2008 SOUTHEASTERN NATURALIST 7(2):301–310
The Effect of Road Crossings on Fish Movements in Small
Etowah Basin Streams
Paul D. Benton1,2, William E. Ensign1,*, and Byron J. Freeman3
Abstract - Increased road construction associated with urbanization may result in
fragmentation and loss of fish populations in streams. In this study, we documented
frequency of movement of fishes through three separate types of road-crossings
(clear-span bridges, box culverts, and tube culverts) in six small streams using
mark-recapture sampling. Upstream movement between areas separated by either
box or tube culverts was lower than upstream movement between similar areas not
separated by a road crossing. Downstream movement between areas separated by
box culverts was also lower than downstream movement between areas without
obstructions. Upstream and downstream movement between areas separated by
clear-span bridges was generally similar to patterns of movement between areas not
separated by a road crossing. Our results indicate that culverts may limit, to some
degree, movements of fishes in small streams.
Introduction
The southeastern United States is the center of freshwater fish diversity
in North America (Warren and Burr 1994, Warren et al. 2000) and fish diversity
in the streams and rivers of Georgia refl ects this pattern. The upper
Etowah River basin, located north of the Atlanta metropolitan area, is a major
contributor to this diversity with over 76 extant species of native fishes
(Burkhead et al. 1997), 4 that are endemic to the basin and 7 that have either
state or federal protected status. Urbanization in the Atlanta metropolitan
area poses a threat to this unique fish assemblage (Walters et al. 2003). Increased
impervious surface and resulting changes to hydrology and water
quality are the most obvious threats to fish diversity in urbanizing areas
(Paul and Meyer 2001, Roy et al. 2005, Schueler 1994, Walsh et al. 2005,
Wang 2001). Urbanization also results in increased density of roads and an
associated increase in the number of streams crossed by roads (Wheeler et
al. 2005).
Road crossings can affect fish movement by acting as physical barriers
or by altering fl ows, thereby limiting a fish’s ability to traverse a crossing
(Gibson et al. 2005, Warren and Pardew 1998). Increased fragmentation
of the stream network reduces the probability of individual movement
from one stream segment to another, potentially altering both population
and community structure of stream fishes (Winston et al. 1991). Stream
1Department of Biological and Physical Sciences, Kennesaw State University, Kennesaw,
GA 30144. 2Current address: Biology Department, Tennessee Tech University,
PO Box 5063, Cookeville, TN 38505.. 3Institute of Ecology, University of Georgia,
Athens, GA 30602. *Corresponding author - bensign@kennesaw.edu.
302 Southeastern Naturalist Vol.7, No. 2
reaches experimentally defaunated or reduced in abundance (or richness)
by droughts, fl oods, or anthropogenic stress show rapid recovery if source
populations have access to the affected reach (Adams and Warren 2005, Bayley
and Osborne 1993, Ensign et al. 1997, Lonzarich et al. 1998, Olmstead
and Cloutman 1974, Peterson and Bayley 1993, Sheldon and Meffe 1995).
Road crossings may prevent or significantly reduce the ability of fishes to
recolonize a reach from which they have been extirpated. Stream fish movements
are also infl uenced by habitat structure and availability of preferred
habitat for a given species (Albanese et al. 2004, Matheny and Rabeni 1995);
therefore, indirect effects on fish movements may also occur as a result of
localized geomorphologic changes in the stream channel upstream and
downstream of the crossing. In this study, we focused on road crossings as
physical barriers and attempted to determine if different types of road crossings
have differential effects on fish movements.
Methods
Six Blue Ridge ecoregion streams in the upper Etowah drainage basin
were sampled twice during the summer of 2003 (Table 1). Two streams
had clear-span crossings, two had box culverts, and two had tube culverts.
Clear-span crossings consisted of a solid road platform suspended
above the stream, usually between concrete pilings set in the channel or
on the stream banks. Box culverts consisted of one or more four-sided,
open-ended concrete boxes set into the stream channel, while tube culverts
consisted of one or more round, galvanized pipes set in the stream
channel. In each of the six streams, sampled reaches were divided into six
cells based on pool and riffle sequences, with three cells upstream and
three cells downstream of the road crossing. Only five cells were sampled
in Noonday Creek since the pool in the most upstream cell was atypically
long (>200 m). During collections, individual cells were isolated
before sampling by placing a block net at the upstream and downstream
end of each cell. On each of the two sampling dates, two separate
Table 1. Summary of site characteristics and time interval between mark and recapture for each
of the sampled streams.
Average Days
sample-cell between
Watershed Average length (m) mark and
Site Crossing type area (km2) width (m) (± std. dev.) recapture
Noonday Creek Clear span 10.1 5.7 22.4 (± 12.1) 33
Clark Creek Clear span 12.0 6.1 24.5 (± 7.0) 34
Sweat Mountain Creek Box culvert 8.2 5.1 32.8 (± 18.2) 29
Scott’s Mill Creek Box culvert 12.8 7.2 37.0 (± 8.6) 31
Possum Creek Tube culvert 14.9 4.5 9.9 (± 11.3) 33
Hickory Log Creek Tube culvert 11.1 4.7 25.3 (± 9.7) 31
2008 P.D. Benton, W.E. Ensign, and B.J. Freeman 303
electroshocking passes were made through each of the cells, and all fishes
collected transferred to holding buckets for processing. After capture,
fishes were anaesthetized lightly with tricaine methanosulfonate, identified
to species, counted, and measured for standard length. On the first
sampling date, each fish was marked with a fluorescent elastomer tag. A
unique combination of tag color and tag position was used to indicate the
capture cell for each fish. To check for tag loss, all fishes were given a
secondary mark by clipping a small piece of the upper portion of the caudal
fin (for sections above the road crossing) or the lower portion of the
caudal fin (for sections below the road crossing). After processing, fish
were placed in instream holding nets, allowed to recover completely, and
returned to the units in which they were captured. At the end of the recovery
period, any mortalities found in the holding net were deleted from
the data sets. All sections were sampled one month later (average time
between between samples was 31.8 days ± 1.8 days; Table 1) in the same
manner. Again, fish were identified to species, measured, and examined
for the presence of marks. For marked fish, the position and color of the
mark was recorded along with the capture cell.
The effect of road crossings on fish movement was determined by
comparing movement between adjacent cells that were not separated
by a road crossing (unobstructed adjacent cells) to movement between
adjacent cells that were separated by one of the three types of road crossings
(obstructed adjacent cells). Fishes that moved more than one cell
upstream or one cell downstream of their marking cell were not included
in the analysis. Given this, a fish’s location during recapture sampling
relative to its cell of marking could be treated as a binomial random variable.
The two possible outcomes were that the fish was found either in its
original cell or the cell immediately adjacent to its original cell. Expected
movement values were based on unobstructed adjacent cell data and compared
to observed values drawn from obstructed adjacent cells separated
by one of the three types of road crossings. Significant differences (p <
0.05) between expected and observed values were determined using a binomial
goodness-of-fit test. Since the relative frequency of upstream and
downstream movement varies seasonally for many fish species (Albanese
et al. 2004, Hall 1972, Matheny and Rabeni 1995), separate analyses were
conducted for both adjacent cell upstream movements and adjacent cell
downstream movements.
Results
Overall, 1264 fish representing 22 species were marked across the
six streams in the first sampling period (Table 2). Four species captured
during the marking period were not marked. Etheostoma scotti Bauer,
Etnier and Burkhead (Cherokee Darter) is listed as a federally threatened
304 Southeastern Naturalist Vol.7, No. 2
species and was not marked to avoid potential mortality. Three species
in the genus Notropis—N. chrosomus (Jordan) (Rainbow Shiner), N.
lutipinnis (Jordan and Brayton) (Yellowfin Shiner), and N. xaenocephalus
(Jordan) (Coosa Shiner)—suffered appreciable mortality as a result
of capture and marking during the marking episodes at the first two
streams sampled and were also eliminated from consideration. In the
second sampling period, 418 marked fish representing 14 species were
recaptured, a 33.1% recapture rate (Table 2). Of the 418 fish recaptured,
284 were recaptured in the same cell and 134 moved upstream or downstream
at least one cell (Table 2). Of the 14 species recaptured, only one,
Semotilus atromaculatus (Creek Chub) failed to move either upstream
or downstream. Of the 134 fish that moved, 83 moved upstream, 51
moved downstream, and 26 moved across a road crossing. Of the latter
26 fish, 23 fish from five different species moved through clear-span
crossings, while only 2 fish moved through a box culvert (1 Micropterus
coosae [Redeye Bass] and 1 Cottus carolinae [Banded Sculpin]), and
Table 2. Summary of number of fish marked and recaptured across all streams and the presence
or absence of movements through a road crossing by that species. For the number recaptured,
separate totals are given for fish recaptured in the cell of marking (same cell) or a cell different
from that of marking (different cell). For crossing movements, the type of crossing is indicated
in parentheses where CS = clear-span, BO = box culvert, and TU = tube culvert.
Crossing
# recaptured movements
Same Different % (type of
Species # marked cell cell recaptured crossing)
Campostoma oligolepis Hubbs and Greene 248 41 51 37.1 Yes (CS)
Cottus carolinae (Gill) 210 47 18 31.0 Yes (BO)
Lepomis macrochirus Rafinesque 205 50 6 27.3 No
Lepomis auritus (Linnaeus) 168 69 16 50.6 Yes (CS)
Lepomis cyanellus Rafinesque 90 35 2 41.1 Yes (CS)
Hypentelium etowanum (Jordan) 90 18 23 45.6 Yes (CS)
Semotilus atromaculatus (Mitchill) 54 7 0 13.0 No
Micropterus coosae Hubbs and Bailey 41 5 3 19.5 Yes (BO)
Fundulus stellifer (Jordan) 39 1 5 15.4 Yes (TU)
Percina nigrofasciata (Agassiz) 30 3 1 13.3 No
Nocomis leptocephalus (Girard) 18 7 3 55.6 No
Percina kathae Thompson 16 1 2 18.8 No
Pomoxis nigromaculatus (Lesueur) 12 0 0 0.0 -
Cyprinella trichroistia (Jordan and Gilbert) 9 0 0 0.0 -
Cyprinella callistia (Jordan) 9 0 1 11.1 No
Micropterus salmoides (Lacepède) 8 0 3 37.5 Yes (CS)
Noturus leptacanthus Jordan 6 0 0 0.0 -
Etheostoma stigmaeum (Jordan) 3 0 0 0.0 -
Moxostoma duquesni (Lesueur) 3 0 0 0.0 -
Lepomis gulosus (Cuvier) 2 0 0 0.0 -
Perca fl avescens (Mitchill) 2 0 0 0.0 -
Ameiurus natalis (Lesueur) 1 0 0 0.0 -
All species 1264 284 134 33.1
2008 P.D. Benton, W.E. Ensign, and B.J. Freeman 305
1 fish (Fundulus stellifer [Southern Studfish]) moved through a tube culvert
(Table 2). In the recapture sampling, a single fish was found with a
fin clip and no discernible elastomer mark. All fish with elastomer marks
had observable fin clips.
In adjacent cells where there was no road crossing separating the two
cells, 24.9% of recaptured fish had moved from the downstream cell to the
adjacent upstream cell, while 13.6% of recaptured fish had moved from the
upstream cell to the adjacent downstream cell (Table 3). There was no significant
difference in frequency of movement between unobstructed cells
and cells separated by a clear-span crossing, where 22.9% of recaptured
fish had moved from the downstream cell to the upstream cell while 15.8%
of recaptured fish had moved from the upstream cell to the downstream
cell (Table 3). Both box culverts and tube culverts significantly reduced the
frequency of upstream movement (6.9%, p = 0.021 and 0.0%, p = 0.046,
respectively; Table 3) and box culverts also reduced downstream movement
(0.0%, p = 0.026; Table 3). Although no downstream movements
were observed through tube culverts, sample sizes were too small to allow
significance testing.
Discussion
Our results indicate that road crossings often serve as potential barriers
to fish movement and the type of crossing determines, at least in part,
the magnitude of reduction in movement observed. Box and tube culverts
restricted short-term movements by fish between adjacent cells separated
by the culverts in four small streams in the Etowah Basin. In experimental
stream trials, Schaefer et al. (2003) found that movement through simulated
culverts varied by culvert type, with highest passage rates through squarewide
culverts (similar to the box culverts in this study), lowest rates through
Table 3. Summary of the number of marked fish found in the cell in which they were marked or
the adjacent upstream or downstream cell. Unobstructed adjacent cells were not separated from
the marking cell by a road crossing, while clear span, box culvert, and tube culvert indicate the
type of road crossing separating the adjacent cell from the marking cell. The binomial p-value
indicates whether the pattern of movement observed in the road crossing cells differed from
that seen in unobstructed cells. For downstream movement through tube culverts, sample size
was too small to allow significance testing.
Unobstructed Clear span Box culvert Tube culvert
Upstream
Same cell 175 27 27 11
Adjacent cell 58 8 2 0
Binomial p-value 0.481 0.021 0.043
Downstream
Same cell 197 32 25 8
Adjacent cell 31 6 0 0
Binomial p-value 0.865 0.026 No test
306 Southeastern Naturalist Vol.7, No. 2
round-smooth culverts, and intermediate rates through round-ribbed culverts
(similar to the tube culverts in this study). In all instances, movement rates
were lower between patches separated by simulated culverts than between
patches not separated by barriers. Similarly, Warren and Pardew (1998)
found culvert crossings limited movement to a greater degree than either
box or ford crossings.
Warren and Pardew (1998) found that movement across their box
crossings was higher than movement between two “natural reaches,” a
result that conflicts with findings in our study. Although the design in
their study is not entirely consistent with ours, movement between their
“natural reaches” is in many ways analogous to movement across our
clear-span crossing. The greater movement probabilities they observed
across their box crossings is most likely related to differences in water
depth and water velocity of box culverts in the two studies. The box culverts
in the Warren and Pardew (1998) study had low water velocities and
depths ranging from 30 cm to 80 cm. Although we did not quantify either
depth or velocity in either of the box culverts we sampled, in both Sweat
Mountain Creek and Scott’s Mill Creek, depths did not appear to exceed
5 cm at the time of sampling and much of the flow through any of the culvert
bays at either stream was less than 2 cm in depth. Water velocity in
the culverts was moderately fast (greater than 20 cm/s), and laminar sheet
flow was apparent at many points in our box culverts. Box culvert depths
similar to those described in Warren and Pardew (1998) would have been
present only under conditions of elevated flow in our streams. Similarly,
flow through the tube culverts in our study was also moderately fast, and
depths were similar to those observed in the box culverts. While depth
and velocity in the tube and box culverts was noticeably shallower and
faster than that in the adjacent upstream and downstream reaches, depth
and velocity in the clear-span crossings was similar to that in the adjacent
reaches. The difference between our results and those of Warren
and Pardew (1998) highlights the importance of not only assessing the
type of culvert, but also the physical characteristics of the culvert and
stream conditions.
The frequency of movement between adjacent cells we observed in
our streams is higher than that observed in other studies of fish movements
in natural reaches. In our study, one of every three fish recaptured
was found in a cell other than the one in which it was marked. In contrast,
Smithson and Johnston (1999) found only 12% of marked Creek Chub,
12% of marked Lepomis cyanellus (Green Sunfish), and 14% of marked
L. megalotis (Rafinesque) (Longear Sunfish) outside of the units in
which they were marked. A fourth species, Fundulus olivaceous (Storer)
(Blackspotted Topminnow) exhibited movement rates similar to those
we observed, with one of every three individuals of this species being
recaptured outside its cell of marking. In a study of movement by three
2008 P.D. Benton, W.E. Ensign, and B.J. Freeman 307
species of darters over a recapture period similar to ours, Roberts and
Angermeier (2007) found between 3% and 7% of recaptured fish outside
their original marking unit. In a much larger stream, Freeman (1995) recaptured
88% of Percina nigrofasciata (Blackbanded Darter) and 93% of
juvenile L. auritus (Redbreast Sunfish) within 33 m of their original point
of capture. Similarly, Matheny and Rabeni (1995) found that Hypentelium
nigricans (Lesueur) (Northern Hog Sucker) tend to remain within a single
pool-riffle sequence over the course of a year, but frequently moved
back and forth from pool to riffle areas during the course of a 24-hour
period. Other studies have suggested that most small stream fishes have
relatively limited home ranges, often analogous in size to a single poolriffle
sequence (Gerking 1959, Hill and Grossman 1987). Given the
diversity of approaches, species, and stream types used in other studies,
direct comparison of our movement rates is speculative at best. However,
Albanese et al. (2004) showed that movement of fishes through areas of
unsuitable habitat was higher than movement through areas of suitable
habitat. Improperly designed culverts can result in significant changes to
streambed morphology directly upstream and downstream of the crossing.
This can include scouring and channel erosion on the downstream side
of the culvert and sediment deposition and reduction in average water
depth on the upstream side of the culvert (Bates et al. 2003). Although
we did not quantify stream channel features, visual inspection of areas
upstream and downstream of the road crossings indicated that these types
of habitat alterations were present in both of the tube culvert streams and
one of the box culvert streams (Sweat Mountain Creek). The higher rates
of movement we observed may have been a response to this alteration
in habitat structure.
Methodologically, summer sampling may have resulted in an underestimation
of adjacent cell movement frequencies in our stream. Evidence indicates
that many temperate stream fishes show limited movement between erosional-
depositional units during the warmer summer months (Roberts and
Angermeier 2007) and increased movement activity during fall and spring
(Hall 1972, Matheny and Rabeni 1995). Longer, directed movements by
stream fishes are often associated with seasonal activities such as spawning,
and even non-migratory forms may show increased local movements during
periods of high fl ow. Hall (1972) found that over 70% of upstream fish movements
through weirs in a North Carolina Piedmont stream occurred during
spring spawning migrations. This seasonal bias may be balanced at least in
part by increased movements associated with high-fl ow events. Albanese et
al. (2004) found increased upstream movement of four cyprinid species and
a catastomid species and increased downstream movement of three cyprinid
species in response to elevated fl ows. During the period between mark and
recapture in our study, there was at least one rain event that resulted in markedly
elevated fl ows.
308 Southeastern Naturalist Vol.7, No. 2
In summary, we feel confident that both box and tube culverts decreased
fish passage between upstream and downstream reaches in our
streams. There is also some evidence to suggest that high between-cell
movement rates may have resulted from habitat alterations associated
with the road crossings. Future research should focus on the relationship
between culvert structure (i.e., depth and velocity characteristics) and fish
passage to ensure appropriate structures are used to protect the diversity
of our running waters.
Acknowledgments
This study was completed as part of an undergraduate research project by
P. Benton under the supervision of W. Ensign. Funding was provided by a grant
from the Georgia Department of Natural Resources and the US Fish and Wildlife
Service for the development of a Habitat Conservation Plan for the Upper Etowah
River Basin. Additional funding was provided by a Mentor-Protégé grant from the
College of Science and Mathematics at Kennesaw State University. Field assistance
was provided by Rani Reece, Chad Landress, Ryan Leitz, and Tim Shirley.
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