Interactions Between the Redside Shiner (Richardsonius
balteatus) and the Steelhead Trout (Salmo gairdneri
in Western Oregon: The Influence of Water ~emperature"
Gordon H. 8eeves2
Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 9733 1 , USA
Fred H. Everest
USDA Forest Service, Pacific Northwest Research Sbtisn, 3200 ieiferson Way, Corvallis, OR 9733 1 , USA
and jarnes D. Hall
Department of Fisheries and Wildlife, Oregon State University, Corvalbis, OR 9733 1, USA
Reeves, G. H.,F. H. Everest, and J. B. Hall. 1987. lnteractions between the redside shiner (Richardsonius
balteatus) and the steeihead trout (Salrno gairdneri) i n western Oregon: the influence of water
temperature. Can. J. Fish. Aquat. Sci. 44: 1603-1613.
Water temperature i n hluenced interactions between redside shiner (Richardsonius balteatus) and juvenile
steelhead trout (Salmo gairdneri) ( 2 1 +) i n the field and laboratory. Trout in cool water when shines were
absent and at intermediate water temperatures with shiner present occupied a similar range of habitats.
Shiner alone i n warm water occupied habitats similar t o trout, but i n the presence of trout occupied slower,
deeper areas than when alone. In laboratory streams, production by trout was the same in the presence
and absence of shiner i n cool water (12-15°C). I n warm water (1%22"C), production by trout decreased b y
9%
in the presence of shiner compared with when shiner were absent. Production of shiner i n cool water
decreased i n the presence of trout, -0.3 g-m-2-d-' together compared with 0.5 g.m-2-d-1 alone, but was
not affected by the presence of trout i n warm water. Trout distribution was not influenced by shiner in coo!
waters, but was influenced at warm temperatures. Shiner occupied all areas of the laboratory channels i n
the absence of trout i n coo! waters but were restricted t o a few pools i n the presence of trout. Distribution
of shiner was not influenced by trout at warm temperatures.
La temperature d e l'eau influe sur les interactions entre le m$ne rose (Wichardsonius balteatus) et la truite
arc-en-ciel (Salms gairdneri) juvknile ( 2 1 +) en milieu waturel et experimental. Les truites gardees en eau
fsaiche en I'absence de menes et 21 des temperatures intermediaires de I'eau en presence de menes ont
frequent6 la meme gamme d'habitats. Les menes 6leves seuls en eau chaude ont frequente des habitats
semblables B ceux utilises par la truite, mais en presence de ceile-ci, ils se sont deplaces vers des zones plus
profondes o h le courant etait plus faible. Dans les cours d'eau experimentaux a eau fraiche (12-15°C)' la
production de la truite etait la m&me en prksence et en absence d u mene. Par contre, elle a baisse de 54 %
en presence d u mene dans u n milieu a eau chaude (I%Zl5C). En eau fraiche, la production dam mene a
baisse en presence d e la truite pour atteindre -0,3 g.m-2=j-' par rapport 2 0,s g.m-2-j-' en I'absence d e
celle-ci, mais en eau chaude la production n'a pas ete aouchee par la presence de la truite. En eau fraiche, le
m6n$ n'influait pas sur la repartition d e la truite, mais c'etait le cas A des tempkratures plus elevc5es. En
$'absenced e la truite, le mene frkquentait tsutes les parties des chenalax expesimentaux a eau fraiche mais
il ktait restreint a queiques trous d'eau en presence de la truite. Celle-ci n'influait pas sus la repartition d u
mene en eau chaude.
Received August 2.3, 1985
Accepted May 4, 1987
(J8395)
everal researchers have examined interspecific interactions between freshwater fish by comparing populations
in sympatry and allopatry (e.g. Everest and Chapman
1972; Nilsssn and Northcote 198I), but few studies have
considered the influence o f environmental conditions on these
interactions. Larkin (1956) noted that, as a rule, freshwater fish
'~echaaicd Paper No. 7789, Oregon Agricultural Experiment
Station.
'hsewt address: USDA Forest Service, Pacific Northwest Research
Station, 3288 Jefferson Way, Csrv-vallis,OR 9733 1, USA
Can. J . Fish. Aquat. Sci., Vol. 44, I987
are adaptable to a wide range o f environmental conditions, and
the outcome o f competitive interactions may vary depending on
these conditions. Sale (1979) and Connell (1988) emphasized
the importance o f considering environmental conditions in
studies o f interspecific interactions. Baltz et d.(8982) showed
that competition for cover on riffles between speckled dace
(Rfainickthys oscukus) and riffle sculpin (Cottus gukesus) is
mediated by water temperature. Dace dominated in w m e r
water because they can function metaboHicalBy without stress
whereas sculpin are stressed. Sculpin prevailed in cooler water.
Water temperatures may also affect interactions between
1603
pescids and other species in lakes (MacLean and Magnuson
1977). Thus, water temperature may influence the composition
of fish communities by influencing not only species survival but
also the outcome of competititve interactions.
Little evidence has been found to suggest that nonsalmonids
compete with salmonids (Hick and Webster 1975; BaHtz and
Moyle 1984). A series of studies at Paul Lake, British
Columbia, however, demonstrated that the introduced redside
shiner (Richardssnius balteatkcs) successfully competed with
rainbow trout (Sakms gairdneri) for food (Larkin and Smith
1954; Grossman 1959; Johannes and Larkin 1961). Rodnick
(1983) found that habitats occupied by adult shiner (>25 mrn
total length) in an Oregon stream were similar to those used by
juvenile steelhead trout ( S . gairdneri) (Everest and Chapman
1972). We observed shiner and juvenile steelhead trout together
in midorder streams throughout western Oregon. Similarity of
habitats along with results from other studies suggested a strong
potential for competitive interaction.
The objective of this study was to determine whether water
temperature altered interactions between the two species. To
this end, we examined the ( I ) distribution of the species done
and together in streams with different temperature regimes and
(2) distribution, production, and behavioral interactions in
laboratory streams.
Materials and Methods
Field
Three streams with different water temperature regimes in the
Umpqua River system of central western Oregon were chosen.
Gsw Creek contained redside shiner, Copeland Creek steelhead
trout, and Steamboat Creek both. Sites, which varied in length
from 50 to 70 rn, were selected with similar physical characteristics (i.e. depth, current velocity, and substrate) and were
studied in late July and early August 1983. Preliminary
observationsleading to the selection of sites were made in many
streams in western Oregon from 1980 to 1982.
The Cow Creek watershed has been subjected to intensive
timber harvest, mining, and livestock grazing. Summer water
temperatureshave exceeded 25"C, but the water was cooler than
normal, 20-22"C, during our observation period because of
cool, overcast weather. Species other than shiner present in the
study area were sculpin (Coetus spp.), dace (Rhinichtbzys spp.),
umpqkcae). No
and Juvenile Umpqua squawfish (P@chocBsei&us
juvenile anadromous salmonids were observed after mid-June,
but juvenile steelhead trout and chinook salmon (Oncorhj~nchus
fshcewyfscha) were present earlier in the year.
The Copeland Creek watershed has had limited land-use
activity because of steep side slopes. Summer water temperatures have reached 20°C and during the study varied from 14 to
19°C. Other than steelhead trout, sculpin were the only species
observed.
Stemboat Creek's watershed is moderately to intensively
logged. Water temperatures ranged from 18 to 21°C. during the
study but normally reach 22°C in summer. Other fish in the
study area besides rehide shiner and steelhead trout were
sculpin, dace, juvenile chinook salmon, cutthroat trout (Salms
ciarki), Umpqua squawfish, sucker (Catssfornus spp.) , and
adult Pacific lamprey (&ddmpetmtridentezta). The last two were
observed on1y at night .
Each site was divided into 3-m squares and the comers
marked with plastic flagging. Two divers, with mask and
snorkel, began at the downstream edge of a site and proceeded
slowly upstream. Species, size, and location of fish were
recorded on a Plexiglas slate with the grid pattern of the site
inscribed on it. Observations were made in the morning (starting
between 0730 and 0800), at midday (starting between 1208and
13001, and in the evening (starting between 1900 and 1930) on
two consecutive days. Observations were also made at night
with underwater lights; because of difficulty in locating grid
markers, only species, size, general location, and activity
patterns were recorded.
Substrate composition, water depth, current velocity 5 cm
below the surface (referred to as surface current velocity), and
mean current velocity (at 8.6 depth of the water column
measured from the surface) were measured the next day.
Measures were made at the comers and midpoints sf each grid
section, or at more frequent intervals when a factor changed
significantly in a short distance. Current velocities were
measured with a portable electronic current meter. Substrate
was grouped into diameter categories of <2, 2-5, 5-10,
20-40, and >40 cm.
Distribution of the species was analyzed in two ways. First,
we examined the distribution of each species alone and together
relative to each physical factor. Measures for each factor were
grouped and the contows of each class drawn on a map of the
site. Classes of depth and velocity were at 15-cm and 15crn.sml intervals, respectively. We calculated the total area of
each class and then estimated the density of fish for each factor.
Separate estimates were made for each time and day.
Distribution relative to the physical factors was also determined with stepwise discriminant function analysis. The range
intervals for each factor were assigned a rank, with 1 the lowest
interval, 2 the next highest, and so on. Data from each day were
combined for this analysis, and separate discriminant functions
were derived for each time of day. All possible pairs of the mean
discriminant score of each group were compared by a t-test to
determine if the means were statistically different.
Laboratory
Tests were conducted in two artificial streams (Reeves et al.
1983) located at the Forestry Sciences Laboratory, Corvallis,
OR, from June to October 1983. Each stream is oval, measuring
4.3 X 4.9 m on the sides, 0.76 m wide, and 0.61 rn deep. They
are set one above the other on a metal frame. Fish are viewed
from the center b o u g h Plexiglas walls. Black plastic curtains
provide cover for observers and restrict outside light and
disturbance. Water temperature, duration and intensity of
photoperiod, filtration, current velocity, and ultraviolet (UV)
sterilization are regulated independently in each channel.
Current velocity was maintained by a Plexiglas paddle wheel at
0- 10 cm-s- . Each channel had four pools (50.0 em deep) and
four riffles (40.63 em deep) sf equal size. Substrate was sand and
pea-gravel in pools and cobble in riffles. Cover was provided in
each pool and on two of the riffles.
Tests were conducted under two daily water temperature
regimes (12-15 and 19-22°C) that represented streams in
watersheds subjected to different intensities of land use. Daily
lows were in the morning and highs in the evening. The
photoperiod was controlled by a timer (Everest and Rodgers
1982) that provided 15 h of light and 9 h of darkness. R e light
phase consisted of a 1.5-h "morning," where lights gradually
increased from zero to full intensity, 12 k of full intensity, and a
1.5-h "evening," where intensity gradually dimmed to zero.
'
Can. J . Fish. Aquat. Sci., Voi.44, 1989
Light cycles were staggered by 45 min so each channel could be
observed under similar light conditions. Nine 60-W incandescent bulbs spaced at equal intervals around the channel were the
sole source of light.
Streams were filled with water 5-6 d before fish were
introduced. Water, from the City of Corvallis water supply, was
continuously passed through a sand filter and a UV sterilizer.
Make-up water was added to each channel at 0.5 L-min-I.
Channels were drained, sterilized, and refilled between tests.
Test fish were captured by electroshocking or seining and
held for 2-3 wk in laboratory tanks before introduction to the
channels. During this period, they were treated with malachite
green to reduce the chance of diseases and parasites and were
acclimated to the temperature regime to which they would be
exposed and to frozen brine shrimp (Artemia spp.).
Individual fish were weighed to the nearest 0.01 g and
measured to the nearest 1.8 mm (fork length) before introduction to the channels. Number and pattern of p m marks on trout
were recorded to aid in identifying individuals. Mean size ( 2 1
SD) of trout in the various trials ranged from 95.0 mm ( k9.8)
md7.2 g(22.9) to 106.4mm(k4.3) and 11.2 g(k8.8). Shiner
ranged from a mean of 71.5 mm ( k 12.0) and 4.8 g (k2.2) to
77.2 mm (k9.9) and 5.5 g (k2.l). Number of trout in achannel
at the start of a trial ranged from 4 to 6 and number of shiner
from 25 to 33.
Test periods were 13 d. One trial with each species alone and
two with both species were run at each temperature regime. One
trial with both species was run in the lower channel and one in
the upper channel. Trials with only shiner and only trout are
referred to as RS and ST, respectively. Trials with both species
are designated WS-ST I and RS-ST II.
In WS-ST trials, trout were introduced to the channels first.
Traps om the upstream and downstream side of the paddle wheel
were opened after 48 h to allow fish that were unable to obtain a
suitable territory to migrate. At the end of 24 h, traps were
closed and shiner introduced. Biomass of shiner introduced was
three times the biomass of trout present at that time. This would
have been a relatively low ratio of shiner to trout biomass in
streams where we had observed the species together. If trout
were affected by shiner when the ratio was low, we inferred that
the effect would also occur at higher ratios. Traps were
reopened after 24 h, and the test period began 24 h later.
The same procedure used in WS-ST trials was followed in
each ST trial. In WS trials, however, traps were open 24 h after
shiner were introduced; the test began 24 h later. Biomass of
shiner introduced in an WS trial was equal to the mean biomass
used in WS-ST trials for that temperature regime.
Frozen brine shrimp were the sole f d source. Daily rations
were equal to 15% of the dry weight of salmonids present at the
start of the test period. The large ration was necessary because
of the poor nutritional quality of the frozen shrimp. Amount of
shrimp fed in WS trials was the same proportion, relative to the
initial biomass of shiner, fed in corresponding RS-ST trials.
Half of the daily ration was presented in the morning, 25% at
midday, and 25% in the evening. Food was delivered to each
stream via a 2.5-cm-diameter BVC pipe that ran in a zigzag
pattern along the entire area available to fish (Reeves et al.
1983).
Observations of distribution and behavior were made during
the morning and evening feedings and before the midday
feeding. During a 35-min period, fish in each pool and each
riffle were observed for 5 min and the number and location of
fish noted. Individual trout were identified whenever possible.
Can. d . Fish. A q w t . Sci., Vok. 44,6987
The number of intra- and interspecific behavioral interactions
was recorded. Only numbers and locations of fish were noted on
the most upstream riffle because viewing was difficult due to
structural obstructions. The observational sequence in each
channel was randomly determined before each session. The
lower channel was always observed first.
The procedure used to estimate production, defined as the
total amount of new tissue elaborated per square metre of available area in a laboratory stream per day, varied depending on
whether we could account for all individuals of a species
(Reeves 1984). When all individuals were recovered, the
amount of new tissue elaborated was calculated as the difference
between the beginning and ending biomass of the species,
which included fish that remained in the channel for the duration
of the trial and fish that migrated during the trial.
When all fish were not accounted for, we assumed that
unrecovered fish lived for half the test period and either gained
or lost weight at the same rate as the population. Weight of
unrecovered fish was estimated to be the sum of the initial
weight plus or minus the estimated change for the population.
The sum of the estimated weight of unrecovered fish was added
to the biomass of migrants and fish that remained in the channel.
The amount of new tissue elaborated was the difference between
this sum and the total initial biomass. We accounted for all trout
except for one in the RS-ST I trial in w m water. We
accounted for all shiner in only the cold WS trial. Two shiner, or
5-6% of the total number, were not recovered in each of the
other trials.
Field
Distribution patterns and habitat preferences of both species
when alone were generally similar at all times of day (Fig. 1).
Both species were distributed across the entire range of a given
habitat feature with few exceptions, and modes for each feature
were at or close to the same value for each species. Shiner
distribution changed more over the course of the day than did
trout distribution. Shiner moved to areas of larger substrate and
greater mean velocity. Trout distribution was more stable.
When the species were observed together, the distribution of
the trout was more similar to that of trout alone than was the
distribution of shiner relative to when shiner were alone. Trout
with shiner, in general, occupied the same range of habitats as
trout alone; however, shiner distribution with trout was generally more restricted, primarily to deep, slow areas, than when
shiner were alone.
Discriminant function analysis described the range of habitats
used at each time of day by the species alone and together when
all physical factors were considered together (Fig. 2). Tolerance
limits (Guttman 1970) provide a method to exmine the range
and extent of overlap of the habitats occupied by each group; the
greater the overlap of the tolerance limits, the greater the
overlap or similarity of habitats used. A large percentage of
observed variation in habitats occupied in the three streams was
accounted for by a single discriminant function. Each derived
discriminant function had a highly significant Wilks' A (P <
0.01), which is a measure of the function's discriminating
power. The discriminant function for the morning accounted for
83.2% of the variation among the groups, which were each
species alone or together. Depth, substrate, and mean current
velocity were the dominant variables. Depth and substrate were
REDSIDE SHINERS
A MORNING
STEELHEAD TROUT
ALONE
06
05
04
03
02
01
00
B. MIDDAY
LL
gz
Z
TOGETHER
020
;Q l Q
0 00
C. EVENING
ALONE
1
9
O
DEPTH (cm)
SUBSTRATE (cm)
1
SURFACE VELOCITY
(cm*s-')
MEAN VELOCITY
(cmes-1)
FIG.1 . Mean density of redside shiner and juvenile steelhead trout alone and together at different times of
day in relation to physical features of study sites. Vertical bars represent upper range. Midday
sbsewlations of the species together on the first day were excluded because s f the presence of c o m o n
mergansers (Mergus merganser). Note difference in scales between the species alone and together.
p s i f vely correlated (P 6 0.0 1) with the discriminant scores,
and mean current velocity was negatively correlated (B 6
0.85). The discriminant function for midday accounted for
85.4% of the among-group variation. All physical factors were
correlated ( P 6 0.01) with the discriminant scores, depth and
substrate were positively correlated, and the velocity measures
negatively con-elated. The discriminant function for the evening
accounted for 84.2% of the among-group variation. Depth and
substrate were positively correlated ( P 6 0.01) and mean
current velocity negatively correlated (P 6 0.05) with the
discriminant scores.
Each species alone occupied similar habitats. The mean
scores of the species alone did not differ (P > 0.05) at any time
of day, m d the statistical tolerance limits overlapped extensive1606
ly, indicating a strong similarity of habitats occupied (Fig. 2A).
Shiner distribution increased over the course of the day, as
indicated by the increased statistical tolerance limits, while trout
distribution was more stable. By evening, shiner were more
widely distributed than were trout.
Trout alone and together occurred in much more similar
habitats thm did shiner alone and together (Fig. 2). The mean
scores of the species together differed (B 6 0.05), however, at
all times from that of the species alone. Shiner in the presence of
trout were at all times in slower, deeper areas with larger
substrate than were shiner done. Only in the afternoon did the
statistical tolerance limits of the shiner groups overlap, and then
only slightly (Fig. 2B).
Trout were observed over a much wider range of habitats than
Can. J . FLh. Aqua$. Sci., Vob. 44, 4987
A. Morning
-4
-3
-2
-1
0
1
Discriminant Score
shallow
small
fast
2
3
4
w deep
Depth
Substrate9.1
dace Velocity
large
slow
B. Midday
-4
-3
-1
-2
0
1
2
3
4
Discriminant Score
-
shallow
small
fast
fast
deep
large
Mean Velocity -slow
Surface Velocity
slow
C. Evening
I
-4
I
I
-3
-2
I
-1
I
I
I
0
1
2
!34
Discriminant Score
P deep
Depth
Mean Velocity -slow
Substrate P
large
shallow
fast
small
8 Redside Shiner ALONE
Steelhead Trout ALONE
Redside Shiner TOGETHER
sl Stellhead Trout TOGETH ER
@
PIG.2. Mean discriminant score, 95% confidence intewal (inner brackets), and 95% tolerance intewd
(outer brackets) for each species alone and together in streams at different times s f day. Only physical
factors that are significantly comlated ( P < 8.85) with the discriminant score are shown. Factors are
shown in the order they entered into the discriminant function.
were shiner when the species were together. Mean scores of
each species differed (P < 0.05) at all times, and extent of
overlap of the statistical tolerance limits varied (Fig. 2). When
shiner and trout were observed in the same areas in the morning
and evening, their behavior and activity were noticeably
different. M ~ sshiner
t
were inactive, holding near the substrate
behind large rocks or in crevices between rocks in the morning.
Can. J . Fish. Aquab. Sei., Vol. 44, 6987
During the same period, trout m v e d throughout the water
column and fed actively. Trout done and shiner alone exhibited
the same type of activity pattern as exhibited by trout with
shiner.
Shiner distribution in the presence of trout was more
restricted in the evening than at any other time of the day (Fig.
2C). Shiner were observed primarily in the deepest areas and in
1607
slow mean current velocities (Fig. 1C). Trout were observed
primarily in deeper water also, but were in areas of higher
current velocities (Fig. 1C). When the two species were
observed in the same area, shiner were in small groups of three
or four fish, generally holding behind large rocks and boulders,
and darting into the water column to attempt to capture items
carried in the current. Shiner that tried to move into or through
areas occupied by trout were quickly driven away.
At night, trout alone and with shiner were observed in the
same general habitats as each other and exhibited similar
behavior. Fish drifted downstream and to stream margins as
light intensity decreased. After dark, fish were found primarily
in areas 30-60 cm deep, with 5-20 cm of substrate, and with
little or no current. They were on the substrate or in crevices in
the substrate and showed no signs of activity, generally not
moving unless a diver attempted to touch them. Large organic
debris was also used for cover by some trout.
Shiner alone and with trout were observed at night in habitats
similar to those described for trout, but their activity differed.
Behavior of shiner alone was very similar to that of trout. Shiner
with trout were more active than those alone; they were
observed swimming about, actively picking at the substrate and
then spitting out material, but we could not tell conclusively if
they were feeding. Often Ixger numbers of shiner occurred in a
given area, but we saw no behavioral interactions between
individuals. Trout in the vicinity were never observed reacting
to shiner. By first light, no shiner were observed in these areas
of Steamboat Creek; they were only observed in the deeper,
slower areas described previously. Trout had also moved away
from stream margins by this time.
Laboratory
Water temperature influenced production, activity, and
distribution of each species in laboratory streams and the effect
of one species on the other. In cool water, trout f e d better
when alone and had a greater impact on shiner than shiner had
on trout. In w m water, shiner fared better, both alone and in
interspecific trials.
Products'sn
Production of each species when alone was influenced by
water temperature. Production by trout alone was 2.4 times
greater in cool water than in w
(Table 1). Number and
biomass of trout were greater in the cool channel than in the
w m thoughok~tthe test period. At the start, six fish were in the
cool channel, totd biomass 47 g, and four in the warm, total
biomass 29 g (Table 1). Four trout remained in the cool channel
during the test and three in the w m . We saw no sign of
infection with Flexibacter csEumnaris in migrants from either
temperature. One resident trout in the warm channel was
infected with F . cs&umnaris, however, and was in poor
condition.
Production by shiner alone was E .5 times greater in w m
than cool water (Table 1). At the start, numbers and biomass of
fish in each channel were nearly equal (Table I). No shiner
migrated from the cool channel, but eight left the w m channel
('0% of the total). Migrants were generally larger individ~als
(X = 6.6 + 1.9 g) than fish that remained in the channel (X =
5.6 + 1.7 g). Fish left the channel though day 13 of the trial.
Four migramts were infected with 8". columnark's and in p r
condition. No pattern of migration was obvious; fish migrated
via both upstream and downstream traps a d at all times of day.
In cool water, production by trout alone was the same as with
TABLE1. Reduction by redside shiner alone (RS), juvenile steelhead
grout alone (ST), and the species together (RS-ST) at different water
temperatures in laboratory streams.
Production (g -rnm2.d- ')
Trial
Temperature ("C)
ST
12-15
19-22
RS
12-15
19-22
RS-ST I
RS-ST 1%
12-65
RS-ST E
RS-ST II
19-22
Steelhead trout
Redside shiner
"Does not include weight change. -1.7 g, of one fish that was
determined after completion of trial to be either a resident rainbow trout
or a precocious steelhead trout.
b~stimate
adjusted to include calculated production of unrecovered
fish.
shiner present (Table I). Presence of trout in cool water had a
pronounced effect on shiner, however. Production by shiner
was negative in both trials when trout were present; the mean
was -0.3 g ~ m - ~ d - ' ,compared with 0.5 g ~ r n - ~ d - when
'
shiner were alone. The number and condition of migrant shiner
differed depending on the presence of trout. No shiner migrated
from the channel when alone, but with trout present, 26%
(10/38) and 20% (7/35) of the shiner left the channels in
RS-ST I and IL respectively. Migrants in RS-ST I were
slightly sn-gller (X = 4.3 2 0-9g) than fish that remained in the
channel (A7- = 4.8 + 1.4 g) but were larger in RS-ST IH,
migrants (X = 6.9 + 2.0 g), and residents (X = 5.2 + 2.2 g).
Individuals migrated primarily at night, with about equal
numbers leaving via the upstream and downstream traps. Over
50% of the migrant shiner were infected with F . coburnnaris and
in poor condition.
In w m water, production by shiner was not affected when
trout were present, but production by trout decreased by an
average of 50% compared with when trout were alone (Table I).
Only one trout maintained a territory successfully and remained
in the channel in each RS-ST trial. All other trout migrated 1-3
d after shiner were introduced md,_on the average, lost some
weight (X = -0.2 g, RS-ST I; X = -0.1 g, RS-ST 11)
before emigrating. These individuals attempted to maintain a
suitable territory before leaving but appeared to be overwhelmed by the number and activity of shiner, which also
captured food more quickly than trout. Four of the five migrant
trout were infected with F . coHumncsris. Over '75% of the
migrant shiner in the RS-ST tests were infected, compared with
50% in the w m RS trial and 50% in RS-ST trials in c m l
water.
Activio
The number and type of behavioral interactions between trout
were not affected by water temperature when they were alone.
No significant differences (ANOVA, P > 0.05) were found
between the number of interactions per fish per observation
perid at any time in the two temperature regimes (Fig. 3). Nips
and chases (Hartman 1965) were the dominant types of
interactions.
Interactions between shiner were influenced by water temperCan. J . Fish. Aqua. Sci., Vol. 44, I987
Steelhead Trout
Redside Shiner
A. Morning
a 601d
El Warm
Midday
2.0
Evening
RG.3. Mean number of interactions per fish per observation jmiod (5 min) for each species when species
were alone and together at different water temperaturesin laboratory streams. Vertical bas represent +2
SE.
ature whew shiner were done. Significantly more behavioral
interactions occurred per individual per observation period
(ANOVA, P < 0.05) at dl times of day in w m water (Fig. 3).
Dominant types of behavior were nips in the w
water and
evictions (Reeves 1984) in the cool water.
Interactions per trout per observation period differed between
trials and by time of day in cool water with shiner (Fig. 3). Trout
Can. 3. Fish. Aquas. Sci., V d . 44, 1987
aggressively responded to any shiner that attempted to enter
their territory, especially during feeding periods. Trout chased
or nipped intruding shiner, which usua88y fad to the nearest
p o l . Mean numbers of interactions per trout in WS-ST I and in
ST were not different (ANOVA, P > 0.05) at any time of day.
Numkr of interactions per trout in the morning and evening
were different (ANOVA, P < 0.05),however, between RS-ST
1689
TABLE2. Mean number of fish observed holding stations during feeding and nodeeding periods when redside shiner were
alone (RS), juvenile steelhead trout were alone (ST), and the species were together (RS-ST) at different water temperatures in
laboratory streams.
Mean no. of steelhead trout
Trial
Time
Upstream
Dswnsgrearn
Significance"
Mean no. of redside shiner
Upstream
Downstream
Significance"
Water terarpeaczture c*ssE
ST
Morning
Afternoon
Evening
RS
b'!orning
Afternoon
Evening
ST-RS 1
Morning
Afternoon
Evening
ST-WS II
Morning
Afternoon
Evening
Water temperature warm
Morning
Afternoon
Evening
Morning
Afternoon
Evening
ST-RS I
ST-RS II
aWilcoxon matched-pairs signed-sank test (Siegel 1956).
bOnly one steelhead trout remained in laboratory streams after trial day 3.
P% and ST. These differences resulted from the number of
interspecific interactions initiated by the &out (ANOVA, P <
0.851,not from an increase in intraspecifie interactions (ANOVA, P > 0.05).
In cool water, shiner activity decreased in the presence of
trout. Fewer interactions were initiated by shiner in both RS-ST'
trials (ANOVA, P < 0.05) than whew they were alone (Fig. 3).
Only 4% (6/145) of the total interactions initiated by shiner
were directed towards trout, and all but one were observed in the
evening. The social organization of the shiner also changed in
the presence of trout (Reeves 1984). Shiner formed a loosely
structured goup, primarily in the most downstream pool sf the
channel, and were much less aggressive than when alone. When
trout were absent, many shiner were territorial and interacted
with any fish that attempted to enter or move through their
territory.
In cool water, shiner activity in the presence of trout
increased noticeably in the late evening. Groups of four to seven
shiner began moving from the last riffle and pool to all areas sf
the channel. Tmut at the same time began to move off riffles into
p o l s or cover on a riffle, as occurred when trout were observed
alone. Trout made very few attempts to interfere with shiner.
86164
Shiner were observed picking at the substrate, both on riffles
and in pools. Shiner were again found primarily on the back of
the last riffle and in the last pool by first Bight. This pattern was
not observed when shiner were alone in cool water or in warn
water whether or not trout were present.
The number of interactions initiated by shiner in w
in general, was not influenced by the presence sf trout.
Interactions per shiner per observation period did not differ
(ANOVA, P > 8.05)whether shiner were alone or with trout,
except in the morning in RS-ST I (Fig. 3). Fewer interactions
per fish (ANOVA, P < 0.05) took place in the presence of trout.
Only 1%(17/1437) of the total interactions initiated by shiner in
the two RS-ST trials were directed towads trout. These were
predominantly nips and chases (Reeves 1984).
Distribution
Distribution of trout within the channel differed with water
temperature when they were alone. Trout were evenly distributed ( P > 0.05, WLBcoxon matched-pairs signed-rank test (Siegel
1956)) between the upstream and downstream halves in cool
water (Table 2). A single trout occupied each of the last three
riffles md the front of the most upstream pool during feeding
Can. J . Fish. Aquat. Sci., VQ!.44, 1987
periods. When food was absent, fish moved to cover on the
riffle where they had been observed feeding or to the head of the
pool immediately downstream from the riffle. Distribution was
different ( P < 0.81) in the w
channel, however. Trout were
primarily restricted to the two downstream riffles; seldom were
trout observed holding station in the upstream half of the
channel (Table 2). Despite this crowding, no differences were
found between the total numbers of behavioral interactions per
individual per observation period in the two temperature
regimes (Fig. 3).
Distribution of shiner alone was generally the same in both
water temperature regimes and was similar to the distribution of
trout in cool water. Shiner were evenly distributed ( P > 0.05) in
the upstream and downstream halves of the channel during
morning feeding periods in cool and w m water (Table 2).
During the evening feeding period, shiner were evenly distributed in w m water (P > 0.05), but more fish were in the
downstream half of the channel in cool water ( P < 0.05).
During the nonfeeding perid, fish were not distributed evenly
(P < 0-05) in either water temperature (Table 2). Shiner were
observed primarily on riffles during feeding periods in both
temperature regimes. Fish generally moved into pools or swam
about the channel in groups of three or four similar-sized
individuals when food was absent.
In cool water, distribution of trout was not affected by shiner,
but the distribution of shiner was restricted when trout were
present (Table 2). Trout in both RS-ST trials were evenly
distributed (P > 0.05) around the channels at d l times and
occupied the same habitats as in the ST trial. Shiner remained in
the back half of the channel ( P < 0.OH), primarily on the back of
the last riffle and in the last pool during daylight.
Each trout that remained in the channel in w m water when
shiner were present occupied a riffle but in different parts of the
channel. The fish in WS-ST' II was restricted to unfavorable,
turbulent habitat on the most upstream riffle. This fish attempted to move to riffles further downstream but was harassed by
shiner and was seldom able to feed. The fish in RS-ST I
successfully maintained a territory on riffle 3, which was less
turbulent than the most upstream riffle, but also initiated more
interactions than the other trout (Fig. 3).
In warm water, distribution of shiner generally did not differ
when trout were present and absent (Table 2). During feeding
periods, shiner were evenly distributed ( P > 0.05) except in
WS-ST 11, when more fish were in the downstream half ( P <
0.05). Shiner continued to inhabit both pools and riffles in the
manner described previously in the RS trial.
Competitive interactions between redside shiner and juvenile
steelhead trout were influenced by water temperature. To
determine if two species are competitors, Connell (1983)
suggested that the abundance of the species be altered and the
responses, relative to controls, either in "breadth of resource use
(e.g. food type, microhabitat type) or in abundance (including
those variables that affect abundance, e. g . natality, mortality,
growth, emigration, immigration, feeding activity, etc .) ," be
measured. Competition is deemed to occur if differences
between test and controls are statistically significant. In the
present study, we did not alter species abundance to test for
competition, but rather varied environmental conditions. We
believe, however, that it is still valid to use Connellqs (1983)
Can. J . Fish. Aquat. Sci., Vo1. 44, I987
criteria. Although not all parameters were statistically significant, such as field distribution, they were in a direction and to an
extent that strongly supports our conclusion that redside shiner
and juvenile steelhead trout do compete, at least for habitat, and
that water temperature influences the outcome of competition.
Cool water favored trout and warm water favored shiner. Baltz
et al. (1982) also demonstrated that water temperature influenced competitive interactions between stream fish.
Werner (in Kern and Werner 1980) believed that niche shifts
by competing species of fish could not be explained on the basis
of physiological differences between the species. Baltz et al.
(1982) found that the outcome of competition for cover between
two fish species was related to the metabolic performance of the
species at a given water temperature. The species that prevailed
was the one least stressed at a given temperature. In the present
study, we believe that one species prevailed under a given
temperature regime because it was better adapted metabolically.
Salmonids are less stressed at cool temperatures (Brett 1952)
and would therefore be expected to perform better than at warn
temperatures. Shiner, on the other hand, were probably less
stressed at w m temperatures, as witnessed by greater activity
and production.
The primary element of competition responsible for the
dominance of each species differed. Trout prevailed in cool
water by interference competition (Miller 1967). Trout were
strongly territorial and prevented or severely limited access of
shiner to food. The energy cost to trout of interacting with shiner
in cool water appeared minimal. Production by trout was the
same whether or not shiner were present, even when trout
initiated significantly more interactions when shiner were
present than when they were absent. Shiner adjusted to their
restricted distribution by changing their social behavior and die1
activity, foraging at midday in areas of faster current and om the
bottom at night. Trout were less active at midday, when
invertebrate drift is lowest (Waters 1969), and made no attempt
to prevent shiner from feeding. Hixon (1980) found that two
competing reef fish coexisted because the less dominant foraged
in preferred areas at times when the dominant was absent.
Shiner dominated in warn water by exploitation competition
(Miller 19671, and to a limited extent by interference competition. Shiner were more active in w m water and responded
more quickly to food than did trout. In w m water with shiner
present, trout initially attempted to maintain a territory. Shiner
were more active, however, occupying positions on riffles and
capturing food more quickly than trout. As a result, most trout
abandoned their attempts to maintain a territory within 2-3 d
and migrated from the channel. Crossman (1959) reported
shiner to be more active feedem than rainbow trout in laboratory
troughs.
Increased susceptibility to disease, as influenced by water
temperature, may have modified interactions between redside
shiner and steelhead trout; each species in the presence of the
other at unfavorable temperatures was more susceptible to F.
colummris. Most migrant trout were infected with F. columnaris in warm water, and more than half of the migrant shiner
were infected in cool water. We can only speculate on the
causes. Additional stress caused by a competitor in a less
favorable environment may cause an organism to be more prone
to disease. Holt et ale(1975) found that susceptibility of juvenile
anadromous salmonids to F. columnarks increased with increasing water temperature. Influence of water temperature on the
susceptibility of shiner to F. cokurnnaris is not now known.
161 1
Various eatostomids and cyprinids, including redside shiner, in
a cool tributary of the McKenzie River, OR, suffered high
mortality rates from F . co&umnaris,whereas resident salmonids
were not affected (A. Amandi, Department of Microbiology,
Oregon State University, Cornallis, OW 9733 1, pers. cornm.).
Bark (1948) found that the outcome of competition between two
species of beetles was influenced by the presence of a sporozoan
parasite. Moore (1983) emphasized the need to consider the
effects of disease and parasites on fundamental processes such
as competition and prey selection. In this study, the extent of
influence of F. cskumnaris on the outcome of competitive
interactions between trout and shiner is not known, but it
appears to have been fairly strong.
Although the on-site effect of some land-management activities may be positive, the cumulative effect of these changes on
other areas of the watershed has received little or no consideration. Salmonid populations may respond favorably to opening
of the riparian canopy (Hawkins et al. 19831, increased water
temperatures (Bums 1972; Holtby and Newcombe 19821, or
both, resulting from land-management activities. Water temperature in midorder streams low in a watershed depends largely
on the temperature of the water entering from upstream.
Midorder streams may be important rearing areas for juvenile
anadromous salmonids, especially chinook salmon and 2 1 +
steelhead trout, and have a more diverse fish community than do
lower order streams. Changes in environmental conditions may
result in a decrease in available habitat for salmonids and alter
the outcome of interactions between sdmonids and potential
competitors. Environmental changes less favorable to salmonids, such as increased water temperature in higher order streams,
could offset any increase in abundance or production of anadromous salmonids that might occur from opening the canopy
along lower order streams by land-management practices, or
could even result in a decrease in the population.
Results from this study demonstrate that competitive interactions between fish can be influenced by water temperature. Past
studies of competition have generally been concerned with the
examination of the species alone and together at different
locations. Future studies should consider differences in envimnmental conditions between sites, either directly or indirectly,
since only small changes may alter results. We believe that this
study also has important implications for fishery and land
management. First, the usefulness of programs designed to
control undesired species which may be held responsible for the
demise of a desired species should be evaluated. Creating and
maintaining conditions favorable to the desired species may be a
better approach than chemical or mechanical controls. Second,
we need to consider the cumulative impact of Imd-management
practices on fish communities. Previous studies have been
concerned with on-site effects of land-management practices
while neglecting the impact on ueas lower in the watershed.
Acknowledgments
We thank Hiram Li, W. Scott Overton, Bmce Menge, and two
anonymous reviewers for their comments on earlier versions of this
manuscript. Sue Hannernan provided invaluable help in the field and
laboratory. Carl Rackmore helped in the design m d constmfion of the
laboratory streams. Martha Brookes provided editorial assistance. We
also wish to extend our appreciation to Terry Roelofs, Jim and Sharon
Van Loan, and all the people at S t e m b o a t Inn for their hospitality and
assistance. This study was funded by a grant from Project WWU-1705
of the USDA Forest Service, Pacific Northwest Research Station,
Conallis, OR 97331.
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