DISPERSAL POTENTIAL AND MOVEMENT PATTERNS OF PECOS
BLUNTNOSE SHINER Notropis simus pecosensis IN THE
PECOS RIVER, NEW MEXICO
By
Nathan M. Chase, B.S.
A thesis submitted to the Graduate School
in partial fulfillment of the requirements
for the degree
Master of Science
Major Subject: Wildlife Science
New Mexico State University
Las Cruces, New Mexico
July 2014
“Dispersal potential and movement patterns of Pecos bluntnose shiner Notropis simus
pecosensis in the Pecos River, New Mexico,” a thesis prepared by Nathan M. Chase
in partial fulfillment of the requirements for the degree, Masters of Science, has been
approved and accepted by the following:
Loui Reyes
Interim Dean of the Graduate School
Colleen A. Caldwell
Chair of the Examining Committee
Date
Committee in charge:
Dr. Colleen A. Caldwell, Chair
Dr. Scott A. Carleton
Dr. David E. Cowley
Dr. William R. Gould
Dr. Chris W. Hoagstrom
ii
ACKNOWLEDGMENTS
First, I would like to thank Dr. Colleen Caldwell for the opportunity to further
my education and pursue work I am passionate about. Her patience, guidance, and
support has taught me that persistence pays off. I thank Dr. Scott Carleton for
teaching me just a small glimpse into the vast ways isotope and elemental work can
be applied. Thanks to Dr. William Gould for his help in data analysis, without which I
would still be lost. I thank Dr. Christopher Hoagstrom for many hours of insight,
helping me understand the Pecos River, and showing passion for a river that most
lack appreciation for. I also thank Dr. David Cowley for help and ideas while working
on this thesis. I would also like to thank James Hobbs, Justin Glessner, Gry Barfod,
and Joel Commisso of the University of California – Davis for assistance in isotopic
analysis, instrument time, and otolith processing.
I would like to thank Susan Oetker, Melissa Mata, and Stephen Davenport of
the U.S. Fish and Wildlife Service for the opportunity to conduct this work, without
the Research-SSP funding, I would not be here. I thank Stephen Davenport and Sara
Blocker for allowing me to go into the field with them, collecting fish, and helped me
understand the river with complex issues that surround water management in New
Mexico. I would like to thank Manuel Ulibarri, William Knight, and Catherine Sykes
of the Dexter National Fish Hatchery and Technology Center for their help during the
swimming stamina trials, allowing me to use their stamina tunnel and raising Pecos
bluntnose shiners for the trials.
I would like to thank many students that have become close friends here at
New Mexico State University, including Bradley Kalb, Seth Hall, Jasmine Johnson,
iii
Chance Roberts, Hunter Falco, Dominique Lujan, Lindsey McCord, Guillermo
Alvarez, Matthew Zeigler, Darren James, and many others that could always make a
frustrating situation seem less serious and manageable.
Finally I would like to thank and dedicate this work to my family and soon to
be wife Stephanie Laird. I thank them for all of their encouragement, support and
patience while pursuing this degree, without them I would not be where I am today.
My father and grandfather taught me how to fish, an obsession I doubt anyone
thought would grow into the passion I have for all things fishy.
iv
VITA
July 18, 1988
Born in Show Low, Arizona
May 2007
Graduated from Blue Ridge High School, PinetopLakeside, Arizona
May 2009
A.S. Northland Pioneer College, Show Low,
Arizona
May 2011
B.S. in Biological Sciences, minor in Chemistry,
Northern Arizona University, Flagstaff, Arizona
2011-Present
Graduate Research Assistant, New Mexico State
University, Las Cruces, New Mexico
v
ABSTRACT
DISPERSAL POTENTIAL AND MOVEMENT PATTERNS OF PECOS
BLUNTNOSE SHINER Notropis simus pecosensis IN THE
PECOS RIVER, NEW MEXICO
By
Nathan M. Chase, B.S.
Master of Science
New Mexico State University
Las Cruces, New Mexico
Dr. Colleen A. Caldwell, Chair
Movement patterns and dispersal potential of the federally-threatened Pecos
bluntnose shiner Notropis simus pecosensis (member of a pelagic broadcast spawning
guild) were successfully characterized using otolith microchemistry. Strontium
isotope ratios (87Sr:86Sr) within fish otoliths were used as a biological tag to track fish
movements from larvae to adult between three isotopically distinct reaches that
encompass 297 km of the Pecos River. Plains killifish Fundulus zebrinus was used to
characterize spatial and temporal patterns of 87Sr:86Sr of the Pecos River. Passive
vi
downriver displacement of propagules was detected followed by upriver dispersal of
young fish within the first year of life with some fish achieving a minimum of 56 km
movement upriver. Retention of propagules was also documented with upriver
resident Pecos bluntnose shiners throughout their lives revealing two dominant life
history movement patterns. Swimming ability of Pecos bluntnose shiner was tested in
a range of age classes revealing upper critical swimming speeds (Ucrit) as high as 43.8
cm/s and 20.6 body lengths/s in 30 d post-hatch fish. Strong swimming ability early
in life supports early upriver dispersal as was observed using otolith microchemistry
in relation to age and confirms movement patterns that were previously unknown for
the species. Pecos bluntnose shiner movement was documented in the population
during years of perennial flow (fish hatched in 2010 and 2011). In contrast,
recruitment was limited during intermittent flow due to drought in 2012. Extremes in
flow regime and habitat degradation continue to threaten freshwater pelagic broadcast
spawning fishes. Understanding movement patterns and dispersal potential may help
conservation and management efforts by improving how flows are managed and
where habitat can be improved for the best allocation of resources available.
vii
TABLE OF CONTENTS
Page
Abstract .............................................................................................................
vi
LIST OF TABLES ............................................................................................
ix
LIST OF FIGURES ..........................................................................................
x
DISPERSAL POTENTIAL AND MOVEMENT PATTERNS OF PECOS
BLUNTNOSE SHINER Notropis simus pecosensis IN THE PECOS
RIVER, NEW MEXICO ...................................................................................
1
Introduction ......................................................................................
1
Methods ............................................................................................
5
Study Area ...................................................................................
5
Bedrock and Pecos River Water Chemistry ................................
8
Movement Assessment using Otoliths from the
Plains Killifish and Pecos Bluntnose Shiner ................................
9
Fish Collection and Otolith Preparation ......................................
10
Age at Movement.........................................................................
13
Swimming Performance ..............................................................
13
Data Analysis ...............................................................................
14
Results .............................................................................................
16
Otolith Microchemistry of Plains Killifish ..................................
16
Otolith Microchemistry of Pecos Bluntnose Shiner ....................
18
Swimming Performance of Pecos Bluntnose Shiner ...................
24
Discussion ........................................................................................
27
Literature Cited.................................................................................
33
viii
LIST OF TABLES
Table
Page
1. Dispersal from below Highway 70 to above Highway 70 (movements
upriver) and retention of Pecos bluntnose shiners as upriver residents
(propagules retained above Highway 70) throughout life. Distance
from Hwy 70 is the minimum detectable distance Pecos bluntnose
shiners swam from downriver isotopically distinct areas to the
capture location. ....................................................................................
19
2. Upriver and downriver movement counts of Pecos bluntnose shiner by
age class. Age at movement is the age of the fish when movement
occurred. Age at capture indicates fish age at time of capture. ............
23
3. Source areas of deposited Pecos bluntnose shiner progeny based on
isotopic analyses for near core (early life) compared to where fish
were captured. Capture location from top to bottom are sites from
upriver to downriver, respectively. .......................................................
23
4. Average total length (TL, mm), critical swimming speed (Ucrit, cm/s),
swimming rate (Body Length/s), and average total distance swam by
four age classes of Pecos bluntnose shiner during swimming stamina
tests. Values in parentheses are two standard errors (SE). Sample
size of 30 fish was used for 30, 60 d, and adult age classes, while 15
fish were tested for 90 d age class. ......................................................
26
ix
LIST OF FIGURES
Figure
Page
1. Study area depicting three reaches of the Pecos River and sample
collection sites. The three reaches (from north to south) represent
anthropogenic influences of Sumner Dam (Tailwater Reach),
undisturbed open range (Rangelands Reach), and agricultural
influences (Farmlands Reach)...............................................................
7
2. Collection sites from upriver to downriver are depicted on the x-axis from
left to right. Bars represent mean (± 2 standard error, SE) of 87Sr:86Sr
values from otoliths of plains killifish. Number of fish captured at
each site is in parentheses. Solid circles represent 87Sr:86Sr values for
water samples taken at four sites. Overall average of 87Sr:86Sr values
for plains killifish from sites above Highway 70 are depicted by
dash-dotted line (0.7083 ± 0.00002) and below Highway 70 is
depicted by dotted line (0.7077 ± 0.000051). .......................................
17
3. Timing and direction of movement for all age classes of Pecos bluntnose
shiner exhibiting dispersal up and downriver. Age at movement
timing represented on the x-axis and movement counts on the y-axis.
Black bars represent downriver movements, gray bars represent
upriver movements. Age at movement: 0+ early, within 30 d posthatch; 0+ mid, 30-60 d post-hatch; 0+ late, 60 d – pre-first winter; 0+
winter, first winter; 1+ early, early second summer; 1+ mid, midsecond summer; 1+ late, pre-second winter. .........................................
20
4. Age distribution from otoliths of Pecos bluntnose shiner used in isotopic
analysis. X-axis from left to right are sites from upriver to downriver
respectively, y-axis are counts. 0+ have not formed an annulus, 1+
have one annulus, and 2+ have two annuli. ..........................................
25
x
INTRODUCTION
Rivers throughout the southwestern Great Plains have experienced dramatic
changes in flow regimes the last 100 years. Altered flow is the result of river
modification that includes damming, channelization, water diversion and groundwater pumping for municipal, industrial, and agricultural uses (Dodds et al. 2004;
Hoagstrom 2008b; Durham and Wilde 2009). Flow intermittency, decreased habitat
complexity, and increased salinity have negatively impacted native fish populations,
especially pelagic broadcast spawning species (pelagophils; Bestgen et al. 1989;
Durham and Wilde 2009; Hoagstrom et al. 2011). For these fishes, spawning occurs
throughout the summer and is cued to high flow, a bet-hedging strategy which
spreads reproduction over several spawning events giving larval fishes multiple
opportunities to recruit (replace the previous generation as adults) into the population
(Durham and Wilde 2005; USFWS 2006). These fishes utilize a reproductive strategy
in which the female releases eggs into the water column whereupon the male
fertilizes them. These eggs are non-adhesive and semi-buoyant which allows them to
remain suspended within the water column and drift downriver while development
occurs (Platania and Altenbach 1998; Propst 1999; USFWS 2006; Cowley et al.
2009). Downriver drift (displacement) facilitates dispersal; however, eggs and fry
(propagules) are at risk if swept into unfavorable habitat such as large impoundments
where they would perish (USFWS 2006; Dudley and Platania 2007). Propagule
retention in slack-water nursery habitat reduces downriver displacement and may be a
key driver for successful recruitment into the population (Dudley and Platania 2007;
1
Hoagstrom and turner 2013). Understanding movement patterns of pelagophils may
assist in recovery of these fishes.
Movement assessments have revealed life history characteristics that were
previously unknown supporting potential changes in management practices
(Gillanders and Kingsford 2000; Hobbs et al. 2010, Wolff et al. 2012). Applications
of these techniques have been used successfully in other systems in a variety of ways,
providing information on stock identification, population mixing, natal origin, and
return of adults to natal streams in a variety of freshwater and saltwater fish species
across the globe (Thorrold et al. 1998; Campana et al. 2000; Barnett-Johnson et al.
2008; Hobbs et al. 2010; Wolff et al. 2012). Isotopic analysis of otoliths have also
revealed information other tagging techniques cannot access, particularly for small
bodied fish species (Hobbs et al. 2010). Fish must reach a minimum size for survival
and successful tag retention (Walther et al. 2008; Muhlfeld et al. 2010). As an
alternative, otolith microchemistry has been used to elucidate movement and lifehistory characteristics (Kennedy et al. 1997; Campana 1999; Barnett-Johnson et al.
2008; Elsdon et al. 2008; Amano et al. 2013). These calcium carbonate structures
record water chemistry (Elsdon et al. 2008) and are viewed as biological recording
devices both spatially (where the fish spent it life) and temporally (how long they
remained in an area) (Campana 1999). Within the otoliths, divalent cations
(magnesium, barium, strontium) are readily substituted for calcium within the
aragonite matrix (calcium-carbonate crystal structure; Fodrie and Herzka 2008;
Muhlfeld et al. 2012). While environmental variables of temperature, salinity, and
2
food influence elemental concentrations, isotopic ratios (87Sr:86Sr) are not affected
(Kennedy et al. 2000). Thus, if the bedrock geology (source of Sr in water) is known,
then the otolith can be used as a reliable biological tag which yield isotopic patterns
of natal origin and movement over a fish’s live span (Campana 1999).
The Pecos River is characterized by wide and shallow braided flows and
unstable erosive sand banks that support fishes well adapted to shifting sand beds
(Bestgen and Platania 1990; Platania and Altenbach 1998; Hoagstrom 2000;
Hoagstrom et al. 2008a) and represents one of the last Great Plains rivers with a long
stretch of unobstructed flow (297 km between Fort Diversion Dam and Brantley
Reservoir). Water diversion and obstruction through damming threatens a guild of
pelagophils that include native speckled chub (Macrhybopsis aestivalis), Rio Grande
shiner (Notropis jemezanus), Pecos bluntnose shiner (N. simus pecosensis), nonnative plains minnow (Hybognathus placitus), and non-native Arkansas River shiner
(N. girardi) (Platania and Altenbach 1998; Dudley and Platania 2007; Hoagstrom et
al. 2011). Though the guild continues to persist, individual species are in decline; Rio
Grande silvery minnow (H. amarus) was extirpated from the Pecos River in the late
1960s (Bestgen and Platania 1991; Platania and Altenbach 1998).
The Pecos bluntnose shiner was state-listed by New Mexico as threatened in
1975 (NMDGF 2012) and federally-listed as threatened in 1987 (USFWS 1987). The
subspecies is relatively short-lived with a lifespan of two to three years in the wild
(Hatch et al. 1985; Bestgen and Platania 1990; Hoagstrom et al. 2008b). From May
through the end of September, spawning was historically cued by high-flow events
3
from snowmelt runoff and summer monsoon rains that increased flow from a few
hours to a few days. Spawning cues currently include summer precipitation, block
releases (large volume and long duration water release) from a large impoundment
(Sumner Dam), and flooding from non-regulated tributary inputs (Hatch et al. 1985;
USFWS 2006; Hoagstrom et al. 2008b). The subspecies was once found throughout
631 river kilometers between Santa Rosa, New Mexico and the Delaware River
Confluence of the New Mexico-Texas border. The range of the species has been
greatly reduced, currently persisting between Sumner Dam and Brantley Reservoir
(Hatch et al. 1985; Platania 1995; Hoagstrom 2000; Hoagstrom et al. 2008b).
Mitigating threats to the species may aid in their recovery, however, little is
known about movement patterns and dispersal potential of this species after larval
development occurs. Movement patterns of juvenile and adult Pecos bluntnose shiner
have not been studied in depth (Hoagstrom et al. 2008b). Hoagstrom et al. (2008b)
documented a notable size reduction from upriver to downriver. The absence of many
adult Pecos bluntnose shiner in the southern-most occupied portion of the river above
Brantley Reservoir (Farmlands Reach) suggests that fish in this lower reach are either
not recruiting into the population or they are moving out of this reach (Hoagstrom et
al. 2008b). In addition, source areas where propagules are deposited, larvae develop,
and eventually recruit into the core population are also unknown (Platania and
Altenbach 2007; Hoagstrom 2008a). Ultimately, recruitment of Pecos bluntnose
shiner is dependent upon where eggs disperse, hatch, and if larvae find refugia in
nursery habitat. If the source of recruitment comes from downriver, those individuals
4
likely must swim upriver to successfully reproduce or their eggs potentially disperse
further downriver into Brantley Reservoir (Platania and Altenbach 1998; Dudley and
Platania; 2007). The success of the fish is further complicated by the timing and
magnitude of block releases from Sumner Dam, which are intended to decrease
evaporative loss between reservoirs and efficiently deliver water for agricultural use.
Without knowing dispersal patterns or movement related to reproduction of the fish,
managers could only presume environmental variables that affect successful
reproduction and recruitment.
The goal of this research was to provide managers with an assessment of
movement patterns such that informed management decisions can be made about
areas in the Pecos River vital to movement and recruitment of Pecos bluntnose shiner
thereby aiding in the conservation of the species. The objectives were to assess
movement patterns, timing, and dispersal potential of Pecos bluntnose shiner utilizing
otolith microchemistry, aging techniques, and swimming performance.
METHODS
Study Area
Currently, the Pecos bluntnose shiner is restricted to the Pecos River mainstem from Sumner Dam to Brantley Reservoir, a distance of 330 km with three
distinct reaches (Propst 1999; Hoagstrom 2003a, 2003b). As part of a long term
monitoring program, the U.S. Fish and Wildlife Service (USFWS) has monitored the
population of Pecos bluntnose shiner throughout a series of permanent sampling sites
5
(Davenport 2010). A subset of these sites was selected in this study. From north to
south, the Tailwater Reach is the most northern reach between Sumner Dam and the
confluence of the River at Taiban Creek for a total of 33 km (Figure 1). The release of
sediment-free water from Sumner Dam leads to channel scour creating unsuitable
habitat where the species has not been collected since 1999 (Kondolf 1997;
Hoagstrom 2003a; Hoagstrom et al. 2008b; Davenport 2010). Sampling was not
conducted in the Tailwater Reach for this study. The middle or Rangelands Reach
contained the following sample sites from north to south: Willow, 6 Mile Draw,
Crockett Draw, Cortez Gasline, Bosque Draw, Gasline, and Highway 70. This reach
is characterized by the most suitable habitat of shifting sand-bed and a braided river
channel extending from Taiban Creek to the Rio Hondo confluence (155 km; Figure
1). All size classes of Pecos bluntnose shiner have been routinely documented within
this reach (Hoagstrom 2003a,b). The Farmlands Reach contained the following
sample sites from north to south: Dexter, Lake Arthur Falls, Highway 82, and
Brantley Inflow. This reach is the most southern section that extends from the Rio
Hondo confluence to Brantley Reservoir (142 km; Figure 1) and is characterized as a
deeply incised narrow channel with a compacted river bed, modified more effective
water delivery (Tashjian 1993). Salinity is elevated in this reach due to the cumulative
effects of diminished stream flow, increased evapotranspiration, saline irrigation
return flows, and brine aquifer intrusion (Hoagstrom et al. 2008a; Hoagstrom 2009).
Dudley and Platania (2007) suggested that transport distances of propagules might
occur three times further during sustained reservoir release flows. Thus, large number
6
Figure 1. Study area depicting three reaches of the Pecos River and sample collection
sites. The three reaches (from north to south) represent anthropogenic influences of
Sumner Dam (Tailwater Reach), undisturbed open range (Rangelands Reach), and
agricultural influences (Farmlands Reach).
7
of propagule and juvenile Pecos bluntnose shiner have been collected in the
Farmlands Reach, likely due to increased downriver displacement of eggs and larvae
caused by the combined effects of block releases and decreased backwater areas
important for retention (Brooks et al. 1994; Platania and Altenbach 1998; Hoagstrom
2000).
Bedrock and Pecos River Water Chemistry
A geologic map revealed differences in bedrock formation throughout the
Pecos River drainage (NMBGR 2003). The dominant bedrock throughout the upper
reaches of the Pecos River is reflected by the Guadalupian Formation from the
Permian period (270-260 million years ago). In contrast, the dominant bedrock
throughout lower reaches of the river was reflected by Piedmont Alluvial Slopes from
the Holocene to lower Pleistocene which spans the most recent glaciations from 2.5
million years ago to present (NMBGR 2003; Walker and Geissman 2009). The
Quaternary Alluvium deposit begins about 16 km north of Roswell (located near
Highway 70 monitoring site) and extends through the rest of the Roswell Basin
(lowest portion of the Pecos bluntnose shiner range) and lies above the Grayburg and
Queen Formations (http://pubs.usgs.gov/ha/ha730/ch_c/C-text7.html, accessioned
May 19, 2013). These formations consist of carbonate (limestone and dolomite) and
evaporite (gypsum and halite). Thus, older bedrock in the upper River reach would be
manifested as higher 87Sr:86Sr values (more time for 87Rb decay to occur) while
younger bedrock in the lower River reach would be manifested as lower 87Sr:86Sr
8
values. Brine aquifer intrusion throughout the lower reach increases sodium, chloride,
magnesium, and calcium (constituents of increased salinity in the Farmlands Reach)
compared to the upper reaches (Rangelands and Tailwater reaches; Miyamoto et al.
2008). Noteworthy changes in dominant bedrock were evident near the Highway 70
sampling site. Thus, 87Sr:86Sr was analyzed from water samples collected above
Highway 70 (Willow), at Highway 70, and below Highway 70 (Highway 82 and
Dexter). Water samples (n = 4) were collected 23-25 April 2012 during base flows to
assess 87Sr:86Sr values of the Pecos River within the Pecos bluntnose shiner range.
The samples were analyzed using Inductively-Coupled Plasma Mass Spectrometry
(ICPMS) at the University of California - Davis Interdisciplinary Center for Plasma
Mass Spectrometry. Values for 87Sr:86Sr in water varied from 0.7082 to 0.7083 in the
upriver reaches (Willow and Highway 70) and from 0.7078 to 0.7079 in the
downriver reaches (Dexter and Highway 82; Figure 3).
Movement Assessment using Otoliths from the Plains Killifish and Pecos Bluntnose
Shiner
While water chemistry revealed differences in 87Sr:86Sr that supports geologic
rock types and where the brine aquifer intrusion begins, these samples represent only
a snapshot for each location and were used only to assess feasibility (if isotopic
values in different areas of the Pecos River did not vary, a movement assessment
using isotopes would not be possible). Plains killifish (Fundulus zebrinus) were
investigated for their use as a reference for 87Sr:86Sr values in place of water samples
at each site. Analysis of 87Sr:86Sr values from fish otoliths is more cost effective than
9
analysis of water samples, in addition, only a single trip to the Pecos River was
necessary to collect fish since plains killifish otoliths record water chemistry while
living side-by-side Pecos bluntnose shiner. The plains killifish is present throughout
the home range of the Pecos bluntnose shiner (Davenport 2010), and typically form
schools containing a variety of size classes (Minckley and Klaassen 1969a). Plains
killifish prefer low velocity shallow water and can tolerate a wide range of
temperatures and salinities (Rahel and Thel 2004). Though considered highly mobile,
movement patterns in this species have not been previously assessed. Plains killifish
may be considered a non-migratory species occupying limited segments of a stream
(Minckley and Klaassen 1969a). Thus, a movement assessment of this species was
conducted prior to their use as a surrogate in place of water samples to characterize
isotopic values of strontium specific to sample collection sites throughout the Pecos
River. As a resident, the species is more likely to remain in one area their entire lives
and presumably capture ambient water chemistry at a particular location (from time
of hatch to the time of capture).
Fish Collection and Otolith Preparation
A variety of sizes of Pecos bluntnose shiner (n = 120, range 29.7-60.1 mm
standard length, SL) and plains killifish (n = 97, range 19.4-55.4 mm SL) were
collected 7-9 November 2012 using a 3.0 m x 1.2 m seine with 3.2 mm mesh. Plains
killifish were collected at nine sites (from north to south: Willow, 6 Mile Draw,
Crockett Draw, Bosque, Gasline, Highway 70, Dexter, Lake Arthur, and Highway 82)
10
while Pecos bluntnose shiners were collected at seven sites (the shiner was not
collected at Lake Arthur Falls or Highway 82 because they were not detected). Fish
were collected just before the onset of winter allowing young fish to grow large
enough to be captured in seines and to ensure that movement during the prior summer
could be detected within otoliths. Fish were euthanized, placed on dry ice, and
transported to the laboratory. Sagittal otoliths were removed, placed into vials with
ultrapure (milli-Q) water and cleaned using an ultrasonic water-bath for 5 minutes to
remove tissue. Otoliths were then rinsed again with milli-Q water, placed in acid
washed vials and allowed to dry under a class 100 laminar-flow hood. After 48 h drytime, otoliths were mounted sulcus side up and affixed to a microscope slide with
Crystalbond (Crystalbond™ 509, Ted Pella Inc. Redding, CA) and sanded using a
MTI Corporation UNIPOL-1210 grinding/polishing machine (1200 grit sand paper
wetted with milli-Q water) to reveal the core to the edge (Thorrold et al. 1998; Hobbs
et al. 2010). Due to the small size of otoliths (600-1200 µm) for both fish species,
cross-sectioning techniques were not used. Otoliths were then rinsed again with milliQ water and re-mounted onto petrographic slides (sanded side up), affixed with
Crystalbond for isotopic analysis.
Laser ablation multi-collector inductively coupled mass spectrometry was
used to assess 87Sr:86Sr in otoliths throughout the life of each fish. Otolith analysis
was conducted at the University of California - Davis Interdisciplinary Center for
Plasma Mass Spectrometry using a New Wave Research UP213 laser ablation system
coupled with a Nu Plasma HR (Nu032) multiple-collection high-resolution double-
11
focusing plasma mass spectrometer system. Line scans across the face of the otolith
from the core to the edge generated 87Sr:86Sr profiles throughout the fish’s life. A
scanning speed of 10 μm/s, laser pulse frequency of 10 Hz, and 65% laser power were
used. A carrier gas (Helium) was used to carry ablated material into the mass
spectrometer where it was mixed with Argon gas before entering the plasma. 87Sr:86Sr
values were normalized in relation to 87Sr:88Sr (0.1135) to correct for instrumental
mass fractionation. 87Rb interference of 87Sr (a possible contaminant found in
industrial argon gas) was monitored by measuring 85Rb minimizing interference
(Hobbs et al. 2010). Instrumental accuracy was ensured using a modern marine
mollusk (an in-house calcium carbonate standard). By ablating this standard, a
comparison was made for each standard run to values known for modern day
seawater to account for any instrumental drift throughout runs (87Sr:86Sr = 0.70918;
Hobbs et al. 2010). Ablations of the standard yielded 87Sr:86Sr = 0.70920 (±
0.000098; n = 49). Samples were adjusted throughout sessions to known values of the
mollusk standard.
After isotopic analysis, otoliths were photographed using a Leica DME
microscope with Leica ICC50 Camera Module with Leica Live Image Building
Software (LAS Software Version 4.4.0, October 2013, Heerbrugg, Switzerland) to
generate whole otolith photographs using a 20x microscope objective. Otolith
photographs were viewed by two independent analysts and the assigned ages were
compared (Miller and Storck 1982). Briefly stated, where age discrepancy occurred at
greater than 10%, a third analysis was performed and ages of the fish were accepted if
12
the third age analysis fell within 10% of one of the first two aging attempts. If no
consensus could be reached, the age for that fish was excluded. Data from the isotopic
analysis was overlaid following the ablation path for each otolith and the ages at
which isotopic shifts occurred were then recorded for each fish.
Age at Movement
For each Pecos bluntnose shiner, the age at which an isotopic shift occurred
was identified from digital images using ImageJ software (Version 1.48i, National
Institute of Health). Distance (microns) was calibrated using a calibration slide to
measure distance from the core to each shift in 87Sr:86Sr values. Fish growth varies
between the warmer summer months (majority of growth occurring during this
season) and cooler autumn/winter (growth is very slow). Daily rings were easily
counted the first year of life. Thus, age at which fish moved were binned into groups
with 0+early representing within 30 days post-hatch, 0+mid representing 30-60 days
post-hatch, 0+late representing 60 days post-hatch to pre-annulus formation, 0+
winter representing within the first annulus (winter), 1+ early representing early
growth after winter (second growth season), 1+ mid representing mid-summer growth
(second growth season), and 1+ late representing late summer-fall growth (second
growth season).
Swimming Performance
Captive propagated Pecos bluntnose shiner were tested at 30 d (n=30, average
20.63 mm total length, TL), 60 d (n=30, average 33.93 mm TL), 90 d (n=15, average
13
46.33 mm TL) post-hatch and wild-caught adults (n=30, 69.13 mm TL) from the
Pecos River using a swim tunnel (Loligo® Systems, Denmark). Water quality was
monitored and maintained such that it did not influence swimming performance
among age classes. Fish were acclimated at one cm/s flow one week prior to the
swimming trials. On test day, individual fish were placed in the stamina tunnel and
allowed to acclimate for one hour at five cm/s. Flow was increased by ten cm/s
increments at five-minute intervals until the fish fatigued and became pinned against
the back screen for more than five seconds (the conclusion of the test). At the
termination of each test, fish were measured for total and standard lengths (mm) and
placed in a recovery tank. Critical swimming speed (Ucrit) was calculated using the
equation from Beamish (1978):
Ucrit = Ui + [(ti/tii) × Uii],
and body lengths per second:
BL/s = Ucrit/TL,
where, Ui = the full interval swam at the highest velocity (cm/s), Uii = the velocity
increment (cm/s), ti = time (s) fish swam in the final increment until becoming pinned,
tii = duration of each increment, TL = total length of individual fish run (Beamish
1978; Adams et al. 1999).
Data Analysis
For both species, a ten-point moving average was used to smooth the 87Sr:86Sr
values. If no isotopic shifts were evident through visual inspection of the data (full
14
data profiles matching one location throughout the fish’s life), the fish was deemed a
resident. When otoliths revealed an isotopic shift (segments of data matching multiple
locations throughout the fish’s life), then it was presumed the fish moved between
areas of unique 87Sr:86Sr chemistry. If an isotopic shift was evident, the isotopic
values between all shifts was partitioned and fish were presumed to have spent that
period of time within one of three isotopically unique reaches. For example, a fish
that spent an early portion of its life in one isotopically unique reach and a later
portion of its life in another isotopically unique reach will be reflected by two
different isotopic values. Each segment of partitioned data was classified
independently of other data segments.
Discriminant function analysis was performed using the PROC DISCRIM
function in SAS (version 9.3, SAS Institute) to assess movement in both species.
Discriminant function analysis was used to assess where fish had spent portions of
their lives by classifying visually partitioned line scan data to isotopically unique
areas. Similar to Clarke et al. (1997), line scans from the core to the edge of otoliths
were used; however, they were not able to quantify fish movements. In other work,
natal origins were determined using discriminant function analysis for near core
isotopic values to classify fish to natal origin (Barnett-Johnson 2008; Humston et al.
2010). The research presented here may be the first attempt to quantify movements by
visually partitioning entire life data-sets from line scans, then classifying partitioned
segments of isotopic values to an area.
15
87
Sr:86Sr data from plains killifish otoliths were used as training data set to
classify all fish into isotopically distinct areas. The test for equal within-group
covariance was not met (χ2 = 10.14, p = 0.006), and was not pooled. The Jackknife
procedure was used for plains killifish data in a cross-validation technique (one
observation is left out) to assess model validity by comparing the predicted to the
known capture location.
Isotopic profiles were inspected for each otolith from Pecos bluntnose shiner
and visually partitioned to assess movement (similar to the plains killifish).
Discriminant function analysis was then used to classify partitioned data to one of the
three areas. Movements were then assessed by differences in isotopic values where
fish spent time from early to late life. For example, an upriver movement was
identified if the isotopic values near the otolith core were classified to downriver
reaches and isotopic values near the otolith edge classified to upriver reaches. The
area fish spent time early in life is unknown and thus early life classification accuracy
cannot be assessed, however, near edge isotopic value classifications were compared
to known capture location to assess classification success rate.
RESULTS
Otolith Microchemistry of Plains Killifish
Isotopic values of the Pecos River throughout sampling locations were
successfully characterized using plains killifish otoliths (Figure 2). Discriminant
function analysis of 87Sr:86Sr values from otoliths of plains killifish captured at all
16
Killifish Otolith Mean Values
0.7084
(n=7)
(n=7)
(n=12)
Upstream Killifish Mean Value
(n=8)
Downstream Killifish Mean Value
(n=14)
0.7082
87Sr:86Sr
(n=9)
0.7080
0.7078
(n=13)
(n=9)
17
(n=12)
0.7076
0.7074
Willow
6 Mile
Draw
Crockett
Draw
Bosque
Gasline
Hwy. 70
Dexter
Lake
Arthur
Hwy. 82
Figure 2. Collection sites from upriver to downriver are depicted on the x-axis from left to right. Bars represent mean (± 2
standard error, SE) of 87Sr:86Sr values from otoliths of plains killifish. Number of fish captured at each site is in parentheses.
Overall average of 87Sr:86Sr values for plains killifish from sites above Highway 70 are depicted by dash-dotted line (0.7083 ±
0.00002) and below Highway 70 is depicted by dotted line (0.7077 ± 0.000051).
sites indicated no isotopic shifts occurred revealing no movement detected among
three isotopically unique areas (above Highway 70, at Highway 70, and below
Highway 70). In addition, no seasonal shifts in isotopic values of the Pecos River
were detected (stability of isotopic values throughout the lives of plains killifish).
Thus, the plains killifish was a suitable surrogate for characterizing Pecos River water
87
Sr:86Sr throughout the study area both spatially (all sites where fishes were
captured) and temporally (throughout the lives of the fishes). Of plains killifish
captured above Highway 70, 91% (50/55) were classified correctly, 56% (5/9) were
classified correctly to Highway 70, and all 34 plains killifish captured below
Highway 70 were classified correctly (100%) using cross validation. Thus, the plains
killifish revealed Highway 70 as an area of mixing or a transition zone of isotopic
values, as expected, due to the shift in bedrock between the two isotopically distinct
areas.
Otolith Microchemistry of Pecos Bluntnose Shiner
Isotopic analysis of otoliths from Pecos bluntnose shiner revealed fish either
moved upriver from below Highway 70, or were life-long residents above Highway
70 (propagule retention in upriver reaches; Table 1). The majority of upriver
movements (74/89) occurred during the growing season (summer and fall) in the first
year of life (0+ age class) before the first annulus was formed (Figure 3). Fish that
moved to the reach above Highway 70 remained within this reach for the remainder
18
Table 1. Dispersal from below Highway 70 to above Highway 70 (movements
upriver) and retention of Pecos bluntnose shiners as upriver residents (propagules
retained above Highway 70) throughout life. Distance from Hwy 70 is the minimum
detectable distance Pecos bluntnose shiners swam from downriver isotopically
distinct areas to the capture location.
Site
Movement upriver
Residents
Distance from
Hwy 70
Willow
25/32 (78%)
7/32 (22%)
56 km
6 Mile
16/19 (84%)
3/19 (16%)
45 km
Crockett
20/23 (87%)
3/23 (13%)
37 km
Bosque
18/23 (78%)
5/23 (22%)
27 km
Gasline
4/4
(100%)
0/4
(0%)
11 km
Total
83/101 (82%)
18/101 (18%)
19
40
Number of Movements
35
Downriver
30
Upriver
25
20
15
10
5
0
0+ early
0+ mid
0+ late
0+ winter 1+ early
1+ mid
1+ late
Age at Movement
Figure 3. Timing and direction of movement for all age classes of Pecos bluntnose
shiner exhibiting dispersal up and downriver. Age at movement timing represented on
the x-axis and movement counts on the y-axis. Black bars represent downriver
movements, gray bars represent upriver movements. Age at movement: 0+ early,
within 30 d post-hatch; 0+ mid, 30-60 d post-hatch; 0+ late, 60 d – pre-first winter;
0+ winter, first winter; 1+ early, early second summer; 1+ mid, mid-second summer;
1+ late, pre-second winter.
20
of their lives and propagules that were retained within this reach remained residents
until the time of capture. Nineteen of twenty movements by fish downriver were
associated with movement upriver later in life. Only four Pecos bluntnose shiners
were captured below Highway 70 (all from the Dexter site) with three of four
classifying as residents in this downriver reach their entire lives (one fish captured in
the lower river reach at the Dexter site classified to Highway 70 throughout it’s life,
the only downriver movement not associated with a later upriver movement).
Dispersal potential of Pecos bluntnose shiner using otolith microchemistry
indicated a minimum upriver movement of 56 km (from Highway 70 to Willow) with
78% (25/32) Pecos bluntnose shiners captured at Willow achieving this distance
(Table 1). One shiner captured at Dexter moved downriver from Highway 70 (58 km)
at age 1+ late (Figure 3) just before the time of capture. The full isotopic profile
(entire life) of this fish classified to Highway 70, thus it was assumed that this fish did
not spend enough time below Highway 70 to allow the otolith to incorporate
downriver water chemistry to record this movement. Pecos bluntnose shiners that
exhibited upriver dispersal had either hatched above or below Highway 70. Of all fish
that dispersed upriver, 46% (38/82) had 87Sr:86Sr values classifying to above Highway
70 near the core of their otoliths indicating that spawning occurred above Highway 70
and these fish were displaced downriver post-hatch (i.e., hatched above Highway 70,
displaced to below Highway 70, then returned to above Highway 70). The remaining
54% (44/82) hatched below Highway 70. In other words, there was no detectable
upriver 87Sr:86Sr value within or near the core suggesting that these fish developed
21
from eggs that drifted below Highway 70 before hatching or that spawning occurred
below Highway 70.
Downriver movements were evident for the earlier portion of life for Pecos
bluntnose shiner before upriver movements occurred (Figure 3). All shiners captured
above Highway 70 exhibiting early life downriver displacement dispersed back
upriver. Movement patterns for both age classes 1+ and 2+ that hatched in 2011 and
2010, respectively, were consistent within one another (Table 2). Progeny were
deposited in river reaches downriver from where shiners were captured, or eggs were
retained within that river segment (Table 3). Isotopic analysis of otoliths revealed all
Pecos bluntnose shiners captured at Gasline, Highway 70, and Dexter sites contained
no near core (early life) 87Sr:86Sr values classifying to above Highway 70 indicating
that these fish hatched at or below Highway 70.
Discriminant function analysis misclassified 25 Pecos bluntnose shiners to
Highway 70 when the fish were actually captured above Highway 70 (75%
classification success rate). Of these shiners misclassified, 9 had high a posteriori
probabilities (> 80% classification probability to the wrong area). All 25
misclassifications were from fish that spent the early part of their lives below
Highway 70. The misclassifications were included in the 89 upriver movements due
to known capture location above Highway 70. Discriminant function analysis
misclassified 10 Pecos bluntnose shiners to above or below Highway 70 when fish
were actually captured at Highway 70 (six classifying to above Highway 70 and four
classifying to below Highway 70; 29% classification success rate). Discriminant
22
Table 2. Upriver and downriver movement counts of Pecos bluntnose shiner by age
class. Age at movement is the age of the fish when movement occurred. Age at
capture indicates fish age at time of capture.
Age at Movement
Age at
Capture
0+
Early
0+
Mid
0+
Late
0+
Winter
1+
Early
1+
Mid
1+
Late
Upriver
1+
2+
3
6
25
4
29
7
1
1
5
2
2
1
0
3
Downriver
1+
2+
9
5
3
1
0
1
0
0
0
0
0
0
0
0
Table 3. Source areas of deposited Pecos bluntnose shiner progeny based on isotopic
analyses for near core (early life) compared to where fish were captured. Capture
location from top to bottom are sites from upriver to downriver, respectively.
Site
Above Highway 70
Highway 70
Below Highway 70
Willow
7/32 (22%)
8/32 (25%)
17/32 (53%)
6 Mile
16/32 (50%)
9/32 (28%)
7/32 (22%)
Crockett
3/23 (13%)
3/23 (13%)
17/23 (74%)
Bosque
5/23 (22%)
5/23 (22%)
13/23 (56%)
Gasline
0/4 (0%)
1/4 (25%)
3/4 (75%)
Hwy. 70
0/14 (0%)
3/14 (21%)
11/14 (79%)
Dexter
0/4 (0%)
1/4 (25%)
3/4 (75%)
23
function analysis misclassified one Pecos bluntnose shiner to Highway 70 when the
fish was actually captured below Highway 70 (3/4 shiners were residents below
Highway 70 throughout life indicating a 75% classification success rate). Age class
distribution was quantified from otoliths revealing that the majority of Pecos
bluntnose shiners captured were 1+ age class followed by the 2+ age class.
Unexpectedly, the least abundant age class captured was 0+ (young-of-year) with
only two captured in the study (both at 6 Mile Draw; Figure 4). All shiners captured
below Highway 70 (Dexter) were 1+ age class while the majority of 2+ age classes
were captured above Highway 70 in the Rangelands Reach (Figure 4). Five Pecos
bluntnose shiners could not be aged, but were residents at sites throughout their lives,
thus eliminating the need for the age at movement assessment.
Swimming Performance of Pecos Bluntnose Shiner
Pecos bluntnose shiner exhibited strong swimming ability, even at an early
age of 30 days post-hatch (Table 4). Upper critical swimming speed (Ucrit) increased
with total length indicating that larger fish perform better at higher flow rates. When
considering size of fish, higher swimming performance (BL/s) was observed in the
youngest fish (30 d post-hatch). Fish younger than 30 days post-hatch could not be
tested with the stamina tunnel (several 30 d shiners escaped from the stamina tunnel
resulting in test termination and were not included in calculations). Total distance
swam was also calculated during swimming trials revealing 30 d post-hatch fish
swam a distance of 0.55 km in 83 min and adult fish swam a distance of 1.04 km in
24
25
Age Class
Age Counts
20
0+
1+
2+
15
10
5
0
Willow
6 Mile
Crockett
Bosque
Gasline
Highway
70
Dexter
Figure 4. Age distribution from otoliths of Pecos bluntnose shiner used in isotopic
analysis. X-axis from left to right are sites from upriver to downriver respectively, yaxis are counts. 0+ have not formed an annulus, 1+ have one annulus, and 2+ have
two annuli.
25
Table 4. Average total length (TL, mm), critical swimming speed (Ucrit, cm/s),
swimming rate (Body Length/s), and average total distance swam of four age classes
of Pecos bluntnose shiner during swimming stamina tests. Values in parentheses are
95% CI. Sample size of 30 fish was used for 30, 60 d, and adult age classes, while 15
fish were tested for 90 d age class.
Age Class
TL (mm)
Ucrit (cm/s)
30 d
21.3 (0.62)
43.8 (4.46)
20.6 (2.02)
0.55 (0.094)
60 d
33.9 (0.92)
49.2 (1.94)
14.5 (0.52)
0.62 (0.031)
90 d
46.3 (0.82)
52.5 (2.48)
11.3 (0.62)
0.68 (0.042)
Adult
69.1 (2.28)
70.3 (3.26)
10.2 (0.54)
1.04 (0.074)
26
BL/s
Total Distance (km)
96 min (Table 4). Water quality was acceptable and consistent throughout all
swimming challenges. Water temperature ranged from 19.7 to 20.6 ˚C, dissolved
oxygen ranged from 7.32 to 7.83 mg/L, pH ranged from 7.51 to 7.74, conductivity
ranged from 2.26 to 2.31 mS/cm.
DISCUSSION
Pecos bluntnose shiner exhibited two patterns of movement lending to
successful recruitment into the population. The first was displacement of propagules
downriver, followed by dispersal upriver after development (43% of fish captured at
or above Highway 70). The second pattern was retention of propagules in upriver
segments where residents remained at or above Highway 70 throughout their lives
(57% of fish captured at or above Highway 70). The combination of propagule
retention and upriver dispersal of juveniles and adults from propagules displaced
downriver suggest that successful fish move to the upriver reach or fish were retained
upriver.
Downriver movements were detected in 14 fish within the first 30 days posthatch indicating that displacement occurred in early life (i.e., post-hatch through
larval stage). Dispersal upriver occurred before formation of the first annulus most
likely after development of the myomeres. Presumably, dispersal upriver allows for
re-colonization and ensures adequate distance for egg development while drifting
downriver (Cross et al. 1985; Durham and Wilde 2008). Cowley et al. (2009)
suggested that bidirectional dispersal (downriver displacement and upriver dispersal)
27
was important prior to construction of impoundments in the historical distribution of
Rio Grande silvery minnow, though impoundments now limit these movements.
Propagules not deposited into slack-water nursery habitat are at risk of further
displacement downriver, especially during high-flow events until they are sufficiently
developed to seek optimal habitat. For example, Hoagstrom et al. (2008a) recorded
high densities of young Pecos bluntnose shiner at Brantley Reservoir Inflow in the
Farmlands Reach during a long block release from Sumner Dam. Many pelagophils
likely spawn during declining flows shortly after peak flows have passed; Low water
velocity (<1cm/s) is sufficient to maintain eggs in suspension (Platania and Altenbach
1998; Dudley and Platania 1999; Dudley and Platania 2007). Timing of spawning
may increase retention rates if high flows alter the river channel and increased water
volume raise the stage of the river out of the main channel and onto the floodplain,
thereby increasing availability of slack-water habitat where retention occurs
(Hoagstrom and Turner 2013).
Retention of propagules and active swimming of juvenile and adult Pecos
bluntnose shiner upriver presumably counter displacement of young fish; however,
those displaced downriver into Brantley Reservoir likely do not recruit into the
population (Dudley and Platania 2007). Downriver displacement of propagules was
advantageous in fishes of Great Plains Rivers with variable flow regimes and long
unobstructed stretches such as the Pecos River, however, persistence of pelagophils is
currently threatened by dams and reservoirs in a region where water is in limited
supply. Minimum distances of unobstructed rivers required by pelagophils to
28
successfully complete their life cycle are difficult to calculate with egg and larval
stages the most vulnerable to downriver displacement (Bestgen et al. 1989; Dudley
and Platania 2007; Hoagstrom et al. 2008b; Worthington et al. 2014). Habitat
complexity and flow regime contributing to propagule retention may be equally if not
more important for the successful recruitment of Pecos bluntnose shiner by
decreasing the number of propagules reaching Brantley Reservoir.
Pecos bluntnose shiner prefers shallower depths coupled with relatively swift
velocity water typical of wide shifting sand bed rivers (Hoagstrom et al 2008a).
Hoagstrom et al. (2008b) associated length classes of Pecos bluntnose shiner with
water velocity and found a positive relationship between increasing water velocity
and fish size. Upper critical swimming speeds (Ucrit, 43 cm/s) for fish as young as 30
d post-hatch and 21 mm total length (TL) revealed that the upper threshold of aerobic
swimming capacity is high for this species at an early age. Caldwell et al. (2010)
reported upper critical swimming speeds (Ucrit, 34.3-44.1 cm/s and 6.3-8.7 BL/s) for
Rio Grande silvery minnow at 116 d post-hatch during a feed optimization study. In
comparison, 90 d post-hatch Pecos bluntnose shiner exhibited higher swimming
capacity (Ucrit, 52.5 cm/s and 11.4 BL/s). Bestgen et al. (2010) reported upper critical
swimming speeds of 51.5 cm/s (53-75 mm TL) for Rio Grande silvery minnow noting
that swimming ability increased with fish size. Though Pecos bluntnose shiner
exhibited strong swimming ability and upriver dispersal, downriver transport of
propagules has potentially tripled from pre-dam/pre-channelization of the river to
distances up to 142 km (Dudley and Platania 2007). Successful fish passage upriver
29
and maintaining position in flow relies on individual fish size, morphology, behavior,
river channel morphology, and flow velocity (Ward et al. 2003; Leavy and Bonner
2009; Bestgen et al. 2010).
Habitat degradation and loss of habitat complexity (backwater nursery habitat
and river connectivity to the floodplain) within the Farmlands Reach may be a
contributing factor to the decline of the species due to channelization of the river,
reducing retention of propagules above Brantley Reservoir before fish have the ability
to swim well (Dudley and Platania 2007). Worthington et al. (2014) suggested that
both increased water velocity and decreased habitat complexity increase transport
distance and rate of propagules thus reducing retention of propagules in rivers of the
Great Plains. In support of Hoagstrom et al. (2008a), isotopic analysis of otoliths
revealed that many Pecos bluntnose shiner propagules swept into the Farmlands
Reach eventually returned upriver after development and recruited into the
population, though unsuccessful fish cannot be accounted for (such as those swept
further downriver into Brantley Reservoir).
Persistence of Pecos bluntnose shiner relies on a multitude of environmental
factors that include timing of pulse flows that cue spawning events, habitat quality,
and perennial flow that maintain river connectivity for bidirectional dispersal to
complete their life cycle. The Southwest experienced one of the most severe droughts
on record during the summers of 2011 and 2012 (http://www.droughtmonitor.unl.edu/archive.h-tml, accessioned November 10, 2012). From 17 July to 20 August 2012,
55 km of the Pecos River dried affecting quality habitat within the Rangeland Reach
30
(Stephen Davenport, personal communication). Davenport (2012) reported very few
0+ age class in 2012 indicating limited spawning success. In addition, river
intermittency presumably halted fish movement. Notably, 6 Mile Draw had the
highest number of fish retained above Highway 70 and was the only site where
young-of-year Pecos bluntnose shiners were captured. This site did not go dry during
the study and consisted of good quality habitat. The majority of fish captured in this
study were age class 1+ with fewer 2+, while no older age class was captured.
Overall, movement of Pecos bluntnose shiner coincided with years of perennial flow
throughout summer and fall before the onset of their first winter.
The use of a surrogate species (plains killifish) provided insight into Pecos
River water chemistry both spatially and temporally. Gillanders (2002) suggested that
variability of water chemistry through time in the water fish inhabit must be
accounted for. The stability of 87Sr:86Sr values in otoliths of plains killifish revealed
that they not only remained within respective river segments, there were also no
detectable seasonal shifts in isotopic values within the study area. Isotopically unique
reaches were larger than movements made by plains killifish, thus allowing the use of
killifish as a surrogate for water samples in this study. The use of a resident fish
species may have future utility in assessing movements of a highly mobile species
such as the Pecos bluntnose shiner.
Use of these techniques revealed new information on life history movement
patterns of both Pecos bluntnose shiner and plains killifish that were previously
undocumented. In summary, this may be the first study that used stable isotopes
31
(87Sr:86Sr) to characterize life history movement patterns and dispersal potential of a
small-bodied Plains River fish. As a relatively short-lived species, Pecos bluntnose
shiner must move upriver (out of poor quality habitat) early in life such that when the
opportunity to spawn occurs, propagules have sufficient distance to drift while
developing. Swimming performance testing confirmed that young Pecos bluntnose
shiner were capable of dispersing upriver early in life. Fish retained in upriver reaches
will have the reproductive advantage during spawning season. Habitat restoration in
the Farmlands Reach would likely benefit the species by returning a perennial reach
of the Pecos River to shifting sand and erosive banks. This would increase backwater
areas important for nursery habitat and retention of young fish above Brantley
Reservoir and potentially increase the success of spawning in lower river sections,
thus, bolstering recruitment into the population. Applications of these techniques are
not limited to the Pecos River, and have been applied elsewhere in a variety of ways,
their use will likely continue to provide information bettering management practices
in the future.
32
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