Project Title: Entiat Effectiveness Monitoring
Project No. 2003-017-00
Contract No. 00047100
Reporting Period: 4/1/2010 –3/31/2011
Work Element 162: Analyze/Interpret Data; Analyze population dynamics at
restored vs. unrestored reaches
Karl Polivka, Ph. D, PNW Research Station, USDA Forest Service
Jenni L. Novak, Cascadia Conservation District
Background
In 2010, we continued to assess
restoration efforts and detect effects on
populations of Chinook salmon
(Oncorhynchus tschawytscha) and steelhead
(O. mykiss) population size, individual
growth and movement at the reach scale.
Our work focused on the Lower Entiat River
in a single reach treated with small
engineered log jams (N = 4) and rock barbs
(N = 6) designed by the Bureau of
Reclamation to enhance salmonid rearing
habitat. These structures formed pools that
averaged 46 cm deep (range: 23 – 68 cm)
and 41 m2 in area (range: 14 – 73 m2). A
geomorphically similar control reach ~ 500
m upstream of the treated reach was used for
comparison of the fish population response
variables listed above. Three hypotheses
remained under consideration: 1) we
expected to observe higher density of fish in
the treated reach compared to the control
reach, 2) fish growth and movement would
show habitat quality and density
dependence, and 3) that restoration would be
mediated by environmental variables.
We compared density between 2009 and
2010. Previous observations included a
substantial numerical response of Chinook
salmon to the restoration treatments.
Steelhead were more variable in density
showing no only slight effects. Furthermore
habitat affinity showed differences between
treated/control reaches and between species.
In 2010 we continued the study of
movement to consider a different time scale
and used the mark-recapture data to estimate
differences in growth.
Methods
We conducted multiple censuses of
fish density in pools created by the
structures in the treated reach and in similar
sized pools in the control reach. We used
snorkeling and seining to capture fish from
August 16 to October 22, 2010. High flow
regimes and sediment load resulted in a later
start in comparison to the 2009 sampling
period, which began July 13th. Each captured
Chinook and steelhead was marked with a
subcutaneous injection of visual implant
elastomer and size data (length and weight)
was observed. Total fish, Chinook, and
steelhead densities were calculated (relative
to the area and depth of the habitat).
Total growth of individual fish was
calculated based on the recapture data
obtained over the entire sampling period.
We calculated growth rate by counting the
number of days between the capture event in
which a fish was first captured and when it
was last captured. We used the difference in
length, standardized by the total number of
days between initial and final captures, as
the measure of growth in mm/day. All
growth data were combined for each species
in each reach. Recaptures were expected to
occur at different times, and some data were
obtained from fish that occupied more than
one pool during the study period; thus, we
did not attempt to calculate average growth
per pool.
The effects of density dependence
were assessed by analyzing growth and
movement of each fish in correlation with
the average density of fish at each pool. To
examine the effect of fish density on growth,
we compared total growth rates with total
and species-specific densities. For each
individual fish, we used the average density
of total fish from the pool in which the fish
was observed during each recapture census.
We used a one-way analysis of covariance
(ANCOVA) to identify differences in mean
growth in the treated reach compared with
the control reach. Mean density, initial
standard length (SL), temperature (total
degree days), and average flow rate per pool
were used as covariates in the analyses
presented here.
In 2009, we observed that habitat
affinity over a 24 hour period was greater in
the treated reach compared with the control
reach for both steelhead and Chinook. In
2010, we collected our data in a way that
allowed us to keep track of individual
recaptures through time during multiple
recapture censuses. We used these
observations to determine whether the
habitat affinity patterns we observed over 24
hr in 2009 hold through longer time periods.
Fish marked in pools at the control and
treated reaches during the initial capture
events (mid-August and early September)
were recaptured during subsequent censuses.
Individuals were given unique color
markings so that they could be grouped by
original capture date and pool. We
calculated the fraction of fish initially
captured at each recapture date (Table 1)
and an average for each pool in the midAugust and early September mark groups.
We analyzed the recapture rates for
differences among categories of mark group
timing (mid-August vs. early September),
species (steelhead vs. Chinook), and reach
(treated vs. control) using a three-way
analysis of variance (ANOVA).
To assess whether temporal
variation in fish density was associated with
environmental variables such as
temperature, flow, dissolved oxygen, and
depth, we analyzed mean density at
microhabitats in each reach with two-way
analysis of covariance (ANCOVA) where
all measured environmental variables were
used as covariates and time was entered as a
random factor. From the multiple regression
output in the covariate analysis, we
examined the influence of environmental
variables on steelhead and Chinook density.
Treatment
8/16 – 8/19
Control
8/23 – 8/26
Week 1 Initial
Captures
Week 2 8/30 – 9/1
9/7 – 9/9
Initial
Captures
Week 3 9/13 – 9/16
9/20 – 9/23
Recaptures
Week 4 9/27 – 9/30
10/21 –
Recaptures
10/22
Week 5 10/18 –
Recaptures
10/20
Table 1. Initial capture and recapture dates
of fish in treated and control reaches during
2010 sampling period.
Results and Discussion
During both 2009 and 2010
sampling periods total fish density changes
over time but not between the treatment
reach compared with the control reach (Figs.
1a, 2a). Chinook and steelhead showed
different patterns of density through the
season. Chinook density was higher in the
treated reach and decreased over time in
both reaches (Figs. 1b, 2b); whereas
steelhead density was more variable.
Chinook density in 2010 was higher in the
treated reach in the mid-August samples
only and rapidly declined to be statistically
indistinguishable from the control reach.
Steelhead density was marginally higher in
the control reach in 2009 and considerably
higher in the control reach in 2010 (Figs. 1c,
2c). Time factors in repeated measures
ANOVA were significant for Chinook and
total fish density but not for steelhead.
We recaptured a total of 49
individual Chinook in pools in the treated
reach (14.1%), but only 7 in the control
reach (25%). ANCOVA indicated that
growth between reaches was not
significantly different (F1, 51 = 0.455, p =
0.503; Fig. 3a), partially due to the
extremely low recapture rate in the control
reach. Initial size was a highly significant
covariate (p = 0.0008) but density was not (p
= 0.411), nor was any other covariate,
suggesting that either the range of density
observed during most of this study was not
great enough to cause intra- and interspecific
competition or that other aspects of chinook
bioenergetics contribute more strongly to
growth than intra- and interspecific
competition. We recaptured 133 (61.9%)
steelhead in the treated reach and 66
(62.9%) in the control reach. Steelhead
grew 1.5 times more in the treated reach
compared with the control reach (F1, 193 =
11.38, p = 0.0009; Fig. 3b). This effect was
independent of density (p = 0.999), despite
the observation that steelhead had higher
density in the control reach through the
study season. Initial size was a strong
correlate of growth in steelhead (p = 0.003).
There was a significant and slightly negative
correlation with total degree days
(beta=0.184, p=0.011).
Few differences in recapture rates
were identified; steelhead showed higher
recapture frequency than Chinook (F1, 60 =
6.17, p = 0.016), but the date of initial
capture and marking also strongly
influenced recapture frequency (F1, 60 = 7.25,
p = 0.009, Fig. 4). For steelhead, the lack of
difference in recapture rates between the
treated and control reach for either the midAugust or early September groups is
consistent with our observation from 2009
that in the late season, steelhead are as likely
to show affinity for pools in the treated
reach as for those in the control reach. Low
recapture rates for Chinook salmon,
particularly in the mid-August group are
likely due to late summer migration of
individuals toward overwintering areas
downstream. This would be consistent with
our observation in both 2009 and 2010 that
Chinook density declines rapidly in mid-tolate August. High variation in recapture
rates among pools across this longer time
scale likely confounded any effects of
habitat/reach. Further study is required to
determine whether longer-term habitat
affinity patterns are affected by habitat
treatments.
ANCOVA showed no overall
difference in density between reaches for
either chinook or steelhead, but the strong
influence of temporal differences described
in Figs. 1 & 2 was apparent and time
interacted significantly with reach.
Covariate analysis showed that some
environmental variables were associated
with chinook and steelhead density (Table
2). Both species are more abundant at
warmer temperatures. It appears that
Chinook prefer deeper water. Flow was not
a significant factor in Chinook density.
Steelhead appeared to prefer shallower,
faster water. Mean flow rates were faster in
the control reach (not shown here), which
may account for higher steelhead density at
control sites.
Our results indicate that species
respond differently to the placement of in-
stream habitat restoration structures.
Steelhead growth showed that, despite lower
total density at the restoration structures,
individuals benefit in terms of fitness
correlates in treated reaches. It is unknown
whether the increased habitat affinity
observed in 2009 is the result of enhanced
foraging opportunities leading to increased
growth. It remains poorly understood why
steelhead density remains, nevertheless,
higher in the untreated reach compared with
the treated reach. It is further
counterintuitive that steelhead density
showed a positive correlation with
temperature, but that growth showed an
inverse relationship with total degree days.
More investigation of steelhead
bioenergetics and optimal temperature is
warranted. Both total density and recapture
rates for Chinook are so low in the untreated
reach that it is difficult to interpret the
observed lack of growth difference, longerterm habitat affinity or lack of density
dependence in either response.
Chinook
R 2 = 0.235
F4, 79 = 6.07 p = 0.0003
FLOW
TEMP
DO
DEPTH
beta
0.157
0.345
-0.067
0.269
t 87
1.62
3.45
-0.67
2.69
p
0.110
0.0009
0.487
0.007
Steelhead
R 2 = 0.164
F4, 79 = 3.86 p = 0.006
FLOW
TEMP
DO
DEPTH
beta
0.201
0.383
0.001
-0.228
t 79
1.88
3.49
0.007
-2.14
Table 2. Multiple regression analysis
p
0.063
0.001
0.994
0.035
a)
Effect
Reach
Time
RXT
F
1.21
53.93
2.17
df
18
36
36
p
0.286
<0.001
0.129
b)
Effect
Reach
Time
RXT
F
25.63
66.45
12.74
df
18
36
36
p
<0.001
<0.001
<0.001
c)
Effect
Reach
Time
RXT
F
3.64
22.42
4.162
df
18
36
36
p
0.073
<0.001
0.024
Figure 1. 2009 mean density of total fish(a),
Chinook(b) and steelhead(c) in reaches treated with
restoration structures and in control (untreated)
reaches July – September, 2009. Differences between
treatment and control reaches and temporal effects
were analyzed with repeated measures ANOVA.
a)
Effect
Reach
Time
RXT
F
0.009
9.10
6.01
df
17
51
51
p
0.924
< 0.001
0.001
b)
Effect
Reach
Time
RXT
F
15.38
18.93
15.93
df
17
51
51
p
0.001
< 0.001
< 0.001
c)
Effect
Reach
Time
RXT
F
11.10
1.56
1.52
df
17
51
51
p
0.004
0.208
0.222
Figure 2. 2010 mean density of total fish(a),
Chinook(b) and steelhead(c) in reaches treated with
restoration structures and in control (untreated)
reaches August – October, 2010. Differences between
treatment and control reaches and temporal effects
were analyzed with repeated measures ANOVA.
Figure 3a. Mean growth of Chinook in treated reach
vs. control reach over the 2010 sampling period.
Figure 3b. Mean growth of steelhead in treated reach
vs. control reach over the 2010 sampling period.
Figure 4. Recapture rates for Chinook and steelhead
over the 2010 sampling period.
Figure 4. Recapture rates for Chinook and steelhead
over the 2010 sampling period.