstream gradient of disturbance,

and its importance as a demonstration area for various restoration projects implemented

as part of Texas Parks and Wildlife Department’s (TPWD) Guadalupe Bass Restoration

Initiative.

Habitat mapping of the South Llano River, Texas.—I followed the protocols described by

Kaeser and Litts (2010) to map instream habitats. A Humminbird 998c SI side scan sonar

unit (Humminbird, Eufaula, Alabama) with the transducer mounted off the starboard bow

of a canoe was used to capture georeferenced images of the river bottom substrate. A

Garmin 78sc (Garmin International, Inc., Olathe, KS) handheld GPS was connected

directly to the control head for trackplotting the course of the canoe during the survey.

The handheld GPS tracklog was set to record a point at 3-s intervals and was placed near

the transducer to ensure maximum accuracy, as recommended by Kaeser and Litts

(2010).

All of the images and waypoints were recorded on an MMC/SD card installed

into the control head prior to the surveys. The images collected were uploaded to a

computer, cropped with IrfanView v. 4.30 (Irfan Skiljan, Wiener Neustadt , Austria),

imported into ArcGIS 10.0 (ESRI, Redland, California), and clipped to form mosaics, or

sonar image maps (SIMs). Georeferenced aerial images (96 x 96 dpi, 1 m2 per pixel) of

the study site collected by unmanned aerial vehicle flyovers in November 2011 were also

acquired from TPWD to assist in creating the instream habitat map. The mosaics were

georeferenced to the proper UTMs zone by importing the trackplotting and waypoint data

and overlaid onto the aerial images.

On each mosaic, substrate types were delineated by using digitized lines,

converted to polygons, and assigned a substrate class (Table 1). Dominate substrate types

were labeled with capital abbreviations; whereas, subordinate substrate classes were

labeled with lowercase abbreviations. Specific structures such as woody debris and

boulders were labeled in ArcGIS with a separate polygon marker, representing a separate

class (Table 1). Mesohabitats, defined as riffles, runs, and pools, were also classified

using this polygon delineation method. Riffles were defined as topographic high points in


9

the bed profile and composed of coarse sediments. At base flows, riffles had a rapid,

shallow flow with steep water-surface gradient (Richards 1982). On the map, many riffles

were characterized as areas where water flowed around and over boulders and was too

shallow (<0.5 m) and rapid to effectively deploy the side scan sonar. Runs were typically

defined as the areas directly upstream and downstream of riffles with fast water, but

deeper and little or no turbulence. Pools were characterized as topographic low points

with finer substrates (e.g., gravel-cobble and gravel-sand). They were generally deeper

and wider areas of the river, slow-flowing, and had a gentle surface slope (Richards

1978).

To complement and verify the side scan sonar mosaic, ground truthing was

performed. A total of 349 sites was point sampled. These sites started at the upstream

crossing of the Hwy 377 road crossing (30.34569°N, 99.90220°W) and continued

downstream every 130 m in the center of the river channel to the dam at Lake Junction

(30.48929°N, 99.75964°W). In shallow areas (<1 m) or areas with minimal turbidity,

sampling was either done by using my hand to feel the bottom substrate, or the bottom

was observed by sight. In turbid or deep areas, an underwater camera (Navroute

Technologies, Miami, Florida) was used to observe the substrate. At each site, a waypoint

was recorded using a handheld GPS 78sc (Garmin International, Inc., Olathe, KS), and

the substrate noted. A subset of 25% of the large specific structures (i.e. large woody

debris and boulders) found on the mosaic layer were randomly selected, located with a

waypoint, and measured to further ensure map scale accuracy. Map classification data

were not in hand during ground truthing. These sites were then compared with the

instream habitat map, discrepancies noted, and an accuracy rate was calculated.

Guadalupe bass PIT-tag telemetry.—In spring 2012, TPWD produced juvenile

Guadalupe bass for stocking in the South Llano River at the A.E. Wood Fish Hatchery in

San Marcos, Texas. On 19 April 2012, approximately 1,500 individuals were transferred

to the Heart of the Hills Fisheries Science Center in Mountain Home, Texas where they

were raised in circular tanks with a flow-through system and well-nourished with the

purpose of rapid growth. Of those fish, 485 of the largest (76.2-101.6 mm TL) were


10

surgically implanted with 12-mm HDX PIT-tags (Oregon RFID, Portland, Oregon) on 30

May 2012. We anesthetized individuals using a 100 mg L-1

solution of tricaine

methanosulfate (MS-222). PIT tags were implanted by first making an incision,

penetrating the peritoneum on the mid-ventral line between the posterior tip of the

pectoral fin and the anterior point of the pelvic girdle, using a scalpel. The transponder

was then inserted by gently pushing it through the incision at a 45° angle into the body

cavity. Fish were allowed to recover for approximately 24 hours post-operation and then

transported and released at three locations within the study site (Figure 2).

Tracking began as early as 5 hrs post-release and was repeated every 10-14 days

during the summer from May 2012 to September 2012 using a LF HDX RFID portable

backpack antenna (Oregon RFID, Portland, Oregon). When another researcher was

unavailable, I tracked fish by starting downstream at the Flatrock Lane road crossing

(30.47919°N, 99.77837°W) and walked upstream in a zig-zag pattern in wadeable areas

(Figure 2) with the antenna in front of me in the water at all times. To survey deeper

areas, another researcher paddled me downstream in a canoe while I held the antenna

submerged in water in front of the bow of the canoe. Once relocated, the ID number of

the bass was recorded, the location was recorded using a handheld GPS 78sc (Garmin

International, Inc., Olathe, KS), and the substrate noted. From 9 November 2012 to 10

November 2012, Guadalupe bass were captured from the South Llano River State Park

downstream to the Flatrock Lane using a boat/barge-mounted electroshocker and scanned

using the portable backpack antenna during a survey of this area for a different, ongoing

project. Six control PIT tags were also deployed (two near each release site) to test the

detection rate of the portable antenna (Figure 2).

Guadalupe bass age and growth.—Guadalupe bass were captured using a combination of

angling, electrofishing, and seining during the spring, summer, and fall of 2012. Angling

occurred in select areas across the entire study area throughout April 2012 – October

2012 (Figure 3). Electrofishing occurred from the northeast Hwy 377 road crossing to the

bridge at County Road 150 on 15 October 2012, and from the South Llano River State

Park to the Flatrock Lane road crossing on 9 November 2012, 10 November 2012, and 20


11

November 2012 (Figure 3). Seining occurred as part of another ongoing project (Cheek

2013) at random locations from approximately 165 m upstream from the waterfall

(30.308455°N, 99.908466°W) to the east edge of the South Llano River State Park

property (30.453289°N, 99.794018°W) on 21-23 June 2012, 3 July 2012, 30 July 2012,

13-15 October 2012, and 17-18 October 2012 (Figure 3). Capture locations were

recorded using a handheld GPS 78sc (Garmin International, Inc., Olathe, KS) with an

accuracy of 3-5 m and acquisition time of 1-38 s. Capture locations of bass caught by

angling were recorded at the location of the angler and not directly where the bass was

caught. Additionally, both electrofishing and seining were completed as transects, and the

capture locations were recorded as the start point of each transect. Bass were typically

caught within 7 m of the angler and transects were 25 m in length. These distances were

accounted for in the data analysis by associating individuals with the habitat within 50-m,

250-m and stream unit areas surrounding their recorded capture locations. Once captured,

individuals were measured to the nearest millimeter-total length (mm-TL), and scales and

fin clips were removed before release. Scales were preserved dry in small coin envelopes,

while fin clips were stored in vials filled with 95% ethanol and placed with their

associated scales in the coin envelopes.

Scales were then prepared for reading by compressing them between two glass

slides and placing them in a petri dish of water. Digital images of each scale were

captured using a compound microscope equipped with a camera (Olympus SZX16,

Infinity 1, Olympus, Tokyo, Japan) and analyzed using ImageJ (Abramoff et al. 2004)

following descriptions for interpreting scale microstructure by DeVries and Frie (1996).

Total length at age was back calculated for each annulus and corrected using the direct

proportion method (DeVries and Frie 1996). All bass were aged assuming a birthdate of

01 January. Second readers were used to assess the reliability of the age estimates from

the first reader. A third reader was used to resolve disagreements between the first and

second readers. If no agreed-upon age was determined from a scale, that scale was not

included in the data analysis.

Sagittal otoliths were also collected from an additional sample of 50 Guadalupe

bass caught by a combination of angling and electrofishing to complement the age


12

estimates from the scales. These individuals were euthanized with an overdose of MS-

222 (>100 mg L-1

). Otoliths were removed by cutting longitudinally through the top of

the skull and across the head. Of the 50 otoliths, 35 were stored in baby oil (Johnson &

Johnson Consumer Companies, Inc., New Brunswick, New Jersey) to enhance ring

appearance while the other 15 were stored dry in the case that the oil cleared the rings.

Digital images of each whole otolith were captured using a compound microscope

equipped with a camera (Olympus SZX16, Infinity 1, Olympus, Tokyo, Japan). These

images were enhanced for clarity and aged using ImageJ (Abramoff et al. 2004).

However, not all otoliths had distinguishable annuli; therefore, 25 otoliths were broken

through the nucleus (or kernel) and burned in a flame following the procedure described

by Chilton and Beamish (1982). The burned otoliths were then mounted on plasticene

and placed under a compound microscope equipped with a camera (Olympus SZX16,

Infinity 1, Olympus, Tokyo, Japan). Digital images were captured and then enhanced

using ImageJ (Abramoff et al. 2004) and the annuli counted.

Guadalupe bass genetics.—Of the 291 Guadalupe bass used for the age and growth

analysis, a haphazard sample of 142 individuals stratified by age classes (age-1 through

age-7) were used for genetic analysis. Based on small sample sizes, all fin clips from ages

1, 5, 6, and 7 were used. Ages 2, 3, and 4 were grouped together and fin clips were

randomly selected. Total genomic DNA isolation and polymerase chain reactions (PCRs)

were completed at the Fish Health and Genetics Laboratory located at the A.E. Wood

Fish Hatchery in San Marcos, Texas.

DNA extractions were done using a high-salt extraction method modified from

Miller et al. (1988). Briefly, 1.5-mL Eppendorph tubes (Eppendorph AG, Hamburg,

Germany) were filled with 300 μL of cell lysis solution (10 mM Tris-HCl, 10 mM

EDTA, 2% SDS, pH 8.0) and 5 µL proteinase K (20 mg/mL). About 1-5 mm3 of fin

tissue was placed into the lysis solution (20 μL buffered blood) and then incubated in a

55°C water bath for 2.25 hours. Once removed from the water bath, the samples were

allowed to cool to room temperature. Next, 120 μL of 7.5-M ammonium acetate was

added to the cell lysis solution and vortexed. The samples were then incubated at 0°C for


13

15 minutes and centrifuged at 13,400 Xg (relative centrifugal force, or RCF) for 5

minutes. The supernatants were removed and placed in new 1.5-mL eppendorph tubes. I

then added 1000 μL of 100% ethanol (non-denatured) and inverted the tubes 50 times to

mix. After incubating for 10 minutes at -80°C, the samples were centrifuged at 13,400 Xg

for 10 minutes. I decanted the supernatant and added 600 μL of 70% ethanol to the

remaining pellet and inverted the samples seven times. The samples were then

centrifuged at 13,400 Xg for 5 minutes and the supernatant decanted. Each eppendorph

tube was inverted at a 10° angle on paper towel and allowed to dry at room temperature

for 20 minutes. The remaining pellets were then re-suspended in 100 μL of TE buffer and

placed in a 4°C freezer to hydrate for 24 hours. Genomic DNA was quantified by

spectrophotometry (NanoDrop 2000c, Thermo Fisher Scientific Inc., Wilmington,

Delaware) and adjusted to a concentration of 50 ng DNA extract/μL before PCR.

Genotypes were obtained at 16 unlinked microsatellite loci (MiSaTPW58,

MiSaTPW167, MiSaTPW106; TPW76, TPW123, TPW96; TPW154, TPW121; TPW115,

Lma121 [Neff et al. 1991], Mdo1 [Malloy et al. 2000]; TPW134, TPW132, TPW25;

MiSaTPW20, and MiSaTPW38) for each individual. These loci possess varying levels of

polymorphism within and among Micropterus species (Lutz-Carrillo et al. 2006).

Reactions were performed in 10 μL volumes using a single-locus and six multiplex PCRs

(Table 2) with an Eppendorf Mastercycler Pro S Thermal Cycler (Eppendorf North

America, Hauppauge, New York). Amplified products were separated by electrophoresis

in a 6.5% polyacrylamide gel and detected by infrared label with a LI-COR 4300 DNA

Sequencer (LI-COR Biotechnology, Lincoln, Nebraska). BioNumerics (version 5.0,

Applied Maths, Kortrijk, Belgium) was used for gel image processing and allele scoring.

Data Analysis.—For the purpose of analysis, I separated the South Llano River into eight

fragments with boundaries defined by potential barriers such as natural features (e.g.

waterfalls), road crossings, and the dam at Lake Junction. I used a cluster analysis to

determine the similarities and differences among the river fragments with the proportions

of mesohabitats and substrate types as independent variables and fragments as the

dependent variables.


14

A von Bertalanffy growth curve, where = length at

time t, = asymptotic length, k is a growth coefficient and is a time coefficient

where length would theoretically be zero (Von Bertalanffy 1938), was fitted to back

calculated total length at age data. To determine the probability that a Guadalupe bass

within a given length interval is a certain age, I created an age-length key with total

length (TL) intervals of 20-mm based on this datum. Instantaneous mortality (Z) of

Guadalupe bass was estimated from the slope of the descending leg of a catch curve

following the procedure described by Ricker 1975.

A U.S. Geological Survey stream gage was not present on the South Llano River

until 16 May 2012. Therefore, discharge from 1915 through 2012 was estimated by

obtaining gage data from the North Llano River (U.S. Geological Survey gage 08148500)

and subtracting them from the data from the Llano River (U.S. Geological Survey gage

08150000; approximately 4.5 km downstream of the confluence of the North and South

Llano Rivers). The North and South Llano Rivers are the only tributaries that contribute

to the discharge rates at the Llano River gage. These were then used to calculate Q90,

Qlow, Qnormal, Qhigh, and Q10 quantiles and the proportion of observations falling within

each quantile annually. Qlow was defined as the discharges rates between the 75th and 90

th

percentile of the total discharge observations for the South Llano River. Flows between

the 25th and 75

th percentile were classified as Qnormal, while Qhigh flows were those

between the 10th and 25

th percentile. In addition to discharge rate, an application of the

Indicators of Hydrologic Alteration v. 7.1 (IHA, The Nature Conservancy) software

package developed by Richter et al. (1996, 1997) was used to characterize within-year

variation in streamflow on the basis of a series of hydrologic attributes (IHA statistics)

organized into four groups: 1) magnitude of monthly water conditions (mean for each

month), 2) magnitude and duration of annual extreme water conditions (i.e. annual

minimums and maximums of 1-, 7-, 30-, and 90-day means), 3) frequency and duration

of high- and low-flow pulses, and 4) rate and frequency of water-condition changes.

Principal component analysis (PCA) was used to reduce the dimensionality of these data

and produce linear combinations of the original variables that summarize the

predominant patterns in the data. The effects of the principal components of hydrological


15

attributes as well as discharge quantiles and fragment on Guadalupe bass growth rates

were assessed using two repeated measures ANCOVA with the IHA statistics and

discharge rate as covariates, fragment and back-calculated age as independent variables,

and individual bass as a subject effect.

The effect of habitat type on Guadalupe bass growth rates was assessed using

ANCOVA with habitat type as a covariate and age as the independent variable. Only

individuals less than age-6 were used in the analysis due to the small sample sizes of age-

6 (n=1) and age-7 (n=3) bass. Additionally, only growth rates from the most recent year,

2012, were analyzed in order to avoid assuming that Guadalupe bass remain in their

location of capture throughout their entire lives. This analysis was done by assessing

instream habitat at three different spatial scales: a fine scale of 50-m radius surrounding

the capture location, an intermediate scale of 250-m radius surrounding the capture

location, and a coarse scale of the stream unit in which the bass was caught, e.g. if a bass

was caught in a riffle mesohabitat, the stream unit area associated with that bass was

defined from its capture location to the next riffle mesohabitat upstream and the next

riffle mesohabitat downstream. These scales were chosen based on the results of

telemetry studies conducted on Guadalupe bass movement suggesting that most

individuals were sedentary, moving < 58 m over the course of a year. Individuals that

were more mobile, moved a mean (±SD) distance of 1,026.8 ± 425.5 m (maximum

distance: 1, 472 m) upstream from the point of initial capture, and a mean (±SD) distance

of 1,539.0 ± 1,641.3 m (maximum distance: 3,420 m) downstream from the capture site

(Perkin et al. 2010). The 50-m and 250-m scales were created using the circle buffer tool

in ArcGIS 10.0, while the stream unit scale was created by using digitized lines. These

scales were then converted to polygons and merged with the underlying mesohabitat and

substrate type polygons. Once merged, the scales were converted to raster datasets and

imported into FRAGSTATS 4.1 (McGarigal et al. 2012). FRAGSTATS was used to

compute patch and class metrics of the habitat types within each scale associated with

each Guadalupe bass.

To assess age class-specific habitat associations at these three scales, I used

discriminant analysis with habitat variables as independent variables and age classes as


16

the dependent groups. Age-3 and older fish were grouped together into a single age class

due to low sample sizes and because Guadalupe bass have reached sexual maturity by

age-3 (Edwards 1980). I assured that there were no violations of parametric assumptions

before running each analysis by running a Levene’s test for homogeneity of variance as

well as plotting the residuals of all variables to check normality. Variables that were not

normally distributed had a Poisson distribution and thus were square root transformed.

Additionally, I checked for correlation between all variables. If variables were highly

correlated, I removed the variable with lower influence in the analysis. All my analyses

were performed using SAS 9.2 (SAS Institute, Inc., Cary, North Carolina).

Table 1. Classification of substrate type and instream cover (Minshall 1984; Snedden

1999, Perkin et al. 2010) used to classify substrates of the South Llano River, Texas

based on side scan sonar imagery collected in October 2011.

Substrate Type Abbreviation Classification

Limestone - bedrock Bedrock Karst limestone

Rock/Boulder Bldr Boulder > 256 mm

Cobble-gravel COgr 2-256 mm, large cobble pieces

dominant

Gravel-cobble GRco 2-256 mm, small gravel pieces dominant

Gravel-sand GRsa 0.0625-64 mm

Large Woody Debris LWD Single log or multiple logs forming a single structure

Submerged Aquatic

Vegetation

SAV Submerged aquatic vegetation


17

Table 2. List of six multiplex polymerase chain reactions (PCRs) used for Guadalupe bass fin clips captured from the South

Llano River, Texas in spring 2012 – fall 2012.

MPX1 MPX3 MPX4 MPX5 MPX6 MPX17

Components Components Components Components Components Components

sterile ddH2O sterile ddH2O sterile ddH2O sterile ddH2O sterile ddH2O sterile ddH2O

PCR Buffer w/o MgCl2 PCR Buffer w/o MgCl2 PCR Buffer w/o MgCl2 PCR Buffer w/o MgCl2 PCR Buffer w/o MgCl2 PCR Buffer w/o MgCl2

MgCl2 MgCl2 MgCl2 MgCl2 MgCl2 MgCl2

dNTP dNTP dNTPs dNTPs dNTPs dNTP

MiSaTPW 58 F TPW 76 F TPW154F TPW115F TPW134F MiSaTPW20 F

MiSaTPW 58 R_CAG TPW 76 R_CAG TPW154R_CAG TPW115R_CAG TPW134R_CAG MiSaTPW20 R_CAG

MiSaTPW 167 F TPW 123F TPW121F Lma121F_CAG TPW132F MiSaTPW38 F

MiSaTPW 167 R_CAG TPW 123R_CAG TPW121R_CAG Lma121R TPW132R_CAG MiSaTPW38 R_CAG

MiSaTPW 106 F TPW96 F CAG IRD 700/800 Mdo1F_CAG TPW25F CAG IRD 700/800

MiSaTPW 106 R_CAG TPW96 R_CAG

Platinum® Taq

DNA Polymerase Mdo1R TPW25R_CAG

Platinum® Taq

DNA Polymerase

CAG IRD 700/800 CAG IRD 700/800 DNA Template CAG IRD 700/800 CAG IRD 700/800 DNA Template

Platinum® Taq

DNA Polymerase

Platinum® Taq

DNA Polymerase

Platinum® Taq

DNA Polymerase

Platinum® Taq

DNA Polymerase

DNA Template DNA Template

DNA Template DNA Template


18

Figure 1. The 48-km study area of the South Llano River located on the Edwards Plateau

and part of the Colorado River Drainage basin in Kimble County, Texas. The upper limit

was approximately 840 m upstream of its confluence with Big Paint Creek (30.29798°N,

99.90688°W) and extended downstream to the dam at Lake Junction. Red areas delineate

road crossings and natural barriers.


19

Figure 2. Release sites of PIT tagged juvenile Guadalupe bass released in the South Llano

River, Texas, and area surveyed with a LF HDX RFID portable backpack antenna

(Oregon RFID, Portland, Oregon) from May 2012 – September 2012.


20

E. D.

B

C. A. B.

J. I. H. G. F.

K.

Figure 3. Survey locations of Guadalupe bass caught from the South Llano River, Texas in

spring 2012 – fall 2012 based on gear type and month. (A) April angling, (B) May angling, (C)

June angling, (D) July angling, (E) August angling, (F) September angling, (G) October

angling, (H) April and October electrofishing, (I) August electrofishing, (J) November

electrofishing, (K) Seine sites.


21

CHAPTER III

RESULTS

Instream habitat types and composition of the South Llano River, Texas.—Of the 349

ground truthed locations, I correctly identified the substrate of 315 locations from the side

scan sonar mosaic, resulting in a 90% accuracy rate. Misidentification occurred primarily

when distinguishing between limestone-bedrock and gravel-sand substrates due to the

similar, somewhat smooth, wavey appearance of each on the sonar image. In these cases,

gravel-sand was initially and incorrectly identified as the substrate; however, this was

corrected for after ground truthing. Other errors included identifying shaded areas on the

sonar image as “unknown.” After ground truthing, these were corrected to submerged

aquatic vegetation as well as gravel-cobble or gravel-sand substrates.

Pools comprised approximately 51% of the surveyed reach (Figure 4) and were

the predominate mesohabitat type by area. Runs (33%) and riffles (16%) constituted

smaller proportions of the river. The dominant substrate type within the South Llano

River was gravel-sand which comprised approximately 42% of the area. Cobble-gravel

(27%), limestone-bedrock (16%), submerged aquatic vegetation (9%) and gravel-cobble

(6%) constituted smaller proportions of available habitat.

Overall, the substrate of the upper reaches in the southern portion of the

watershed consisted of mostly bedrock. Substrate proportions of cobble and gravel

increased downstream. Instream structures such as boulders and large woody debris

tended to increase downstream as well. In general, the fragments clustered into four

groups: headwater reaches consisting of mostly bedrock riffles and runs (Fragments I-II),

transitional reaches where pools and finer substrates, such as cobble-gravel, gravel-

cobble, and gravel-sand, became more prominent (Fragments III-IV), midstream reaches

that lacked bedrock substrates and consisted of the more typical riffle-run-pool

complexes (Fragments V-VII), and a downstream reach impacted by the impoundment at

Lake Junction and dominated by gravel-sand substrates with a decrease in the amount of

boulders and an increase in the amount of large woody debris (Fragment VIII) (Figure 4).


22

Guadalupe bass PIT-tag telemetry.—The six control PIT tags were not relocated during

every tracking event. The greatest detection of control tags occurred during walking

surveys (mean ± SD: 36% ± 3%, range: 0-100%). During canoe surveys, detection rates

ranged from 0-33% (mean ± SD: 14% ± 15%). Nine PIT-tagged Guadalupe bass were

relocated from May-August 2012, November 2012, and July 2013. Four were relocated

using the backpack antenna. The remainders were recaptured using a boat-mounted

electrofisher in November 2012 and July 2013 (Table 3). Total length (TL) of those

recaptured ranged from 154 mm to 175 mm. The average distance traveled by relocated

Guadalupe bass was 1,761 ± 1,612-m (mean ± SD); however, one individual was

relocated 4,106-m upstream from its release site. The predominate direction of travel was

upstream (n = 7); though one individual traveled downstream (release site 1), and one

remained in the mesohabitat of its release site. The majority of relocated bass was found

in run mesohabitats (56%) with submerged aquatic vegetation instream cover (33%).

Additionally, all bass were relocated within approximately 15 ± 22-m (mean ± SD)

instream cover, i.e. boulders, large woody debris, or submerged aquatic vegetation (Table

3).

Guadalupe bass population demographics-age and growth.—Scales from 291 Guadalupe

bass were used for age and growth analysis. However, regardless of preparation, it was

difficult to discern annuli on the otoliths (Figure 5A); therefore, only otoliths with annuli

that were clearly distinguishable were used to complement the age estimates from the

scales (Figure 5B). Age-0 and age-3 bass constituted approximately 54% of captured

Guadalupe bass; however, individuals as old as seven were encountered (Table 4, Figure

6). Gear selectivity appeared to play a role in the ages of bass captured. The seine was

biased towards younger fish, whereas individuals age-2 and older were most often

captured by angling and electrofishing. Finally, the instantaneous mortality estimate, Z,

based on the catch curve for age-3+ bass was 0.493 ± 0.181.

I fit a Von Bertalanffy growth curve to the back calculated length at age data for

Guadalupe bass from all gear types combined that yielded parameters of =

531.6±62.45, k = 0.135±0.02 and = -0.252±0.06 (Figure 7). Similarly, I fit a Von


23

Bertalanffy growth curve to just the length at age data for Guadalupe bass that yielded

parameters of = 529.8±72.56, k = 0.133±0.03 and = -0.240±0.07 (Figure 7).

Generally, back-calculated total lengths at a given age were in agreement with those

observed in captured fish of the same age (Table 4). Furthermore, back-calculated total

lengths indicated that Guadalupe bass exhibit their highest growth rate during their first

year and then maintain a relatively high growth rate in subsequent years. Individuals tend

to grow approximately 84 mm by age-1 with growth decreasing to about 60 mm from

age-1 to age-2 (Table 4).

Guadalupe bass genetics.—Eight hybrids were detected from the sample of 142

Guadalupe bass, or a hybridization rate of 5.6%. Of the eight hybrids detected, five

exhibited smallmouth bass introgression, and three exhibited largemouth bass

Micropterus salmoides introgression. Approximately 86% of all age-1 bass caught for

this project were tested, constituting 8.5% of the sample of 142 Guadalupe bass. None of

these age-1 bass were the offspring of hatchery pairings made in 2011. Additionally, no

age-0 bass were tested due to lack of fin clips.

Stepwise discriminant analysis derived 3 of 162, 0 of 173, and 3 of 181 variables

from the stream unit scale, 250-m scale, and 50-m scale, respectively that best

discriminated among hybrids and pure strain Guadalupe bass. Of the 3 variables from the

stream unit and 50-m scales, none were highly correlated (r ≥ 0.70; McGarigal et al.

2000), and thus none were eliminated prior to the discriminant function analysis (DFA).

At the stream unit scale, the DFA explained just 5% of the variation between

hybrids and pure strain Guadalupe bass. The first axis accounted for 100% of the

explained variation (Table 6). The axis consisted primarily of an increasing percentage of

pool mesohabitat and perimeter-area ratios of boulders within run mesohabitats as well as

decreasing perimeter-area ratios of pool gravel-cobble habitats. Mean class scores on this

axis indicated that hybrids associated more with pool gravel-cobble perimeter area ratios

(mean ± SD: can1 = -1.41 ± 1.13) than did their pure strain counterparts. At the 250-m

scale, no canonical correlations were identified by the DFA related to hybrids and pure-

strain Guadalupe bass (F1,284<3.42, P>0.07). However, at the 50-m scale, DFA again


24

identified one canonical axis corresponding to hybrids and pure-strain Guadalupe bass

and accounted for 100% of the variation (Table 6). The axis consisted mainly of

increasing percentages of run gravel-cobble habitat and perimeter-area ratios of run

submerged aquatic vegetation habitat as well as decreasing total edge. Mean class scores

on this axis indicated that hybrids associated more with greater percentages of run gravel-

cobble habitat and perimeter-area ratios of run submerged aquatic vegetation habitat

(mean ± SD: can1 = 1.37 ± 1.48) than did pure strain Guadalupe bass.

Relation between habitat and Guadalupe bass growth.—Age alone explained most of the

variation in the most recent year (2012) of Guadalupe bass growth rates of individuals

younger than age-6 at all scales (39%, 37%, and 37% at the stream unit, 250-m, and 50-m

scales, respectively; Table 7). At the stream unit scale, growth rates were also positively

correlated with riffle cobble-gravel contiguity (F1,265=16.87, P<0.01; Table 7A);

however, this variable alone explained just 4% of the variation (F1,270=12.11, P<0.01,

R2=0.04). At the 250-m scale, growth rates were positively correlated with pool bedrock

contiguity (F1,270=7.24, P<0.01) and negatively correlated with pool submerged aquatic

vegetation perimeter-area ratios (F1,274=8.06, P<0.01; Table 7B). Pool submerged aquatic

vegetation perimeter-area ratios on its own was not significant and explained less than

1% of the variation (F1,280=1.12, P=0.29, R2=0.004), whereas pool bedrock contiguity

explained just 2% of the variation (F1,280=4.99, P=0.03, R2=0.02). Finally, at the 50-m

scale, growth rates were positively correlated with 3 habitat variables: riffle gravel-cobble

total edge (F1,269=5.59, P=0.02), riffle boulders perimeter-area ratios (F1,269=6.16,

P=0.01), and run bedrock perimeter-area ratios (F1,269=12.80, P<0.01; Table 7C). Both

riffle gravel-cobble total edge (F1,276=1.59, P=0.21, R2=0.006) and riffle boulders

perimeter-area ratios (F1,276=2.64, P=0.11, R2=0.01) were not significant on their own

and explained less than 1% of the variation. Approximately 3% of the variation in growth

rate was explained by run bedrock perimeter-area ratios (F1,276=9.07, P<0.01, R2=0.03).

Guadalupe bass age-specific habitat associations.—Stepwise discriminant analysis

selected 22 of 97, 21 of 101, and 13 of 102 variables from the stream unit scale, 250-m


25

scale, and 50-m scale, respectively, that best discriminated among Guadalupe bass age-

classes. Any highly correlated variables (r ≥ 0.70; McGarigal et al. 2000) were eliminated

from each scale prior to discriminant analysis. This resulted in removing: 1 of 22, 5 of 21,

and 0 of 13 from the stream unit, 250-m, and 50-m scales, respectively. Discriminant

analysis was used to select the most informative variables from the remaining datasets

which maintained: 8 of 21, 9 of 16, and 7 of 13 from the stream unit, 250-m scale, and

50-m scale, respectively (Table 8).

At the stream unit scale, the DFA had two significant canonical axes. Both the

first and second axis accounted for 55% and 37% of the explained variation, respectively.

Furthermore, the first canonical axis was positively correlated with just 2 of the 8 most

informative habitat variables, riffle gravel-sand perimeter-area ratios and run gravel-

cobble total edge, while being negatively correlated with the remaining 6 variables (Table

9). The second canonical axis was also positively correlated with riffle gravel-sand

perimeter-area ratios as well as pool boulder perimeter-area ratios and pool bedrock total

edge, and being negatively correlated with the remaining 5 variables (Table 9, Figure 8).

Crossvalidation demonstrated that the DFA classified individuals into age classes with a

50% error rate. The habitat variables at this scale best predicted the age-0 age class given

the habitat with which each individual was associated (error rate = 18%; Table 10).

The canonical correlation biplot at this scale revealed three primary divisions

amongst Guadalupe bass age-specific habitat associations which included age classes that

used either runs with gravel substrates, pools, or mostly riffles containing instream cover

(Figure 8A). Age class scores on these 2 axes indicated that age-0 Guadalupe bass were

positively associated with riffle gravel-sand perimeter area ratios and run gravel-cobble

total edge. However, age-1 Guadalupe bass were more loosely associated with pools. The

age class scores in the biplot further illustrated that age classes-2 and 3+ Guadalupe bass

appear to group together and were primarily associated with a mixture of riffle

mesohabitats and the total edge of instream cover such as boulders and submerged

aquatic vegetation.

The DFA conducted at the 250-m scale resulted in the first two axes accounting

for 54% and 39% of the explained variation, respectively. Additionally, axis 1 was


26

positively correlated with more pools and rocky-fine substrates while having a negative

correlation with the percentage of riffle bedrock habitats, run gravel-sand perimeter-area

ratios, and run submerged aquatic vegetation total edge (Table 9). Axis 2 was primarily

positively correlated with run gravel-sand total edge and pool bedrock contiguity.

Crossvalidation demonstrated that the DFA classified individuals into age classes with a

60% error rate. Similar to the stream unit scale, the habitat variables at this scale best

predicted the age-0 age class given the habitat with which each individual was associated

(error rate = 23%; Table 10).

The biplot of the 250-m scale revealed three primary divisions amongst

Guadalupe bass age-specific habitat associations which included age classes that used

either runs with gravel or submerged aquatic vegetation and riffle bedrock habitats, the

total edge of runs with gravel-sand substrates, or the contiguity of instream cover

structures within pools as well as rocky-fine substrates (Figure 8B). Contrary to the

stream unit scale, age-0 bass were associated with greater percentages of riffle bedrock

habitat and the total edge of submerged aquatic vegetation in runs. Class scores for age-1

individuals demonstrated a loose association with run gravel-sand total edge.

Furthermore, age classes-2 and -3+ appeared to group together again, associating with

greater percentages of rocky-fine substrates and pool boulder contiguity (Figure 8B).

At the 50-m scale, the first two axes of the DFA accounted for 77% and 13% of

the explained variation, respectively. Axis 1 was positively correlated with the percentage

of pool mesohabitat as well as the percentage of run submerged aquatic vegetation and

negatively correlated with the remaining 5 most informative variables (Table 8). Axis 2

primarily had a positive correlation with the percentage of large woody debris. The error

rate of the DFA revealed by crossvalidation was greatest at this scale (60%). Continuing

with the trend, the habitat variables at this scale best predicted the age-0 age class given

the habitat with which each individual was associated (error rate = 16%; Table 10).

Contrary to the other scales, the canonical correlation biplot at the 50-m scale

revealed four separations amongst the four Guadalupe age classes and their habitat

associations (Figure 8C). Age class scores on the two axes illustrated that age-0 bass

associated strongly with instream cover and less turbulent water (i.e. submerged aquatic


27

vegetation and run and pool habitats). Age-1 individuals also used submerged aquatic

vegetation cover, but also faster moving water (i.e. run habitats). In contrast to the stream

unit and 250-m scales, age classes-2 and -3+ did not appear to group together. Age-2

Guadalupe bass associated more with run cobble-gravel perimeter-area ratios and

percentages of large woody debris, whereas age-3+ bass used the contiguity of boulders

within pool habitats (Figure 8C).

Influence of discharge rate and fragment on Guadalupe bass growth rates.—Subtracting

North Llano River discharge rates from Llano River discharge rates resulted in the

following South Llano River discharge quantiles: Q90=0.99 m-3

s-1

, Qlow=1.44 m-3

s-1

,

Qnormal=2.10 m-3

s-1

, Qhigh=2.75 m-3

s-1

, and Q10=3.88 m-3

s-1

. The hydrologic profile of the

South Llano River during the period encompassed by the lifespans of the Guadalupe bass

used in this study (2004-2012) can be roughly divided into three periods (Figure 9). A

period of “typical” discharges that were dominated by flows between the 25-75th

percentiles predominated during 2004-2007, followed by 2-year period of decreasing

discharges (2008-2009), then severe drought and extremely low discharges (2010-2012).

Overall, the proportion of discharge observations falling in the Q90 range in a

given year had the greatest influence on Guadalupe bass growth rates. Residuals from the

von Bertalanffy model were negatively correlated to the proportion of Q90 discharge rates

observed during a particular year over the first three years of growth (F3,542=10.62,

P<0.01; Figure 10). Similarly, the proportions of one-, seven-, thirty-, and ninety-day

annual minimum discharge means negatively correlated with Guadalupe bass growth

rates during their first three years of growth (F3,199=8.37, P<0.01). A positive trend

between Q10 discharge observations and Guadalupe bass growth rates was also observed

(F3,542=2.02, P=0.07). Furthermore, of the 291 Guadalupe bass used for this analysis, 0

were caught in Fragment I, 27 were caught in Fragment II, 20 were caught in Fragment

III, 7 were caught in Fragment IV, 33 were caught in Fragment V, 70 were caught in

Fragment VI, 75 were caught in Fragment VII, 55 were caught in Fragment VIII, and 4

individuals did not have associated GPS coordinates. However, the results of my analysis


28

demonstrated that fragment had no influence on Guadalupe bass growth rates

(F6,530=0.60, P=0.73).


29

Table 3. Relocated and recaptured PIT-tagged Guadalupe bass and associated habitat type in the South Llano River, TX from

May – August 2012, November 2012, and July 2013.

ID

Release

Date

Release

Site

Recapture

Date

Recapture

TL (mm)

Recapture

Location

Mesohabitat

Substrate type

Distance from

release (m)

Distance to cover

(Bldr, LWD, SAV)

(m)

226000050338 31-May-12 1 11-Nov-12 154

30.47438°N,

99.78326°W Run SAV 504 0

226000049669 31-May-12 2 1-Jun-12 -

30.47833°N,

99.78227°W Pool GRsa 27 53

226000049956 31-May-12 2 8-Aug-12 -

30.47437°N,

99.78324°W Run SAV 506 0

226000050372 31-May-12 3 2-Jul-12 -

30.47401°N,

99.783589°W Run SAV 1,015 0

226000050372 31-May-12 3 22-Jul-12 -

30.47169°N,

99.78448°W Run GRco 1,296 3

226000049919 31-May-12 3 9-Nov-12 165

30.45496°N,

99.78857°W Riffle COgr 4,106 12

226000050362 31-May-12 3 9-Nov-12 161

30.45383°N,

99.78723°W Pool GRsa 3,904 10

226000049660 31-May-12 3 9-Nov-12 157

30.45623°N,

99.78588°W Riffle COgr 3,534 4

226000049904 31-May-12 2 13-Jul-13 175

30.47083°N,

99.78494°W Run GRsa 961 55


30

Table 4. Mean (±SE) back-calculated total length (TL) at each annulus of Guadalupe bass captured in the South Llano River,

Texas from April – November 2012.

TL (mm) at capture

________________

Back calculated TL (mm) at age

_____________________________________________________________________________________________

Age class

Year class

N

Mean

Range

1

2

3

4

5

6

7

0 2012 79 55.5 ± 1.5 35-91

I 2011 14 106.6 ± 8.1 69-171 84.8 ± 5.9

II 2010 55 167.4 ± 3.5 106-211 78.0 ± 2.6 138.1 ± 3.1

III 2009 79 216.0 ± 3.1 152-293 80.9 ± 2.4 142.1 ± 2.9 188.4 ± 2.9

IV 2008 49 244.4 ± 3.9 200-310 88.0 ± 4.4 137.4 ± 4.2 184.2 ± 4.2 219.8 ± 4.0

V 2007 11 293.9 ± 8.2 248-330 98.5 ± 7.9 159.5 ± 5.2 204.0 ± 7.9 240.4 ± 9.7 271.3 ± 8.9

VI 2006 1 341 - 133 183 231 271 296 318

VII 2005 3 364.7 ± 18.5 333-397 129.7 ± 12.5 180 ± 12.5 227.3 ± 14.4 255.7 ± 13.5 288.7 ± 16.8 320.7 ± 13. 344 ± 13.7

Mean TL (mm) at age 83.9 ± 1.7 141.6 ± 1.9 189.3 ± 2.3 225.8 ± 3.8 276.4 ± 7.4 320 ± 9.5 344 ± 13.7

Mean annual growth (mm) 83.9 ± 1.7 58.1 ± 1.4 46.2 ± 1.2 35.3 ± 1.4 30.1 ± 1.7 29.5 ± 4.3 23.3 ± 5.2


31

Table 5. Age-length key based on the total length (TL) at age and age at capture of

Guadalupe bass captured in the South Llano River, Texas from April 2012 – November

2012. Numbers in rows give the percent probability that a Guadalupe bass within the 20-

mm length interval is a certain age.

Age

TL (mm) 0 1 2 3 4 5 6 7

30-49 100 0 0 0 0 0 0 0

50-69 97 3 0 0 0 0 0 0

70-89 86 14 0 0 0 0 0 0

90-109 11 78 11 0 0 0 0 0

110-129 0 20 80 0 0 0 0 0

130-149 0 10 90 0 0 0 0 0

150-169 0 6 71 24 0 0 0 0

170-189 0 4 57 39 0 0 0 0

190-209 0 0 41 48 10 0 0 0

210-229 0 0 3 63 34 0 0 0

230-249 0 0 0 50 47 3 0 0

250-269 0 0 0 36 57 7 0 0

270-289 0 0 0 33 44 22 0 0

290-309 0 0 0 11 44 44 0 0

310-329 0 0 0 0 50 50 0 0

330-349 0 0 0 0 0 50 25 25

350-369 0 0 0 0 0 0 0 100

370-389 0 0 0 0 0 0 0 0

390-409 0 0 0 0 0 0 0 100

Total 79 14 55 79 49 11 1 3 291


32

Table 6. Discriminant analysis of hybrids versus pure strain Guadalupe bass at the stream

unit and 50-m buffer scale. No clusters were identified at the 250-m scale (F1,284<3.42,

P>0.07).

Dimension Canonical

correlation

Variance

explained

F df 1 df 2 P

Stream

unit

1 0.22 0.05 4.75 3 271 <0.01

50-m 1 0.23 0.06 5.10 3 278 <0.01


33

Table 7. Results from the ANCOVA of habitat variables influencing the most recent year

of growth (2012) of Guadalupe bass younger than age-6 at (A) stream unit, (B) 250-m,

and (C) 50-m scales captured in the South Llano River, Texas from April 2012 –

November 2012.

A. Parameter Estimate Standard Error t Value P value

Intercept 30.72 4.55 6.75 <0.01

Age-0 22.92 4.91 4.67 <0.01

Age-1 51.37 5.93 8.67 <0.01

Age-2 28.84 5.03 5.74 <0.01

Age-3 13.81 4.90 2.82 <0.01

Age-4 2.77 5.09 0.55 0.59

Age-5 0 . . .

Riff COgr Contig 9.93 2.42 4.11 <0.01

B. Parameter Estimate Standard Error t Value P value

Intercept 32.60 4.66 6.99 <0.01

Age-0 23.06 4.90 4.71 <0.01

Age-1 54.61 6.14 8.90 <0.01

Age-2 27.42 5.03 5.45 <0.01

Age-3 13.21 4.94 2.68 <0.01

Age-4 1.86 5.12 0.36 0.72

Age-5 0 . . .

Pool SAV P:A -0.55 0.19 -2.84 <0.01

Pool Bdrk Contig 6.38 2.37 2.69 <0.01

C. Parameter Estimate Standard Error t Value P value

Intercept 28.52 4.60 6.20 <0.01

Age-0 22.94 4.87 4.71 <0.01

Age-1 55.35 6.06 9.14 <0.01

Age-2 28.32 4.99 5.68 <0.01

Age-3 15.54 4.84 3.21 <0.01

Age-4 4.74 5.07 0.94 0.35

Age-5 0 . . .

Riff GRco TE 1.41 0.60 2.36 0.02

Riff Bldr P:A 0.02 0.01 2.48 0.01

Run Bdrk P:A 0.19 0.05 3.58 <0.01


34

Table. 8. Most informative habitat variables selected from the discriminant analysis that

best discriminated among age classes (Age-0, Age-1, Age-2, Age-3+) of Guadalupe bass

captured in the South Llano River, TX from April 2012 – November 2012.

Variable Description

Stream unit

Riff GRsa P:A Riffle gravel-sand habitat perimeter area ratio

Run GRco TE Run gravel-cobble habitat total edge

Pool Bldr P:A Pool boulder habitat perimeter area ratio

Pool Bdrk TE Pool bedrock habitat total edge

Riff SAV TE Riffle submerged aquatic vegetation habitat total

edge

Riff Bldr TE Riffle boulder habitat total edge

Pool Bldr TE Pool boulder habitat total edge

Riff GRco P:A Riffle gravel-cobble habitat perimeter area ratio

250-m

%Riff Bdrk Percentage of riffle bedrock habitat

Run GRsa P:A Run gravel-sand habitat perimeter area ratio

Run SAV TE Run submerged aquatic vegetation habitat

perimeter area ratio

Run GRsa TE Run gravel-sand habitat total edge

Pool Bdrk Contig Pool bedrock habitat contiguity

Run LWD Contig Run large woody debris habitat contiguity

% Rocky-fine Percentage of rocky-fine substrate

Pool Bldr Contig Pool boulder habitat contiguity

Run COgr TE Run cobble-gravel habitat total edge

50-m

% Pool Total area of pool mesohabitat

Run SAV Prop Proportion of run submerged aquatic vegetation

habitat

Pool Bldr Contig Pool boulder habitat contiguity

% Bedrock Percentage of bedrock substrate

Run SAV TE Run submerged aquatic vegetation habitat total

edge

Run COgr P:A Run cobble-gravel habitat perimeter area ratio

% LWD Percentage of large woody debris structures


35

Table 9. Description of variables by scale and correlation coefficients between habitat

variables and the first and second canonical axes. Bolded values indicate the most

correlated variables for that axis.

Variable Description Axis 1 Axis 2

Stream unit

Riff GRsa P:A Riffle gravel-sand habitat perimeter area ratio 0.6104 0.1669

Run GRco TE Run gravel-cobble habitat total edge 0.6825 0.0339

Pool Bldr P:A Pool boulder habitat perimeter area ratio -0.0684 0.7460

Pool Bdrk TE Pool bedrock habitat total edge -0.7695 0.5429

Riff SAV TE Riffle submerged aquatic vegetation habitat

total edge -0.6539 -0.0626

Riff Bldr TE Riffle boulder habitat total edge -0.5707 -0.3009

Pool Bldr TE Pool boulder habitat total edge -0.4990 -0.3315

Riff GRco P:A Riffle gravel-cobble habitat perimeter area

ratio

-0.4853 -0.3020

250-m

% Riff Bdrk Percentage of riffle bedrock habitat -0.5746 -0.3635

Run GRsa P:A Run gravel-sand habitat perimeter area ratio -0.5964 -0.3587


total edge

-0.6731 0.2684

Run GRsa TE Run gravel-sand habitat total edge -0.3162 1.2413

Pool Bdrk Contig Pool bedrock habitat contiguity 0.1757 0.6040

Run LWD Contig Run large woody debris habitat contiguity 0.4367 0.1690

% Rocky-fine Percentage of rocky-fine substrate 0.7950 -0.0891

Pool Bldr Contig Pool boulder habitat contiguity 0.3506 -0.3040

Run COgr TE Run cobble-gravel habitat total edge 0.4230 -0.4361

50-m

% Pool Percentage of pool mesohabitat 1.5730 0.2158

% Run SAV Percentage of run submerged aquatic

vegetation habitat

1.4539 0.1355

Pool Bldr Contig Pool boulder habitat contiguity -0.5477 -0.2086

% Bedrock Percentage of bedrock substrate -0.8644 -0.2141


total edge

-1.0767 -0.2025

Run COgr P:A Run cobble-gravel habitat perimeter area ratio -0.5032 0.3911

% LWD Percentage of large woody debris structures -0.2982 0.7743


36

Table 10. Percent of observations classified into each age class and error rates by scale

from crossvalidation of the discriminant analysis of Guadalupe bass captured in the South

Llano River, Texas from April 2012 – November 2012.

Stream unit Percent classified into age class

From age class 0 1 2 3+

0 82 0 3 15

1 0 44 19 38

2 15 8 31 46

3+ 25 7 23 44

Priors 25 25 25 25

Total Error Rate 18 56 69 56 50

250-m Percent classified into age class


0 77 0 16 6

1 0 0 43 57

2 18 5 35 42

3+ 14 1 34 50

Priors 25 25 25 25


50-m Percent classified into age class


0 84 9 1 5

1 7 0 14 79

2 36 11 23 30

3+ 39 14 17 30

Priors 25 25 25 25



37

I II III IV V VI VII VIII

To

tal

Num

ber

0

100

200

300

400

500

600

700

Boulders

LWD

Fragment

Figure 4. Mesohabitat and substrate type proportions within the eight fragments of the

South Llano River, Texas, surveyed October 2011. (A) Fragment I, (B) Fragment II, (C)

Fragment III, (D) Fragment IV, (E) Fragment V, (F) Fragment VI, (G) Fragment VII, (H)

Fragment VIII, (I) amount of boulders and large woody debris (LWD) in each fragment.

A. B. C.

D.

D. E. F.

H.

G. H. I.


38

Figure 5. Images of age-2 scales and their associated otoliths from Guadalupe bass caught

in the South Llano River, Texas. (A) An example of a bass with discernible annuli in

scales but not otoliths, (B) an example of a bass with discernible annuli in both scales and

otoliths.

A.1 B.1

A.2 B.2

A.3 B.3


39

Age-Frequency (n=291)

Age (years)

0 1 2 3 4 5 6 7

Fre

qu

ency

0

20

40

60

80

Figure 6. Age frequency distribution of Guadalupe bass captured in the South Llano

River, Texas in spring 2012 – fall 2012.


40

Age (years)

0 1 2 3 4 5 6 7

TL

(m

m)

0

100

200

300

400

back calculated

length at age

at capture

Lt= 537.9(1 - e

-0.1335(t-(-0.2518)))

Lt= 529.8(1 - e

-0.1329(t-(-0.2395)))

Figure 7. Von Bertalanffy growth curve based on back calculated total length at age of

Guadalupe bass captured in the South Llano River, Texas from April 2012 – November

2012. Black circles represent back calculated total lengths (TL) at age, green circles

represent actual lengths at age, and yellow circles represent at capture total lengths.


41

Can1

-3 -2 -1 0 1 2 3

Can

2

-3

-2

-1

0

1

2

3

4

5

Age-0

Age-1

Age-2

Age-3+

Pool Bldr P:A

Riff SAV TE

Run GRco

TE

Run GRSa P:A

Pool Bdrk TE

Riff Bldr TERiff GRco P:APool Bldr TE

A.

Can1

-3 -2 -1 0 1 2 3

Can

2

-3

-2

-1

0

1

2

3

4

5

Age-0

Age-1

Age-2

Age-3

Run GRsa TE

% Riff Bdrk

Pool Bdrk Contig

Pool Bldr Contig

Run LWD Contig

% Rocky- Fine

Run COgr TE

Run GRsa P:A

Run SAV TE

B.

Can1

-4 -3 -2 -1 0 1 2 3 4 5

Can

2

-2

-1

0

1

2

3

Age-0

Age-1

Age-2

Age-3

Pool Bldr Contig

% LWD

% Pool

% Run

SAV

Run COgr

P:A

Run SAV

TE

% Bedrock

C.

Figure 8. Canonical correlation biplot of age-

specific habitat associations of Guadalupe bass

captured in the South Llano River, Texas from

April 2012 – November 2012 at the (A) stream

unit scale, (B) 250-m scale, and (C) 50-m scale.


42

2004 2005 2006 2007 2008 2009 2010 2011 2012

Pro

po

rtio

n o

f o

bse

rvat

ion

s

0.0

0.2

0.4

0.6

0.8

1.0

Q90

Qlow

Qnormal

Qhigh

Q10

Period 1 Period 2 Period 3

Figure 9. Proportions of discharge rates (m-3

s-1

) observed in the South Llano River, Texas from

2004 to 2012.


43

0.0 0.4 0.8

-40

0

40

80

A.

0.0 0.4 0.8

-40

0

40

80

B.

0.4 0.6 0.8

-40

0

40

80

C.

Q90

Figure 10. Guadalupe bass residuals from the von Bertalanffy model were negatively

correlated to the proportion of Q90 discharge rates observed during a particular year over

the first three years of growth (F3,542=10.62, P<0.0001) of Guadalupe bass captured in the

South Llano River, Texas from April 2012 – November 2012. (A) back-calculated age-1

(n=209), (B) back-calculated age-2 (n=195), (C) back-calculated age-3 (n=142).

Mean

Resi

du

als

(m

m/y

ear)


44

CHAPTER IV

DISCUSSION

Habitat mapping of the South Llano River, Texas.—Sonar mapping is not only efficient,

but also provides a means to visualize whole-channel, underwater, geospatially

referenced features that would otherwise be difficult or impossible to view using

traditional methods in turbid, deep, and non-wadeable areas. The technique used here has

been shown to be a rapid, accurate, and inexpensive method of creating high resolution,

spatially detailed maps of continuous, instream habitat (Kaeser and Litts 2010, Kaeser et

al. 2012). For example, Kaeser et al. (2012) created an instream habitat map of the Flint

River in Georgia using side scan sonar. Their accuracy assessment resulted in a range of

72% to 100% accuracy rates, suggesting that a one-pass sonar survey may be sufficient

for mapping streams consisting of similar substrate classes as the Flint River (e.g. sand,

rocky-fine, rocky-boulder). Furthermore, these high accuracies demonstrate that their

Flint River map may serve as a complete and reliable source of habitat information for

the future research and management of species of conservation need. Based on my 90.3%

accuracy rate, I can reasonably say that the created instream habitat map of the South

Llano River may also serve as a comprehensive and reliable source of habitat information

for not only Guadalupe bass, but other species within the river as well.

The South Llano River is divided into eight river fragments due to road crossings

and natural barriers. My results demonstrated that these eight fragments clustered into

four groups: less disturbed, upstream reaches constituted by bedrock riffles and runs,

transitional reaches consisting of mostly pools and finer substrates, midstream reaches

with the typical riffle-run-pool complexes, and the downstream reach directly impacted

by the dam at Lake Junction. Furthermore, this fragmentation and damming could be one

explanation of the overall dominance of pool mesohabitats as well as gravel-sand

substrate types within the South Llano River. Previous studies have demonstrated that

fragmentation by road crossings and dams alter the downstream flux of water and

sediment, resulting in more pools and storage of water upstream as well as increased

sedimentation (Ward and Stanford 1979, Collier et al. 1996, Poff and Hart 2002).


45

Since fragmentation is likely to remain unabated within the South Llano River,

and conservation efforts are already underway, this river may offer a unique model

system for developing a “guiding image” (Palmer et al. 2005) for restoration on the

Edwards Plateau. A guiding image would be one that describes the dynamic, ecologically

healthy river that could exist in a given area. The South Llano River is considered to be a

relatively pristine river with minimal human disturbance due to its hydrological regime,

good water quality, and diverse fish assemblages that are representative of the Edwards

Plateau (Bayer et al. 1992). Additionally, the system offers a natural experiment by way

of an upstream-downstream gradient of habitat degradation (Bayer et al. 1992). Stream

classification systems using aerial photography and habitat maps have been used

previously as a basis for developing guiding images for restoration (Koebel 1995,

Kondolf and Larson 1995), and have been suggested to work best as guides to restoration

when developed for specific regions (Kondolf et al. 2003). A pragmatic approach to

restoration on the Edwards Plateau could be to move rivers towards the most ecologically

dynamic state possible rather than attempt to recreate unachievable or unknown historical

conditions (Middelton 1999, Choi 2004, Palmer et al. 2004).

Associated with the expected population increase on the Edwards Plateau will be

greater demands for ground water as well as habitat degradation due to erosion from

construction and poor land use practices, non-point source pollution (TPWD 2005), and

continued habitat fragmentation via the construction of road crossings. The rivers and

streams of the Edwards Plateau are expected to experience decreased dissolved oxygen

and increased turbidity, temperatures, and risk of introduction and establishment of

nonnative species (Bezanson and Wolfe 2001, TPWD 2005). For instance, the South

Llano River turbidity levels have already been reported as relatively high during the past

2-3 years (Richardson 2012, personal observation). This may be due, in part, to the Oasis

Fire that occurred in April 2011, leaving behind large deposits of ash and soil that lay

unanchored and ready to wash into the river (Richardson, 2012). This habitat map may be

used to potentially prioritize restoration activities and sites as well as act as a benchmark

for comparison and assessment of future monitoring and restoration efforts.


46

Guadalupe bass PIT-tag telemetry.—The use of PIT tags is a research method

increasingly used to monitor habitat associations, spatial movements, and migratory

patterns of fish. They have also been used to identify individual fish in studies designed

to track responses to environmental stressors (Zydlewski et al. 2001, 2006, Cucherousset

et al. 2005). Each tag is encoded with a unique identifying numeric sequence and

available in many different sizes (typically 8.4-60 mm). They are relatively inexpensive,

long-lasting, easy to implant, and have high retention rates (Zydlewski et al. 2006). There

has been some controversy as to the size of fish tagged without inhibiting the individual’s

growth and survival. In this study, the smallest Guadalupe bass successfully PIT-tagged

with a 12-mm tag was 76.2 mm; however, smaller fish have been tagged in other studies.

For example, Dixon and Mesa (2011) showed that Moapa White River springfish

Crenichthys baileyi moapae as small as 40 mm were able to be successfully PIT-tagged

with 9-mm tags and exhibited only minor effects on survival as well as no tag loss.

Several other studies have demonstrated that the implantation of PIT tags has minimal

effects on mortality, growth rates, swimming, and feeding (Gries and Letcher 2002,

Ruetz et al. 2006, Newby et al. 2007, Archdeacon et al. 2009). Keeler et al. (2007)

effectively used PIT tags to measure survival probabilities and assist in future application

of the slimy sculpin Cottus cognatus as a bioindicator.

While these studies demonstrate the successful use of PIT tags, the current study

was not as successful. Due to the low detection distance of the portable backpack antenna

(maximum: approximately 50 cm), only nine individuals were relocated. The low

detection range coupled with the variable depth of the tracking area in the South Llano

River (approximately 0-4 m) could be one reason for the low detection rate. Cucherousset

et al. (2005) suggested that given their limitations in detection range, the use of 12-mm

PIT tag detection systems should be restricted to shallow streams, i.e. the maximum

water depth in their study was 32 cm. Another reason could be that increased mobility

and wariness of Guadalupe bass may have affected the relative likelihood of detection

because fish could have been frightened by the antenna and fled the area before they

could be detected. This reason highlights a major limitation of portable PIT tag detectors

when used on mobile stream fish that display pronounced escape behavior (Roussel et al.


47

2000). Furthermore, the general behavior of certain species could result in low detection

rates. For example, Guadalupe bass are sometimes active, drift feeders (Edwards 1980).

However, cottid fishes like the slimy sculpin are nocturnally active, cryptic, and benthic

and have limited mobility; they typically hide under stones during the day and move just

short distances when startled (Gray 2004). Less active, benthic species may be more

easily detected. However, the additional low detection rates of the stationary, control tags

in this study suggest that even if Guadalupe bass were sedentary, they would only be

detected a mean of 36% of the time during walking surveys and a mean of 14% of the

time during canoe surveys. Additionally, earlier work on Atlantic salmon Salmo salar

parr using a portable 23-mm PIT tag detector revealed that the detection efficiency was

affected by the presence of dense riparian vegetation and overhanging branches that

hindered the operator in moving the antenna (Roussel et al. 2000). Similarly, dense

instream cover and structural complexity (e.g. submerged aquatic vegetation, large

woody debris, and boulders) may prevent effective coverage of potential fish refugia with

the antenna. In this study, I did not determine how habitat characteristics may alter the

efficiency of detection. However, specific habitat features such as the undercut banks and

large woody debris in the tracking area of the South Llano River may have accounted for

this low detection rate as well. Furthermore, the quality of the circuit board in the

portable antenna appears to decrease relatively quickly (within 3 months), resulting in

decreasing detection distance with increasing period of use (S.K. Brewer, personal

communication). Finally, mortality may have also caused low detection rates. Previous

studies have demonstrated that the proportion of hatchery-reared fish in the wild

surviving to adulthood is in decline (Nickleson 1986, Beamish et al. 1992, Blaxter 2000).

In the case of salmonids typically, less than 5% of all hatchery-reared fish make it to

adulthood (McNeil 1991). This number is even less for other species (e.g. chum salmon

Oncorhynchus keta 1-3%, and <1% for cod Gadus morhua; Salvanes 2001). Most of the

mortality of stocked fish occurs in the first few days following release rather than over

the subsequent months (Blaxter 2000, Svasand et al. 2000), perhaps accounting for the

low detection rate of the tagged, hatchery-reared Guadalupe bass.


48

Despite the low detection rate, seven of the nine Guadalupe bass that were

detected were found over 500 m from their release site, with 4.1 km upstream as the

greatest distance traveled. Wild Micropterus spp. have been previously demonstrated to

be sedentary in streams and rivers with movements of less than 1.6 km (Funk 1957), but

more mobile largemouth and smallmouth bass individuals have been found to travel up to

24 km (Funk 1957, Lyons and Kanehl 2002, VanArnum et al. 2004). Brown (1961) found

that released hatchery-reared smallmouth bass had rapid dispersal (>1 km) and

disappearance due to movement or possible high mortality. Additionally, Perkin et al.

(2010) found that during their eight months of tracking radio-tagged Guadalupe bass,

movement ranged from no movement (remaining within a single mesohabitat) to moving

3.4 km from the point of initial capture. This variation in movement is known for several

riverine fishes (Funk 1957, Gatz and Adams 1994, Smithson and Johnson 1999) and is

most likely attributed to both biotic (e.g. genetics, population size, and life history

components) and abiotic conditions (e.g. habitat availability and suitability; Funk 1957,

VanArnum et al. 2004, Stormer and Maceina 2009). Furthermore, perhaps the movement

observed in this study can be explained by exploratory movements (Jennings and Shepard

2003, Grabowski and Jennings 2009). As hatchery-reared fish, they are new to the South

Llano River and could be traveling due to biotic interactions or to find the most suitable

habitat. Grabowski and Jennings (2009) noted that transplanted robust redhorse

Moxostoma robustum exhibited an exploratory phase for the first 3 months before

adopting behavior patterns, similar to brown trout Salmo trutta (Aarestrup et al. 2005)

and paddlefish Polyodon spathula (Pitman and Parks 1994). It has also been argued that

hatchery-reared fish are unable to disperse upstream due to lesser stamina (Vincent 1960,

Green 1964); however, that is contradicted in this study of only nine relocated bass, and

others (Jorgensen and Berg 1991).

Guadalupe bass population demographics-age and growth.—This study represents the

first detailed description of growth rates of wild Guadalupe bass. The scale method, using

annulus counts, has been commonly used for estimating the age and growth of other

Micropterus spp. (Carlander 1977, Maraldo and MacCrimmon 1979) because of the


49

relative ease of obtaining and preparing scales. There is also no need to sacrifice the fish.

However, scales tend to underestimate age in older fish (Sylvester and Berry 2006,

Taylor and Weyl 2012). Sagittal otoliths typically portray more distinct annuli, but that

was not the case in this study. It appeared not to matter whether Guadalupe bass otoliths

were stored dry or in mineral oil; the otoliths remained opaque, and annuli were difficult

to determine. Scales proved to be the only useful indicators of age for this analysis.

Similarly, Maraldo and MacCrimmon (1979) reported that both largemouth bass scales

and otoliths proved to be good indicators of age and growth, and that scale annuli could

be accurately identified to age-7+.

Many black bass species such as largemouth, smallmouth, and spotted bass

Micropterus punctulatus exhibit their highest growth rates during their first few years

leading up to maturity and then growth decreases significantly in succeeding years

(Mansueti 1961, Stuber et al. 1982, Wiegmann et al. 1992, Beamesderfer and North

1995, Lyons 1997). However, my results suggest that while Guadalupe bass exhibit their

highest growth rate during their first year, they maintain relatively high growth rates in

subsequent years. The slight decrease in growth after age-2 and in succeeding years is

likely due to the attainment of sexual maturity. This timing of decreased growth is

consistent with the reported age of maturity for Guadalupe bass (age 1-age 2; Edwards

1980). In contrast, other Micropterus spp. often reach maturity between the age of 3-5

years (Stuber et al. 1982, Lyons 1997, Rohde 1996). Additionally, while Guadalupe bass

grow rapidly in their first year, the approximate growth of 84 mm is small in comparison

to similar species such as largemouth bass and spotted bass. In their first year of growth,

riverine largemouth bass typically grow up to 254 mm, while spotted bass average

approximately 100-125 mm (Tennessee Wildlife Resources Agency 2005). These

differences in growth may be, in part, attributable to differential metabolic demands

placed on each species from the relative flow velocities encountered in the different

environments which they inhabit (Edwards 1980). Finally, Lee’s phenomenon which

occurs when back-calculated lengths at a given age are observed to decrease with

increasing age of the fish (Lee 1912) did not appear to occur in this study (Table 4).


50

Guadalupe bass genetics.—As a result of introductions of nonnative fishes,

homogenization of North American ichthyofauna is occurring (Rahel 2000). The

resulting introgressive hybridization poses the threat of loss and replacement of native

species by hybrids (Allendorf et al. 2001). Thus, the extirpation and extinction of native

species can occur through introgressive hybridization (Rhymer and Simberloff 1996).

Smallmouth bass have been stocked within the range of Guadalupe bass

beginning in 1958 with intensive stockings to increase sport fishing in 1974 (Garrett

1991). Hybridization between Guadalupe bass and introduced smallmouth bass has been

reported since 1979 (Edwards 1979, Whitmore 1983, Littrell et al. 2007, Bean et al.

2013). However, hybridization within the South Llano River has been reported as low

(3%; Harvey 2011). Similarly, the percentage of Guadalupe bass and smallmouth bass

hybrids within my sample was low (3.5%) with an even lower percentage of Guadalupe

bass and largemouth bass hybrids (2.1%). The Guadalupe River subbasin has experienced

a decline in hybridization rates from 30% (Garrett 1991) to 13.7% (Bean et al. 2013) due,

in part, to persistent stocking of Guadalupe bass over an 18-yr period. With the

continuous stocking of Guadalupe bass in the South Llano River since 2011, the

hybridization rate should remain low.

Because only eight hybrids were detected from the sample of 142 Guadalupe

bass, the discriminant analysis had low explanatory power. At the stream unit scale, my

results suggested that the hybrids were associated with higher pool gravel-cobble

perimeter-area ratios than did their pure strain Guadalupe bass counterparts. Pure

Guadalupe bass are typically associated more with runs and riffle tailraces (Boyer et al.

1977, Edwards 1980, Perkin et al. 2010). However, further analysis involving a larger

sample of hybrids is needed in order to determine whether hybrids are actually utilizing

different habitat than pure Guadalupe bass.

Relation between habitat and Guadalupe bass growth.—Habitat type has been

documented to affect the growth of numerous species (Werner and Hall 1988, Sogard

1992, Tupper and Boutilier 1997). For example, Tupper and Boutilier (1995b) found that

growth of young of year cod Gadus morhua in St. Margaret’s Bay was higher in seagrass


51

beds than rocky reef, cobble, or sand bottoms. They also attributed the higher growth

rates to greater prey density in the seagrass habitat. However, few studies have examined

the influence of detailed riverscape data such as the combination of both substrate type

and mesohabitat on fish growth.

My results suggest that habitat variables at all scales had a relatively minor

influence on growth as age alone explained most of the variation in the most recent year

of growth in Guadalupe bass younger than age-6. Age was expected to influence growth

based on previous studies demonstrating that growth tends to vary by age (Von

Bertalanffy 1938, Wiegmann et al. 1992, Beamesderfer and North 1995, Lyons 1997).

However, the low influence of habitat on growth observed in this study was not expected.

Ecological theory suggests that fish should associate with habitat that maximizes energy

gain (growth), while minimizing the risk of mortality (Gilliam and Fraser 1987, Gotceitas

1990). Since Guadalupe bass are drift feeders at younger ages (Edwards 1980), certain

habitat variables such as the contiguity, or spatial connectedness, of riffle cobble-gravel

habitats were expected to positively influence growth rates in that potential prey reside in

the rocky substrate and could drift with the higher current velocity of riffle mesohabitats.

Similarly, if fish density increases with certain habitats, such as greater percentages of

submerged aquatic vegetation in pools, competition could contribute to expected findings

of slower growth at these sites.

The resulting low influence of habitat on growth observed in this study could be

attributed, in part, to a few factors. First, the year of growth studied coincided with a year

of extreme drought in Texas, resulting in extremely low discharge rates. Schlosser 1982

and Lamouroux 2008 suggest that downstream changes in water velocity and the amount

of water can alter the quantity of habitat suitable for different species and life-stages

based on factors like swimming performance that affect the ability to use different

habitats. Available habitat is therefore sensitive to water velocity and water quantity,

which increases systematically downstream and also varies according to the natural flow

regime and anthropogenic demands (Poff et al. 2003). Perhaps Guadalupe bass were

utilizing many different habitats during this year of drought because suitable habitat for

growth was not available. Secondly, the stream unit, 250-m, and 50-m scales used in this


52

analysis were based on a study demonstrating that a population of Guadalupe bass did not

move great distances (< 58 m; Perkin et al. 2010). In the current study, Guadalupe bass

movement could have been underestimated. They may move greater distances than

expected in general or because the year of extreme low discharges forced them to seek

different habitat. Further analysis on Guadalupe bass growth rates during periods of

“normal” stream flow could help determine if habitat does influence growth.

Guadalupe bass age-specific habitat associations.—The degree of overlap in habitat use

by age classes of Guadalupe bass appears to be quite variable and dependent upon the

scale of analysis and/or the age class considered. In this study, classification success

among age classes using DFA was not very high (50%, 40%, and 34%, respectively for

stream unit, 250-m, and 50-m scales), indicating overlap in habitat use (Table 10).

However, the high classification success of age-0 Guadalupe bass at all scales

(82%, 77%, and 84%, respectively for stream unit, 250-m, and 50-m scales)

demonstrated that these young-of-year most likely associate with much different habitat

than older age classes, or that they are more sedentary. This included greater perimeter-

area ratios of run mesohabitats with gravel-sand substrates at the stream unit and 250-m

scales as well as greater percentages of pool and run mesohabitats with submerged

aquatic vegetation at the 50-m scale. The use of run mesohabitats may imply the

importance of velocity. For example, velocity has been demonstrated to influence first-

year growth and survival of smallmouth bass (Livingstone and Rabeni 1991, Brewer

2011) by possibly influencing feeding activities and swimming performance (Simonson

and Swenson 1990). Additionally, runs are typically shallower than pools and may offer a

warmer, more optimal temperature for age-0 Guadalupe bass. Brewer (2008) studied

temperature selection by young-of-year smallmouth bass and found that they generally

used the warmest temperature available unless it exceeded 32°C. Sullivan et al. (2013)

studied the growth of fingerling Guadalupe bass in five different temperature groups and

found that the optimal temperature for growth was 27-28°C. Moreover, the association

with greater percentages of submerged aquatic vegetation most likely represents a refuge

habitat from predators and greater velocities during high rainfall events. These results are


53

in agreement with those of Edwards (1980), who found that during the spring spawning

season, Guadalupe bass nesting areas were apart from, but always near, a source of slow

to moderately moving water. From these spawning areas, age-0 individuals tended to

occupy gradually swifter waters and increasing water depths, i.e. the run areas

surrounding riffles, during their first summer and fall (Edwards 1980). These run areas

can often be constituted by greater patch complexities of gravel-sand substrates due to

depositions from the fast-flowing water of riffles directly upstream of runs.

In contrast, the extremely low classification success of age-1 Guadalupe bass

(43%, 0%, and 0% for stream unit, 250-m, and 50-m scales, respectively) could indicate

overlap between this age class and other age classes, specifically age-2 and 3+ (Table

10), or could have simply resulted from the small sample size of age-1 individuals (n =

14). My results demonstrated loose associations with the total edge of habitats such as

bedrock, gravel-sand, and submerged aquatic vegetation. Edge effects relate to the

influence that a patch edge can have in determining species composition and processes

within a patch (Ries et al. 2004, Fletcher et al. 2007). The importance of edges in the

distribution and abundance of species has been known since Leopold (1933) used the

term “edge effects” to describe an increase in game species in patchy landscapes.

Recently, edges have been associated with the core habitat for specialist species because

they provide access to resources that are spatially separated by a boundary, maximizing

the ability to use resources from both patches (Ries et al. 2004). The use of patch edges

by age-1 Guadalupe bass could be explained by this availability of resources from both

patches in conjunction with their transition into adulthood. Edwards (1980) reported that

Guadalupe bass consume a large number of Ephemeroptera (mayfly) larvae when young

and then gradually shift to consuming terrestrial Hymenoptera (bees and wasps),

Hemiptera, and fish as they grow larger to subadult sizes. Edge habitats may offer a range

of prey options. Furthermore, edge habitats may offer easily accessible refuge. However,

a larger sample size of age-1 Guadalupe bass could help to determine stronger

associations with these habitats.

Overall, the classification success of ages-2 and 3+ was a little higher than age-1

Guadalupe bass; however, the low percentages still demonstrate possible overlap in


54

habitat associations and potentially greater movement than expected. Moreover, the

biplots demonstrated the grouping of age classes 2 and 3+ (Figure 8). This is likely due to

all individuals having attained sexual maturity by these ages (Edwards 1980). Habitat

associations included the total edge of submerged aquatic vegetation and boulders within

riffle and pool mesohabitats at the stream unit scale, and the contiguity of large woody

debris and boulders within run and pool mesohabitats as well as the percentage of rocky-

fine substrates at the 250-m scale. The connectedness of these instream structures (large

woody debris, boulders, submerged aquatic vegetation) may offer greater areas of

minimal energy expenditure with respect to abiotic or biotic conditions such as high

velocities and predation (Edwards 1980, Raibley et al. 1997). Additionally, Edwards

1980 found that the fish most represented in adult Guadalupe bass diets are blacktail

shiner Cyprinella venusta, which are most common in pools and runs of clear rivers with

small rocks and sand substrates, typically in areas with sparse vegetation and strong

current (Page and Burr 1991). This could explain some of the associations with runs and

pools as well as rocky-fine substrates found in this study.

These age classes, however, did not group together at the 50-m scale and

exhibited more loose associations at this scale, suggesting that perhaps adult Guadalupe

bass location is influenced by more coarse scale parameters. Previous studies have

demonstrated the segregation of riverine fish within stream segments by using different

types of these larger scale stream units (Bisson et al. 1982, 1988, Sullivan 1986). In these

studies, fish distinguished between riffles and pools as well as subclasses of pools (e.g.

eddies, backwater) defined by stream unit position, forming constraint and flow. Benthic

invertebrates also appeared to use different types of stream units (Hawkins 1984). Further

research is needed to examine occupancy of Guadalupe bass age classes at finer scales.

Influence of discharge rate and fragment on Guadalupe bass growth rates.—My results

demonstrated that, while each river fragment contained different proportions of

mesohabitat and substrate type, fragment did not relate to Guadalupe bass growth rates.

Previous studies suggest that this species typically does not move great distances (Perkin

et al. 2010); thus, fragment habitat may be too broad of a scale. Additionally, this could


55

suggest that habitat type is not the greatest factor influencing growth rates, or that

Guadalupe bass move more than expected so that their classified associations are not

entirely correct, complementing the low correlations of growth rate and habitat type as

mentioned previously. Kirkham and Fischer (2004) compared growth rates of fish

between fragmented sites on Polecat Creek, Illinois and observed no significant

difference in growth rates. They suggest that the reason for the absence of differences in

growth rates between sites may be due to the overall phosphorous deficiency within the

stream (Kirkham and Fischer 2004). Similarly, Guadalupe bass growth rates are likely

influenced by a combination of factors such as habitat type, water quality, prey

availability, and discharge.

My analysis identified the proportion of discharge observations falling in the Q90

range in a given year most significantly related to Guadalupe bass growth rates. The IHA

analysis complemented this by demonstrating a negative correlation between the

proportions of one-, seven-, thirty-, and ninety-day annual minimum discharge means and

growth rates. In a spring-fed stream system that does not appear to experience much flow

alteration, this level of sensitivity is surprising. However, the 2-yr period of severe

drought and extremely low discharges from 2010-2012 may have assisted in exposing

this result. Edwards (1980) reported a strong preference by Guadalupe bass for moving

water habitats during all but winter and spring months. Similarly, Perkin et al. (2010)

found that Guadalupe bass were readily responsive to changes in the flow regime,

gradually shifting toward pools with greater depths during a period of extreme low flow

in the Pedernales River during the summer. This response to periods of stream drying by

moving from preferred habitats is common in other riverine fish and Micropterus species

(Stormer and Maceina 2009).

During droughts, the effects of low discharge rates may be exacerbated by

groundwater and surface-water withdrawal. In many situations, surface-water bodies gain

water from groundwater sources, and in others, the surface-water body is a source of

groundwater recharge and causes changes in groundwater quality (Winter et al. 2002). As

a result, withdrawal of water from streams can deplete groundwater or conversely,

pumping groundwater can deplete water in streams, decreasing stream discharge rates


56

(Winter et al. 2002). As stated previously, velocity has been demonstrated to influence

first-year growth of smallmouth bass (Livingstone and Rabeni 1991, Brewer 2011).

Specifically, velocity has been shown to influence feeding activities and swimming

performance (Simonson and Swenson 1990). In periods of low discharge or the absence

of flowing water, fish are unable to drift feed, which eliminates a feeding tactic often

used by Guadalupe bass (Edwards 1980). Artificial reduction of stream discharge has

contributed to lower production of rainbow trout Oncorhynchus mykiss, a species that

also uses drift feeding (Rimmer 1985). Activities that could negatively affect Guadalupe

bass growth rates could include stream dewatering (Hurst et al. 1975) and aquifer

drawdowns (Bowles and Arsuffi 1993). However, watershed management approaches

that mimic natural flow regimes have favored the recruitment of native fish (Probst and

Gido 2004). Finally, my results demonstrated a positive trend between Q10 discharge

observations and Guadalupe bass growth rates, suggesting that Guadalupe bass may favor

these higher discharge conditions. Further analysis could involve examining intra-annual

or seasonal discharge related to growth in order to determine if growth rates are

significantly and positively correlated with higher discharges.

Conclusions.—Before habitat restoration actions can be addressed, ecological

relationships between an organism and its physical environment need to be defined and

understood. Because little growth information currently exists for Guadalupe bass,

predictions from my results can possibly identify areas with potentially fast fish growth

and provide a relatively quick a priori basis for fisheries management. Moreover, these

results represent testable hypotheses for further research (e.g. higher discharge rates

suggest higher growth rates). Because of the low introgressive hybridization in this

system, the most significant threat to the continued survival of Guadalupe bass may be

the continuing decreases in stream flows (Edwards 1980, TPWD 2005). A species that is

dependent upon aquifer discharges would be a direct indicator of the overall health of the

ecosystem. However, further analysis on the influence of aquifer discharges, possible

run-off discharges, and water quality components (e.g. temperature, dissolved oxygen,

and turbidity) would help in determining if this species can be used as an indicator of


57

stream health on the Edwards Plateau. Continued research on this ecosystem and

Guadalupe bass as well as other species responses to restoration efforts will provide a

more complete understanding of aquatic biodiversity conservation. If restoration efforts

in the South Llano River are successful, future restoration efforts should focus on

ecosystems with similar patterns of stream flows, habitat types, and introgression.


58

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