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2014 SOUTHEASTERN NATURALIST 13(1):40–55
Habitat Use and Dispersal of a Reintroduced
Etheostoma sitikuense (Citico Darter) Population
W. Keith Gibbs1,*, Jason E. Miller1,2, S. Bradford Cook1, and Matt A. Kulp3
Abstract - Etheostoma sitikuense (Citico Darter), a federally protected fish endemic to the
southeastern United States, was extirpated from Abrams Creek in Great Smoky Mountains
National Park in 1957. The species was reintroduced from 1993–2001, but recovery efforts
have thus far achieved only partial success, due in part to limited knowledge of Citico
Darter habitat use. After distribution of the reintroduced population was established, we
monitored Citico Darters in a 4-km section of Abrams Creek using underwater observation.
We evaluated macro- and microhabitat use over four summers using principal components
analysis to determine macrohabitat variables influencing Citico Darter distribution, and
used classification tree methods to analyze microhabitat use. We analyzed dispersal using
linear regression to compare historical stocking data with current Citico Darter distribution
data. We identified percentage of pools and cobble/small boulder substrates as the most significant
macrohabitat variables influencing Citico Darter presence. This species most often
occupied microhabitats away from riffles under intermediate-sized cover rocks. Dispersal
of reintroduced Citico Darters was limited in Abrams Creek. Results of this study can be
used to identify additional reintroduction zones and assist in further conservation efforts.
Introduction
The southeastern United States has the greatest diversity and endemicity of
freshwater fishes in North America (Warren et al. 2000); however, ratios of imperilment
are also highest (Warren and Burr 1994). The southeastern physiographic
region known as the Eastern Interior Highlands, particularly the Tennessee and
Cumberland River drainages, comprises the most endemic, imperiled fish fauna
in the United States (Starnes and Etnier 1986, Warren and Burr 1994). At least
83 indigenous taxa of the more than 290 described fish species within Tennessee
merit designation under state or federal protective status due to continued threats
from anthropogenic activities (Etnier and Starnes 1991, Warren et al. 2000). Characterization
of habitat use of imperiled taxa is vital to understanding life-history
requirements to preserve existing populations and identify potential reintroduction
sites within historical ranges where anthropogenic degradation has been alleviated
and suitable habitat remains.
Darters, especially the subgenus Catonotus of the genus Etheostoma (Percidae),
represent a large proportion of the imperiled taxa within Tennessee (Etnier
and Starnes 1991). Etheostoma sitikuense Blanton (Citico Darter), a Catonotus
1Department of Biology, Tennessee Technological University, Cookeville, TN 38505.
2Current address - Burgess Falls State Natural Area, 4000 Burgess Falls Drive, Sparta, TN
38583. 3Resource Management Division, Great Smoky Mountains National Park, Gatlinburg,
TN 37738. Corresponding author - kgibbs@tntech.edu.
Manuscript Editor: Clifton Ruehl
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2014 Vol. 13, No. 1
originally thought to represent the federally endangered Etheostoma percnurum
Jenkins (Duskytail Darter), was recently re-described and considered morphologically
distinct from the other 3 geographically isolated, extant populations within
the Duskytail Darter complex, which also includes Etheostoma lemniscatum Blanton
(Tuxedo Darter) and Etheostoma marmorpinnum Blanton (Marbled Darter)
(Blanton and Jenkins 2008). The only known natural population of Citico Darters
remains in Citico Creek, a tributary of the Little Tennessee River, located in Monroe
County, TN.
The relict distribution of this species complex within the Tennessee and Cumberland
River drainages suggests a previously wide distribution (Etnier and Starnes
1993). Isolation of remaining populations is attributed to habitat degradation (i.e.,
siltation) and extensive impoundment within both drainages (Etnier and Starnes
1993). The 3 re-described species within the species complex, including the Citico
Darter, should be considered highly endangered and included under the protective
status as designated for the Duskytail Darter until individual imperilment listings
and recovery plans can be established. An objective of the Duskytail Darter recovery
plan is to establish additional viable populations within its historical range
(USFWS 1993).
An isolated population within the species complex was extirpated from Abrams
Creek, Great Smoky Mountains National Park (GSMNP), Blount County, TN in
1957 as a result of rotenone application (Lennon and Parker 1959, Simbeck 1990).
Comparison of specimens collected from Abrams Creek before rotenone application,
plus previous free-flowing connectivity to the Little Tennessee River between
Abrams and Citico Creeks (creek mouths separated by <10 km of the Little Tennessee
River) indicated that they were conspecific and justified reintroductions of
captively propagated Citico Darters from Citico Creek into Abrams Creek from
1993–2001 (Shute et al. 2005). Evidence of Citico Darter reproduction within
Abrams Creek was first observed in 1995 (Shute et al. 2005), and observation of
eggs and young-of-year continued through the duration of this study, yet long-term
viability of the Abrams Creek population is not assured, and continued monitoring
and habitat protection may be necessary.
The Citico Darter and other members in the species complex are relatively
small (28–64 mm total length [TL]) benthic species, generally tan to brown in
appearance, with 10–15 dark vertical bars along the sides, and 6–7 dark dorsal
saddles (Etnier and Starnes 1993, Jenkins and Burkhead 1994). As outlined by an
additional recovery plan objective, life-history characteristics of natural populations
within the species complex have been documented (e.g., Eisenhour and Burr
2000, Jenkins and Burkhead 1994, Layman 1991, Rakes et al. 1992). As with other
Catonotus, members of the species complex, including the Citico Darter, are eggclusterers
(Layman 1984) as exhibited by males clearing and maintaining nesting
cavities beneath cover rocks where females invert and lay clusters of adhesive eggs
(Etnier and Starnes 1993). Members of the species complex have been confirmed to
spawn from April through June (Etnier and Starnes 1993, Layman 1991, Rakes et
al. 1992). As nocturnal insectivores, species within the complex feed primarily on
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mayfly nymphs, chironomid larvae, and microcrustaceans while spending daylight
hours beneath cobble and small-boulder substrate (Etnier and Starnes 1993, Layman
1991, Jenkins and Burkhead 1994).
Although other members of the species complex occur in relatively large systems
in low-velocity habitats with large substrates (Etnier and Starnes 1993),
habitat use of the introduced population of Citico Darters within Abrams Creek is
unknown. The distribution of introduced Citico Darters was recently documented
in Abrams Creek (Gibbs 2009), and habitat use should be studied at multiple spatial
scales to fulfill recovery plan objectives—specifically, to determine the biological
and ecological requirements of Citico Darters in Abrams Creek (USFWS 1993).
Macrohabitat (i.e., reach-level) features affect the distribution of fishes at a large
scale, while microhabitat (i.e., habitat within 1 m2) studies are important to identify
specific stream locations fish utilize based on multiple abiotic and biotic factors
(Muhlfeld et al. 2001). Macrohabitat and microhabitat data are necessary to identify
potential reintroduction sites with suitable habitat outside current Citico Darter
distributions and to build statistical models useful for management and conservation
efforts within current distributions.
The overall goal of this study was to determine habitat use and dispersal of
introduced Citico Darters in Abrams Creek. Specifically, our objectives were to
(1) characterize macro- and microhabitat utilized by Citico Darters and (2) determine
Citico Darter dispersal from reintroduction sites. Results of this study will
assist National Park Service (NPS) personnel, tasked with restoring and conserving
the Citico Darter within Abrams Creek, by identifying precise locations within
stream reaches occupied by the species for preservation of specific stream habitats,
as well as aid in potential future reintroduction efforts.
Field-Site Description
Abrams Creek, a moderate-size 5th-order stream, is located in the southwestern
portion of GSMNP. The Abrams Creek watershed (225 km2) is comprised of ≈348.0
km of streams, and the majority of it lies within park boundaries (Parker and Pipes
1990). Limestone bedrock within the watershed increases pH, conductivity, and alkalinity
(Shaffer 2004). Abrams Falls, a 6.0-m waterfall, bisects Abrams Creek into
two distinct systems and functions as a barrier against upstream fish passage (NPS
2010). The lower, 23.5-km section of Abrams Creek extends from Abrams Falls to
an embayment of Chilhowee Reservoir, an impoundment of the Little Tennessee
River. This lower section is a coolwater stream, with temperatures averaging <23
°C in summer. Pools, deep runs, and short cascades are dominant habitat types, with
cobble and bedrock as the principal substrate types (Shaffer 2004). Stream width
and stream discharge average 18 m and 27.4 m3/s, respectively, and the average
gradient is 3.5% (Lennon and Parker 1959, Shaffer 2004). Reintroduction sites for
Citico Darters were located only in the lower section of Abrams Creek (Rakes and
Shute 2007).
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Methods
Historically, studies of stream-dwelling species have relied on backpack electrofishing
equipment or seines for collections (Hayes et al. 1996, Reynolds 1996).
However, due to the imperiled status of Citico Darters, and the inability to effectively
seine Abrams Creek, we used underwater observation (i.e., snorkeling;
Dolloff et al. 1996). This method avoids the unnecessary mortality associated with
electrofishing.
We conducted snorkeling surveys during daylight hours when underwater visibility
was ≥2 m to maximize observations, but only surveyed after mid-July of each
year to ensure spawning fish were not disturbed. We established lanes of equidistant
width that were parallel to shore, and a minimum of 4 people snorkeled each lane,
moving upstream to reduce startling fish and to optimize observations (Dolloff et
al. 1996). Movable rocks larger than gravel were gently lifted to allow embedded
sediment to wash downstream and determine Citico Darter presence under cover
rocks within each reach. No species within lower Abrams Creek are similar in appearance
to Citico Darters; however, all snorkelers were required to observe several
individuals with a trained surveyor prior to making independent observations to
ensure accurate identification and correct methodology.
Macrohabitat
We collected macrohabitat data between May and September of 2007 and 2008.
Beginning at the embayment, lower Abrams Creek was divided into 2-km sections
that were subdivided into consecutive 200-m reaches. A 1-m cascade was identified
as a potential barrier to upstream darter passage ≈17.2 river kilometers (rkm) from
the embayment. We randomly selected three 200-m reaches within each 2-km section
downstream of the cascade. We delineated a 200-m reach with representative
habitat above the cascade to confirm effectiveness of the barrier. This survey design
resulted in 27 total reaches (≈30% of the 18 rkm upstream of the embayment) being
sampled. We calculated distance from embayment from the downstream start point
of each randomly selected reach using latitude-longitude coordinates obtained with
a Garmin GPSmap 76Cx.
We measured macrohabitat parameters in each randomly selected reach prior
to snorkeling. We classified habitat types as riffle, run, or pool as described
by Overton et al. (1997). We measured lengths of all units of each habitat type
within each reach to quantify percentages. We delineated transects every 20 m
and recorded wetted widths (m) to determine average width for each reach. We
measured depth (cm) at 3 equidistant locations along each transect to calculate
average reach depth (McMahon et al. 1996) and visually classified substrate using
a modified Wentworth (1922) scale (silt [fines], sand [0.1–2 mm], gravel [2–60
mm], cobble [60–300 mm], small boulder [300–500 mm], large boulder >500
mm], and bedrock). We visually estimated percentages of dominant substrate
types within 0.25-m radius at each location that depth was measured to calculate
percentage of substrate composition within each reach.
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Snorkeling surveys were conducted as previously described. Upon positive
identification of at least 1 Citico Darter, we considered a reach to be a present location,
whereas we considered sites in which no Citico Darters were encountered as
absent locations. We calculated catch per unit effort (CPUE) as number of Citico
Darters per person hour snorkeled within each reach. Absent locations upstream
and downstream of current Citico Darter distribution were confirmed during microhabitat
study.
Microhabitat
We collected microhabitat data from June 2009 to September 2010. Eight 200-m
reaches within the Citico Darter’s distribution, identified during macrohabitat
sampling, were used for microhabitat analysis. Snorkel surveys were conducted
in each reach, following previously described methods. When a Citico Darter was
encountered, the cover rock was carefully replaced and a lead weight (85 g) marked
with highly visible forestry flagging was placed on the cover ro ck.
Upon survey completion, we recorded microhabitat variables (i.e., habitat
within a 0.25-m radius) at each occupied location. We measured depth (cm) with
a top-setting wading rod and velocities (m/s) at substrate and at 60% total depth
with a Marsh-McBirney Model 2000 Flow Meter. We measured dissolved oxygen
(DO [mg/l]), temperature (°C), and conductivity (mS) at substrate with a Yellow
Springs Instrument (YSI) Model 85 meter. We visually assessed habitat type, substrate
beneath cover rock, and dominant substrate within a 0.25-m radius using
the previously described categories. We measured dimensions (cm) of cover rocks
along the two longest axes to calculate approximate surface area (cm2). We also
measured the distance to nearest bank (m) and distance to nearest riffle (m). Presence
of multiple specimens within a 0.25-m radius of an occupied location was
recorded if observed.
All microhabitat variables measured at occupied locations were measured at
unoccupied locations to determine overall habitat availability within each reach
and for analytical comparisons. We designated unoccupied locations as 3 randomly
selected points along the 7 furthest transects from the greatest concentration of observed
occupied locations, resulting in 21 unoccupied locations within each reach
(Schmidt 2007). We did not measure unoccupied locations if they were within 5 m of
an occupied location. If Citico Darters were widely distributed within a reach, fewer
unoccupied locations were measured due to proximity of potential unoccupied points
to occupied locations. Before measurements were taken, potential unoccupied locations
were observed underwater to ensure no Citico Darters were present.
Dispersal
We obtained stocking records (i.e., locations and # of individuals stocked)
from 1993–2001 from Conservation Fisheries, Inc. (CFI) to compare with CPUE
of randomly selected reaches within current Citico Darter distribution. We calculated
distances of stocking locations from surveyed reaches using ArcView
9.2 GIS (ESRI 2007). We tabulated stocking densities within 1 km upstream and
downstream of each surveyed reach at 200-m intervals resulting in comparisons
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between CPUE and average number of individuals stocked within 200 m, 400 m,
600 m, 800 m, and 1000 m.
Statistical analysis
Due to small sample size (n = 27) of reaches, we used principal components
analysis (PCA) to determine the influence of macrohabitat variables on Citico Darter
distribution. PCA is a multivariate ordination technique based on eigenvectors of
principal components accounting for the greatest variation among samples (Kwak
and Peterson 2007). PCA is ideal for reducing dimensionality of highly correlated
multivariate data, as is typical of in-stream habitat data, to ≤5 interpretable ordination
axes (Clarke and Warwick 2001). Kwak and Peterson (2007) recommended
retaining all components with eigenvalues >1. Macrohabitat variables calculated
as percentages (i.e., habitat type and substrate composition) were approximately
normalized using an arcsine transformation (Zar 1999), whereas average width
and depth were kept continuous. We performed PCA using Primer v6 software
(PRIMER-E 2006).
We used classification tree methodology, developed by Breiman et al. (1984),
to describe microhabitat use within reaches identified as being occupied by Citico
Darters during macrohabitat surveys. Classification and regression trees (CART)
are ideal for modeling complex ecological data with categorical and numeric explanatory
variables (Breiman et al. 1984, De’ath and Fabricius 2000). Classification
trees split data into the most parsimonious dichotomous groupin gs of the categorical
response variable (i.e., occupied or unoccupied) by hierarchically partitioning
the most influential explanatory variables (De’ath and Fabricius 2000). Continuous
variables (i.e., temperature, conductivity, depth, DO at substrate, DO at 60% depth,
velocity at substrate, velocity at 60% depth, cover rock area, distance to bank, and
distance to riffle) were kept in original form, whereas categorical data (i.e., habitat
type, cover rock type, basal substrate, and dominant substrate) were assigned numerical
values (e.g., riffle = 1, run = 2, pool = 3) to retain their categorical nature.
We conducted classification tree analyses using Salford Systems CART 6.0 software
(Steinberg and Colla 1995). We set no stopping rules, which allowed for full
tree growth with each terminal node containing individuals from only 1 response
category. We used the default setting of 10-fold cross-validation to select optimal
sub-trees based on relative error of misclassification rates. We selected the smallest
tree within 1 standard error of the tree with the lowest relative error as the best
model (Steinberg and Colla 1995).
We used linear regression to associate stocking abundance to Citico Darter
abundance, as represented by CPUE. We compared the number of Citico Darters
stocked within 200 m, 400 m, 600 m, 800 m, and 1000 m upstream and downstream
of sampled reaches with CPUE to determine dispersal ability of Citico Darters away
from stocking locations. We performed regression analyses using Statistical Analysis
Software (SAS) 9.2 (SAS Institute, Inc. 2008).
These analyses are intended to guide future conservation efforts within Abrams
Creek by allowing identification of additional habitat for monitoring natural
expansion of current Citico Darter distribution and habitat suitable for reintroductions
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outside their current range if necessary. These models should be validated with additional
data collected during long-term monitoring of this reintroduced population.
Results
Macrohabitat
Citico Darters were observed in 5 reaches spanning 4.0 rkm (≈22%) of the 18
rkm of lower Abrams Creek sampled during 2007–2008. No individuals were observed
within 3.6 rkm downstream of the 1-m cascade barrier. The first 3 principal
components had eigenvalues >1 and accounted for 81.0% of variation among sites
(Table 1). Based on variable loadings, Citico Darters most often occurred in reaches
with more pools and intermediate-sized substrates (i.e., cobble and small boulder;
Fig. 1, Table 1). Most reaches occupied by Citico Darters were not typical of sampled
reaches throughout lower Abrams Creek (Fig. 1). This finding may represent
limited reach-level habitat suitability for Citico Darters within lower Abrams Creek
and habitat limitations to distribution extensions.
Microhabitat
In total during 2009–2010, we collected microhabitat data from 220 locations
occupied by Citico Darter from 7 sites on lower Abrams Creek within the
distribution range established from macrohabitat surveys. Congruent with macrohabitat
results, the majority (≈88%) of Citico Darters occupied locations away
(>6.1 m) from riffles under intermediate-sized (>100 cm2) cover rocks (Fig. 2).
Only 14 of 220 (6.4%) individuals occupied locations ≤6.1 m away from riffles.
Of the 206 individuals located >6.1 m from a riffle, only 13 (6.3%) occupied locations
under cover rocks ≤100 cm2. Most individuals (≈85%) occupying locations
away from riffles under intermediate-sized cover rocks were in local habitats
(i.e., ≤1 m2) dominated by cobble and small-boulder substrates (Fig. 2). Based
on these results, sampling within and outside of current Citico Darter distribution
and additional reintroductions should occur in long pools comprised predominately
of intermediate-sized substrates.
Table 1. Variable loadings for principal components 1–3 for reach-level macrohabitat within lower
Abrams Creek. Percentage of variation explained by each princip al component in parentheses.
Axis
Variable PC1 (36.1%) PC2 (27.0%) PC3 (17.8%)
% cobble/small boulder 0.551 -0.116 -0.102
% pool 0.393 0.430 -0.006
% riffle 0.153 -0.488 0.441
% gravel 0.079 -0.414 -0.434
Avg. depth -0.004 0.604 -0.165
Stream width -0.029 0.130 0.582
% run -0.477 -0.085 -0.402
% large boulder/bedrock -0.532 0.060 0.282
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Figure 1. Ordination plots of principal components analysis (PC1 [36.1%] v. PC2 [27.0%]
and PC1 v. PC3 [17.8%]) for reach-level macrohabitat within lower Abrams Creek. Values
above present points are catch per unit ef fort.
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Dispersal
Citico Darters were stocked in several locations throughout their current distribution
in lower Abrams Creek over 8 years (Fig. 3). Average stocking densities
ranged from 5.6–57.4 fish/year (Fig. 3). We tabulated average stocking densities at
Figure 2. Classification tree analysis for microhabitat data of occupied (present) and unoccupied
(absent) locations of Citico Darters within lower Abrams Creek. Child nodes represent
the most parsimonious split of the preceding node based on the predictor variable in italics.
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200-m intervals upstream and downstream of each site surveyed for macrohabitat
analyses. CPUE was dependent on average stocking density at all distances within 1
rkm of each sampled reach (Table 2), yet the most significant relationship and bestfitting
model was between CPUE and average number of individuals stocked within
200 m (Fig. 4, Table 2). The positive relationship between CPUE and average
stocking density indicates limited dispersal of Citico Darters away from stocking
locations. Therefore, successful reintroductions of Citico Darters in lower Abrams
Creek were dependent on >5 years of consistent yearly stocking of ≥25 individuals
per year in close proximity (≤200 m) to long pool habitats with an abundance of
intermediate-sized cover rocks.
Figure 3. Average number of individuals stocked within current Citico Darter distribution
(≈10 rkm from embayment) in relation to catch per unit effort of reaches sampled during
macrohabitat surveys.
Table 2. Results of linear regression analyses comparing CPUE to average stocking densities at 200-m
intervals upstream and downstream from surveyed reaches within current Citico Darter distribution.
Distance from site F P R2
200 m 52.0 0.0020 0.9286
400 m 18.1 0.0131 0.8190
600 m 16.8 0.0149 0.8076
800 m 19.8 0.0112 0.8319
1000 m 15.8 0.0166 0.7974
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Discussion
Species within the genus Etheostoma inhabit a variety of habitats ranging from
swift headwater streams to non-flowing swamps and ponds (Page 1983); however,
relatively few lotic darter species occur away from highly oxygenated, turbulent
riffle and run habitats. Typically, members of the subgenus Catonotus are riffle and
run specialists (Etnier and Starnes 1993); yet, members of the Duskytail Darter species
complex have generally been associated with slow-moving waters of moderate
depth (0.3–1.2 m), in medium- to large-sized drainages (Etnier and Starnes 1993,
Jenkins and Burkhead 1994). Etheostoma lemniscatum Blanton (Tuxedo Darter)
and Etheostoma marmorpinnum Blanton (Marbled Darter), 2 other members within
the species complex (Blanton and Jenkins 2008), were found to use similar habitat.
Tuxedo Darters were found to use pool habitats at intermediate depths in the Big
South Fork of the Cumberland River, TN and KY (Davis 2010). Marbled Darters
were associated with pools and utilized cobble substrate in Little River, Blount
County, TN (Layman 1991). Results from this study confirmed that Citico Darters
exhibited similar habitat utilization as other members within the Duskytail Darter
species complex.
At the macrohabitat level, presence of Citico Darters was strongly associated
with availability of intermediate-sized (i.e., cobble and small boulder) substrates
and pool habitats. Reaches with Citico Darters present were dominated by cobble,
and most individuals were found beneath cobble or small-boulder cover rocks.
Figure 4. Relationship between catch per unit effort and average number of individuals
stocked within 200 m over 8 years in lower Abrams Creek.
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Selectivity of Citico Darters to cobble substrates is congruent with the specialized
reproductive behavior exhibited by the species complex (e.g., Etnier and Starnes
1993, Jenkins and Burkhead 1994). Although populations within the species
complex are highly localized, habitat selection is consistent, particularly in the
Tennessee River drainage. Throughout the life-history literature, Citico Darters
and their close relatives have been associated with “slabrock” or cobble substrates
during breeding seasons, depositing eggs on the undersides of these rocks (e.g.,
Etnier and Starnes 1993, Jenkins and Burkhead 1994, Layman 1991, Rakes et al.
1992). Percentage of pool habitat was the variable most highly associated with
Citico Darter presence and it should be noted that the highest observation totals
(i.e., abundance) were within sites with the greatest amounts of pool habitat.
Ultimately, abundance of pool habitat and intermediate-sized substrates were associated
with abundance of Citico Darters in lower Abrams Creek. These results
provide quantitative evidence corroborating observational data of previous studies
regarding habitat use of other species within the Duskytail Darter complex.
At the microhabitat level, this study determined that Citco Darters most utilized
intermediate-sized (>100 cm2) cover rocks located away from riffles in areas
dominated by cobble and small boulders. These results are similar to other studies’
findings that intermediate-sized substrates generally provide the best habitat
for both benthic fishes and macroinvertebrates in lotic environments (Wood and
Armitage 1997). However, differences in microhabitat use were most accurately
illustrated by distance from riffle habitat in determining Citic o Darter presence.
Most Citico Darters (>90%) observed in Abrams Creek were found in pools,
and individuals were rarely found <4 m from the nearest bank. Citico Darters were
generally found in microhabitats with current velocities averaging <0.1 m/s and
frequently concentrated away from shallow littoral habitats at significant distances
from riffles. Many habitat variables were correlated; however, CART analysis
reflected the Citico Darter’s predilection for microhabitats away from riffles in
moderately deep, slow-moving water, typical of pools.
Presence of pool habitat, as denoted by distance from riffles during microhabitat
analyses, was the most consistent habitat variable influencing Citico Darter presence
in Abrams Creek at both the macro- and microhabitat spatial scales. The
section of lower Abrams Creek that supports the greatest numbers of Citico Darters
is not only the area that has been the most heavily stocked, but, of reaches sampled
in this study, it is also the only contiguous section comprised mostly of pool habitat.
Other areas within lower Abrams Creek were also extensively stocked, yet lack of
suitable habitat (i.e., pools with intermediate-sized substrates) within those areas
precluded establishment of viable Citico Darter populations.
The definitive objective of the Duskytail Darter recovery plan is “to restore viable
populations” … “to a significant portion of its historic range” and ultimately
remove the species from the endangered species list (USFWS 1993). For long-term
viability, Soule (1980) suggests a population size of 1500–2000 individuals. Any
species within the Duskytail Darter complex can be reclassified as threatened if it is
determined that “three distinct viable populations exist”, either naturally occurring
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or reintroduced, and no threats to their survival are anticipated. Excluding reintroduced
populations, the new species designations within the species complex
(Blanton and Jenkins 2008) have resulted in only 1 natural population of each of the
4 species. Determination of biological and ecological requirements of each population
must also be completed, and management strategies must be implemented and
deemed successful prior to reclassification (USFWS 1993). This study addressed
some of the biological and ecological requirements necessary for viability of this
reintroduced population of Citico Darters.
Although Citico Darters currently occupy <25% of the study area, reproductive
success and relative abundance of the species, particularly in areas within close
proximity to stocking sites, were comparable to the Citico Creek source population
(Shute et al. 2005). Personal observations of nest-guarding males, as well as juveniles,
provided direct evidence that the Abrams Creek population is reproducing.
Considering longevity of individuals within the species complex is between 2–3
years (Layman 1991) and Abrams Creek stocking efforts ceased in 2001 (Shute et
al. 2005), individuals observed during this study were, at minimum, the 2nd naturalized
generation.
Distributions appeared static over the course of this study. However, as this study
demonstrates, short-term Citico Darter dispersal ability is limited and may require
several additional years for natural extension of distribution range, provided suitable
habitat is available within close proximity to current distribution. If the Abrams
Creek population is viable, allowing natural dispersion is preferable due to costs
associated with collecting and propagating fish in captivity. However, the species’
long-term ability to naturally disperse and colonize new areas is unknown. Population
augmentation with transplanted or captively propagated individuals should be
avoided until the current population density within Abrams Creek can be estimated
with greater certainty (Williams et al. 1988) and long-term dispersal ability assessed
through continued monitoring beyond the Citico Darter’s current range.
American Fisheries Society Guidelines for reintroductions (Williams et al.
1988) suggest monitoring to determine viability of reintroduced populations and
then additional stocking only if warranted. It is unknown whether current conditions
warrant continued stocking, or if carrying capacity has been achieved in lower
Abrams Creek. Implementation of long-term (10+ yrs.) monitoring programs can
determine current population sizes, detect population trends, and infer long-term
population viability (Davis et al. 2011). Monitoring protocols, if implemented,
should be based on those completed for similarly imperiled species with similar
habitat use, such as protocols established for the Tuxedo Darter (Davis 2010,
Davis et al. 2011). Research concerning genetic viability of the population is also
recommended, as results might influence decisions regarding the need for further
augmentation to enhance genetic diversity.
Finally, young-of-year individuals were observed during all 4 years of this study,
throughout the species’ distribution within Abrams Creek. Past surveys (Rakes and
Shute 2007) have also documented reproduction, providing additional evidence
that the Abrams Creek population is currently self-sustaining. However, preserving
Southeastern Naturalist
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W.K. Gibbs, J.E. Miller, S.B. Cook, and M.A. Kulp
2014 Vol. 13, No. 1
this population remains a priority, and future conservation efforts will likely play
a large role in determining the fate of this species. Such efforts should include
long-term monitoring of population trends within lower Abrams Creek, investigation
of genetic viability, and continued reintroductions if warranted by results of
population and genetic analyses. Knowledge of reach-level and microhabitat use,
specifically in areas with higher percentages of pools and intermediate-sized substrates
in locations away from riffles under cover rocks >100 cm2, recognition of
the limited dispersal ability of stocked individuals, and other suggestions presented
here should be utilized to further enhance Citico Darter recove ry efforts.
Acknowledgments
We would especially like to acknowledge Steve Moore of the Great Smoky Mountains
National Park for his guidance and help during planning and implementing this project.
We are appreciative of Justin Murdock for his editorial comments. We are grateful to the
anonymous reviewers whose comments improved this manuscript. Funding for this project
was provided by the Tallassee Fund (Alcoa Power Co.), the National Park Service, and the
Tennessee Technological University Center for the Management, Utilization, and Protection
of Water Resources. The authors are especially grateful to the numerous individuals that
assisted with this project, including J.R. Shute and Patrick Rakes of Conservation Fisheries,
Inc., whose tireless efforts conserving rare and endangered native fishes resulted in the
reintroduction efforts of Citico Darters into Abrams Creek.
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