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
Copyright 2013, Jillian Groeschel
Texas Tech University, Jillian Groeschel, December 2013
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).
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Texas Tech University, Jillian Groeschel, December 2013
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 PIT-tag telemetry...................................................................... 22
Guadalupe bass population demographics-age and growth............................... 22
Guadalupe bass genetics......................................................................................23
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 PIT-tag telemetry...................................................................... 46
Guadalupe bass population demographics-age and growth............................... 48
Guadalupe bass genetics......................................................................................50
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
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Texas Tech University, Jillian Groeschel, December 2013
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 agespecific 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 agespecific 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.
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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) backcalculated age-3 (n=142)......................................................................... 43
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Texas Tech University, Jillian Groeschel, December 2013
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
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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
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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 s 1 , 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).
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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habitat associations and patterns in order to assist in the assessment of restoration efforts
targeting this species.
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
estimates from the scales. These individuals were euthanized with an overdose of MS222 (>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
12
Texas Tech University, Jillian Groeschel, December 2013
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.
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Texas Tech University, Jillian Groeschel, December 2013
A von Bertalanffy growth curve,
time t,
where
= asymptotic length, k is a growth coefficient and
= length at
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 Q 90,
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 90th
percentile of the total discharge observations for the South Llano River. Flows between
the 25th and 75th percentile were classified as Qnormal, while Qhigh flows were those
between the 10th and 25th 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
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Texas Tech University, Jillian Groeschel, December 2013
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 age6 (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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
DNA Polymerase
Mdo1R
TPW25R_CAG
DNA Polymerase
CAG IRD 700/800
CAG IRD 700/800
DNA Template
CAG IRD 700/800
CAG IRD 700/800
DNA Template
Platinum® Taq
Platinum® Taq
Platinum® Taq
Platinum® Taq
Platinum® Taq
Platinum® Taq
DNA Polymerase
DNA Polymerase
DNA Polymerase
DNA Polymerase
DNA Template
DNA Template
DNA Template
DNA Template
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Texas Tech University, Jillian Groeschel, December 2013
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.
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Texas Tech University, Jillian Groeschel, December 2013
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.
19
Texas Tech University, Jillian Groeschel, December 2013
A.
B.
C.
D.
B
E.
F.
G.
H.
I.
J.
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.
K.
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Texas Tech University, Jillian Groeschel, December 2013
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, gravelcobble, 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).
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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 purestrain Guadalupe bass (F1,284<3.42, P>0.07). However, at the 50-m scale, DFA again
23
Texas Tech University, Jillian Groeschel, December 2013
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 gravelcobble 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
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Texas Tech University, Jillian Groeschel, December 2013
scale, and 50-m scale, respectively, that best discriminated among Guadalupe bass ageclasses. 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 gravelcobble 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
25
Texas Tech University, Jillian Groeschel, December 2013
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
26
Texas Tech University, Jillian Groeschel, December 2013
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-3s-1, Qlow=1.44 m-3s-1,
Qnormal=2.10 m-3s-1, Qhigh=2.75 m-3s-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 Q 90 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 Q 90 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
27
Texas Tech University, Jillian Groeschel, December 2013
demonstrated that fragment had no influence on Guadalupe bass growth rates
(F6,530=0.60, P=0.73).
28
Texas Tech University, Jillian Groeschel, December 2013
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
29
Texas Tech University, Jillian Groeschel, December 2013
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.
Age class
Year class
0
2012
I
2011
II
2010
III
2009
IV
2008
V
2007
VI
2006
VII
2005
Mean TL (mm) at age
Mean annual growth (mm)
TL (mm) at capture
________________
Back calculated TL (mm) at age
_____________________________________________________________________________________________
N
Mean
Range
1
2
3
4
5
6
7
79
14
55
79
49
11
1
3
55.5 ± 1.5
106.6 ± 8.1
167.4 ± 3.5
216.0 ± 3.1
244.4 ± 3.9
293.9 ± 8.2
341
364.7 ± 18.5
35-91
69-171
106-211
152-293
200-310
248-330
333-397
84.8 ± 5.9
78.0 ± 2.6
80.9 ± 2.4
88.0 ± 4.4
98.5 ± 7.9
133
129.7 ± 12.5
83.9 ± 1.7
83.9 ± 1.7
138.1 ± 3.1
142.1 ± 2.9
137.4 ± 4.2
159.5 ± 5.2
183
180 ± 12.5
141.6 ± 1.9
58.1 ± 1.4
188.4 ± 2.9
184.2 ± 4.2
204.0 ± 7.9
231
227.3 ± 14.4
189.3 ± 2.3
46.2 ± 1.2
219.8 ± 4.0
240.4 ± 9.7
271
255.7 ± 13.5
225.8 ± 3.8
35.3 ± 1.4
271.3 ± 8.9
296
288.7 ± 16.8
276.4 ± 7.4
30.1 ± 1.7
318
320.7 ± 13.
320 ± 9.5
29.5 ± 4.3
344 ± 13.7
344 ± 13.7
23.3 ± 5.2
30
Texas Tech University, Jillian Groeschel, December 2013
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 20mm length interval is a certain age.
TL (mm)
30-49
50-69
70-89
90-109
110-129
130-149
150-169
170-189
190-209
210-229
230-249
250-269
270-289
290-309
310-329
330-349
350-369
370-389
390-409
Total
0
100
97
86
11
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
79
1
0
3
14
78
20
10
6
4
0
0
0
0
0
0
0
0
0
0
0
14
Age
3
0
0
0
0
0
0
24
39
48
63
50
36
33
11
0
0
0
0
0
79
2
0
0
0
11
80
90
71
57
41
3
0
0
0
0
0
0
0
0
0
55
31
4
0
0
0
0
0
0
0
0
10
34
47
57
44
44
50
0
0
0
0
49
5
0
0
0
0
0
0
0
0
0
0
3
7
22
44
50
50
0
0
0
11
6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25
0
0
0
1
7
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25
100
0
100
3
291
Texas Tech University, Jillian Groeschel, December 2013
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
Stream
unit
50-m
Variance
explained
0.05
F
df 1
df 2
P
1
Canonical
correlation
0.22
4.75
3
271
<0.01
1
0.23
0.06
5.10
3
278
<0.01
32
Texas Tech University, Jillian Groeschel, December 2013
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
Intercept
Age-0
Age-1
Age-2
Age-3
Age-4
Age-5
Riff COgr Contig
Estimate
30.72
22.92
51.37
28.84
13.81
2.77
0
9.93
Standard Error
4.55
4.91
5.93
5.03
4.90
5.09
.
2.42
t Value
6.75
4.67
8.67
5.74
2.82
0.55
.
4.11
P value
<0.01
<0.01
<0.01
<0.01
<0.01
0.59
.
<0.01
B. Parameter
Intercept
Age-0
Age-1
Age-2
Age-3
Age-4
Age-5
Pool SAV P:A
Pool Bdrk Contig
Estimate
32.60
23.06
54.61
27.42
13.21
1.86
0
-0.55
6.38
Standard Error
4.66
4.90
6.14
5.03
4.94
5.12
.
0.19
2.37
t Value
6.99
4.71
8.90
5.45
2.68
0.36
.
-2.84
2.69
P value
<0.01
<0.01
<0.01
<0.01
<0.01
0.72
.
<0.01
<0.01
C. Parameter
Intercept
Age-0
Age-1
Age-2
Age-3
Age-4
Age-5
Riff GRco TE
Riff Bldr P:A
Run Bdrk P:A
Estimate
28.52
22.94
55.35
28.32
15.54
4.74
0
1.41
0.02
0.19
Standard Error
4.60
4.87
6.06
4.99
4.84
5.07
.
0.60
0.01
0.05
t Value
6.20
4.71
9.14
5.68
3.21
0.94
.
2.36
2.48
3.58
P value
<0.01
<0.01
<0.01
<0.01
<0.01
0.35
.
0.02
0.01
<0.01
33
Texas Tech University, Jillian Groeschel, December 2013
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
Stream unit
Riff GRsa P:A
Run GRco TE
Pool Bldr P:A
Pool Bdrk TE
Riff SAV TE
Riff Bldr TE
Pool Bldr TE
Riff GRco P:A
250-m
%Riff Bdrk
Run GRsa P:A
Run SAV TE
Run GRsa TE
Pool Bdrk Contig
Run LWD Contig
% Rocky-fine
Pool Bldr Contig
Run COgr TE
50-m
% Pool
Run SAV Prop
Pool Bldr Contig
% Bedrock
Run SAV TE
Run COgr P:A
% LWD
Description
Riffle gravel-sand habitat perimeter area ratio
Run gravel-cobble habitat total edge
Pool boulder habitat perimeter area ratio
Pool bedrock habitat total edge
Riffle submerged aquatic vegetation habitat total
edge
Riffle boulder habitat total edge
Pool boulder habitat total edge
Riffle gravel-cobble habitat perimeter area ratio
Percentage of riffle bedrock habitat
Run gravel-sand habitat perimeter area ratio
Run submerged aquatic vegetation habitat
perimeter area ratio
Run gravel-sand habitat total edge
Pool bedrock habitat contiguity
Run large woody debris habitat contiguity
Percentage of rocky-fine substrate
Pool boulder habitat contiguity
Run cobble-gravel habitat total edge
Total area of pool mesohabitat
Proportion of run submerged aquatic vegetation
habitat
Pool boulder habitat contiguity
Percentage of bedrock substrate
Run submerged aquatic vegetation habitat total
edge
Run cobble-gravel habitat perimeter area ratio
Percentage of large woody debris structures
34
Texas Tech University, Jillian Groeschel, December 2013
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
Riff GRsa P:A
Run GRco TE
Pool Bldr P:A
Pool Bdrk TE
Riff SAV TE
Riff Bldr TE
Pool Bldr TE
Riff GRco P:A
% Riff Bdrk
Run GRsa P:A
Run SAV TE
Run GRsa TE
Pool Bdrk Contig
Run LWD Contig
% Rocky-fine
Pool Bldr Contig
Run COgr TE
% Pool
% Run SAV
Pool Bldr Contig
% Bedrock
Run SAV TE
Run COgr P:A
% LWD
Description
Stream unit
Riffle gravel-sand habitat perimeter area ratio
Run gravel-cobble habitat total edge
Pool boulder habitat perimeter area ratio
Pool bedrock habitat total edge
Riffle submerged aquatic vegetation habitat
total edge
Riffle boulder habitat total edge
Pool boulder habitat total edge
Riffle gravel-cobble habitat perimeter area
ratio
250-m
Percentage of riffle bedrock habitat
Run gravel-sand habitat perimeter area ratio
Run submerged aquatic vegetation habitat
total edge
Run gravel-sand habitat total edge
Pool bedrock habitat contiguity
Run large woody debris habitat contiguity
Percentage of rocky-fine substrate
Pool boulder habitat contiguity
Run cobble-gravel habitat total edge
50-m
Percentage of pool mesohabitat
Percentage of run submerged aquatic
vegetation habitat
Pool boulder habitat contiguity
Percentage of bedrock substrate
Run submerged aquatic vegetation habitat
total edge
Run cobble-gravel habitat perimeter area ratio
Percentage of large woody debris structures
35
Axis 1
Axis 2
0.6104
0.6825
-0.0684
-0.7695
-0.6539
0.1669
0.0339
0.7460
0.5429
-0.0626
-0.5707
-0.4990
-0.4853
-0.3009
-0.3315
-0.3020
-0.5746
-0.5964
-0.6731
-0.3635
-0.3587
0.2684
-0.3162
0.1757
0.4367
0.7950
0.3506
0.4230
1.2413
0.6040
0.1690
-0.0891
-0.3040
-0.4361
1.5730
1.4539
0.2158
0.1355
-0.5477
-0.8644
-1.0767
-0.2086
-0.2141
-0.2025
-0.5032
-0.2982
0.3911
0.7743
Texas Tech University, Jillian Groeschel, December 2013
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
From age class
0
1
2
3+
Priors
Total Error Rate
250-m
From age class
0
1
2
3+
Priors
Total Error Rate
50-m
From age class
0
1
2
3+
Priors
Total Error Rate
0
82
0
15
25
25
18
0
77
0
18
14
25
23
0
84
7
36
39
25
16
Percent classified into age class
1
2
0
3
44
19
8
31
7
23
25
25
56
69
Percent classified into age class
1
2
0
16
0
43
5
35
1
34
25
25
100
65
Percent classified into age class
1
2
9
1
0
14
11
23
14
17
25
25
100
77
36
3+
15
38
46
44
25
56
50
3+
6
57
42
50
25
50
60
3+
5
79
30
30
25
70
66
Texas Tech University, Jillian Groeschel, December 2013
A.
B.
C.
D.
E.
F.
700
Boulders
LWD
600
Total Number
500
400
300
200
100
0
H.
G.
I
II
III
IV
V
VI VII VIII
I.
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.
37
Texas Tech University, Jillian Groeschel, December 2013
A.1
B.1
A.2
B.2
A.3
B.3
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.
38
Texas Tech University, Jillian Groeschel, December 2013
Age-Frequency (n=291)
80
Frequency
60
40
20
0
0
1
2
3
4
5
6
7
Age (years)
Figure 6. Age frequency distribution of Guadalupe bass captured in the South Llano
River, Texas in spring 2012 – fall 2012.
39
Texas Tech University, Jillian Groeschel, December 2013
400
-0.1335(t-(-0.2518))
Lt= 537.9(1 - e
)
-0.1329(t-(-0.2395))
Lt= 529.8(1 - e
)
TL (mm)
300
200
100
back calculated
length at age
at capture
0
0
1
2
3
4
5
6
7
Age (years)
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.
40
Texas Tech University, Jillian Groeschel, December 2013
5
5
Age-0
Age-1
Age-2
Age-3+
4
Age-0
Age-1
Age-2
Age-3
4
Run GRsa TE
3
3
Pool Bldr P:A
Pool Bdrk Contig
2
Pool Bdrk TE
Can2
Can2
2
1
1
Run SAV TE
Run GRSa P:A
0
Run LWD Contig
Run GRco
TE
Riff SAV
TE
0
Pool Bldr Contig
-1
-1
Riff Bldr TE
% Riff Bdrk Run GRsa P:A
Riff GRco P:A
Pool Bldr TE
Run COgr TE
-2
-3
-2
A.
-3
-3
-2
-1
0
1
2
3
B.
-3
-2
Can1
2
Can2
% Pool
% Run
SAV
0
3
April 2012 – November 2012 at the (A) stream
unit scale, (B) 250-m scale, and (C) 50-m scale.
Run SAV
TE
% Bedrock Pool Bldr
Contig
C.
-2
2
captured in the South Llano River, Texas from
1
-3
1
specific habitat associations of Guadalupe bass
Run COgr
P:A
-4
0
Figure 8. Canonical correlation biplot of age-
Age-0
Age-1
Age-2
Age-3
% LWD
-1
-1
Can1
3
-2
% RockyFine
-1
0
1
2
3
4
5
Can1
41
Texas Tech University, Jillian Groeschel, December 2013
Proportion of observations
1.0
0.8
0.6
Q90
Qlow
Qnormal
Qhigh
0.4
Q10
0.2
0.0
2004
2005
2006
Period 1
2007
2008
2009
Period 2
2010
2011
2012
Period 3
Figure 9. Proportions of discharge rates (m-3s-1) observed in the South Llano River, Texas from
2004 to 2012.
42
Texas Tech University, Jillian Groeschel, December 2013
80
40
0
-40 A.
Mean Residuals (mm/year)
0.0
0.4
0.8
80
40
0
-40 B.
0.0
0.4
0.8
80
40
0
-40 C.
0.4
0.6
0.8
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).
43
Texas Tech University, Jillian Groeschel, December 2013
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).
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Texas Tech University, Jillian Groeschel, December 2013
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.
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Texas Tech University, Jillian Groeschel, December 2013
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.
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Texas Tech University, Jillian Groeschel, December 2013
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.
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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).
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
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
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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 perimeterarea 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 firstyear 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
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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
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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 rockyfine 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
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Texas Tech University, Jillian Groeschel, December 2013
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
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Texas Tech University, Jillian Groeschel, December 2013
(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
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Texas Tech University, Jillian Groeschel, December 2013
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.
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Texas Tech University, Jillian Groeschel, December 2013
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