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Growth and Habitat Use of Guadalupe Bass in the South Llano River, Texas

  • Metro Wastewater Reclamation District


Predicting how stream fishes may respond to habitat restoration efforts is difficult due, in part, to an incomplete understanding of how basic biological parameters such as growth and ontogenetic habitat shifts interact with flow regime and riverscape ecology. We assessed age-specific Guadalupe Bass Micropterus treculii habitat associations at three different spatial scales in the South Llano River, a spring-fed stream on the Edwards Plateau of central Texas, USA, and the influence of habitat and flow regime on growth. Substrates were classified using a low-cost side-scan sonar system. Scale microstructure was used to determine age and to back-calculate size at age. Over 65% of captured Guadalupe Bass were age-2 or age-3, but individuals ranged from 0-7 years of age. Habitat associations overlapped considerably among age classes 1-3+, but age-0 Guadalupe Bass tended to associate with greater proportions of pool and run mesohabitats with submerged aquatic vegetation. While habitat metrics across multiple scales did not have a large effect on growth, river discharge was negatively correlated with growth rates. Understanding age-specific Guadalupe Bass habitat associations at multiple scales will increase the effectiveness of restoration efforts directed at the species by assisting in determining appropriate ecological requirements of each life-history stage and spatial scales for conservation actions.
Growth and habitat use of Guadalupe Bass in the South Llano River, Texas 1
Jillian R. Groeschel-Taylor1,2, Seiji Miyazono1,3, Timothy B. Grabowski4,5, and Gary 3
P. Garrett6 4
1Texas Cooperative Fish and Wildlife Research Unit, Department of Natural Resources 6
Management, Texas Tech University, Lubbock, Texas USA 7
2Current address: Metro Wastewater Reclamation District, Denver, Colorado USA 8
3Current address: Graduate School of Science and Technology for Innovation, 9
Yamaguchi University, Yamaguchi Japan 10
4U.S. Geological Survey, Texas Cooperative Fish and Wildlife Research Unit, Texas 11
Tech University, Lubbock, Texas USA 12
5Current address: U.S. Geological Survey, Hawaii Cooperative Fishery Research Unit. 13
University of Hawaii at Hilo, Hilo, Hawaii USA 14
6Texas Natural History Collections and Department of Integrative Biology, University of 15
Texas, Austin, Texas USA 16
Correspondence: S. Miyazono; Graduate School of Science and Technology for 18
Innovation, Yamaguchi University, Yamaguchi 755-8611 Japan; E-mail: 19; Phone: +81 090-9577-5571 20
Running head: Growth and habitat use of Guadalupe Bass 21
Keywords: age-specific habitat use; habitat-specific growth; side-scan sonar habitat 22
mapping 23
Abstract 24
Predicting how stream fishes may respond to habitat restoration efforts is difficult 26
due, in part, to an incomplete understanding of how basic biological parameters such as 27
growth and ontogenetic habitat shifts interact with flow regime and riverscape ecology. 28
We assessed age-specific Guadalupe Bass Micropterus treculii habitat associations at 29
three different spatial scales in the South Llano River, a spring-fed stream on the 30
Edwards Plateau of central Texas, USA, and the influence of habitat and flow regime on 31
growth. Substrates were classified using a low-cost side-scan sonar system. Scale 32
microstructure was used to determine age and to back-calculate size at age. Over 65% of 33
captured Guadalupe Bass were age-2 or age-3, but individuals ranged from 0-7 years of 34
age. Habitat associations overlapped considerably among age classes 1-3+, but age-0 35
Guadalupe Bass tended to associate with greater proportions of pool and run 36
mesohabitats with submerged aquatic vegetation. While habitat metrics across multiple 37
scales did not have a large effect on growth, river discharge was negatively correlated 38
with growth rates. Understanding age-specific Guadalupe Bass habitat associations at 39
multiple scales will increase the effectiveness of restoration efforts directed at the species 40
by assisting in determining appropriate ecological requirements of each life-history stage 41
and spatial scales for conservation actions. 42
Key words: age-specific habitat use, habitat-specific growth, side-scan sonar 43
habitat mapping 44
Received: February 26, 2018; Accepted: November 11, 2019; Published Online Early: November 46
2019; Published: xxx 47
Citation: Groeschel-Taylor JR, Miyazono S, Grabowski TB, Garrett GP. 2019. Growth and 49
habitat use of Guadalupe Bass in the South Llano River, Texas. Journal of Fish and Wildlife 50
Management X(X):xx-xx; e1944-687X. 51
This Online Early paper will appear in its final typeset version in a future issue of the Journal of 53
Fish and Wildlife Management. This article has been accepted for publication and undergone full 54
peer review but has not been through the copyediting, typesetting, pagination and proofreading 55
process, which may lead to differences between this version and the Version of Record. The 56
findings and conclusions in this article are those of the author(s) and do not necessarily represent 57
the views of the U.S. Fish and Wildlife Service. 58
Introduction 61
Human-induced habitat degradation and alteration of flow regimes have been 63
established as major stressors to the ecological integrity of rivers and streams (Poff et al. 64
1997; Poff and Zimmerman 2010) as well as major factors driving the decline of 65
freshwater fish diversity in North America (Warren et al. 2000). Stream management 66
depends on a solid understanding of biota-habitat relationships and, as such, specific 67
habitat classifications and associations are critical components of stream science and 68
management. For example, managers often rely on empirical descriptions of habitat use 69
to infer factors that limit the growth, survival, and abundance of a species (Hawkins 70
1993). The quantification of habitat as well as a species’ associations with that habitat at 71
different ontogenetic stages provides a basis for predicting response to changes in habitat 72
availability. Both the quality and quantity of available habitat affect the structure and 73
composition of resident biological communities and populations (Meffe and Sheldon 74
1988; Calow and Petts 1994; Maddock 1999). In addition, the species-habitat 75
associations in lotic systems could vary with spatial scales (Cheek et al. 2016). Therefore, 76
understanding age-specific habitat associations at multiple spatial scales may help predict 77
how a species will respond to disturbance or degradation and assist in determining 78
appropriate ecological requirements for each life-history stages and spatial scales for 79
conservation actions. 80
The official Texas state freshwater fish, Guadalupe Bass Micropterus treculii is 81
endemic to the streams and rivers of the northern and eastern Edwards Plateau in central 82
Texas, including portions of the Brazos, Colorado, Guadalupe, and San Antonio basins as 83
well as portions of the lower Colorado River off the Edwards Plateau downstream of 84
Austin (Koppelman and Garrett 2002; Hubbs et al. 2008). It is currently listed as a 85
species of greatest conservation need by the state of Texas due to the chronic threats 86
posed by hydrological alteration and habitat degradation (Birdsong et al. 2015), and the 87
acute threat of introgression with introduced Smallmouth Bass Micropterus dolomieu 88
(Edwards 1979; Whitmore and Butler 1982; Whitmore 1983; Bean et al. 2013). 89
While the hybridization threats are managed through stocking and opportunistic 90
removal of hybrids during droughts (Fleming et al. 2015), Guadalupe Bass face a more 91
chronic and persistent threat in that the entirety of their range overlaps or is immediately 92
upstream of some of the fastest-growing urban areas in Texas (Murdock et al. 2002). 93
Habitat loss and degradation and decreased stream flow due to changing land-use patterns 94
and increased water demands are thought to have contributed to declines in abundance 95
and local extirpations (Hurst et al. 1975; Edwards 1979, 1980; Garrett et al.2015). 96
However, detailed data on the relationship between Guadalupe Bass and their habitat at 97
multiple spatial scales are lacking. In particular, the habitat associations of juveniles are 98
poorly understood (Edwards 1980; Perkin et al. 2010). In addition, detailed description of 99
growth rates of wild Guadalupe Bass and the relationships with flow regimes are limited. 100
Conservation efforts specifically dedicated to restoring habitat for Guadalupe 101
Bass are currently underway in the South Llano River, located on the Edwards Plateau in 102
central Texas (Birdsong et al. 2015), for example the Texas Guadalupe Bass Restoration 103
Initiative implemented by Texas Parks and Wildlife in 2010 is a conservation effort 104
committed to conserving Guadalupe Bass populations by involving willing landowners in 105
landscape conservation activities at watershed scales. These types of activities include 106
reducing or eliminating actions that degrade riparian systems and water quality, reduce 107
water quantity, favor nonnative species, and fragment the river (Birdsong et al. 2015; 108
Garrett et al. 2015). However, there are no studies evaluating the effectiveness of the 109
conservation efforts in the region. Understanding the factors controlling the habitat use 110
and growth of Guadalupe Bass populations in the region is important to help to evaluate 111
which conservation efforts are effective. 112
Based on these research gaps, the objectives of this study were to examine the 113
influence of discharge on Guadalupe Bass growth rates and to determine age-specific 114
habitat associations at three different spatial scales. The working hypotheses are (1) the 115
Guadalupe Bass growth rates could be influenced by the amount and variability of the 116
river discharge, (2) the habitat use could vary among the age classes, and (3) the age-117
specific habitat associations could change with spatial scales. Results of this work will 118
help to develop conservation and management strategies (e.g., prioritizing conservation 119
areas, developing flow recommendation, etc.) for Guadalupe Bass throughout their 120
geographic distribution. 121
Materials and methods 123
Study area 125
The South Llano River is a second order, spring-fed stream located on the 127
Edwards Plateau within the Colorado River Basin, approximately 200 km west of San 128
Antonio (Figure 1). It is approximately 175 km in length, but only the lower 53 km 129
maintains year-round discharge due to the numerous springs that supply water to this 130
portion of the river (Groeschel 2013). The remainder of the river is ephemeral, and 131
contains flowing water only after heavy precipitation events (Groeschel 2013). Aquatic 132
systems on the Edwards Plateau, such as the South Llano River, exhibit high levels of 133
biodiversity and endemism (Conner and Suttkus 1986; Abell et al. 2000; Hubbs et al. 134
2008), but also face numerous threats that are ultimately related to the rapidly increasing 135
human population of central Texas (Bowles and Arsuffi 1993). The changes in land use 136
and increased demand for water associated with this rapidly increasing urban population 137
is expected to result in altered water quality and quantity for the aquatic systems of 138
central Texas (Bowles and Arsuffi 1993; O’Driscoll et al. 2010; Aitkenhead-Peterson et 139
al. 2011). 140
For example, changed land and water use along the increasing urban population 141
may cause agricultural and municipal water supply diversions, irrigation and treated 142
sewage effluent return flows, and changes in run-off dynamics associated with 143
impervious surfaces (Pease et al. 2017). In addition, overgrazing and other land-use 144
practices on some properties bordering the river have resulted in erosional banks and the 145
potential for elevated sediment loads and altered channel morphology (Edwards et al. 146
2004). Because the aquatic faunas have high endemism in this region, these human 147
activities may cause species extinctions. However, at present the South Llano River is 148
considered to be a relatively pristine river with minimal human disturbance due to its 149
relatively unaltered hydrological regime, good water quality, and diverse benthic 150
macroinvertebrate and fish assemblages that are representative of the Edwards Plateau 151
(Bayer et al. 1992; Broad et al. 2016; Cheek et al. 2016). 152
Age and growth 154
Guadalupe Bass were captured using a combination of angling, electrofishing, and 156
seining during the spring, summer, and fall of 2012. Angling was conducted along the 157
entire river corridor, haphazardly from sunrise to sunset on the following dates in 2012: 158
21 April; 20, 28, 30 May; 25 June; 3 July; 4, 31 August; 14, 15, 16 September; 18 159
October. Electrofishing was conducted with pulsed DC power at 120 pulses s_1 (Hz) 160
with voltage and pulse width adjusted to maintain an output of approximately 4 A along 161
50 m transects. Electrofishing occurred from the northeast Hwy 377 road crossing to the 162
bridge at County Road 150 on 15 October 2012, and from the South Llano River State 163
Park to the Flatrock Lane road crossing on 9 November 2012, 10 November 2012, and 20 164
November 2012. Fishes were surveyed seasonally using a 3.96×1.22×2.00m bag seine 165
with a 0.5cm mesh pulled along a 25m transect. Seining occurred at random locations 166
from approximately 165 m upstream from the waterfall (30°18'30.44"N, 99°54'30.48"W) 167
to the east edge of the South Llano River State Park property (30°27'11.84"N, 168
99°47'38.46"W) on 21-23 June 2012, 3 July 2012, 30 July 2012, 13-15 October 2012, 169
and 17-18 October 2012. Capture locations were recorded using a WAAS-enabled 170
handheld GPS unit (GPSMAP 78sc; Garmin International, Inc., Olathe, Kansas) with an 171
accuracy of 3-5 m. Capture locations of Guadalupe Bass caught by angling were recorded 172
at the location of the angler and not directly where the bass was caught. 173
Once captured, individuals were measured to the nearest millimeter total length 174
(mm TL), and scales were removed and stored dry in envelopes. A fin clip was taken and 175
stored in 95% ethanol and later genotyped following the protocols described by Lutz-176
Carrillo et al. (2006) to ensure no Guadalupe Bass X Smallmouth Bass hybrids were used 177
in our analyses. All captured Guadalupe Bass were released alive. Of the 291 Guadalupe 178
bass used for the age and growth analysis, a haphazard sample of 142 individuals 179
stratified by age classes (age-1 through age-7) were used for genetic analysis. Based on 180
small sample sizes, all fin clips from ages 1, 5, 6, and 7 were used. Ages 2, 3, and 4 were 181
grouped together and fin clips were randomly selected. Total genomic DNA isolation and 182
polymerase chain reactions were completed at the Fish Health and Genetics Laboratory 183
located at the A.E. Wood Fish Hatchery in San Marcos, Texas. 184
Scales were prepared for reading by compressing them between two glass slides 185
and placing them in a petri dish of water. Digital images of each scale were captured 186
using a compound microscope equipped with a camera (Olympus SZX16, Infinity 1, 187
Olympus, Tokyo, Japan) and analyzed using ImageJ (Abramoff et al. 2004) following 188
descriptions for interpreting scale microstructure by DeVries and Frie (1996). Total 189
length at age was back-calculated for each annulus and corrected (the size at scale 190
formation above the pectoral fin, 26 mm TL, for Smallmouth Bass) using the direct 191
proportion method (Everhart 1949; DeVries and Frie 1996). All Guadalupe Bass were 192
aged assuming a birthdate of 01 January. Second readers were used to assess the 193
reliability of the age estimates from the first reader. A third reader was used to resolve 194
disagreements between the first and second readers. If no agreed-upon age was 195
determined from a scale, that scale was not included in the data analysis (n = 31). 196
Although scales have been commonly used for estimating the age and growth of 197
other Micropterus spp. (Carlander 1977; Maraldo and MacCrimmon 1979; Gaeta et al. 198
2011), scales tend to underestimate age in older fishes (Maceina and Sammons 2006; 199
Sylvester and Berry 2006; Taylor and Weyl 2012). However, being able to release 200
captured individuals alive was an important consideration in this study due to the 201
conservation status of Guadalupe Bass and a concurrent population estimation study 202
being conducted in the South Llano River. Currently specific references on age 203
estimation accuracy for Guadalupe Bass do not exist. However, Largemouth Bass 204
Micropterus salmoides ages estimated from scales and otoliths tend to be consistent for 205
the first 6-8 years of life (Maraldo and MacCrimmon 1979; Maceina and Sammons 206
2006). Guadalupe Bass older than age-8 have were not reported from examination of the 207
sagittal otoliths of 271 individuals collected from throughout the Colorado River Basin in 208
central Texas (Pease et al. 2017). 209
Habitat mapping 211
Side-scan sonar surveys were conducted in October 2011 and June 2012. The 213
protocols described by Kaeser and Litts (2010) and Kaeser et al. (2012) were used to map 214
instream habitats. Briefly, a Humminbird 998c SI side scan sonar unit (Humminbird, 215
Eufaula, Alabama) with the transducer mounted off the starboard bow of a canoe was 216
used to capture georeferenced images of the river bottom substrate. A WAAS-enabled 217
handheld GPS unit (GPSMAP 78sc; Garmin International, Inc., Olathe, Kansas) was 218
connected directly to the control head for generating a trackplot of the course of the 219
canoe during the survey. The handheld GPS was set to record a point at 3-s intervals and 220
was placed near the transducer to ensure maximum accuracy, as recommended by Kaeser 221
and Litts (2010). 222
The collected images were cropped with IrfanView v. 4.30 (Irfan Skiljan, Wiener 223
Neustadt, Austria), imported into ArcGIS 10.0 (ESRI, Redland, California) to form 224
mosaics, or sonar image maps. Georeferenced aerial images (96 x 96 dpi, 1 m2 per pixel) 225
of the study site collected by unmanned aerial vehicle flyovers in November 2011 were 226
used to assist in creating the instream habitat map (Cheek et al. 2016). On each mosaic, 227
substrates classes (Kaeser and Litts, 2010; Kaeser et al. 2012) and subclasses (Barnhardt 228
et al. 1998) were delineated from resulting sonar imagery in ArcMap 10 (ESRI, 229
Redlands, California) based on dominant (>50%) and subordinate (<50%) substrate types 230
within a given area. Additionally, instream structures 100 cm in length (e.g., boulders 231
and large woody debris) were identified and assigned to separate classes. Mesohabitat 232
types (i.e., runs, riffles, and pools) were delineated from a combination of aerial images 233
and side-scan sonar generated depth profiles. 234
To complement and verify the side scan sonar mosaic, ground truthing was 235
performed at a total of 349 randomly selected sites. In shallow areas (<1 m) or areas with 236
minimal turbidity, sampling was either done by hand to feel the bottom substrate, or the 237
bottom was observed by sight. In turbid or deep areas, an underwater camera (Navroute 238
Technologies, Miami, Florida) was used to observe the substrate. A subset (25%) of the 239
large specific structures (i.e. large woody debris and boulders) were measured to further 240
ensure map scale accuracy. In addition, an accuracy rate (# of incorrectly assigned 241
points/total number of sites selected and sampled) was calculated. 242
South Llano River discharge 244
The North and South Llano Rivers are the only tributaries that contribute to the 246
discharge measured at the Llano River gage. However, stream gage data was not 247
available from the South Llano River prior to 16 May 2012. Therefore, discharge from 248
1915 through 2012 was estimated by obtaining gage data from the North Llano River 249
(U.S. Geological Survey gage 08148500) and subtracting them from the data from the 250
Llano River (U.S. Geological Survey gage 08150000; approximately 4.5 km downstream 251
of the confluence of the North and South Llano Rivers). These were then used to 252
calculate Q90, Qlow, Qnormal, Qhigh, and Q10 quantiles and the proportion of observations 253
falling within each quantile annually. Qlow was defined as the discharges rates between 254
the 75th and 90th percentile of the total discharge observations for the South Llano River. 255
Flows between the 25th and 75th percentile were classified as Qnormal, while Qhigh flows 256
were those between the 10th and 25th percentile. 257
Data analyses 259
A von Bertalanffy growth curve, Lt = L
(1 - e-k(t-t0)), where Lt = length at time t 261
(age), L = asymptotic length, k is a growth coefficient and t0 is a time coefficient where 262
length would theoretically be zero (Ogle 2016), was fitted to both the length at age and 263
mean back-calculated total length at age data separately using PROC NLIN in SAS 9.4 264
(SAS Institute, Carey, North Carolina). The value of L
was set at 432 mm TL, the 265
reported TL of the world record Guadalupe Bass recently captured from the mainstem 266
Colorado River downstream of Austin, Texas (Texas Parks and Wildlife News 2014) due 267
to the model failing to converge on realistic values of L
, when fitting the Von 268
Bertalanffy growth curves. The residuals from the mean back-calculated length at age 269
growth curve were calculated across the growth history of each individual (Grabowski et 270
al. 2012). We used the residuals to know whether an individual Guadalupe Bass reached 271
a larger/smaller size at age than predicted size at age by the von Bertalanffy growth 272
model (Grabowski et al. 2012). Discharge was classified into quantiles, and the 273
proportion of annual observations within each flow quantile was calculated for each year. 274
The effects of the principal components of hydrological attributes as well as the South 275
Llano River discharge quantiles on the residuals from the back-calculated length at age 276
growth curve were assessed using a mixed linear model, with the flow quantiles as fixed 277
effects, back-calculated age as a random effect, and individual Guadalupe Bass as a 278
subject effect. 279
The habitat associated with captured Guadalupe Bass was assessed at three spatial 280
scales: a fine scale within a 50-m radius surrounding the capture location, an intermediate 281
scale within a 250-m radius surrounding the capture location, and a coarse scale of the 282
stream unit in which the bass was caught, e.g. if a bass was caught in a riffle mesohabitat, 283
the stream unit area associated with that bass was defined from its capture location to the 284
adjacent upstream and downstream riffles. These scales were selected based on the 285
results of telemetry studies conducted on Guadalupe Bass movement suggesting that 286
most individuals were sedentary, moving on average < 60 m over the course of a year 287
(Perkin et al. 2010). The 50-m and 250-m scales were created using the circle buffer tool 288
in ArcGIS 10.0, while the stream unit scale was created by using digitized lines. These 289
scales were then converted to polygons and merged with the underlying mesohabitat and 290
substrate type polygons. Once merged, the scales were converted to raster datasets and 291
imported into FRAGSTATS 4.1 (McGarigal et al. 2012). FRAGSTATS was used to 292
compute patch and class metrics of the habitat types within each scale associated with 293
each Guadalupe bass (Table 1). 294
Discriminant function analysis (DFA) was used to assess age class-specific 295
habitat associations at these three scales performed using PROC DISCRIM in SAS 9.4 296
(SAS Institute, Carey, North Carolina) as described by McGarigal et al. (2000). Age-3 297
and older fish were grouped together into a single age class due to low sample sizes of 298
older individuals and that these individuals were all likely to be sexually mature 299
(Edwards 1980). The habitat variables for the DFA that best discriminated among age 300
classes (age-0, age-1, age-2, age-3+) of Guadalupe Bass were chosen using a step-wise 301
selection procedure (PROC STEPDISC) implemented in SAS 9.4 (SAS Institute, Carey, 302
North Carolina). The effect of habitat type on Guadalupe bass growth rates was assessed 303
using ANCOVA with habitat type as a covariate and age as the independent variable. 304
Only individuals less than age-6 were used in the analysis due to the small sample sizes 305
of age-6 (n=1) and age-7 (n=3) bass. Only growth rates from the most recent year, 2012, 306
were analyzed in order to avoid assuming that Guadalupe bass remain in their location of 307
capture throughout their entire lives. This analysis was done by assessing instream habitat 308
at the three different spatial scales. 309
We assessed all parametric assumptions of normality and independence, and 310
made transformations as appropriate, in particular, many of the habitat variables 311
generated by FRAGSTATS needed to undergo a square root transformation to 312
approximate a normal distribution. All statistical analyses were performed using SAS 9.4 313
(SAS Institute, Carey, North Carolina). A significance level of α = 0.05 was used for all 314
hypothesis tests and the Holm-Bonferroni method (Holm 1979) was used to correct for 315
multiple comparisons. 316
Results 318
Scales from 291 Guadalupe Bass were used for age and growth analysis. Eight 320
hybrids were detected from the sample of 142 Guadalupe bass, or a hybridization rate of 321
5.6%. Age-0 and age-3 bass constituted approximately 54% of captured Guadalupe Bass; 322
however, individuals as old as seven were encountered (Table 2). Von Bertalanffy growth 323
curve fitted to the back-calculated length at age data for Guadalupe Bass yielded 324
parameter estimates (±SE) for k = 0.20±0.01 and t0 = -0.04±0.09 that were not 325
appreciably different from the curve fitted to the length at capture data (k = 0.20±0.01; t0
= -0.46±0.14; Figure 2). Individuals tend to reach approximately 84 mm TL by age-1 327
with growth decreasing to about 60 mm per year from age-1 to age-2 (Table 2). 328
At the stream unit scale, age-0 Guadalupe Bass tended to be associated with an 329
increase in the size of gravel substrate habitat patches in runs (Figure 3a). Both age-1 330
individuals and older fish were associated with the availability of edge habitats along 331
patches of boulders and submerged aquatic vegetation in riffles at the stream unit scale. 332
Age-1 fish were also associated with patches of boulder habitats with relatively high 333
perimeter to area ratios, suggestive of larger numbers of smaller boulders (Figure 3a). 334
The association with larger patches of gravel in runs was also evident at the 250-m spatial 335
scale, but age-0 individuals also exhibited an association with an increase in edge habitat 336
adjacent to submerged aquatic vegetation in runs and the availability of bedrock habitat 337
in riffles (Figure 3b). At the 250-m spatial scale, 1-3+ year old Guadalupe Bass were 338
associated with areas of greater contiguity of large woody debris and boulders in runs and 339
pools as well as relatively higher proportions of rocky-fine substrates. However, the 340
amount of edge habitat associated with gravel-sand patches in runs was also important to 341
age-1 individuals (Figure 3b). At the 50-m spatial scale, the proportion of pool habitat 342
and submerged aquatic vegetation in runs were most closely associated with age-0 343
individuals (Figure 3c). At the 50-m spatial scale, there was no appreciable difference 344
between 1, 2, and 3+ year old individuals as all three groups were associated with the 345
availability of edge habitat along patches of submerged aquatic vegetation in runs, the 346
distance between boulders in pools, and the proportion of bedrock (Figure 3c). 347
Even though there was clear separation amongst most of the age classes in their 348
habitat associations at different spatial scales, we did not detect a strong influence of any 349
of the measured habitat characteristics on the most recent year of growth. Age alone 350
explained most of the variation in the most recent year of Guadalupe Bass growth at all 351
spatial scales. At the stream unit scale, growth was also positively correlated with riffle 352
cobble-gravel contiguity (F1,265=16.87, P<0.01); however, this variable alone explained 353
just 4% of the variation. At the 250-m scale, growth was positively correlated with pool 354
bedrock contiguity (F1,270=7.24, P<0.01) and negatively correlated with pool submerged 355
aquatic vegetation perimeter-area ratios, explaining 2% and 1% of the variation 356
respectively. Growth rates were positively correlated with three habitat variables at the 357
50-m scale: riffle gravel-cobble total edge (F1,269=5.59, P=0.02), riffle boulders 358
perimeter-area ratios (F1,269=6.16, P=0.01), and run bedrock perimeter-area ratios 359
(F1,269=12.80, P<0.01), but together only explained about 3% of the variation in growth. 360
In contrast, stream discharge explained a much greater proportion of the 361
variability in growth. The hydrologic profile of the South Llano River during the period 362
encompassed by the lifespans of the Guadalupe Bass used in this study (2004-2012) can 363
be roughly divided into three periods (Figure 4). A period of “typical” discharges during 364
2004-2006 that were dominated by flows within the 25-75th percentile was followed by a 365
high flow year in 2007. The remaining years were characterized by moderate to severe 366
drought and extreme low flows (2008-2012). Overall, the proportion of discharge 367
observations falling in the Q90 range in a given year had the greatest influence on 368
Guadalupe Bass growth rates. Residuals from the von Bertalanffy model were negatively 369
correlated to the proportion of Q90 discharge rates observed during a particular year over 370
the first three years of growth (F1,339=48.83, P<0.01; Figure 5). 371
Discussion 373
This study represents the first detailed description of growth rates of wild 374
Guadalupe Bass, and our results suggest that the habitat use could vary among the age 375
classes. The association of age-0 Guadalupe Bass with run mesohabitats at all three 376
spatial scales suggests that higher current velocities or environmental factors associated 377
with higher current velocities are important to their survival. Current velocity has been 378
demonstrated to influence first-year growth and survival of Smallmouth Bass, by possibly 379
influencing feeding activities and swimming performance (Simonson and Swenson 1990; 380
Livingstone and Rabeni 1991; Brewer 2011). Furthermore, runs in the South Llano River 381
are typically shallower and warmer than pools during summer and fall (Cheek and 382
Grabowski 2014) and thus may offer a more optimal temperature regime for age-0 383
Guadalupe Bass (27-28°C, Sullivan et al. 2013). Thermally-driven habitat preferences 384
have been noted in stream-dwelling age-0 Smallmouth Bass which tend to use habitat 385
with the warmest temperature available < 32°C (Brewer 2008). Moreover, the proportion 386
of submerged aquatic vegetation, as well as the availability of edge habitat around it, 387
seemed to be important factors associated with the presence of age-0 Guadalupe Bass at 388
the finest spatial scales. 389
There was greater overlap in the habitat associations among older age classes of 390
Guadalupe Bass than with age-0 counterparts and the availability of edge habitats seemed 391
to be an important factor at multiple spatial scales for these older fish. Edge effects on the 392
distribution and abundance of species have been known since Leopold (1933) coined the 393
term to describe an increase in game species in patchy landscapes. For older age classes 394
of Guadalupe Bass, edges likely provide access to resources that are spatially separated 395
by a boundary (Ries et al. 2004), such as prey and refuge from current velocity or 396
predators. Furthermore, the contiguity, or spatial proximity of instream structures or 397
habitat features, such as large woody debris, boulders, and submerged aquatic vegetation, 398
to each other also became more influential for older age classes. This may reflect a 399
change in the perception of available habitat with increasing body size, i.e., larger fish 400
may be more likely to move between patches of structure within a certain distance 401
elevating the importance of the spatial arrangements of these patches whereas smaller 402
fish may be more likely to remain in a single habitat patch rendering the total size of the 403
habitat more important. 404
While the size-selective habitat associations exhibited by Guadalupe Bass were 405
expected, the minimal influence of habitat on recent growth observed in this study was 406
not. The literature suggests that fish should associate with habitat that maximizes somatic 407
and/or gonadal growth, while minimizing the risk of mortality (Gilliam and Fraser 1987; 408
Gotceitas 1990). Since Guadalupe Bass are drift feeders at younger ages and feed 409
primarily on benthic macroinvertebrates as they age (Edwards 1980), certain habitat 410
variables such as the contiguity of riffle cobble-gravel habitats were expected to 411
positively influence growth. The resulting low influence of habitat on growth observed in 412
this study could be attributed, in part, to a few factors. The year of growth evaluated in 413
this study coincided with an extreme drought in Texas. It is possible that changes in 414
habitat availability or suitability effectively equalized all habitats in terms of ability to 415
support Guadalupe Bass growth. However, the three spatial scales used in our analysis 416
were based on telemetry studies indicating that Guadalupe Bass typically do not move 417
great distances (< 60 m; Perkin et al. 2010). Still, movement could have been 418
underestimated as individuals may have been more mobile due to the drought (see 419
Matthews and Marsh-Matthews 2003 for review). Alternatively, factors at scales coarser 420
than those encompassed by this study, such as those at the watershed scale, may have a 421
greater influence on growth than those at finer scales. However, a replication our study 422
design across several watersheds would be required to address this possibility. 423
While we did not detect a strong relationship between habitat and growth, the 424
growth rates of young (age 1-3) Guadalupe Bass were negatively correlated to the 425
proportion of Q90 discharge observations during that year of growth. This is in contrast to 426
riverine populations of Largemouth Bass in the southeastern U.S. (Rypel 2009) and 427
Smallmouth Bass in the midwestern U.S. (Paragamian and Wiley 1987) which exhibited 428
higher growth rates during periods of drought. Edwards (1980) reported a strong 429
preference by Guadalupe Bass for moving water habitats during most of the year. 430
Similarly, Perkin et al. (2010) found that Guadalupe Bass were responsive to changes in 431
the flow regime, gradually shifting toward pools with greater depths during a summer 432
period of extreme low flow in the Pedernales River. While we captured individuals 433
outside of pools even during extreme low flows on the South Llano River, it is possible 434
that the productivity of riffles and runs was reduced. Periods of low discharge can reduce 435
the growth rates of drift feeding fishes (Rimmer 1985; Hakala and Hartman 2004; Nislow 436
et al. 2004; Harvey et al. 2006), potentially reducing the efficacy of a feeding strategy 437
often used by young Guadalupe Bass (Edwards 1980) and not typically used by 438
Largemouth Bass or Smallmouth Bass. Our results suggest that Guadalupe Bass could be 439
flow-dependent, but high flow extreme could negatively affect the growth. 440
The results of this study are relevant to the advancement of our current 441
understanding of lotic fish conservation. Age-0 Guadalupe Bass tended to associate with 442
greater proportions of pool and run mesohabitats with submerged aquatic vegetation. This 443
suggests the importance of riparian vegetation management for the recruitment of 444
Guadalupe Bass in riverine systems. The ontogentic shifts in habitat association at 445
multiple spatial scales exhibited by Guadalupe Bass render it difficult to assign an 446
appropriate scale at which to target conservation efforts. However, identifying the habitat 447
features and qualities fish species associate with at different points in their life history 448
combined with a thorough habitat inventory and understanding of the population 449
structure would offer the potential to create an adaptive approach that can be customized 450
to work in specific watersheds. In addition, our results suggest that hydrologic alteration 451
such as significant flow release from dams and extreme decrease in river discharge would 452
negatively affect the growth of Guadalupe Bass because the extreme high and low flow 453
conditions were negatively related to the Guadalupe Bass growth in our study. These 454
conservation implications may be useful for not only Guadalupe Bass but also other fish 455
species with similar life history traits in different lotic systems. 456
Supplemental Material 458
Table S1. Fish identification number, total length (mm TL), age (yrs), and variables 459
describing habitat within the riffle-run-pool complex containing the capture location of 460
Guadalupe Bass Micropterus treculli sampled during April-November 2012 from the 461
South Llano River, Texas, USA. The habitat variables include the proportion of area 462
encompassed by gravel-cobble substrate in riffle (%riff_COgr) and pool (%pool_COgr) 463
habitat and boulders in run habitat (%run_bldr); the perimeter:area ratio of boulders in 464
pool habitat (pool_bldr_P:A) and gravel-cobble (riffle_GRco_P:A), gravel-sand 465
(riffle_GRsa_P:A) and cobble-gravel (riffle_COgr_P:A) substrates in riffle habitat; the 466
total edge (m) of gravel-cobble substrate in run habitat (run_GRco_TE), bedrock 467
substrate (riff_BR_TE), boulders (riff_bldr_TE), and submerged aquatic vegetation 468
(riff_SAV_TE) in riffle habitat, boulders (pool_bldr_TE) and cobble-gravel substrate 469
(pool_COgr_TE) in pool habitat, and all submerged aquatic vegetation (total_SAV_TE); 470
and the contiguity of gravel-sand substrate (pool_GRsa_contig) and submerged aquatic 471
vegetation (pool_SAV_contig) in pool habitat, boulders in riffle habitat(riff_bldr_contig), 472
bedrock substrate in run habitat (run_BR_contig), cobble-gravel substrate in riffle habitat 473
(riff_COgr_contig), large woody debris in run habitat (run_LWD_contig), and bedrock 474
substrate in riffle habitat (riff_BR_contig). 475
Table S2. Identification number, total length (mm TL), age (yrs), cohort, age at back-477
caluclated length, back calculated total length (mm TL), growth (mm/yr), and proportion 478
of stream discharge observations falling below Q90, between Q90-Q75 (Qlow), between 479
Q75-Q25 (Qnormal), between Q25-Q10 (Qhigh), and above Q10 during the year of the 480
back-calculated length estimate for Guadalupe Bass Micropterus treculli captured during 481
April-November 2012 from the South Llano River, Texas, USA. 482
Table S3. Fish identification number, total length (mm TL), age (yrs), and variables 484
describing habitat within a 50-m radius of the point of capture of Guadalupe Bass 485
Micropterus treculli sampled during April-November 2012 from the South Llano River, 486
Texas, USA. The habitat variables include the proportion of area encompassed by pool 487
habitat (%pool), bedrock substrate (%BR), large woody debris (%LWD), submerged 488
aquatic vegetation in run habitat (run_SAV_prop), cobble-gravel substrate in run habitat 489
(run_COgr_prop), and boulders in riffe habitat (riffle_bldr_run); the total edge (m) of 490
submerged aquatic vegetation in run habitat (run_SAV_TE); the perimeter:area ratio of 491
cobble-gravel substrate in run habitat (run_COgr_P:A) and gravel-sand substrate in riffle 492
habitat (riffle_GRsa_P:A); and the contiguity of boulders in run habitat (run_bldr_contig) 493
and gravel-sand substrate (pool_GRsa_contig), cobble-gravel substrate 494
(pool_COgr_contig), and boulders (pool_bldr_contig) in pool habitat. 495
Table S4. Fish identification number, total length (mm TL), age (yrs), and variables 497
describing habitat within a 250-m radius of the point of capture of Guadalupe Bass 498
Micropterus treculli sampled during April-November 2012 from the South Llano River, 499
Texas, USA. The habitat variables include the proportion of area encompassed by riffle 500
habitat with bedrock substrate (%riff_BR) and rocky-fine substrate (%rocky-fine); the 501
perimeter:area ratio of submerged aqautic vegetation in riffle habitat (riffle_SAV_P:A), 502
gravel-sand substrate in riffle (riffle_GRsa_P:A) and run (run_GRsa_P:A) habitats, and 503
submerged aqautic vegetation in run habitat (run_SAV_P:A); the total edge (m) of 504
submerged aquatic vegetation in run (run_SAV_TE) and pool (pool_SAV_TE) habitats, 505
cobble-gravel substrate in pool habitat (pool_COgr_TE), and gravel-sand 506
(run_GRsa_TE), gravel-cobble (run_GRco_TE), and cobble-gravel (run_COgr_TE) 507
substrates in run habitat; the contiguity of large woody debris in run habitat 508
(run_LWD_contig), bedrock substrate in pool habitat (pool_BR_contig), boulders in pool 509
habitat (pool_bldr_contig), and gravel-sand substrate in run habitat (run_GRsa_contig); 510
and the landscape contagion index (contag). 511
Table S5. Mean size (mm) ± SD of Guadalupe Bass collected by three sampling 513
techniques (angling, electrofishing, and seining) on each month in 2012 from the South 514
Llano River, Texas, USA. The numbers in the parentheses indicate the captured number 515
of Guadalupe Bass. 516
Reference S1. Cheek BD, Grabowski TB. 2014. Evaluating habitat associations of a fish 518
assemblage at multiple scales in a minimally disturbed stream on the Edwards Plateau, 519
central Texas. U.S. Department of Interior, Fish and Wildlife Service, Cooperator 520
Science Series FWS/CSS-104-2014, Washington, D.C. Available: 521
104_Cheek_Grabowski_2014-1.pdf (August 2019). 523
Reference S2. Pease JE, Grabowski GB, Pease AA. 2017. Variation and plasticity and 525
their interaction with urbanization in Guadalupe Bass populations on and off the Edwards 526
Plateau. U.S. Department of Interior, Fish and Wildlife Service, Cooperator Science 527
Series FWS/CSS-125-2017, Washington, D.C. Available: https://usgs-cru-individual-528 529
(August 2019). 530
Acknowledgements 532
We thank M. Bean, M. Berlin, T. Birdsong, B. Cheek, Q. Chen, C. Craig, C. 533
Holmes, K. Linner, D. Logue, J. Mueller, B. Perkins, B. Skipper, M. Vanlandeghem, and 534
members of the Texas Tech Bass Anglers Association and the Red Raider Bass Fishing 535
Team for their assistance in the field and laboratory. T. Arsuffi, K. Lopez, S. Richardson, 536
R. Stubblefield, and the members of the Llano River Watershed Alliance provided access 537
and logistical support. Assistance with the genetic identification of hybrids was provided 538
by D. Lutz-Carrillo at the genetics lab at the Fish Health and Genetics Laboratory at A.E. 539
Wood State Fish Hatchery. M.A. Barnes, S.K. Brewer, and A. Pease provided comments 540
on earlier drafts that greatly improved this manuscript. We thank the journal reviewer and 541
the associate editor for their comments that improved the final manuscript. This research 542
was supported by Texas Parks and Wildlife Department through U.S. Fish and Wildlife 543
Service State Wildlife Grant T-60 and the U.S. Geological Survey (cooperative 544
agreement number G11AC20436). It was conducted under the auspices of the Texas 545
Tech University Animal Care and Use Committee (AUP 11062-08). Cooperating 546
agencies for the Texas Cooperative Fish and Wildlife Research Unit are the U.S. 547
Geological Survey, Texas Tech University, Texas Parks and Wildlife Department, and 548
the Wildlife Management Institute. 549
Any use of trade, product, website, or names is for descriptive purposes only and 550
does not imply endorsement by the U.S. Government. 551
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Table 777
Table. 1. Most informative habitat variables selected from the discriminant function 778
analysis that best discriminated among age classes (Age-0, Age-1, Age-2, Age-3+) of 779
Guadalupe Bass Micropterus treculii captured in the South Llano River, TX from April 780
2012 – November 2012. 781
Table 2. Mean (±SE) back-calculated total length (TL) at each scale annulus of 782
Guadalupe Bass Micropteru treculii from the South Llano River, Texas captured during 783
April–November 2012. 784
Figures 786
Figure 1. Map of the South Llano River study area in Kimble and Edwards County, 788
Texas in 2012. Road crossings and other barriers are indicated by lines crossing the river. 789
The upper limit of the study area was approximately 1.5 km upstream of upstream most 790
barrier. Inset map shows location of the study area within Texas. 791
Figure 2. Von Bertalanffy growth curve fitted to observed and back-calculated lengths at 793
age of Guadalupe Bass Micropterus treculii captured from the South Llano River, Texas 794
during April–November 2012. 795
Figure 3. Discriminant function analysis biplots of age-specific habitat associations of 797
Guadalupe Bass Micropterus treculii at three different spatial scales in the South Llano 798
River, Texas during April–November 2012. The stream unit scale (a), i.e., the riffle-run-799
pool complex the individual was captured from is presented (a), while the characteristics 800
of the river in a 250-m (b) and 50-m (c) buffer around the capture location of the fish are 801
presented in the remaining panels. 802
Figure 4. Annual proportion of observations of discharge within flow quantiles from the 804
South Llano River, Texas during 2004–2012. 805
Figure 5. Regression of mean residuals by cohort from von Bertalanffy model of back-807
calculated lengths at age against the proportion of Q90 discharge rates observed during 808
that year for Guadalupe Bass Micropterus treculii captured from the South Llano River, 809
Texas during 2011-2012. The period represented by the individuals presented in this 810
figure encompasses 2004–2012. Error bars represent 95% confidence intervals around the 811
mean residuals. Individual observations are represented by gray-filled circles. 812
Table. 1.
Variable Description
Axis 1 Axis 2
Channel unit buffer
Riff GRsa P:A Riffle gravel-sand habitat perimeter area ratio 0.61 0.17
Run GRco TE Run gravel-cobble habitat total edge 0.68 0.03
Pool Bldr P:A Pool boulder habitat perimeter area ratio -0.06 0.75
Pool BR TE Pool bedrock habitat total edge -0.77 0.54
Riff SAV TE Riffle submerged aquatic vegetation habitat total
edge -0.65 -0.06
Riff Bldr TE Riffle boulder habitat total edge -0.57 -0.30
Pool Bldr TE Pool boulder habitat total edge -0.50 -0.33
Riff GRco P:A Riffle gravel-cobble habitat perimeter area ratio -0.49 -0.30
250-m buffer
%Riff BR Percentage of riffle bedrock habitat -0.57 -0.36
Run GRsa P:A Run gravel-sand habitat perimeter area ratio -0.60 -0.36
Run SAV TE Total edge of submerged aquatic vegetation
habitat in a run -0.67 0.27
Run GRsa TE Run gravel-sand habitat total edge -0.31 1.24
Pool BR Contig Pool bedrock habitat contiguity 0.18 0.60
Run LWD Contig Run large woody debris habitat contiguity 0.44 0.17
% Rocky-fine Percentage of rocky-fine substrate 0.80 -0.09
Pool Bldr Contig Pool boulder habitat contiguity 0.35 -0.30
Run COgr TE Run cobble-gravel habitat total edge 0.42 -0.44
50-m buffer
% Pool Percentageof pool mesohabitat 1.57 0.22
Run SAV Prop Proportion of run submerged aquatic vegetation
habitat 1.45 0.14
Pool Bldr Contig Pool boulder habitat contiguity -0.55 -0.21
% BR Percentage of bedrock substrate -0.86 -0.21
Run SAV TE Run submerged aquatic vegetation habitat total
edge -1.08 -0.20
Run COgr P:A Run cobble-gravel habitat perimeter area ratio -0.50 0.39
% LWD Percentage of large woody debris structures -0.30 0.77
Table 2.
TL (mm) at capture Back-calculated TL (mm) at age
class Year
class n Mean Range 1 2 3 4 5 6 7
0 2012 79 56 ± 2 35-91
I 2011 14 107 ± 8 69-171 85 ± 6
II 2010 55 167 ± 4 106-211 78 ± 3 138 ± 3
III 2009 79 216 ± 3 152-293 81 ± 2 142 ± 3 188 ± 3
IV 2008 49 244 ± 4 200-310 88 ± 4 137 ± 4 184 ± 4 220 ± 4
V 2007 11 294 ± 8 248-330 99 ± 8 160 ± 5 204 ± 78 240 ± 10 271 ± 9
VI 2006 1 341 133 183 231 271 296 318
VII 2005 3 365 ± 19 333-397 130 ± 13 180 ± 13 227 ± 14 256 ± 14 289 ± 17 321 ± 13 344 ± 14
Mean TL (mm) at age 84 ± 2 142 ± 2 189 ± 2 226 ± 4 276 ± 7 320 ± 10 344 ± 14
Mean annual growth (mm) 84 ± 2 58 ± 1 46 ± 1 35 ± 1 30 ± 2 30 ± 4 23 ± 5
... We validated BEM using empirical growth of a Guadalupe bass population in the South Llano River. We estimated agespecific growth using back-calculated length-at-age measurements of scales taken from fish spawned between 2005(Groeschel-Taylor et al., 2019. Lengths-at-age were converted to masses-at-age using von Bertalanffy equations of Guadalupe bass (Groeschel-Taylor et al., 2019). ...
... We estimated agespecific growth using back-calculated length-at-age measurements of scales taken from fish spawned between 2005(Groeschel-Taylor et al., 2019. Lengths-at-age were converted to masses-at-age using von Bertalanffy equations of Guadalupe bass (Groeschel-Taylor et al., 2019). We used BEM to project growth beginning on Julian day 1 and ending on Julian day 365. ...
... These projections require four inputs: (i) initial fish mass, (ii) proportion of maximum consumption at which an individual feeds (C P ), (iii) the activity multiplier of respiration (R ACT ) and (iv) mean daily water temperature during the projection period. Fish mass was assumed to be 6.4 g for age-1 fish (Groeschel-Taylor et al., 2019), C P to be 0.5 and R ACT to be 1.0. We estimated mean daily water temperatures for all 17 reaches within the South Llano River study area of Groeschel-Taylor et al. (2019) using a two-step approach. ...
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Rising water temperature under climate change is affecting the physiology, population dynamics and geographic distribution of freshwater taxa. We propose a novel application of individual-based bioenergetics modelling (BEM) to assess the physiological impacts of warming on freshwater fishes across broad spatial extents. We test this approach using the Guadalupe bass (Micropterus treculii), a species of conservation and recreational significance that is endemic to central TX, USA. We projected historical-to-future changes (middle 20th century to end of 21st century) in daily bioenergetics of individual fish across 7872 stream reaches and compared this output to changes in reach occupancy derived from traditional species distribution modelling (SDM). SDMs project an 8.7% to 52.1% decrease in reach occupancy, depending on model parameterizations and climate change scenarios. Persistence is projected in the central Edwards Plateau region, whereas extirpations are projected for the warmer southeastern region. BEM projected a median 79.3% and 143.2% increase in somatic growth of age-1 Guadalupe bass across historically occupied reaches under moderate and severe climate change scenarios, respectively. Higher end-of-year body size under future climate was caused by a longer growing season. Future scenarios exploring suppressed or enhanced prey consumption suggest that small changes in prey availability will have relatively greater effects on growth than forecasted changes in temperature. Projected growth was geographically discordant with SDM-based habitat suitability, suggesting that SDMs do not accurately reflect fundamental thermal niche dimensions. Our assessment suggests that for locations where the species persists, Guadalupe bass may benefit from warming, although realized consumption gains will depend on seasonal, spatially varying changes in prey availability and other biotic and abiotic factors. More generally, we demonstrate that uniting species-specific BEM with spatially explicit climate change projections can elucidate the physiological impacts of climate change—including seasonal variation—on freshwater fishes across broad geographic extents to complement traditional SDM.
... We recorded perch locations with a handheld GPS unit. Following Groeschel (2013), we classified reaches of the river into three mesohabitats as pool, run, or riffle, and scored these as 1, 2, or 3, respectively. Mesohabitats were defined by presence of visible depth, substrate, and surface-agitation (Groeschel 2013). ...
... Following Groeschel (2013), we classified reaches of the river into three mesohabitats as pool, run, or riffle, and scored these as 1, 2, or 3, respectively. Mesohabitats were defined by presence of visible depth, substrate, and surface-agitation (Groeschel 2013). On some occasions, kingfishers flushed from perches before we could record their location. ...
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Current northward expansion of Ringed Kingfisher (Megaceryle torquata) and Green Kingfisher (Chloroceryle americana) into central Texas places them in aquatic systems with the temperate Belted Kingfisher (Megaceryle alcyon). Recent contact among the three species provides an opportunity to assess resource partitioning. A 23.5-km stretch of the South Llano River near Junction, Texas, USA was surveyed to determine seasonal abundance and compare foraging perch characteristics among the species. Data were collected on 7 foraging perch characteristics for 250 kingfisher observations across 26 surveys. Mean encounter rate for Green, Belted, and Ringed kingfishers per river kilometer was 0.48, 0.22, and 0.09, respectively. Green Kingfishers were present year-round, while the Belted and Ringed kingfishers were absent or rare from mid-spring to mid-summer. Characteristics of foraging perches were similar among the species with the exception of perch height, with Green Kingfisher having lower perches (142.3 cm ± 126.6 SD) than both Belted (550.8 cm ± 449.4 SD) and Ringed kingfishers (551.1 cm ± 422.7 SD). Mean perch heights of Green Kingfishers averaged higher during surveys when Belted Kingfishers were absent (210.5 cm ± 191.0 SD, n = 36) compared to surveys when Belted Kingfishers were present (124.0 cm ± 89.1 SD, n = 129).
Technical Report
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Native Fish Conservation Areas of the southwestern USA consist of springs, ciénegas, creeks, rivers, and associated watersheds uniquely valued in preservation of freshwater fish diversity. These freshwater systems were identified through a spatial prioritization approach that identifies areas critically important to the long-term persistence of focal fish species. Through a shared mission of collaborative stewardship, conservation partnerships have formed among non-governmental organizations, universities, and state and federal agencies to plan and deliver actions to restore and preserve native freshwater fishes and aquatic habitats within the Native Fish Conservation Areas. Furthermore, the Native Fish Conservation Areas have increased awareness of the ecological, recreational, and economic values of freshwater systems in the region, and helped increase interest and capacity of local landowners, communities, and recreational users (e.g., paddlers, anglers) to act as advocates and local stewards of these systems. By facilitating partnership development, coordinating multi-species, watershed-based conservation planning, and leveraging technical and financial resources toward strategic conservation investments, Native Fish Conservation Areas have served as a catalyst for collaborative, science-based stewardship of native freshwater fishes and aquatic habitats in the southwestern USA. Efforts described herein to prioritize and deliver a network of Native Fish Conservation Areas in the southwestern USA offer a successful case study in multi-species and watershed approaches to freshwater fish conservation transferrable to other states and regions of the USA. This report offers a synthesis of recent (2011-2018) multi-species aquatic assessments, Native Fish Conservation Area prioritizations, conservation planning, and conservation delivery within the southwestern USA explicitly focused on implementation of the Native Fish Conservation Areas approach.
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An efficient, low-cost approach for mapping habitat features in navigable streams is needed to support the research and management of aquatic ecosystems at the landscape level. We developed a method that uses high-resolution (455 kHz) side-scan sonar imagery obtained with the inexpensive (~$2000) Humminbird® Side Imaging system and ArcGIS to produce sonar image maps (SIMs) used to interpret and map habitat features such as substrates and large woody debris, in addition to continuously recording depth along the survey route. This method was recently demonstrated and evaluated in several small streams in southwestern Georgia (30–50 m width, 40 km mapped). To evaluate the feasibility of this method for mapping substrate and depth in larger rivers and over greater spatial extents, we conducted a sonar survey and generated SIMs for 124 km of the lower Flint River (85–140 m width). We interpreted the SIMs to digitize and classify substrate and bank boundaries. To assess classification accuracy, we visually inspected substrate at randomly assigned reference locations. A comparison of reference and map data revealed an overall classification accuracy of 84%. These results were consistent with previous findings and indicate that low-cost side-scan sonar is also an effective mapping tool for larger rivers. The sonar survey did, however, result in more missing and unsure substrate data and a lower map accuracy for fine-textured substrates than previously achieved when mapping smaller streams. We found a strong, positive relationship (r2 = 0.89) between the sonar range and the proportion of unsure substrate in the map, suggesting that a multi-pass, parallel-transect sonar survey could be used to maintain high-image resolution when stream widths exceed 100 m and/or obstructions, such as islands, are encountered. Applications for sonar-based habitat maps are widespread and numerous. The ability to produce these maps efficiently at low-cost is within the grasp of researchers and managers alike. Copyright © 2012 John Wiley & Sons, Ltd.
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Animals commonly choose among habitats that differ both in foraging return and mortality hazard. However, no experimental study has attempted to predict the level of increase in resources, or the decrease in mortality hazard, which will induce a forager to shift from a safer to a more hazardous (but richer) foraging area. Here we present and test a model that specifies the choice of foraging areas ("habitats") that would minimize total mortality risk while allowing collection of some arbitrary net energy gain. We tested the model with juvenile creek chubs (Semotilus atromaculatus) in an experimental field stream in which the foragers could utilize a foodless refuge and choose between two foraging areas that differed in experimentally manipulated resource densities (Tubifex spp. worms in sediments) and mortality hazard (adult creek chubs). For the case tested, the model specified a simple rule: "use the refuge plus the site with the lowest ratio of mortality rate (μ) to gross foraging rat (f)," i.e., "minimize μ./f." Independent prior measurements of mortality hazard (as a function of predator density) and gross foraging rate (as a function of resource density) allowed us to predict the resource level in the more hazardous foraging site that should induce a shift from the safer to the more hazardous site. The chubs' preferences in subsequent choice experiments agreed well with the theoretical predictions. The "minimize μ/f" rule (deaths per unit energy), perhaps in modified form, provides a simple alternative to the "maximize f" (energy per unit time) criterion that applies to long-term rate maximization when predation hazard does not differ among choices.
Unfortunately, I cannot provide full text to this book. You may be interested in the on-line materials for the book, including a link to how to purchase it, but also links to supplements and R code scripts, at
Interspecific hybridization among micropterids was once thought to be rare but has been documented in several cases of North American endemics. Introduction of the nonnative Smallmouth Bass Micropterus dolomieu across Texas has threatened to eliminate the Guadalupe Bass M. treculii genome throughout its native range via introgression between the species. In 1992, the Texas Parks and Wildlife Department began a stocking program in the Guadalupe River watershed to restore the genetic integrity of the local population. More than 600,000 hatchery-reared Guadalupe Bass fingerlings (~30 mm total length) were stocked in Johnson Creek over a 19-year period, and 360,000 fish were released in the North Fork, South Fork, and main-stem Guadalupe River over a 5-year period. Annual genetic monitoring indicated that hybridization significantly declined in all stream segments (P < 0.001) during the period of time when stocking occurred. Initially high hybridization rates (range, 20–100%; mean = 43.4%) were reduced to 0–24.2% (mean = 11.4%) at the termination of stocking. Linear regression indicated that hybridization in the North Fork and main-stem stream segments declined faster (9.0% per year) than all other test stream segments, whereas the South Fork Guadalupe River and upper Johnson Creek declined at 0.9% per year and lower Johnson Creek declined at 1.9% per year. Our data show that supplemental stocking is an effective approach to genetic restoration of compromised populations and should be considered as a viable management and conservation tool.
We quantitatively sampled fish assemblages and measured habitat structure in upper coastal plain streams of the central Savannah River drainage, South Carolina. Fish species abundances ordinated in principal component space based on 15 habitat variables were arrayed along gradients of velocity and stream size (depth and width) and their covariates such as substrate and cover. The majority of species' centroids oriented toward slower, deeper habitats with depositional substrates and cover. Size classes within some species were well separated, indicating change in habitat use with age, whereas others clustered closely, indicating consistent habitat use through ontogeny. In an ordination based on species distributions and abundances (detrended correspondence analysis) species again oriented along velocity and stream size gradients. Although taxonomically related species had distinct optima, most genera and families clumped into similar regions, indicating a phylogenetic component to assemblage composition. A Mantel comparison of species ordinations on PCA and DCA axes resulted in high and significant concordance, indicating that these independent techniques produce the same conclusion regarding response of fishes to habitat parameters. Much site-to-site variation in composition of coastal plain fish assemblages can be attributed to variation in habitat structure, primarily current velocity and stream size.
The introduction of smallmouth bass (Micropterus dolomieui) into the range of the endemic Guadalupe bass (M. treculi) on the Edwards Plateau in south-central Texas has resulted in hybridization between these species. Sympatric populations of smallmouth bass and Guadalupe bass from two discrete locations on the Edwards Plateau were analyzed on the basis of biochemical genetics and meristics. Electrophoretic and meristic evidence revealed no interspecific hybrids in Lake Travis. It appears that smallmouth bass have not adapted well in this lake, perhaps contributing to the lack of genetic exchange with Guadalupe bass. In contrast, the Canyon Lake populations are actively interbreeding, and diagnostic allozyme loci clearly revealed genetic introgression between these two species. Genetic analysis proved to be a more sensitive tool for detecting F2 or backcross individuals than the meristic index. The genetic integrity of Guadalupe bass appears to be seriously threatened in at least part of its highly restricted range.