Transactions of the American Fisheries Society 142:1495–1507, 2013
C American Fisheries Society 2013
ISSN: 0002-8487 print / 1548-8659 online
DOI: 10.1080/00028487.2013.815662
ARTICLE
Assessing Effects of Stocked Trout on Nongame Fish
Assemblages in Southern Appalachian Mountain Streams
Daniel M. Weaver1
North Carolina Cooperative Fish and Wildlife Research Unit, Department of Applied Ecology,
North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695, USA
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Thomas J. Kwak*
U.S. Geological Survey, North Carolina Cooperative Fish and Wildlife Research Unit,
Department of Applied Ecology, North Carolina State University, Campus Box 7617, Raleigh,
North Carolina 27695, USA
Abstract
Fisheries managers are faced with the challenge of balancing the management of recreational fisheries with that of
conserving native species and preserving ecological integrity. The negative effects that nonnative trout species exert
on native trout are well documented and include alteration of competitive interactions, habitat use, and production.
However, the effects that nonnative trout may exert on nongame fish assemblages are poorly understood. Our
objectives were to quantify the effects of trout stocking on native nongame fish assemblages intensively on one
newly stocked river, the North Toe River, North Carolina, and extensively on other southern Appalachian Mountain
streams that are annually stocked with trout. In the intensive study, we adopted a before–after, control–impact (BACI)
experimental design to detect short-term effects on the nongame fish assemblage and found no significant differences
in fish density, species richness, species diversity, or fish microhabitat use associated with trout stocking. We observed
differences in fish microhabitat use between years, however, which suggests there is a response to environmental
changes, such as the flow regime, which influence available habitat. In the extensive study, we sampled paired stocked
and unstocked stream reaches to detect long-term effects from trout stocking; however, we detected no differences in
nongame fish density, species richness, species diversity, or population size structure between paired sites. Our results
revealed high inherent system variation caused by natural and anthropogenic factors that appear to overwhelm any
acute or chronic effect of stocked trout. Furthermore, hatchery-reared trout may be poor competitors in a natural
setting and exert a minimal or undetectable impact on native fish assemblages in these streams. These findings
provide quantitative results necessary to assist agencies in strategic planning and decision making associated with
trout fisheries, stream management, and conservation of native fishes.
Stocking surface waters with hatchery-reared trout species
(family Salmonidae) to support local recreational fisheries is
common practice among state and federal agencies in the United
States. Trout fishing is among the most popular freshwater fishing pursuits in the United States behind that of black bass and
closely tied with panfish and catfish (USFWS and USCB 2006).
To meet the demand for recreational angling, supplemental fish
stocking is common; 70 facilities, 48 U.S. states, and 8 Canadian provinces stocked 276 million sport fish during 1995–1996
(Heidinger 1999). In 2004, U.S. federal hatcheries produced
and stocked 9.4 million trout in 16 states, and 6.8 million U.S.
anglers spent US$4.8 billion on trout fishing in 2006 (USFWS
2006). In North Carolina during 2008, approximately 92,000
anglers fished for trout and spent $146 million (NCWRC 2009).
*Corresponding author: [email protected]
1
Present address: Maine Cooperative Fish and Wildlife Research Unit, Department of Wildlife Ecology, University of Maine, 5755 Nutting
Hall, Orono, Maine 04469, USA.
Received March 19, 2013; accepted June 11, 2013
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WEAVER AND KWAK
Trout fishing is economically important at national and local
scales and provides funding for conservation efforts through
license fees.
Fisheries managers in state and federal agencies must consider constituent desires in managing recreational fishing, and
one such consideration is whether to manage a self-sustaining
fishery or one supported by stocking. Because many states face
high angler use demands, stocking sport fishes is a common
management option. However, nonnative fish stocking may
force unnatural sympatry between introduced and native fish
species (Fausch 1988). According to Lassuy (1995), 83% of
the fish introductions affecting threatened or endangered fish
species in the United States were intentional. Eighty-eight percent of those involved sport fishing in some aspect. Overall, nonnative species are considered the second-most prevalent threat
to imperiled fishes in the United States, preceded only by habitat destruction as a causal factor (Wilcove et al. 1998; Jelks
et al. 2008). Thus, fisheries managers must balance constituent
desires while also conserving native species and protecting
biodiversity.
Introductions of Brown Trout Salmo trutta, Rainbow Trout
Oncorhynchus mykiss, and Brook Trout Salvelinus fontinalis
across the United States have exerted negative direct and indirect effects on native trout species. Similar diet compositions and
habitat use occur between allopatric native Brook Trout and introduced Brown Trout and Rainbow Trout (Nyman 1970; Fausch
and White 1981; Larson and Moore 1985), as well as observed
shifts in Brook Trout microhabitat use followed by weight loss
when in sympatry with Brown Trout (DeWald and Wilzbach
1992). Juvenile Cutthroat Trout O. clarkii had reduced survival
in the presence of nonnative Brook Trout (Peterson et al. 2004).
Over a 21-year period, introduced Brown Trout replaced native Brook Trout as measured in biomass and annual production
(Waters 1983, 1999). Such interactions may reduce the competitive abilities of native trout, further affecting their condition
and reproduction necessary for maintaining viable populations,
and may decrease angling quality. Understanding the dynamics
of stocked and native trout interactions may provide insight into
analogous interactions with nongame fishes.
The effects of nonnative stocked trout on native nongame
fishes are largely unknown, and few published studies have
evaluated their impacts. Introduced trout can exert negative
density-dependent effects on nongame fish, and negative effects are likely to increase with increasing trout density, or with
the introduction of multiple nonnative predators (Bryan et al.
2002; Robinson et al. 2003). Large nonnative trout, particularly
Brown Trout, prey on nongame species during spring, summer,
and fall seasons, and nongame fish abundance may decrease
in stocked reaches relative to unstocked reaches (Garman and
Nielsen 1982). Nonnative trout may also compete with nongame
fish, alter their behavior, and decrease their growth rates in sympatry (Freeman and Grossman 1992; Ruetz et al. 2003; Zimmerman and Vondracek 2006), as well as disrupt the structure of
local native species assemblage (Walsh and Winkelman 2004).
Results of these previous studies conducted in regions with and
without the presence of native trout support a general conclusion that nonnative trout may exert lethal and nonlethal effects
on native fish assemblages.
While many of the aforementioned studies provide insight to
predict effects on a single or few fish species, they may not be
extrapolated to infer community-level effects, such as the densities and resources used by fish assemblages. Thus, our objectives
were to (1) determine whether population density, microhabitat use, and assemblage composition of native nongame fishes
were altered by trout stocking in one river and (2) assess potential differences in total catch, assemblage composition, and
population size structure of nongame fishes in multiple stocked
streams, each paired with a reference stream. Our intensive
study (objective 1) was designed to determine short-term effects on nongame fish assemblage structure, as the study river
was to be newly stocked with trout. Our extensive study (objective 2) was designed to reveal long-term effects from trout
stocking, as these streams have been stocked annually for many
years.
STUDY AREA
We conducted this research in the coldwater Appalachian
Mountain streams and rivers of North Carolina. Our intensive
research took place on the North Toe River in the town of Spruce
Pine (Figure 1). The North Toe River is a high-gradient tributary
to the French Broad River that includes the South Toe River
and Nolichucky River, ultimately flowing west to the Tennessee
River. The North Toe watershed spans 474 km2, and land cover
is primarily forest and wetland (87%) and pasture (11%), with
urban area, cultivated cropland, and surface waters making up
less than 1% each (NCDENR 2003, 2011). An 18.2-km segment
of the North Toe River from Grassy Creek to the South Toe River
that encompasses our study area was listed as impaired by the
North Carolina Division of Water Quality based upon excessive
turbidity and habitat degradation, and was assigned a “fair”
bioclassification (NCDENR 2003). This area receives runoff
and effluent from the town of Spruce Pine and several other
point-source discharges, including municipal, construction, and
mining sources. The native fish assemblage of the river is typical
of the area and is composed of Smallmouth Bass Micropterus
dolomieu and sunfishes Lepomis spp. as sport fishes that coexist
with multiple species and families of coolwater and warmwater
nongame fishes.
Our extensive sampling was conducted at 14 sites located
in the southern Appalachian Mountains of western North Carolina (Figure 1). Historically, much of western North Carolina
supported native Brook Trout populations in stream habitats;
however, many of these have been greatly reduced or extirpated, largely due to historical and current land use practices
(MacCrimmon and Campbell 1969; Hudy et al. 2008). Intensive fish stocking programs in the United States began in the
late 1800s, and nonnative Rainbow Trout and Brown Trout were
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EFFECTS OF STOCKED TROUT ON NONGAME FISH
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FIGURE 1. Intensive sampling sites on the North Toe River (inset) and extensive sampling sites located throughout western North Carolina. For intensive
sampling, the treatment reach, in the town of Spruce Pine, received trout stocking and was located upstream from the two reference reaches that were not stocked.
For extensive sampling, we sampled delayed-harvest (DH), stocked, trout waters (black circles) paired with reference reaches (R) that did not receive trout stocking
(gray circles).
introduced to the eastern United States at that time. Stocking of
native and nonnative trout species has occurred over the past
100 years (Nielsen 1999).
METHODS
Trout stocking and angling.—We studied southern Appalachian trout streams managed by the North Carolina Wildlife
Resources Commission (NCWRC). Trout stocking in a 3.7-km
section of the North Toe River followed NCWRC procedures
for a delayed-harvest trout fishery. Trout stockings took place in
October and November 2008, when 3,800 total catchable trout
were stocked each month using Brook Trout (40%), Rainbow
Trout (40%), and Brown Trout (20%). Following the October
stocking, trout fishing was regulated under catch-and-release
angling only. Supplemental stockings then occurred in March,
April, and May 2009 with 3,800 trout of the same species and
proportions each month. Harvest was permitted after the first
weekend in June at seven trout per day with no size limit. Trout
are harvested to near depletion within 2 weeks after the season is
opened (Besler et al. 2005). The other delayed-harvest streams
that we extensively sampled followed a similar monthly stocking schedule (i.e., October–November, March–May) as used for
the North Toe River, and each stream received varying trout
densities determined by the width or size of each stream.
Intensive study design.—Three 1-km study reaches (mean
width, 24.9 m) were delineated on the North Toe River, one
reach located within the designated trout stocking area (treatment) and two reaches that did not receive trout stocking located
approximately 5.5 km downstream (reference 1 and reference
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WEAVER AND KWAK
2; Figure 1). The two reference reaches had not been previously
stocked with trout, nor were they stocked for the duration of
our study. We selected reference reaches that we considered to
be outside the potential spatial scale of impact from our treatment reach (i.e., the reference fish assemblages would not be
affected by trout stocking in the treatment reach), but limited the
longitudinal distance between reference and treatment reaches
to minimize ecological variation known to occur longitudinally
in river systems (Vannote et al. 1980). Sites were selected for
similarity in river discharge, width, geomorphology, and physical features, but were not identical, owing to the heterogeneous lotic environment. We included two reference reaches for
stronger inference of results; the primary intent of impact assessment design is to determine whether reference and treatment
reaches change in the same way before and after the treatment,
which does not require identical sampling sites (Downes et al.
2002).
We used an experimental paired multiple before–after,
control–impact (MBACI) design (Stewart-Oaten et al. 1986;
Underwood 1994; Downes et al. 2002) to assess the changes in
nongame fish assemblage structure on the North Toe River associated with trout stocking. The before–after, control–impact
(BACI) approach has been applied in the past to examine effects
of habitat rehabilitation on stream trout populations (Quinn and
Kwak 2000; Solazzi et al. 2000) and to monitor adverse chemical or biological impacts (Likens et al. 1970). Multiple stocking
events (October 2008–May 2009) allowed examination of acute
and chronic changes in the fish assemblage.
To quantify these changes, we sampled the fish assemblage
before and after the trout stocking events. We sampled three river
reaches in succession (within 1 week) monthly between May
and September during 2008 and 2009 for a total of 10 sampling
occasions. We assumed independence among sampling times as
fish assemblages are dynamic over long periods (i.e., months)
as seasonal variables, such as temperature and flow, determine
suitable and available habitat (Bain et al. 1988).
Fish density, habitat use, and availability.—We quantified
nongame fish density and habitat use in the sampling reaches
using snorkeling techniques and the strip-transect method (Ensign et al. 1995; Hewitt et al. 2009). We used twice the distance
that the farthest fish was observed from the transect midline at
each reach and sampling date as a transect width for quantifying
our sampling area and expressing fish count per area (fish/ha).
We applied snorkeling techniques to quantify fish density in this
river due to their versatility in collecting detailed information
on fish occurrence and microhabitat use without fish injury or
mortality, and because environmental conditions in the North
Toe River (see Table 1) were not suitable for electrofishing due
to its size and geomorphology (Dunham et al. 2009).
Sampling reaches were delineated to ensure that three primary macrohabitat types—pools, riffles, and runs—were represented in proportion to their occurrence in the reach (Kwak and
Peterson 2007). Ten transects, each 30 m long, were randomly
TABLE 1. Microhabitat variable statistics for the stocked treatment and two
unstocked reference reaches on the North Toe River, North Carolina.
Variable
Mean or mode
SE
Minimum–
maximum
Stocked (N = 163)
Stream width (m)
24.40
1.40 18.60–33.70
Depth (m)
0.33
0.02
0–1.36
Mean velocity (m/s)
0.20
0.02
0–1.06
Dominant substrate
Cobble
Distance to cover (m)
1.37
0.14
0–8.00
Dominant cover type
Boulder
Reference 1 (N = 178)
Stream width (m)
26.80
1.68 19.10–37.20
Depth (m)
0.29
0.02
0–1.22
Mean velocity (m/s)
0.17
0.02
0–1.04
Dominant substrate
Sand
Distance to cover (m)
2.70
0.25
0–16.00
Dominant cover type
Boulder
Reference 2 (N = 151)
Stream width (m)
23.60
2.31 10.30–38.20
Depth (m)
0.28
0.02
0–1.30
Mean velocity (m/s)
0.21
0.02
0–1.40
Dominant substrate
Bedrock
Distance to cover (m)
1.93
0.17
0–8.00
Dominant cover type Boulder, bedrock
chosen as representative subsamples from each site based proportionately on the available macrohabitat at the site and sampled for the study duration. Prior to snorkeling, a lead-line rope
was laid down parallel to the current, followed by a 15-min
waiting period to minimize fright bias (Bain et al. 1985). Then
one snorkeler proceeded upstream along the lead-line rope and
identified fish to species and estimated their focal depths in relation to total water column depth. The location of each fish or
group of fish along the transect was marked by placing a small
weight at the exact location.
Upon conclusion of each strip-transect survey, we measured
microhabitat characteristics for each individual or group fish
point location. Depth, mean column velocity, and focal velocity were measured with a top-set wading rod and a MarshMcBirney model 2000 digital flowmeter. Mean column velocity
was measured at 60% of the total depth from the surface (depths
≤1.0 m) or was calculated as the average of measurements at
20% and 80% of the total depth (depths >1.0 m). Focal velocity
was measured at the observed location and depth of each fish
or group of fish. Substrate composition was determined as the
greatest percent coverage of a substrate type according to a modified Wentworth particle-size classification at each fish location
(Bovee and Milhous 1978). Substrate was converted to a continuous variable for analysis as (1) silt–clay, (2) sand, (3) gravel,
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EFFECTS OF STOCKED TROUT ON NONGAME FISH
(4) cobble, (5) boulder, and (6) bedrock. Cover type and distance
to cover were recorded as the nearest physical object associated
with each fish location. Finally the distances to each bank from
each fish location were measured using a digital rangefinder. At
each reach we also measured water temperature (◦ C), dissolved
oxygen (mg/L), specific conductivity (µS/cm), pH, and turbidity (NTU) using a Hydrolab model MS5 multi-probe datasonde
and Surveyor 4a display unit.
We quantified habitat availability in cross-sectional instream
habitat surveys at each study reach once during base flow conditions (Simonson et al. 1994). At each reach, 15 evenly spaced
stream widths were measured to obtain a mean stream width
(MSW), and cross-sectional transects were spaced two MSW
apart, with the location of the first transect selected randomly.
At equally spaced points on each transect, we measured total
depth, mean column velocity, substrate composition, distance
to nearest cover, cover type, and distance to nearest bank.
Fishes were grouped into seven fish guilds based upon their
habitat use, behavior, and morphological traits. These fish guilds
included (1) Central Stoneroller Campostoma anomalum, (2)
River Chub Nocomis micropogon, (3) shiners: Notropis spp.,
Cyprinella spp., and Luxilus spp., (4) juvenile Cyprinidae, (5)
Catostomidae, (6) Centrarchidae, and (7) Percidae (darters). We
estimated nongame fish density (fish/ha), species richness, and
species diversity as Shannon’s diversity index (H ) (Shannon
and Weaver 1949; Kwak and Peterson 2007) for each reach and
date.
We performed a three-factor ANOVA to detect changes in the
nongame fish assemblage as a result of trout stocking (Downes
et al. 2002). The three main effects included reach (treatment
or reference), period (before or after trout stocking), and sampling time (May through September for 2008–2009). The mixed
model included two terms partitioning spatial variation and six
terms partitioning temporal variation. The primary terms testing the effects of trout stocking were (1) the interaction between
stocked and reference reaches for a chronic effect, and (2) the interaction between stocked and reference reaches and sampling
occasions within the periods before and after trout stocking
for an acute effect. An estimate of within-treatment variation
was derived from the two replicated reference reaches, comparisons between stocked and references reaches were derived from
their repeated measurements, and variation was partitioned into
model components (Downes et al. 2002). The general model for
this analysis was
y = µ + BA + T(BA) + CI + L(CI) + (BA × CI)
+ [CI × T(BA)] + [L(CI) × BA] + [L(CI) × T(BA)]
+ error,
where y is the measured response variable (i.e., fish density,
species richness, and species diversity), µ is the grand mean of
the measured response variable, BA is the mean effect of the
before or after period (i.e., 2008 before, 2009 after), T(BA) is the
1499
mean effect of sampling date (i.e., month) within the before or
after period, CI is the mean effect of the control (i.e., unstocked
downstream reference sites) or impact treatment (i.e., stocked
treatment site), L(CI) is the effect of location (i.e., site) within
the control or impact treatment, (BA × CI) is the effect of the
before or after period in the control or impact treatment (i.e., the
chronic BACI effect), CI × T(BA) is the effect of the control or
impact treatment on a sampling date within the before or after
period (i.e., the acute BACI effect), L(CI) × BA is the random
site effect in the control or impact treatment in the before or
after period, and L(CI) × T(BA) is the random site effect in
the control or impact treatment on a sampling date within the
before or after period. A majority of the response data (67%)
conformed to the normality assumption for ANOVA (Shapiro–
Wilk W test: P > 0.05; Zar 1996).
Nongame fish microhabitat use and availability were analyzed using a multivariate principal component analysis (PCA)
of depth, mean column velocity, substrate, distance to cover,
and distance to bank. Principal components were developed
based on the correlation matrix of the variables from the habitat
availability surveys for all three reaches. The PCA extracted linear descriptions of the combined univariate parameters that explained the maximum amount of variation within the data. Two
principal components were retained with eigenvalues greater
than 1.0 (Kwak and Peterson 2007). Component scores for fish
microhabitat use were then calculated using the coefficients
derived from the availability components. We calculated arithmetic means and 95% confidence intervals of PCA scores for
each fish guild, which represented microhabitat use by each
guild throughout the study period (2008–2009). We also sorted
mean component scores among fish guild, period (before or after trout stocking), and reach (treatment or reference). These
guild-specific means of habitat use were then plotted with SE to
indicate shifts in microhabitat use before and after trout stocking
between reaches.
Extensive fish sampling.—We sampled a total of seven rivers
and streams among four basins managed for delayed trout harvest (i.e., trout stocked through fall and winter with harvest delayed until late spring), each paired with a reference reach that
did not receive trout stocking. Paired sites were selected within
the same river basin, upstream, downstream, or adjacent to one
another to minimize potential confounding influences, and selection criteria included stream size, geomorphology, riparian
features, trout management designation, and stream access.
We used a one-pass CPUE as an index of fish density in
the paired reaches to detect biological trends in nongame fish
density (Simonson and Lyons 1995). These paired sites were
sampled once during July–August 2009. During this period,
the majority of trout in the stocked reaches were harvested to
near depletion (Besler et al. 2005). At each site, we sampled a
100-m reach with two Smith-Root pulsed-DC backpack electrofishers and two dip-netters. Sampling personnel moved in
an upstream direction and typically began and ended at a riffle
habitat. All fish were collected during sampling and identified
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WEAVER AND KWAK
to species and counted. A maximum of 50 randomly chosen
individuals per species at each site were weighed (±0.01 g),
measured (±1 mm TL), and returned to the stream. Ten stream
widths were measured at 10-m intervals along the 100-m reach
to obtain a MSW. Water temperature, dissolved oxygen, specific
conductivity, pH, and turbidity were measured at each site using
a Hydrolab model MS5 multi-probe datasonde and Surveyor 4a
display unit.
Among paired sites, we estimated nongame fish catch
(fish/ha), mean individual nongame fish weight, species richness, species diversity (H ), and trout TL, weight, and relative
weight (Wr ; Anderson and Neumann 1996) for each stocked
site and its paired reference site. We tested differences between
paired sites for normality using a Shapiro–Wilk test, then conducted paired t-tests (α = 0.05) if data did not differ from a
normal distribution and a Wilcoxon signed rank test if they
did. Of all estimated parameters, only trout TL differed from a
normal distribution.
RESULTS
Intensive Study: Short-Term, Before–After Comparisons
We observed a total of 3,489 nongame fish and 6 trout representing 6 families and 21 species in the North Toe River during snorkeling surveys from May 2008 to September 2009. All
nongame fish were included in our density, species richness, and
species diversity MBACI analyses, and nearly all of those fit into
our seven fish guilds (N = 3,448) for multivariate microhabitat analyses. We observed a total of three individual trout (two
Brown Trout and one Brook Trout) poststocking in the treatment
reach, three trout (two Brook Trout and one Brown Trout) in ref-
erence reach 2, and no trout in reference reach 1. The distance
from the midline of the farthest fish observed averaged 1.82 m
(SE, 0.137) in 2008 and 1.29 m (SE, 0.087) in 2009, which corresponded to an average total area snorkeled of 0.109 ha in 2008
and 0.078 ha in 2009. The three sampling reaches had similar
physical parameters, characteristic of a medium-sized river with
large average widths (23.6–26.8 m) and relatively shallow mean
depths (0.28–0.33 m; Table 1). Substrate composition included
all six categories from sand to boulder that varied in abundance
among reaches; the treatment reach was dominated by cobble
substrates, while sand and bedrock were prevalent at the two
reference reaches (Table 1).
Stream conditions varied seasonally and annually in study
reaches. The North Carolina Department of Environmental and
Natural Resources (NCDENR) designated our study area as experiencing severe to exceptional drought during most of 2008,
and drought conditions lessened and eventually lifted during
2009. During the study period, water temperature ranged from
0.6◦ C to 26.3◦ C, and higher temperatures were observed during 2008 compared with 2009, reflective of drought conditions
(Figure 2). We also observed increases in mean turbidity from
5.2 NTU in 2008 to 6.7 NTU in 2009, and decreases in specific conductivity from 157.9 µS/cm in 2008 to 74.5 µS/cm in
2009 before and after trout stocking. We did not observe any
differences in dissolved oxygen or pH between years.
Our analysis of fish density, species richness, and species diversity revealed meaningful trends, but the MBACI three-factor
ANOVA did not reveal any significant differences in those parameters as a result of trout stocking. The MBACI three-factor
ANOVA detected no significant relative change in fish density
(P = 0.943), species richness (P = 0.670), or diversity (P =
FIGURE 2. Monthly minimum, mean, and maximum hourly stream temperatures in the reach stocked with trout on the North Toe River, North Carolina, relative
to upper thermal tolerance limits of trout species (Eaton et al. 1995).
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EFFECTS OF STOCKED TROUT ON NONGAME FISH
0.935) as acute effects that would have corresponded to the initial trout stocking during October–November 2008 (Figure 3).
Similarly, we detected no significant relative changes in fish
density (P = 0.753), species richness (P = 0.512), or diversity
(P = 0.116) as chronic effects that would have corresponded
to all stocking events (October 2008–May 2009; Figure 3).
Overall, means of fish density, species richness, and diversity were higher in 2008 compared with 2009; however, this
trend was statistically significant only for species diversity (P =
0.030).
Nongame fish density generally increased from May to August then decreased in September during each year (Figure 3a).
Species richness and diversity among all sites showed no consistent trends (Figure 3b, c). Fish density, species richness, and
diversity all appeared more variable in 2009 after trout stocking
compared with corresponding 2008 data among all reaches, and
in a few transect samples in reference reaches we observed no
fish during periods associated with high flows.
The PCA results for fish microhabitat use revealed that specific habitats were occupied by each fish guild during the entire
study period (Figure 4). Component loadings indicated a habitat gradient from the riverbank to the thalweg for component 1
and from riffle to run–pool habitat for component 2 (Table 2).
Catostomids and percids primarily occupied riffle habitat in
the thalweg, characterized by relatively high velocity and deep
water. Central Stoneroller, River Chub, and shiners were primarily located in habitat intermediate between the bank and
thalweg and favored either riffle habitat (River Chub and Central Stoneroller) or marginal habitats between riffles and runs–
pools (shiners). Centrarchids and juvenile cyprinids primarily
occupied run–pool habitat near the bank. With the exception of
juvenile cyprinids, fish generally shifted their microhabitat use
(before and after stocking, from 2008 to 2009) toward deeper
water and run and pool microhabitats associated with higher
flows in 2009 (Figure 5). A general pattern in microhabitat use
between years was that fish in reference reach 1 shifted in a
similar direction as fish in the treatment reach, and fish in reference reach 2 shifted in other directions. We observed too few
trout during this study component (six individuals in total) to
TABLE 2. Principal component (PC) loadings according to habitat parameter
of two retained components for available habitat in the North Toe River, North
Carolina, among the stocked treatment and two unstocked reference reaches
(N = 492).
Variable
PC1
PC2
Distance to bank (m)
Depth (m)
Mean velocity (m/s)
Substrate
Distance to cover (m)
Eigenvalue
Variance explained (%)
0.62
0.40
0.54
0.37
0.16
1.56
31.00
0.38
−0.03
−0.32
−0.45
0.74
1.36
27.00
1501
quantify their habitat use distribution; thus, we did not include
them in the PCA.
Extensive Study: Long-Term, Paired-Site Effects
Analysis of paired sampling sites revealed no significant difference in nongame fish catch, population size structure, species
richness, or species diversity between stocked and unstocked
reaches (Table 3). Mean catch, species richness, and diversity
were higher in stocked sites than in unstocked reference sites,
whereas nongame fish weight was lower in stocked sites. We
sampled 34 individual trout among stocked sites and 47 trout at
reference sites. Sampled trout were smaller in mean size (TL and
weight) at reference sites than at stocked sites, but differences
were not statistically significant (P = 0.625 and P = 0.869,
respectively), and their mean Wr , an index of condition, was
equivalent between sites (P = 0.788).
DISCUSSION
We sought to quantify the effects of trout stocking on
nongame fish assemblages at two spatial and temporal scales.
Our intensive study on the North Toe River failed to detect
any acute or chronic short-term effects of newly initiated trout
stocking on nongame fish habitat use or assemblage structure;
however, we observed nongame fish responding to changing environmental conditions. Similarly, our extensive research among
paired stream reaches did not detect any long-term effects of
multiple years of trout stocking on fish assemblages. We suggest that the variability of the nongame fish assemblage in response to natural and anthropogenic effects over the course of
our study, as well as the poor competitive abilities and low poststocking occupancy of hatchery-reared trout, reflect the trends
we observed.
Increases in fish densities from May to August in the North
Toe River during each year were largely owing to recruitment
of juvenile cyprinids. Spawning, particularly for cyprinids, generally occurs during May and June (Etnier and Starnes 1993),
and the number of juveniles we observed was generally higher
during the late summer months (i.e., July and August). We also
observed slightly higher fish density estimates and species richness and diversity during 2008 than in 2009. These findings
concur with those of Grossman et al. (1998) who associated
drought conditions with higher total numbers of species as well
as an increase in the number of species dwelling in the water
column.
We observed fish guilds that occupied microhabitats similar
to those identified in other research. Central Stonerollers and
darters occupied moderate to swift riffle habitat (Aadland 1993;
Ashton and Layzer 2010), while sunfishes were typically found
in moderate to deep pools (Figure 4). Several fish guilds in
our research exhibited examples of niche segregation and niche
overlap in microhabitat use. Moyle and Baltz (1985) observed
juvenile fishes spatially segregated from adults, a finding similar
to what we demonstrated for juvenile and adult cyprinids. We
WEAVER AND KWAK
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1502
FIGURE 3. Fish density, species richness, and species diversity in the North Toe River, North Carolina, May–September 2008 before trout stocking and May–
September 2009 after trout stocking. F and P statistics are presented for three-factor MBACI ANOVA testing for an acute effect and chronic effects (see text for
explanation).
1503
EFFECTS OF STOCKED TROUT ON NONGAME FISH
TABLE 3. Comparisons of number of fish sampled, catch, fish weight, species richness, and species diversity of seven stocked stream sites and paired unstocked
reference sites (paired t-tests).
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Variable
Number of fish sampled
Catch (fish/ha)
Mean
SE
Minimum–maximum
Fish weight (g)
Mean
SE
Minimum–maximum
Species richness
Mean
SE
Minimum–maximum
Species diversity (H )
Mean
SE
Minimum–maximum
Stocked sites
Reference sites
t-value
P-value
2,100
1,307
3,582.1
1,267.7
748.7–10,183.9
2,689.7
977.6
1,026.3–8,378.9
−1.129
0.302
8.26
2.33
3.09–21.05
10.62
3.59
2.16–29.75
1.281
0.248
10.00
1.15
7–14
9.00
1.27
3–13
–0.764
0.474
1.66
0.13
1.15–2.20
1.50
0.22
0.42–2.09
−0.849
0.428
found substantial niche overlap between catostomids and percids, which is probably a function of their benthic adaptations
(i.e., large pectoral fins and streamlined body form). In addition
to indicating niche overlap, the size of ellipses for each guild in
Figure 4 may provide a general description of niche breadth or
habitat specificity.
Annual variability in weather conditions may partially explain the patterns we observed in the nongame fish assemblage
FIGURE 4. Fish assemblage microhabitat use during the entire study period
(May 2008–September 2009) in the North Toe River, North Carolina. Component loadings (Table 2) indicated a habitat gradient from the riverbank to the
thalweg for component 1 and from riffle to run–pool macrohabitats for component 2. Ellipses represent the mean (center point) and 95% confidence intervals
(boundaries) of component scores.
between years. Extreme to exceptional drought conditions existed in 2008, but were less prevalent in 2009 (NCDENR 2010).
Our estimates of fish density, species richness, and species diversity are much more variable in 2009 compared with 2008.
Variability in flow regime can determine available habitat and
ultimately influence fish assemblage structure (Vannote et al.
1980; Moyle and Baltz 1985; Poff and Allan 1995). Drought
conditions during 2008 might have favored stable fish assemblages, whereas the 2009 high flows and corresponding variable
habitat might have acted as a short-term disturbance to those
assemblages (Bain et al. 1988; Grossman et al. 1998). In addition, fish microhabitat use might have also been affected by
the drought, as available habitat changed (Grossman et al. 1998;
Figure 5).
Anthropogenic activities other than trout stocking may be
significant influences on fish assemblage structure in the North
Toe River. Sedimentation, riparian degradation, and both pointand nonpoint-source pollutants can alter and reduce primary
productivity, benthic fauna, feeding guilds, and overall species
richness and recruitment (Berkman and Rabeni 1987; Guidetti
et al. 2003; Meador and Goldstein 2003). In addition to cumulative effects of watershed land use changes, the North Toe River is
affected by urbanization from the town of Spruce Pine and industrialization from adjacent feldspar and mica mining operations,
even though these land uses occur in less than 1% of the watershed (NCDENR 2003). The “fair” bioclassification of this portion of the river indicates the disproportionate impacts of these
activities (NCDENR 2003). Natural and anthropogenic effects
vary spatially and temporally, which might have reduced our
ability to detect a nongame fish response to trout stocking (Chapman 1998). Relative to this high variability in environmental
WEAVER AND KWAK
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1504
FIGURE 5. Shifts in principal component scores describing microhabitat use of seven fish guilds in the North Toe River, North Carolina, before (open ellipses)
and after (solid ellipses) trout stocking among the treatment reach (black ellipses) and two reference reaches (gray ellipses). Ellipses represent the mean (center
point) and SE (boundaries) of the component score.
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EFFECTS OF STOCKED TROUT ON NONGAME FISH
conditions, any effect of trout stocking was undetectable in our
intensive and extensive studies.
Furthermore, water temperature might have also affected the
behavior and occupancy of stocked trout. Maximum temperatures on the North Toe River during 2009 ranged from 22.3◦ C to
23.5◦ C from June to August. These are slightly above the thermal maximum for Brook Trout (22.3◦ C) and are near those for
Brown Trout and Rainbow Trout (approximately 24◦ C; Eaton
et al. 1995). These temperatures are not optimal for sustaining trout, and during summer months, any remaining trout
(not harvested) would experience thermal stress, which can impair metabolic functions and competitive abilities with species
adapted to warmer temperatures (Elliott 1994; Taniguchi et al.
1998). Thus, the potential for direct and indirect thermal stress
in trout at higher water temperatures may lessen their impact on
nongame fishes.
The low numbers of trout we observed in our intensive
study may be due to multiple factors including sampling efficiency, poststocking behavior, river temperature, and interacting
sources of mortality (fishing and natural). Snorkeling efficiency
can be variably biased by season, stream habitat characteristics,
and target species (Thurow et al. 2006; Weaver 2010). Weaver
(2010) found snorkeling efficiencies in the North Toe River
averaged 11.2% to 18.1% between fall and summer seasons
among nongame fish present, and the probability of detecting
the occupancy of a fish guild by snorkeling averaged 58.4%.
Thurow et al. (2006) estimated similar snorkeling efficiency for
Bull Trout Salvelinus confluentus (12.5%). Our similar results
between intensive research on one newly stocked stream and extensive paired sampling among multiple stocked and unstocked
streams suggest low trout persistence in stocked waters after
stocking. The treatment effect that we sought to quantify, however, was the stocking of 20,000 trout in the treatment reach
that we intensively studied and similar stocking rates in other
streams, and we had no measurement or estimate of their survival or occupancy.
The poststocking behavior of the hatchery-reared trout may
further lessen their impact and retention in the area of stocking. Other investigators have observed catchable-size hatchery
trout occupying energetically unprofitable areas in rivers, displaying unnecessary hostile behaviors towards other fish, and
making long-distance movements, unlike wild resident trout
that are relatively sedentary (Helfrich and Kendall 1982; Bachman 1984; Mesa 1991; Berejikian et al. 1996; Bettinger and
Bettoli 2002). Stocked trout face other human sources of mortality and removal, including catch-and-release hooking mortality
and illegal harvest; Schisler and Bergersen (1996) found hooking mortality in Rainbow Trout to range from 3.9% to 32.1%
among varying bait types. While stocked trout appear to be
poor competitors in natural systems, they can readily establish
naturalized nonnative populations, as they have in southern Appalachian streams for over 100 years (King 1939). The numbers
of trout that we detected in reference reaches in both intensive
and extensive study components may reflect naturalized pop-
1505
ulations of stocked fish (as evidenced by juvenile individuals)
or migrating fish that were recently stocked. Stocking sterile
triploid trout, as is current practice in North Carolina streams,
may reduce the risk of establishing nonnative populations.
Our findings in an open-river setting complement and improve upon previous instream enclosure and field studies (e.g.,
Walsh and Winkelman 2004; Zimmerman and Vondracek 2006)
to discern the effects of stocked trout on nongame fish assemblages and may be most applicable to river conservation and
management. Our results confirm the utility of in situ experimental designs like the BACI design, as well as the importance of
multiple reference reaches and complementary extensive sampling, when attempting to detect an ecological or behavioral
response. These findings at multiple spatial and temporal scales
provide quantitative results available to assist state and federal
agencies as well as conservation groups in decision making
and planning for recreational trout fisheries and stream conservation and management. Sound management practices with a
biological basis are the most efficient means to develop sustainable sport fisheries, improve angling opportunities, and preserve
biodiversity in stream ecosystems.
ACKNOWLEDGMENTS
We thank Ben Wallace, Justin Dycus, Patrick Cooney, Scott
Favrot, Brad Garner, Christen Brown, Michael Fisk, Josh Raabe,
Stephen Poland, Kyle Rachels, and Jeremy Remmington for
their assistance in the field. Comments from Doug Besler, Rob
Dunn, Julie Harris, and Ken Pollock improved earlier versions
of this manuscript. This project was funded with Sport Fish
Restoration Funds through the NCWRC (Project F-68, Study
10). Jake Rash, Doug Besler, Mallory Martin, and Kent Nelson of the NCWRC administered funding and offered guidance
and insight in this project. The North Carolina Cooperative Fish
and Wildlife Research Unit is jointly supported by North Carolina State University, NCWRC, U.S. Geological Survey, U.S.
Fish and Wildlife Service, and the Wildlife Management Institute. Any use of trade, product, or firm names is for descriptive
purposes only and does not imply endorsement by the U.S.
Government.
REFERENCES
Aadland, L. P. 1993. Stream habitat types: their fish assemblages and relationship
to flow. North American Journal of Fisheries Management 13:790–806.
Anderson, R. O., and R. M. Neumann. 1996. Length, weight, and associated
structural indices. Pages 447–482 in B. R. Murphy and D. W. Willis, editors.
Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda,
Maryland.
Ashton, M. J., and J. B. Layzer. 2010. Summer microhabitat use by adult
and young-of-year Snail Darters (Percina tanasi) in two rivers. Ecology of
Freshwater Fish 19:609–617.
Bachman, R. A. 1984. Foraging behavior of free-ranging wild and hatchery
Brown Trout in a stream. Transactions of the American Fisheries Society
113:1–32.
Downloaded by [Thomas J. Kwak] at 19:52 22 September 2013
1506
WEAVER AND KWAK
Bain, M. B., J. T. Finn, and H. E. Booke. 1985. A quantitative method for
sampling riverine microhabitats by electrofishing. North American Journal
of Fisheries Management 5:489–493.
Bain, M. B., J. T. Finn, and H. E. Booke. 1988. Streamflow regulation and fish
community structure. Ecology 69:382–392.
Berejikian, B. A., S. B. Mathews, and T. P. Quinn. 1996. Effects of hatchery
and wild ancestry and rearing environments on the development of agonistic
behavior in steelhead trout (Oncorhynchus mykiss) fry. Canadian Journal of
Fisheries and Aquatic Sciences 53:2004–2014.
Berkman, H. E., and C. F. Rabeni. 1987. Effect of siltation on stream fish
communities. Environmental Biology of Fishes 18:285–294.
Besler, D. A., J. C. Borawa, and D. L. Yow. 2005. Creel survey of North Carolina’s hatchery supported trout fisheries. North Carolina Wildlife Resources
Commission, Division of Inland Fisheries, Federal Aid in Fish Restoration,
Project F-24–21, Raleigh.
Bettinger, J. M., and P. W. Bettoli. 2002. Fate, dispersal, and persistence of
recently stocked and resident Rainbow Trout in a Tennessee tailwater. North
American Journal of Fisheries Management 22:425–432.
Bovee, K. D., and R. Milhous. 1978. Hydraulic simulation in instream flow
studies: theory and techniques—instream flow information paper 5. U.S.
Fish and Wildlife Service Biological Report 78(33).
Bryan, S. D., A. T. Robinson, and M. G. Sweetser. 2002. Behavioral responses
of a small native fish to multiple introduced predators. Environmental Biology
of Fishes 63:49–56.
Chapman, M. G. 1998. Improving sampling designs for measuring restoration in
aquatic habitats. Journal of Aquatic Ecosystem Stress and Recovery 6:235–
251.
DeWald, L., and M. A. Wilzbach. 1992. Interactions between native Brook
Trout and hatchery Brown Trout: effects on habitat use, feeding, and growth.
Transactions of the American Fisheries Society 121:287–296.
Downes, B. J., L. A. Barmuta, P. G. Fairweather, D. P. Faith, M. J. Keough, P. S.
Lake, B. D. Mapstone, and G. P. Quinn. 2002. Monitoring ecological impacts:
concepts and practice in flowing waters. Cambridge University Press, New
York.
Dunham, J. B., A. E. Rosenberger, R. F. Thurow, C. A. Dolloff, and P. J. Howell.
2009. Coldwater fish in wadeable streams. Pages 119–138 in S. A. Bonar,
W. A. Hubert, and D. W. Willis, editors. Standard methods for sampling
North American freshwater fishes. American Fisheries Society, Bethesda,
Maryland.
Eaton, J. G., J. H. McCormick, B. E. Goodno, D. G. O’Brien, H. G. Stefany,
M. Hondzo, and R. M. Scheller. 1995. A field information-based system for
estimating fish temperature tolerances. Fisheries 20(4):10–18.
Elliott, J. M. 1994. Quantitative ecology and the Brown Trout. Oxford University
Press, New York.
Ensign, W. E., P. L. Angermeier, and C. A. Dolloff. 1995. Use of line transect
methods to estimate abundance of benthic stream fishes. Canadian Journal of
Fisheries and Aquatic Sciences 52:213–222.
Etnier, D. A., and W. C. Starnes. 1993. The fishes of Tennessee. University of
Tennessee Press, Knoxville.
Fausch, K. D. 1988. Tests of competition between native and introduced
salmonids in streams: what have we learned? Canadian Journal of Fisheries
and Aquatic Sciences 45:2238–2246.
Fausch, K. D., and R. J. White. 1981. Competition between Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta) for positions in a Michigan stream. Canadian Journal of Fisheries and Aquatic Sciences 38:1220–
1227.
Freeman, M. C., and G. D. Grossman. 1992. A field test for competitive interactions among foraging stream fishes. Copeia 1992:898–902.
Garman, G. C., and L. A. Nielsen. 1982. Piscivority by stocked Brown Trout
(Salmo trutta) and its impact on the nongame fish community of Bottom
Creek, Virginia. Canadian Journal of Fisheries and Aquatic Sciences 39:862–
869.
Grossman, G. D., R. E. Ratajczak Jr., M. Crawford, and M. C. Freeman. 1998.
Assemblage organization in stream fishes: effects of environmental variation
and interspecific interactions. Ecological Monographs 68:395–420.
Guidetti, P., A. Terlizzi, S. Fraschetti, and F. Boero. 2003. Changes in Mediterranean rocky-reef fish assemblages exposed to sewage pollution. Marine
Ecology Progress Series 253:269–278.
Heidinger, R. C. 1999. Stocking for sport fisheries enhancement. Pages 375–
401 in C. C. Kohler and W. A. Hubert, editors. Inland fisheries management in North America, 2nd edition. American Fisheries Society, Bethesda,
Maryland.
Helfrich, L. A., and W. T. Kendall. 1982. Movements of hatchery-reared Rainbow, Brook, and Brown trout stocked in a Virginia mountain stream. Progressive Fish-Culturist 44:3–7.
Hewitt, A. H., T. J. Kwak, W. G. Cope, and K. H. Pollock. 2009. Population
density and instream habitat suitability of the endangered Cape Fear Shiner.
Transactions of the American Fisheries Society 138:1439–1457.
Hudy, M., T. M. Thieling, N. Gillespie, and E. P. Smith. 2008. Distribution,
status, and land use characteristics of subwatersheds within the native range
of Brook Trout in the eastern United States. North American Journal of
Fisheries Management 28:1069–1085.
Jelks, H. L., S. J. Walsh, N. M. Burkhead, S. Contreras-Balderas, E. Dı́az-Pardo,
D. A. Hendrickson, J. Lyons, N. E. Mandrak, F. McCormick, J. S. Nelson,
S. P. Platania, B. A. Porter, C. B. Renaud, J. J. Schmitter-Soto, E. B. Taylor,
and M. L. Warren Jr. 2008. Conservation status of imperiled North American
freshwater and diadromous fishes. Fisheries 33:372–407.
King, W. 1939. A program for the management of fish resources in Great
Smoky Mountains National Park. Transactions of the American Fisheries
Society 68:86–95.
Kwak, T. J., and J. T. Peterson. 2007. Community indices, parameters, and
comparisons. Pages 677–763 in C. S. Guy and M. L. Brown, editors. Analysis
and interpretation of freshwater fisheries data. American Fisheries Society,
Bethesda, Maryland.
Larson, G. L., and S. E. Moore. 1985. Encroachment of exotic Rainbow Trout
into stream populations of native Brook Trout in the southern Appalachian
Mountains. Transactions of the American Fisheries Society 114:195–203.
Lassuy, D. R. 1995. Introduced species as a factor in extinction and endangerment of native fish species. Pages 391–396 in H. L. Schramm Jr. and R.
G. Piper, editors. Uses and effects of cultured fishes in aquatic ecosystems.
American Fisheries Society, Symposium 15, Bethesda, Maryland.
Likens, G. E., F. H. Bormann, N. M. Johnson, D. W. Fisher, and R. S. Pierce.
1970. Effects of forest cutting and herbicide treatment on nutrient budgets in
the Hubbard Brook watershed-ecosystem. Ecological Monographs 40:23–47.
MacCrimmon, H. R., and J. S. Campbell. 1969. World distribution of Brook
Trout, Salvelinus fontinalis. Journal of the Fisheries Research Board of
Canada 26:1699–1725.
Meador, M. R., and R. M. Goldstein. 2003. Assessing water quality at large
geographic scales: relations among land use, water physicochemistry, riparian condition, and fish community structure. Environmental Management
31:504–517.
Mesa, M. G. 1991. Variation in feeding, aggression, and position choice between
hatchery and wild Cutthroat Trout in an artificial stream. Transactions of the
American Fisheries Society 120:723–727.
Moyle, P. B., and D. M. Baltz. 1985. Microhabitat use by an assemblage of
California stream fishes: developing criteria for instream flow determinations.
Transactions of the American Fisheries Society 114:695–704.
NCDENR (North Carolina Department of Environment and Natural Resources).
2003. Basinwide assessment report: French Broad River basin. NCDENR,
Division of Water Quality, Environmental Sciences Section, Raleigh.
NCDENR (North Carolina Department of Environment and Natural Resources). 2010. Drought monitoring status of North Carolina. NCDENR, Division of Water Resources, Raleigh. Available: www.ncwater.org/
Drought Monitoring/dmhistory/. (March 2013).
NCDENR (North Carolina Department of Environment and Natural Resources).
2011. French Broad River basinwide water quality plan. NCDENR, Division
of Water Quality, Planning Section, Raleigh.
NCWRC (North Carolina Wildlife Resources Commission). 2009. The economic impact of mountain trout fishing in North Carolina. NCWRC, Federal
Aid in Fish Restoration, Project F-86, Raleigh.
Downloaded by [Thomas J. Kwak] at 19:52 22 September 2013
EFFECTS OF STOCKED TROUT ON NONGAME FISH
Nielsen, L. A. 1999. History of inland fisheries management in North America. Pages 3–30 in C. C. Kohler and W. A. Hubert, editors. Inland fisheries
management in North America, 2nd edition. American Fisheries Society,
Bethesda, Maryland.
Nyman, O. L. 1970. Ecological interaction of Brown Trout, Salmo trutta L., and
Brook Trout, Salvelinus fontinalis (Mitchill), in a stream. Canadian FieldNaturalist 84:343–350.
Peterson, D. P., K. D. Fausch, and G. C. White. 2004. Population ecology of
an invasion: effects of Brook Trout on native Cutthroat Trout. Ecological
Applications 14:754–772.
Poff, N. L., and J. D. Allan. 1995. Functional organization of stream fish assemblages in relation to hydrological variability. Ecology 76:606–627.
Quinn, J. W., and T. J. Kwak. 2000. Use of rehabilitated habitat by Brown Trout
and Rainbow Trout in an Ozark tailwater river. North American Journal of
Fisheries Management 20:737–751.
Robinson, A. T., S. D. Bryan, and M. G. Sweetser. 2003. Habitat use by nonnative Rainbow Trout, Oncorhynchus mykiss, and native Little Colorado
Spinedace, Lepidomeda vittata. Environmental Biology of Fishes 68:205–
214.
Ruetz, C. R., III, A. L. Hurford, and B. Vondracek. 2003. Interspecific interactions between Brown Trout and Slimy Sculpin in stream enclosures.
Transactions of the American Fisheries Society 132:611–618.
Schisler, G. J., and E. P. Bergersen. 1996. Postrelease hooking mortality of
Rainbow Trout caught on scented artificial baits. North American Journal of
Fisheries Management 16:570–578.
Shannon, C. E., and W. Weaver. 1949. The mathematical theory of communication. University of Illinois Press, Urbana.
Simonson, T. D., and J. Lyons. 1995. Comparison of catch per effort and removal
procedures for sampling stream fish assemblages. North American Journal of
Fisheries Management 15:419–427.
Simonson, T. D., J. Lyons, and P. D. Kanehl. 1994. Quantifying fish habitat
in streams: transect spacing, sample size, and a proposed framework. North
American Journal of Fisheries Management 14:607–615.
Solazzi, M. F., T. E. Nickelson, S. L. Johnson, and J. D. Rodgers. 2000. Effects
of increasing winter rearing habitat on abundance of salmonids in two coastal
Oregon streams. Canadian Journal of Fisheries and Aquatic Sciences 57:906–
914.
Stewart-Oaten, A., W. W. Murdoch, and K. R. Parker. 1986. Environmental
impact assessment: “pseudoreplication” in time? Ecology 67:929–940.
1507
Taniguchi, Y., F. J. Rahel, D. C. Novinger, and K. G. Gerow. 1998. Temperature
mediation of competitive interactions among three fish species that replace
each other along longitudinal stream gradients. Canadian Journal of Fisheries
and Aquatic Sciences 55:1894–1901.
Thurow, R. F., J. T. Peterson, and J. W. Guzevich. 2006. Utility and validation
of day and night snorkel counts for estimating Bull Trout abundance in firstto third-order streams. North American Journal of Fisheries Management
26:217–232.
Underwood, A. J. 1994. On beyond BACI: sampling designs that might reliably
detect environmental disturbances. Ecological Applications 4:3–15.
USFWS (U.S. Fish and Wildlife Service). 2006. Economic effects of Rainbow
Trout production by the national fish hatchery system. USFWS, Atlanta,
Georgia.
USFWS (U.S. Fish and Wildlife Service), and USCB (U.S. Census Bureau).
2006. 2006 national survey of fishing, hunting, and wildlife-associated recreation. USFWS and USCB, Washington, D.C.
Vannote, R. L., G. W. Minshall, K. W. Cummins, J. R. Sedell, and C. E. Cushing. 1980. The river continuum concept. Canadian Journal of Fisheries and
Aquatic Sciences 37:130–137.
Walsh, M. G., and D. L. Winkelman. 2004. Fish assemblage structure in an
Oklahoma Ozark stream before and after Rainbow Trout introduction. Pages
417–430 in M. J. Nickum, P. M. Mazik, J. G. Nickum, and D. D. MacKinlay,
editors. Propagated fish in resource management. American Fisheries Society,
Symposium 44, Bethesda, Maryland.
Waters, T. F. 1983. Replacement of Brook Trout by Brown Trout over 15 years in
a Minnesota stream: production and abundance. Transactions of the American
Fisheries Society 112:137–146.
Waters, T. F. 1999. Long-term trout production dynamics in Valley Creek,
Minnesota. Transactions of the American Fisheries Society 128:1151–1162.
Weaver, D. M. 2010. Effects of stocked trout on native nongame riverine fishes.
Master’s thesis. North Carolina State University, Raleigh.
Wilcove, D. S., D. Rothstein, J. Dubow, A. Phillips, and E. Losos. 1998. Quantifying threats to imperiled species in the United States. BioScience 48:607–
615.
Zar, J. H. 1996. Biostatistical analysis, 3rd edition. Prentice-Hall, Upper Saddle
River, New Jersey.
Zimmerman, J. K. H., and B. Vondracek. 2006. Interactions of Slimy Sculpin
(Cottus cognatus) with native and nonnative trout: consequences for growth.
Canadian Journal of Fisheries and Aquatic Sciences 63:1526–1535.