Changes in Fish Community Structure and Effects on
Blackside Dace (Chrosomus cumberlandensis) Populations
Following Beaver Colonization in Davis Branch,
Cumberland Gap National Historical Park, Bell County,
Kentucky
Michael C. Compton, Michael A. Floyd, and Douglas E. Stephens
Southeastern Naturalist, Volume 12, Special Issue 4 (2013):112–128
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M.C. Compton, M.A. Floyd, and D.E. Stephens
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Changes in Fish Community Structure and Effects on
Blackside Dace (Chrosomus cumberlandensis) Populations
Following Beaver Colonization in Davis Branch,
Cumberland Gap National Historical Park, Bell County,
Kentucky
Michael C. Compton1, Michael A. Floyd2,*, and Douglas E. Stephens3
Abstract - Davis Branch in Cumberland Gap National Historical Park was considered
important for the recovery of the Federally threatened Chrosomus cumberlandensis
(Blackside Dace). Monitoring of the Davis Branch population began in 1990. Castor
canadensis (North American Beaver) colonization was reported in 1994, and a series
of dams have persisted in the upper section of the stream. The pervasive effects of
Beavers on Blackside Dace populations were unknown. Our goals were: 1) to characterize
the fish community structure and relative abundance of Blackside Dace within
the assemblage, 2) to determine the direct and indirect effects of beaver dams on the
fish community, and Blackside Dace population, 3) to monitor the age structure of
the Blackside Dace population, and 4) to recommend management actions that will
enhance the Blackside Dace population within Davis Branch. Fishes were collected
from eight stations annually from 1990–2010, except for 2003–2005. Stations were
delineated within downstream and upstream sections based on Beaver presence, and
within three periods, prior (1990–1993), post (1994–2002), and recent (2006–2010).
Fish community structure indicated distinct downstream and upstream assemblages
prior to Beaver colonization, with the relative abundance of Blackside Dace approximately
6% and 18%, respectively. The fish assemblage and relative abundance of
Blackside Dace shifted over time, with the relative abundance of Lepomis gulosus
(Warmouth), Lepomis auritus (Redbreast Sunfish), and Chrosomus erythrogaster
(Southern Redbelly Dace) increasing, and Blackside Dace decreasing; only 25 Blackside
Dace were encountered from 2006–2010. Comparison of Blackside Dace age
classes between the 3 periods indicated the 0+ age class decreased over time and 1+
and 2+ age classes increased initially but eventually declined within both the downstream
and upstream sections. It is speculated that the continued presence of beaver
dams increased stream temperatures downstream and upstream, altered the flow regime,
and changed the available habitat, thus creating conditions more suitable for
centrarchid species and Southern Redbelly Dace, which probably preyed upon and
out-competed Blackside Dace, respectively. It is recommended that the National Park
Service and its partners 1) develop a Beaver management program, 2) return Davis
Branch to its free-flowing, pre-Beaver condition, 3) significantly decrease nonnative
species and decrease native centrarchid species to abundances prior to Beaver
colonization, and 4) establish a Davis Branch Blackside Dace propagation and reintroduction
program.
1Kentucky State Nature Preserves Commission, 801 Schenkel Lane, Frankfort, KY 40601.
2US Fish and Wildlife Service, 330 West Broadway, Suite 265, Frankfort, KY 40601. 3PO
Box 243, Whitley City, KY 42653. *Corresponding author - mike_floyd@fws.gov.
Ecology and Conservation of the Threatened Blackside Dace, Chrosomus cumberlandensis
2013 Southeastern Naturalist 12(Special Issue 4):112–128
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2013 Southeastern Naturalist Vol. 12, Special Issue 4
Introduction
The federally threatened Chrosomus cumberlandensis (Starnes and Starnes)
(Blackside Dace) was first reported from Davis Branch, Cumberland Gap National
Historical Park (CUGA), Bell County, KY, by Starnes and Starnes (1978).
Subsequent surveys by Starnes (1981) and O’Bara (1990), and the species’
recovery plan (USFWS 1988), ranked the Blackside Dace population in Davis
Branch as excellent, and O’Bara (1990) considered it one of 9 populations most
important to the species’ continued existence. Davis Branch continues to be one
of only two Blackside Dace streams in public ownership that are located outside
of the Daniel Boone National Forest, Winchester, KY.
Due to the importance of Davis Branch toward Blackside Dace recovery,
CUGA initiated a monitoring program for the stream that included annual surveys
at several mainstem locations. In 1994, a large Castor canadensis Kuhl
(North American Beaver) dam and pond were discovered at approximately 2.9
km upstream of the confluence with Little Yellow Creek. Beaver activity increased
over subsequent years, resulting in the construction of at least 15 dams
and the inundation of a continuous 1-km reach in the upper section of the Davis
Branch mainstem (Fig. 1). Within this area, Davis Branch was transformed from
a free-flowing, shaded, gravel/cobble stream to a series of ponds and canal-like
reaches with decreased canopy cover and silty substrates. As habitat conditions
changed, the status of the Blackside Dace population was a serious concern and
continued monitoring was conducted.
Beavers cause profound changes to stream habitats through dam building and
manipulation of riparian trees (Collen and Gibson 2001, Muller-Schwarze
and Sun 2003). These habitat alterations can influence fish communities in a
number of ways (Collen and Gibson 2001). Positive effects include increased
production for some species (Gard 1961, Hanson and Campbell 1963, Neff
1957); creation of pool habitats preferred by large-bodied species such as trout,
centrarchids, and esocids (Gard 1961, Neff 1957, Pullen 1971, Rupp 1955); creation
of cover associated with lodge debris and food caches (France 1997, Gibson
1969); reduced bed and bank erosion below dams and more stable downstream
flows (Apple et al. 1984, Parker 1986); trapping of sediment in streams with high
sediment loads (Grasse 1951, Macdonald et al. 1995); and creation of refugia
during low-flow periods (Hanson and Campbell 1963). Beavers can negatively
affect fish communities through creation of migration barriers (Gard 1961, Knudsen
1962, Munther 1983, Schlosser 1995); increased water temperatures and
siltation of spawning substrates (Cook 1940, Knudsen 1962, Rohde and Arndt
1991); and creation of habitats for avian, mammalian, and piscine predators (Dubuc
et al. 1990, Grover and Baldassarre 1995, Collen and Gibson 2001).
In this paper, we evaluate Davis Branch fish community data collected from
1990–2010. We attempt to show the effect of Beaver colonization on the fish community
structure and the Blackside Dace population by comparing the data within
three periods—an initial period with no Beaver activity (prior: 1990–1993), an
immediate period following Beaver colonization (post: 1994–2002), and a period
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after Beaver establishment (recent: 2006–2010). Project goals included: 1) to
characterize the fish community structure and relative abundance of Blackside
Dace within the assemblage, 2) to determine the direct and indirect effects of
Figure 1. Generalized map of Davis Branch stations within Cumberland Gap National
Historical Park (gray shading). Hashed area indicates inundated portion of Davis Branch
affected by Castor canadensis (Beaver) dams. Stations 1–3 were classified as downstream
and stations 4–8 were classified as upstream.
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Beaver colonization on the fish community structure and Blackside Dace population,
3) to monitor the age structure of the Blackside Dace population, and 4) to
make management recommendations that benefit Blackside Dace persistence in
Davis Branch.
Study Area
Davis Branch is located in the Central Appalachians (Level III) and Cumberland
Mountain Thrust Block (Level IV) ecoregions (Woods et al. 2002) of
southeastern Kentucky. Its catchment (3.7 km2) lies almost entirely (>90%) within
the boundary of CUGA, a 97-km2 national park that straddles the ridgeline of
Cumberland Mountain in Kentucky, Tennessee, and Virginia (Fig. 1). Elevations
within the Davis Branch watershed range from approximately 347 m to 633 m
above mean sea level. Davis Branch is roughly 4.5 km long and flows southward
to its confluence with Little Yellow Creek, just east of Middlesboro, KY. Prior to
the establishment of CUGA, several farms and home sites were located along the
stream, but land use within the watershed now consists primarily of second- and
third-growth forest. The lower 0.1 km of Davis Branch is bordered on the northwest
by a residential neighborhood within the city limits of Middlesboro.
Davis Branch is characterized as a cool, upland stream with gravel and
cobble substrates and moderate gradient (D.E. Stephens, unpubl. data). Riffle/
pool ratios range from 60/40 in the headwaters to 30/70 near the mouth (D.E.
Stephens, unpubl. data). Riparian vegetation is dominated by Platanus occidentalis
L. (Sycamore), Tsuga canadensis (L.) Carriere (Eastern Hemlock),
Magnolia macrophylla Michx. (Bigleaf Magnolia), Rhododendron maximum
L. (Rhododendron), Carpinus caroliniana Walter (American Hornbeam), Fagus
grandifolia Ehrh. (American Beech), and Liriodendron tulipifera L. (Tulip
Poplar). Beavers have significantly modified approximately 1.2 km of the
Davis Branch mainstem, resulting in several ponds, wetlands, and canal-like
reaches. These areas are characterized by reduced canopy cover, reduced flow,
and silty substrates.
Methods
Field surveys
Fish surveys in Davis Branch were conducted at 8 stations during 1990–2010
(Figs. 1, 2). Each station encompassed a stream reach approximately 200 m in
length. Because of stream conditions and other study logistics, not all stations
were surveyed annually, and no surveys were conducted during 2003–2005.
Surveys were completed in early spring or fall to avoid disruption of Blackside
Dace reproduction. Surveys were conducted in an upstream direction, and fishes
were captured using a battery-powered, backpack electrofisher (Smith-Root,
Vancouver, WA). All available habitats (e.g., riffles, pools, runs, undercut banks
with root mats, and woody debris jams) were searched, and captured fishes were
identified in the field, enumerated, recorded, and released. Electrofishing time
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(seconds) and total length (mm) of Blackside Dace were recorded during each
sampling effort.
Data analyses
Fish community data were classified temporally and spatially based on the
initial presence and location of beaver dams. Temporally, data were grouped
into three periods: prior to Beaver colonization (prior: 1990–1993), during
early pond establishment (post: 1994–2002), and established pond development
(recent: 2006–2010). Spatially, stations 1–3 and stations 4–8 were grouped as
downstream and upstream stations, respectively, based on beaver dam location.
These groupings mitigated the absence of data from missed sampling years
(2003–2005) and absence of annual sampling from some stations.
We used nonmetric multidimensional scaling (NMS) to identify any potential
differences and gradients in fish community structure across the temporal and
spatial scales. The NMS was conducted using PC-ORD v. 6.0 software (McCune
and Mefford 2011) and followed the general procedure outlined in McCune and
Grace (2002). We used the Bray-Curtis similarity coefficient (Bray and Curtis,
1957, McCune and Grace, 2002) based on a power transformation (p = 0.5) of
abundances. The data were computed with 250 iterations, 50 real runs, and 50
randomized runs.
Figure 2. Photographs of Davis Branch. (A) Station 1, upstream view (April 2005); (B)
Station 6, downstream view (April 2005); (C) Station 7, upstream view—beaver dam and
pond (November 2011); (D) Station 8, upstream view (April 2005).
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We used the nonparametric multi-response permutation procedure (MRPP, PCORD
v. 6.0; McCune and Mefford 2011) to determine if fish community structure
differed significantly among the spatial and temporal categories. We tested the null
hypotheses of 1) no difference in fish community structure between downstream
and upstream stations prior to Beaver colonization, 2) no differences between
temporal periods within the downstream fish communities, and 3) no differences
between temporal periods within the upstream fish communities.
We calculated the relative abundance of each species encountered, for each
spatial group across each temporal period, to determine if certain species were
dominant or if a species made a noticeable shift within the community. A catchper-
unit-effort (CPUE) was then calculated for selected species (i.e., Blackside
Dace) and compared across the temporal periods. The CPUE was the log (x +
1) transformed result of the total number of individuals encountered divided
by the number of 15-second electrofishing units of the total electrofishing time
(seconds). We then used the Mann-Whitney U-tests to test the hypothesis of no
difference in CPUE for a species across temporal periods (P < 0.05).
Lastly, a frequency histogram of all Blackside Dace TL (mm) measurements
was made to determine the appropriate cut-off for age classes. The 0+ age class
was <40 mm TL, 1+ was 40–60 mm TL, and 2+ was >60 mm TL. These classifications
were similar to previous descriptions by Starnes and Starnes (1981:368)
and Etnier and Starnes (1993:244–245). A CPUE, as described above, was made
for each age class across the temporal periods. The Mann-Whitney U-test was
used to test the hypothesis of no difference in Blackside Dace age class CPUE
across temporal periods (P < 0.05).
Results
Nearly 20,000 individuals, representing 5 families and 23 species, were encountered
during 76 surveys completed during 1990–2010 (Table 1). Semotilus
atromaculatus (Creek Chub), Lepomis auritu (Redbreast Sunfish), and Catostomus
commersonii (White Sucker) were the most common species, and they
represented 65% of the total abundance. Lampetra aepyptera (Least Brook Lamprey),
Campostoma anomalum (Central Stoneroller), Luxilus chrysocephalus
(Striped Shiner), Pimephales notatus (Bluntnose Minnow), Hypentelium nigricans
(Northern Hog Sucker), Ambloplites rupestris (Rock Bass), and Etheostoma
caeruleum (Rainbow Darter) were present primarily in the downstream section.
Only Cyprinella spiloptera (Spotfin Shiner) was present (1 individual) exclusively
in the upstream section. In general, Blackside Dace and Southern Redbelly
Dace were more abundant in the upstream section than in the downstream section
across each temporal period (Table 1). Blackside Dace were detected during 52
of the 76 surveys, and 1508 individuals were encountered.
NMS produced a 2-dimension solution with a final stress of 16.1. The first and
second axes accounted for 34% and 54% of the variation, respectively. The fish
community structure among the different categories was distinct, and temporal
and spatial gradients were evident along the first and second axes, respectively
(Fig. 3). The separation of the fish community structure in ordinational space
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Table 1. Species abundance of Davis Branch fishes downstream and upstream of beaver dams and across temporal periods. Numbers in parentheses indicate
the total number of surveys, total richness, and total abundance.
Downstream Upstream
Species Prior Post Recent Prior Post Recent
Petromyzontidae
Lampetra aepyptera (Abbott) (Least Brook Lamprey) 24 41 12
Cyprinidae
Campostoma anomalum (Rafinesque) (Central Stoneroller) 62 342 87 5 4 1
Chrosomus cumberlandensis (Starnes & Starnes) (Blackside Dace) 97 490 2 333 561 25
Chrosomus erythrogaster Rafinesque (Southern Redbelly Dace) 78 1609 283 292 1665 420
Cyprinella spiloptera (Cope) (Spotfin Shiner) 1
Luxilus chrysocephalus Rafinesque (Striped Shiner) 166 323 241 3 4
Notemigonus crysoleucas (Mitchill) (Golden Shiner) 1
Notropis buccatus (Cope) (Silverjaw Minnow) 2
Pimephales notatus (Rafinesque) (Bluntnose Minnow) 6 79 20
Rhinichthys obtusus Agassiz (Western Blacknose Dace) 141 331 162 10 18 3
Semotilus atromaculatus (Mitchill) (Creek Chub) 779 2525 322 1000 1152 425
Catostomidae
Catostomus commersonii (Lacepede) (White Sucker) 83 614 80 109 918 85
Hypentelium nigricans (Lesueur) (Northern Hog Sucker) 18 47 15 3
Moxostoma erythrurum (Rafinesque) (Golden Redhorse) 2
Centrarchidae
Ambloplites rupestris (Rafinesque) (Rock Bass) 14 69 20
Lepomis auritus (Linnaeus) (Redbreast Sunfish) 71 1273 288 3 399 239
Lepomis gulosus (Cuvier) (Warmouth) 2 302 1 30
Lepomis macrochirus Rafinesque (Bluegill) 4 35 30 2 26
Micropterus punctulatus (Rafinesque) (Spotted Bass) 7 1
Micropterus salmoides (Lacepede) (Largemouth Bass) 3 1
Percidae
Etheostoma caeruleum Storer (Rainbow Darter) 78 181 73
Etheostoma kennicotti (Putnam) (Stripetail Darter) 68 107 57 61 49 50
Etheostoma sagitta (Jordan & Swain) (Arrow Darter) 5 32 1 18 50 2
Surveys (76): 10 27 8 8 16 7
Richness (23): 16 21 20 10 13 12
Abundance (19,773): 1694 8113 1999 1834 4823 1310
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was significant across all spatial and temporal categories based on the MRPP
(Table 2). Spatially, distinct fish assemblages were observed for each temporal
Table 2. Results of MRPP pairwise comparison of disturbance categories.
Category Comparison T A P-value
Prior: Downstream vs. upstream -8.594 0.226 <0.001
Post: Downstream vs. upstream -23.139 0.155 <0.001
Recent: Downstream vs. upstream -3.615 0.100 0.005
Downstream: prior vs. post -7.310 0.067 <0.001
Downstream: post vs. recent -8.847 0.088 <0.001
Downstream: prior vs. recent -6.577 0.132 <0.001
Upstream: prior vs. post -10.965 0.123 <0.001
Upstream: post vs. recent -4.915 0.507 <0.001
Upstream: prior vs. recent -5.703 0.230 <0.001
Figure 3. Non-metric multidimensional scaling scatterplot of Davis Branch stations.
Stations were grouped into disturbance categories based on their spatial and temporal
relation to beaver dams. Spatially, stations were assigned as upstream (circles) and downstream
(squares) of beaver dams. Temporally, stations were assigned as prior-beaver dam
construction (white), post-beaver dam construction (gray), and recent (black). MRPP
results indicate that the distances in ordination space between each disturbance group
was significantly different. Axis 1 indicates the temporal shift in fish community structure
following beaver colonization. Axis 2 indicates the longitudinal spatial shift in fish community
structure in Davis Branch from upstream to downstream.
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period. Prior to Beaver colonization, the fish community had distinct upstream
and downstream faunas (A = 0.226, P < 0.001) and maintained that separation
during the post-colonization period (A = 0.155, P < 0.001) and recent colonization
period (A = 0.100, P = 0.005). Temporally, the fish assemblages were distinct
within both the downstream and upstream sections, and shifted over time. Downstream,
the fish community prior and post (A = 0.067, P < 0.001), prior and recent
(A = 0.088, P < 0.001), and post and recent periods were separate (A = 0.132,
P < 0.001). Upstream, the fish community prior and post (A = 0.123, P < 0.001),
prior and recent (A = 0.507, P < 0.001), and post and recent periods were separate
(A = 0.230, P < 0.001).
Increased species diversity and changes in minnow and sunfish abundances
were the primary factors in the observed succession in community structure
(Fig. 4). Prior to Beaver colonization, 10 species were present in the upstream
section, and the community was comprised predominantly of small-bodied
fishes, such as Blackside Dace, Southern Redbelly Dace, Creek Chubs, and
Stripetail Darters. The downstream assemblage was more diverse with 16 species,
but it was still comprised predominantly of small-bodied fishes, such as
Central Stoneroller, Striped Shiner, and Blacknose Dace. In addition, largerbodied
species, such as sunfish, were more diverse and abundant. Following pond
establishment, Northern Hog Sucker was the only species extirpated, and 4 new
species immigrated into the upstream section even though the habitat changed
from lotic to lentic. Downstream of the ponds, the habitat remained lotic (Fig.
2A, B), but the hydrology was altered. No species were extirpated, and 5 new
species, mostly centrarchids (i.e., Lepomis gulosus [Warmouth] and Micropterus
spp.), immigrated into the downstream section following pond establishment.
Creek Chubs decreased across the temporal periods within both sections, but
other species were mostly static (i.e., Central Stoneroller downstream, and Blacknose
Dace upstream) or fluctuated among temporal periods (i.e., Striped Shiner
downstream, and White Sucker upstream). Sunfish diversity and abundance increased
within both sections following beaver pond establishment.
Immediately following Beaver colonization (post), Blackside Dace CPUE
values were not significantly different from those prior to colonization for the
downstream and upstream sections (Fig. 5). However, the population during the
recent period had decreased substantially and was significantly different from
earlier periods (prior and post). Southern Redbelly Dace CPUE values increased
significantly following the initial Beaver colonization but decreased in the following
period and ultimately were not significantly different than those prior to
Beaver colonization, for either the downstream and upstream sections.
Changes in CPUE values for Centrarchidae in the downstream section were
significant and increased during each subsequent period (Fig. 5). Warmouth, Micropterus
salmoides (Largemouth Bass), and Micropterus punctulatus (Spotted
Bass) were only encountered after Beaver colonization. Warmouth abundance
increased greatly during the recent period. In the upstream section, Centrarchidae
CPUE values were significantly different following Beaver colonization. War121
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2013 Southeastern Naturalist Vol. 12, Special Issue 4
Figure 4. Stacked bars of the Davis Branch fish taxa across temporal periods for the upstream
(A) and downstream (B) sections. In general, cyprinid abundance decreased and
centrarchid abundance increased over time. BSD = Blackside Dace, SRBD = Southern
Redbelly Dace.
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mouth and Lepomis macrochirus (Bluegill) were only encountered after Beaver
colonization, and they increased in abundance over time. For both sections, the
abundance of the nonnative Redbreast Sunfish increased greatly following Beaver
colonization, and it was one of the most common species encountered.
The Blackside Dace age class structure between the downstream and upstream
sections indicated the CPUE values for each age class were greater in the upstream
section, and that separate patterns were observed over time. Recent CPUE
values for each age class were near zero (Fig. 6). For the downstream section,
the Mann-Whitney U-test indicated that the median CPUE values for the 0+, 1+,
and 2+ age classes were not significantly greater immediately following Beaver
colonization (U = 118.0, P < 0.485; U = 182.5, P < 0.103; U = 176.0, P < 0.159,
Figure 5. Box plots of downstream (A) and upstream (B) Blackside Dace, downstream
(C) and upstream (D) Southern Redbelly Dace, and downstream (E) and upstream (F)
Family Centrarchidae CPUE values across temporal periods. Significant difference of
CPUE (Mann-Whitney U-test: P < 0.005) across temporal periods is indicated by a distinct
letter among the box plots.
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respectively), but were significantly lower after prolonged colonization (U =
27.0, P < 0.039; U = 17.0, P < 0.011 U = 22.0, P < 0.030, respectively). In the
upstream section, the 0+ and 1+ Blackside Dace age class decreased immediately
following colonization but were not significantly different than prior to coloniza-
Figure 6. Median CPUE values for Blackside Dace age classes upstream and downstream
across temporal periods. Blackside Dace were able to persist immediately after
Beaver colonization but recruitment ceased at some point between 1994–2002, which
contributed to the collapse of the population.
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tion (U = 41.0, P < 0.156; U = 49.0, P < 0.358, respectively). The 2+ age class
CPUE was significantly greater immediately following colonization (U = 100.0,
P < 0.027). However, after prolonged (greater than 10 years) colonization all age
classes were significantly lower than the previous period (U = 22.0, P < 0.041;
U = 4.5, P < 0.001 U = 19.0, P < 0.031, respectively).
Discussion
Distinct upstream and downstream fish assemblages were identified within
Davis Branch prior to Beaver colonization. The dynamic spatial and temporal
activities of Beavers, pond age, pond placement within the watershed, valley
shape, and the larger-scale stream network can influence the successional shift
in community structure and diversity following pond establishment (Johnston
and Naiman 1987, Schlosser and Kallemeyn 2000, Snodgrass and Meffe 1998).
In addition, dam integrity and precipitation can influence dispersal rates and
the connectivity of downstream and upstream fishes (Schlosser 1995, Schlosser
and Kallemeyn 2000, Snodgrass and Meffe 1998). Intact dams and periods of
reduced precipitation decrease upstream colonization from downstream sources,
reduce hydrologic dynamics, and can result in decreased dissolved oxygen
levels, thus selecting for more tolerant species (Schlosser and Kallemeyn
2000). In our study, the upstream and downstream sections maintained distinct
assemblages following pond establishment, but exhibited similar successional
community-structure shifts. In general, centrarchid diversity and abundance
increased within the upstream and downstream sections. Redbreast Sunfish
and Southern Redbelly Dace became the predominant species, while Blackside
Dace and Creek Chub abundances decreased. Most other species were static or
did not exhibit a noticeable pattern.
The Blackside Dace population initially showed little change after pond establishment
within the upstream and downstream sections. However, after prolonged
Beaver colonization (greater than 10 years), the population eventually collapsed
in the upstream section, with only one individual encountered since 2007. The
extreme upstream section contained a small reach of lotic habitat likely essential
for spawning (Fig. 2D), but a series of droughts during the past decade reduced
that habitat and forced the remaining individuals into the inundated stream portion
(Fig. 2C). Recruitment was never substantial in the downstream section (Fig. 6),
suggesting suitable spawning habitat was only present within the upstream section
prior to Beaver colonization. We speculate that Blackside Dace were heavily
preyed upon as centrarchid diversity and abundance increased within the lentic
habitat, and the cumulative factors of habitat alteration, drought, decreased downstream
connectivity, and reduced spawning habitat most likely resulted in the
collapse of the Blackside Dace population within the upstream section.
The downstream Blackside Dace population collapsed after prolonged Beaver
colonization, but it did not show a measurable difference immediately following
pond establishment. Prior to Beaver colonization, the Blackside Dace population
within the downstream section consisted mostly of adult individuals (Fig. 6),
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2013 Southeastern Naturalist Vol. 12, Special Issue 4
which suggested minimal recruitment and that colonization would have to come
either from upstream, from Little Yellow Creek, or a combination of the two. The
shift in community structure was similar within the downstream and upstream
sections, and predation from centrarchid species most likely played a role in the
population dynamics, but the abiotic factors that contributed to the population
collapse within the downstream section were different from those in the upstream
section. Droughts and the establishment of beaver dams over the last decade have
diminished the hydrologic fluxes downstream, thus reducing habitat complexity
and likely concentrating species in pools, which increased predation success.
Dam presence also limited the colonization from upstream to downstream sites,
which increased the importance of Little Yellow Creek as a source for Blackside
Dace into Davis Branch. However, the downstream reaches of Little Yellow
Creek and most tributaries of Yellow Creek have been degraded by a variety of
anthropogenic activities; therefore, water quality and habitat conditions have not
supported a robust population of Blackside Dace.
Other factors not measured in our study but which may have contributed to
the changes in community structure and Blackside Dace populations after Beaver
colonization are alterations in the nutrient cycle and temperature regime.
It has been documented that the abundance of standing material increases, and
decomposition and transportation rates of material are altered following pond
establishment (Hodkinson 1975, Francis et al. 1985, McDowell and Naiman
1986, Naiman et al. 1991, Smith et al. 1991). Aquatic plant, invertebrate, and fish
communities are also altered by changes in water quality (Clifford et al. 1993,
Feldman 1995, Smith et al. 1991). Although only a few species demonstrated a
significant change in abundance following Beaver colonization, several species
showed consistent increases in abundance over time (i.e., Central Stoneroller,
Striped Shiner, Bluntnose Minnow, and White Sucker). These species are associated
with nutrient and temperature increases in eastern Kentucky’s mountain
headwater streams (Compton et al. 2003). As Beaver colonization persists,
canopy cover within the watershed decreases, resulting in increased temperatures
and primary production, as well as increased coarse particulate organic material
within the stream.
Management implications
The presence and influence of beaver colonization within Blackside Dace
streams is not a unique phenomenon, and the two species have coexisted for
centuries. In our study, we demonstrated that prolonged Beaver colonization was
detrimental to the local persistence of Blackside Dace. However, in the largerscale
context of a drainage basin (i.e., Cumberland), the two species can persist
through source/sink dynamics (Pulliam 1988), where Beaver activity influences
the dispersal of fishes in and out of ponds, based on their habitat tolerances
(Schlosser 1995). Meffe and Sheldon (1988) and Snodgrass and Meffe (1998)
suggested that Beaver colonization influenced the evolution of stream fishes,
where the distribution of impounded, unimpounded, and previously impounded
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streams created a mosaic of habitats, and species’ habitat preferences allowed for
resource partitioning and persistence. Unfortunately, Beaver and Blackside Dace
distributions across eastern Kentucky no longer resemble pre-settlement distributions
due to landscape alteration and stream degradation. Streams that have
high water quality, like Davis Branch, serve as refuges for both species. Historically,
the Blackside Dace population within Davis Branch was recognized as an
important population in the eastern extent of the species’ range (O’Bara 1990);
therefore, its restoration within Davis Branch would be beneficial for the dace’s
overall recovery. Below, we recommend several management actions to benefit
the Federally threatened Blackside Dace within the Cumberland Gap National
Park, with the goal of species restoration and maintenance within Davis Branch:
1. Removal and management of Beavers within Davis Branch.
2. Removal of existing beaver dams and restoration of the stream channel
and flow patterns present prior to Beaver colonization.
3. Restoration of the riparian zone.
4. Development of a systematic program to significantly reduce the nonnative
Redbreast Sunfish population and to decrease native centrarchid
species abundances.
5. Establish a Blackside Dace propagation and reintroduction program for
Davis Branch.
Acknowledgments
We would like to thank Mark Woods (Park Superintendent), Jenny Beeler (Biologist),
Megan Blanchard (GIS Specialist), Amy Wilson (Biologist) and other CUGA staff
for their invaluable assistance with many aspects of this project, but especially for the
creation of the map used in this paper. Field assistance was provided by Carrie Allison,
Jonathan Baxter, Dirk Bradley, Stephanie Brandt, Sue Bruenderman, Jeff Duncan, Danny
Parks, Tim Pinion, Matt Thomas, and John Williams. Virgil Lee Andrews, Jr. (Field Supervisor,
Kentucky Ecological Services Field Office) provided financial support in the
form of equipment and travel expenses. The Kentucky Aquatic Resource Fund provided
financial support for publication costs.
Disclaimer
The findings and conclusions in this article are those of the authors and do not necessarily
represent the views of the US Fish and Wildlife Service.
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