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Seasonal Changes in Habitat Availability and the Distribution and
Abundance of Salmonids along a Stream Gradient from Headwaters to
Mouth in Coastal Oregon
Gordon H. Reevesa; Jack D. Sleeperb; Dirk W. Langc
a
U.S. Forest Service, Pacific Northwest Research Station, Corvallis, Oregon, USA b U.S. Forest Service,
Siuslaw National Forest, Corvallis, Oregon, USA c U.S. Forest Service, Cordova, Alaska, USA
First published on: 18 May 2011
To cite this Article Reeves, Gordon H. , Sleeper, Jack D. and Lang, Dirk W.(2011) 'Seasonal Changes in Habitat Availability
and the Distribution and Abundance of Salmonids along a Stream Gradient from Headwaters to Mouth in Coastal
Oregon', Transactions of the American Fisheries Society, 140: 3, 537 — 548, First published on: 18 May 2011 (iFirst)
To link to this Article: DOI: 10.1080/00028487.2011.572003
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Transactions of the American Fisheries Society 140:537–548, 2011
American Fisheries Society 2011
ISSN: 0002-8487 print / 1548-8659 online
DOI: 10.1080/00028487.2011.572003
ARTICLE
Seasonal Changes in Habitat Availability and the
Distribution and Abundance of Salmonids along a Stream
Gradient from Headwaters to Mouth in Coastal Oregon
Gordon H. Reeves*
Downloaded By: [Reeves, Gordon H.][National Forest Service] At: 16:35 1 June 2011
U.S. Forest Service, Pacific Northwest Research Station, 3200 Southwest Jefferson Way, Corvallis,
Oregon 97331, USA
Jack D. Sleeper
U.S. Forest Service, Siuslaw National Forest, 4077 Southwest Research Way, Corvallis, Oregon 97331,
USA
Dirk W. Lang
U.S. Forest Service, Post Office Box 280, Cordova, Alaska 99574, USA
Abstract
Visual estimation techniques were used to quantify seasonal habitat characteristics, habitat use, and longitudinal
distribution of juvenile steelhead Oncorhynchus mykiss, coastal cutthroat trout O. clarkii clarkii and coho salmon O.
kisutch in a coastal Oregon basin. At the channel unit scale, fish distribution was not proportional to habitat type
availability. Pool habitats contained a disproportionate percentage of the salmonid assemblage, and the percentage of
fish in pools increased as flow decreased. Large woody debris formed 57–68% of pool habitats and was significantly
correlated with pool volume, maximum pool depth, slow surface velocity in pools, and pieces of small woody debris.
At the reach and basin scales, longitudinal distribution of the total salmonid assemblage generally did not differ
from habitat distribution seasonally or between years. Abundance in the reaches varied annually, and the fish
species were longitudinally segregated within the basin: coastal cutthroat trout occurred in the uppermost reaches,
steelhead occupied the lowest reaches, and coho salmon inhabited the middle reaches. This study demonstrates
that the basinwide distribution of salmonids varies among species, age-classes, seasons, and years. These results
suggest that our understanding of salmonid distribution and abundance could be greatly enhanced by adopting a
basinwide, community, seasonal perspective. In addition, the methods described here offer one way to assess the
seasonal distribution and abundance of salmonids in a relatively quick, inexpensive, nondestructive manner.
Fish managers are increasingly required to consider larger
spatial and temporal scales when developing and evaluating
management options and potential impacts of proposed actions.
This requires an understanding of the distribution of species
and life history stages over relatively large spatial scales (e.g.,
watershed) and how patterns of distribution change through
time (seasonally). The distribution of juvenile salmonids in
streams has primarily been investigated at the relatively small
mesoscale of habitat types (e.g., pool and riffle) by focusing
on the fish species and age-classes that are generally associated
with specific habitat types (e.g., Bisson et al. 1988; Roper et
al. 1994). The observed patterns of habitat selection in such
studies often represent only a single season (mainly summer),
even though seasonal shifts in habitat selection are known to
occur (Nickelson et al. 1992; Valdimarsson et al. 2000; Reeves
et al. 2010). In addition, other physical and biological processes
interact to create a continually changing stream environment
for fish. However, habitat selection—and thus fish distribution
*Corresponding author: greeves@fs.fed.us
Received April 28, 2010; accepted December 15, 2010
537
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538
REEVES ET AL.
in a basin—may change temporally and spatially as physical
conditions change throughout the stream (Bisson et al. 1982;
Torgersen et al. 1999).
Few studies have considered how seasonal use and interactions among fish species and age-classes affect fish longitudinal distribution. Studies on the longitudinal distribution of fish
populations have focused on differences in species diversity and
abundance (Sheldon 1968; Hughes and Gammon 1987; Quist
et al. 2004). Distribution has been related to the distribution of
spawning habitat (Hartman and Gill 1968), habitat types (Bisson
and Sedell 1984; Inoue and Nunokawa 2002), food availability (Hawkins et al. 1983; Wilzbach 1985), feeding efficiency
(Wilzbach and Hall 1985; Taniguchi et al. 1998), and environmental variables (Quist et al. 2004; Taylor et al. 2005). In
most of these studies, the number of sites sampled is small relative to the entire stream basin, which leaves the distribution
over large areas unknown. Such gaps make it difficult for researchers to determine where distributional differences begin
and end or how the differences are related to the basinwide
distribution of the fish assemblage and habitat characteristics.
Sampled fragments of the whole system are often used to piece
together an understanding of fish distribution and can provide
unclear or inaccurate results (Fausch et al. 2002). Studies that
have assessed fish abundance in contiguous reaches have found
that abrupt changes in species abundance and composition can
occur over relatively short distances (Cederholm and Scarlett
1982; Newman and Waters 1989; Decker and Erman 1992).
These patterns appear to be relatively consistent among years
and seem to be related to habitat characteristics and life history
patterns.
Seasonal migrations of stream salmonids are well recognized. Salmonids have been observed to undertake extensive
longitudinal migrations (Meyers et al. 1992; Murphy et al.
1997). Changes in distribution occur as adults seek suitable
spawning areas (Trotter 1989), as fry disperse from spawning
areas and establish feeding territories (Chapman 1962), and as
habitat conditions change (Bilby and Bisson 1987; Meyers et al.
1992). These movements can be particularly pronounced during increased streamflows, when side-channel ponds (Peterson
1982) and small tributaries (Hartman and Brown 1987; Ebersole
et al. 2006) become reconnected to the main channel. Few studies have assessed how these patterns influence the longitudinal
distribution of the assemblage as a whole, and few have related
seasonal patterns in longitudinal fish distribution to seasonal
habitat characteristics.
The objective of our study was to determine seasonal abundance and distribution of juvenile salmonids throughout an entire drainage basin and to relate fish distribution to habitat availability and characteristics. This information is necessary to (1)
improve the understanding of the seasonal dynamics of juvenile salmonid habitat use relative to habitat availability and (2)
identify factors that influence the distribution of salmonids in
coastal Oregon basins.
FIGURE 1. Location of the Cummins Creek basin in Oregon and eight study
reaches used to examine salmonid and habitat distributions. Each reach was
approximately 1.1 river kilometer.
METHODS
Study area.—Cummins Creek is located on the central Oregon coast, about 48 km south of the city of Newport (Figure
1). This 14-km2 basin, which lies within the volcanic geology
of the Yachats Basalt Formation, drains directly into the Pacific
Ocean. The elevation ranges from 754 m to sea level. Topography is steep; side slopes average 25–35% in the lower basin and
15–25% in the upper basin. The gradient of Cummins Creek
averages 2.5% in the lower 7 km and then gradually increases
to 4.5% in the upper part of the basin (U.S. Department of Agriculture, Forest Service, unpublished data). The Cummins Creek
basin is relatively undisturbed by human activities; less than 1%
of the basin has been disturbed by timber harvest.
Tributaries to Cummins Creek are located primarily in the upper basin, and only the lower sections of these tributaries support
fish. For this study, sampling was restricted to the main channel
of Cummins Creek. Several of the tributaries had experienced
recent debris torrents that delivered considerable amounts of
large woody debris (LWD) to Cummins Creek (Reeves et al.
2003). The largest deposits were located 4.2, 5.0, and 8.8 km
upstream from the mouth.
Cummins Creek has mild stream temperatures (generally
5–15◦ C) throughout the year. Precipitation in the Cummins
Creek basin falls mainly as rain, primarily between November
and April. Precipitation during the study period averaged 200
cm/year at nearby Tenmile Beach (T. Smith, Yachats, Oregon,
unpublished data), which is approximately 6 km south of
Cummins Creek. Flows in Cummins Creek were estimated by
using the gage recordings at Big Creek, which was located
10 km south and for which flows were highly correlated with
the Cummins Creek stage height (r = 0.95, P < 0.01; Sleeper
1993). Estimated streamflow in Cummins Creek ranged from
0.1 to 13.5 m3/s during the 19-month sampling period (Table
1). Streamflow was highest and most variable from November
to March. Lowest flows usually occurred in early fall. Based on
539
SEASONAL CHANGES IN SALMONID DISTRIBUTION
TABLE 1. Sampling dates, percentage of units snorkeled by habitat type (SC = side channel; VFT = valley floor tributary) average stream temperature (temp.),
and estimated streamflow for Cummins Creek, Oregon. Habitat was not surveyed in June or October 1988.
Streamflow between surveys (m3/s)
Units snorkeled (%)
Sampling period
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28 Sep–5 Oct 1987
11–13 Apr 1988
8–9 Jun 1988
15–18 Aug 1988
21–22 Oct 1988
13–16 Apr 1989
Pool Glide Riffle
20
33
33
33
33
33
12
12
12
12
12
20
12
5
5
5
5
5
SC
VFT
Temp. (◦ C)
Survey average
streamflow
(m3/s)
0
0
50
50
50
50
0
0
50
50
50
50
10
11
14
12
11
0.1
1.6
1.7
0.2
0.2
1.1
the flow records from the Alsea River (20 km north of Cummins
Creek), flows during the study were slightly lower than the
long-term average reported by the U.S. Geological Survey
(http://waterdata.usgs.gov/nwis/nwisman/?site 14306500&
agency cd = USGS).
Substrate throughout Cummins Creek is primarily cobble
(8–15 cm in diameter) intermixed with gravel (2–8 cm; Sleeper
1993). A few small boulders (>15 cm) can be found in the
upper basin and at tributary junctions. Large concentrations of
spawning gravels are found above debris deposits at river kilometers 4.2 and 5.0, and smaller patches are found in pool tailouts
throughout the basin.
The fish assemblage in Cummins Creek consists of steelhead Oncorhynchus mykiss, coastal cutthroat trout O. clarkii
clarkii, coho salmon O. kisutch, sculpins Cottus spp., and Pacific lampreys Lampetra tridentata. North American beavers
Castor canadensis influence fish habitat availability and quality
in some parts of the watershed, particularly in fall (September
and October), when beaver dams are most extensive in the main
channel. However, most dams are washed out by the first major
storms in November, except for dams situated on the floodplain
out of the main channel.
Sitka spruce Picea sitchensis, western hemlock Tsuga heterophylla, Douglas-fir Pseudotsuga menziesii, red alder Alnus
rubra, and bigleaf maple Acer macrophyllum dominate the overstory, while salmonberry Rubus spectabilis, western swordfern
Polystichum munitum, and salal Gaultheria shallon dominate
the understory.
Fish and habitat sampling.—Habitat and fish surveys were
conducted in September 1987, April 1988, August 1988, and
April 1989 (Table 1). In June and October 1988, fish abundance
was surveyed but the habitat was not. For both of these abundance surveys, habitat characteristics were assumed to be identical to those identified in the previous habitat survey (i.e., April
and August 1988, respectively) because estimated streamflow
did not change between the sampling periods. This assumption
is based on similar stage height of Cummins Creek in April and
June 1988 and in August and October 1988, and it is supported
Average
Peak
1.8
1.6
0.5
0.2
3.1
11.3
3.2
1.6
0.5
13.5
by the high correlation between stage height and habitat volume
(r = 0.99, df = 2, P = 0.07; Sleeper 1993). In addition, U.S.
Geological Survey gaged streamflow in the nearby Big Creek
basin (31 km2) demonstrated similar flows during the April and
June sample periods and during the August and October periods.
Habitat units were classified as pool, glide, riffle, side channel
(Bisson et al. 1982), or valley floor tributary. Valley floor tributaries were the low-gradient portions of tributaries that were
located along the floodplain of Cummins Creek. In general,
they resembled side channels. Split flows (areas where the main
channel of the stream was split into two or more channels) were
considered main-channel habitats and were separated into pool,
glide, or riffle habitat types. In summer, when very little flow
went through one side of a split flow, it was classified as a side
channel.
During habitat surveys, the average length, width, and depth
of each unit of a given habitat type were visually estimated by
following the methods of Hankin and Reeves (1988). Beginning
at the downstream end of a unit, dimensions of each habitat
unit in the basin were estimated and recorded. To correct for
estimator bias, dimensions in approximately 5% of the units
were measured to develop correction factors for each habitat
type (Hankin and Reeves 1988).
Habitat characteristics that might influence fish distribution
were also recorded during habitat surveys. The two-dimensional
(flat plane) area of LWD accumulations was estimated for mainchannel units in August 1988 and April 1989. Pieces of small
woody debris (length < 1 m; diameter < 8 cm) were estimated
for each unit in April 1989 by using three abundance classes
(5–15, 16–25, and >25 pieces). Locations where wood was
responsible for the formation of a given pool were noted. Maximum pool depth was measured for all pools in August 1988 but
was too deep to permit measurement at higher flows in April
and June. Because low-velocity areas are scarce during moderate to high streamflow and because velocity has been shown
to influence fish distribution (e.g., Bustard and Narver 1975), a
visual estimate of the pool area that had a surface velocity less
than 0.5 m/s was recorded for all pools in April 1989.
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540
REEVES ET AL.
Fish numbers were sampled in systematically selected habitat
units. A random starting point was determined for each habitat
type at the start of each sampling period. The point depended
on the percentage of units of a given habitat type that were to be
sampled (Table 1). For example, if 33% of the pools were to be
sampled, the first pool to be examined was randomly selected
from among the first three (downstream-most) pools in a section.
Every third pool was then sampled. This scheme ensured that
units would be sampled from along the entire section and not
just in a relatively small portion, which could have happened
with a simple random sampling method.
Divers using mask and snorkel counted the number of fish
in each sampled unit by beginning downstream and proceeding
slowly upstream. Areas providing cover were carefully searched
to locate hiding fish. Two divers were used in larger units; they
partitioned the unit, each counting fish in part of the unit. The
estimate for the unit was the sum of the individual divers’ estimates. In small units, a single diver made the counts. All fish
counts were made between 0900 and 1600 hours when visibility
was good (i.e., averaging approximately 4 m).
Fish were classified by species and size-class (estimated ageclass). Divers identified and counted all age-0 and age-1 steelhead, coastal cutthroat trout, and coho salmon. It was assumed
that both coho salmon and steelhead proceeded to the next ageclass just prior to the April sampling period. Age-1 coho salmon
and age-2 steelhead were expected to migrate to the ocean as
smolts during April–June and were classified as presmolts during those sampling periods. Age-0 coastal cutthroat trout could
not be differentiated from steelhead; therefore, we classified all
age-0 trout as steelhead because age-1 steelhead were two to
eight times more abundant than age-1 coastal cutthroat trout in
all sampling periods.
In April 1988, only coastal cutthroat trout larger than 20 cm in
fork length were classified as coastal cutthroat trout, and smaller
age-1 coastal cutthroat trout were counted as age-1 steelhead.
However, after the initial sampling periods, we determined that
coastal cutthroat trout between 10 and 20 cm could be distinguished from steelhead; therefore, from June 1988 to April
1989, both small (10–20 cm) and large (>20 cm) coastal cutthroat trout were identified.
Because the relationship between diver counts and the actual
number of fish present was unknown, the estimated populations
are relative rather than absolute estimates. We assumed that a
constant fraction of each species and age-class were observed
in each habitat type during each sampling period. Hankin and
Reeves (1988) found strong correlations (r > 0.94) between
diver counts in Cummins Creek (July 1985) and electrofishing
estimates of abundance for age-1 steelhead and coho salmon
in riffles and for coho salmon in pools. The relationship was
not as strong (r = 0.61) for age-1 steelhead in pools. Hankin
and Reeves (1988) estimated the ratios of electrofishing to diver
counts at between 0.97 and 1.05 for age-1 steelhead in pools,
age-1 steelhead in riffles, and age-1 coho salmon in pools; the
ratio was estimated at 1.36 for age-1 coho salmon in riffles.
Thus, diver counts and electrofishing produced similar estimates
of fish abundance. The same divers were used during snorkel
surveys when possible to minimize variance of estimates of fish
abundance among sampling periods.
Habitat availability and fish population estimates were summarized for eight contiguous reaches, each measuring 1.1 km
in stream length (Figure 1). In general, Cummins Creek is geomorphically uniform throughout the study area. As a result,
a uniform reach length was used to simplify the sampling and
analysis.
Estimates of fish abundance and distribution.—The fish sampling scheme was designed to focus sampling effort in pool habitats, where the salmonid populations are concentrated (Hankin
and Reeves 1988). For pools, the mean relative density of a given
species or age-class was calculated for each reach. The calculated mean density was then multiplied by the total estimated
available pool habitat within that reach to estimate abundance
in pools within that reach.
Fish abundance in pools within a given reach x (Nprx ) was
estimated as follows:
Nprx = (Dprx )(Hprx ),
where Dprx = mean relative density of fish in pools within reach
x, and Hprx = total pool habitat in reach x. Because glides, riffles,
side channels, and valley floor tributaries were not sampled
frequently enough to obtain mean fish densities in each reach,
a mean relative density was calculated for the lower (reaches
1–4) and upper (reaches 5–8) halves of the basin. Estimating
half-basin densities would act to lessen reach-level differences
in fish abundance if such differences existed. Each density was
then multiplied by the total available habitat of that particular
type for each reach. Summing population estimates from each
habitat type in each reach produced reach-level estimates of fish
abundance. Within a given habitat type and reach, we assumed
that fish densities observed in sampled units were characteristic
of all units in that reach (or half basin, depending on the habitat
type).
We estimated fish abundance in glides, riffles, side channels,
and valley floor tributaries for each reach x in a manner similar
to that exemplified below (for glides):
Ngrx = (Dgrx )(Hgrx ),
where Ngrx = estimated number of fish in glides within reach
x, Dgrx = mean relative density of fish in glides within reach x
based on values for reaches 1–4 or 5–8, and Hgrx = total glide
habitat within reach x.
The total number of fish in reach x (Nrx ) was then estimated
as:
Nrx = Nprx + Ngrx + Nrrx + Nscrx + Nvf rx ,
SEASONAL CHANGES IN SALMONID DISTRIBUTION
541
where Nrrx = estimated number of fish in riffles within reach x,
Nscrx = estimated number of fish in side channels within reach
x, and Nvfrx = estimated number of fish in valley floor tributaries
within reach x. The total number of fish in the basin (Nb ) was
calculated as:
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Nb = Nr1 + Nr2 · · · + Nr8 ,
where Nr1 = estimated number of fish in reach 1, Nr2 = estimated number of fish in reach 2, and so on.
The coefficient of variation for each species and age-class
was used to determine which measure of unit size should be
used to estimate fish abundance. In general, variation was lowest
with area in April–June samples and was lowest with volume in
August–October samples. For this reason, fish abundance was
estimated based on area in April 1988, June 1988, and April
1989 and based on volume in August 1988 and October 1988.
The chi-square goodness-of-fit statistic was used to determine whether fish were distributed in proportion to habitat both
longitudinally and by habitat type. The chi-square test compared
the percentage of fish in a given habitat type or reach with the
percentage of habitat available. An independent Student’s t-test
was used to determine differences in habitat characteristics between the upper and lower halves of the basin. When calculating
probabilities, we log transformed all habitat and fish data to meet
the assumption of normality.
RESULTS
Habitat Use
In each sampling period except August 1988, the salmonid
assemblage used habitat types in proportions that were significantly different from the proportional availability of habitat
types (P < 0.01; Table 2). Age-0 steelhead were the only species
or age-class that used habitat types in proportion to their availability in some sampling periods (P > 0.10) or that used riffle
habitats in greater proportion than their availability. Age-0 steelhead were noticeably absent from the surveys in April of each
year. Disproportionate use of riffle habitats by age-0 steelhead
occurred in August 1988, when fish abundance was highest and
when streamflow was near its annual low.
Pool habitats contained a disproportionate percentage of the
salmonid assemblage and the older age-classes (age-1 and presmolt steelhead, presmolt coho salmon, and coastal cutthroat
trout) in each sampling period (Table 2). More than 79% of age1 cutthroat trout (>10 cm) were located in pools during each
sampling period. Except for age-0 steelhead, the proportion of
the various species and age-classes found in pools was highest during low-flow periods in August and October 1988. As
low-flow conditions persisted from August to October 1988, the
assemblage abundance decreased by 9% in pool habitats and by
55% in riffle habitats (Figure 2).
Side channels and valley floor tributaries contained a disproportionate number of coho salmon fry in June 1988 and April
1989 (Table 2). These habitat types constituted 5% of the total
FIGURE 2. Estimated relative abundance of steelhead, coho salmon, and
coastal cutthroat trout and their combined abundance (total salmonids) in Cummins Creek, Oregon, by age-class and habitat type, 1987–1989.
habitat available at these times but contained 20–60% of the
total coho salmon fry in the basin. During June 1988 and April
1989, coho salmon fry densities in these habitat types were 8–31
times the densities in main-channel habitat. Abundance of coho
salmon fry in floodplain habitats decreased as streamflow decreased from June to August such that these combined habitats
were only used in proportion to their availability by August
(Table 2).
Large woody debris was instrumental in forming and maintaining pool habitats and floodplain habitats in Cummins Creek.
In August 1988 and April 1989, 57–68% of the pool habitats
were noted as having been formed by LWD. Large woody debris
was positively correlated with pool volume in August 1988 (r =
0.38, df = 159, P ≤ 0.01) and April 1989 (r = 0.27, df = 140, P
≤ 0.01), with maximum pool depth in August 1988 (r = 0.44,
df = 155, P ≤ 0.01), and with the area of slow surface velocity
(<0.5 m/s) within pools in April 1989 (r = 0.25, df = 131, P ≤
0.01). In April 1989, LWD was also positively correlated with
pieces of small woody debris (r = 0.40, df = 31, P = 0.02),
which added habitat complexity and cover. Pieces of LWD at
the heads of side channels were responsible for diverting flow
into many of these habitats. In addition, pools within floodplain
habitats were often formed and maintained by pieces of LWD or
beaver dams. Beaver dams also increased pool area and volume
in the main channel in late summer.
542
REEVES ET AL.
TABLE 2. Proportion of habitat type (SC = side channel; VFT = vallege floor tributary) and use by salmonid species and age-class or size class in Cummins
Creek, Oregon, and associated chi-square value and probability α = 0.05; blank cells not sampled; asterisks = not present; # = counts were included with steelhead
counts)
Steelhead
Downloaded By: [Reeves, Gordon H.][National Forest Service] At: 16:35 1 June 2011
Date
Habitat
type
Habitat
(%)
Age 0
Age 1
60
20
20
70
20
10
Pool
Glide
Riffle
SCa
VFTa
χ2
P
54
21
25
Pool
Glide
Riffle
SCa
VFTa
χ2
P
24
14
62
Pool
Glide
Riffle
SC
VFT
χ2
P
22
13
60
3
2
29
12
52
4
3
4.2
0.38
Pool
Glide
Riffle
SC
VFTb
χ2
P
58
10
29
3
43
13
44
0
Pool
Glide
Riffle
SC
VFTb
χ2
P
58
10
29
3
1.71
0.42
∗
∗
∗
56
12
32
0
3.78
0.29
Presmolt
∗
∗
∗
55
18
27
49
21
30
0
0
58.06
<0.01
75
7
18
0
62
19
19
28.14
<0.01
Volume, Sep 1987
85
15
0
Presmolt 10–20 cm
∗
∗
∗
Area, Apr 1988
51
13
36
∗
∗
∗
∗
38.14
<0.01
Volume, Oct 1988
93
3
0
4
55.35
<0.01
#
#
#
>20 cm
88
7
5
>10cm
#
#
#
46.74
<0.01
76
24
0
91.78
41.35
181.81
<0.01
<0.01
<0.01
Area, Jun 1988
92
60
100
8
16
0
0
4
0
0
10
0
0
10
0
289.65 166.93
354.55
<0.01
<0.01
<0.01
Volume, Aug 1988
∗
∗
85
∗
∗
9
∗
∗
2
∗
∗
4
13.06
<0.01
82
10
8
0
Age 0
Coastal cutthroat trout
44. > 51
<0.01
13.79
<0.01
60.94
<0.01
15.54
<0.01
Coho salmon
#
#
#
73
7
19
1
9.56
0.02
∗
∗
∗
∗
72
12
16
0
12.61
<0.01
70
18
12
11.93
<0.01
84
16
0
#
#
#
212.29
<0.01
82
18
0
0
0
230.56
<0.01
Salmonid
assemblage
79
21
0
0
0
217.61
<0.01
86
6
8
0
33.12
<0.01
92
8
0
0
52.33
<0.01
59
18
23
76.72
<0.01
81
19
0
0
0
226
<0.01
80
6
13
1
20.11
<0.01
79
11
10
0
23.15
<0.01
51
16
23
5
5
67.57
<0.01
64
10
24
2
1.82
<0.01
76
8
14
2
14.08
<0.01
543
SEASONAL CHANGES IN SALMONID DISTRIBUTION
TABLE 2.
Continued.
Steelhead
Downloaded By: [Reeves, Gordon H.][National Forest Service] At: 16:35 1 June 2011
Date
Habitat
type
Pool
Glide
Riffle
SC
VFT
χ2
P
Habitat
(%)
32
15
48
4
1
Age 0
Age 1
∗
47
20
33
0
0
18.39
<0.01
∗
∗
∗
∗
Coho salmon
Presmolt
Age 0
Coastal cutthroat trout
Presmolt 10–20 cm
Area, Apr 1989
60
26
83
14
10
14
26
4
1
0
41
2
0
19
0
38.65 709.38
129.37
<0.01
<0.01
<0.01
83
14
3
0
0
128.54
<0.01
>20 cm
>10cm
Salmonid
assemblage
94
6
0
0
0
178.53
<0.01
86
12
2
0
0
140.81
<0.01
57
15
15
9
4
57.47
<0.01
a
Side-channel and valley floor tributary habitats did not occur in September 1987 or April 1988.
Valley floor tributary habitats did not occur in August 1988 or October 1988.
b
FIGURE 3. Percent longitudinal habitat availability in reaches 1–8 of Cummins Creek, Oregon (Figure 1), and use of reaches by steelhead, coho salmon, and
coastal cutthroat trout (various age-classes) and by all species combined (all species) in 1987–1989. Relative abundance is shown by circle size, which is scaled to
the percentage of the estimated total number for the stream at each time period (source: Sleeper 1993).
Downloaded By: [Reeves, Gordon H.][National Forest Service] At: 16:35 1 June 2011
544
REEVES ET AL.
Longitudinal Distribution
Although each species was distributed throughout the basin,
there was a general trend in longitudinal distribution during most
sampling periods. Abundance was greatest for steelhead in the
lower basin, for coastal cutthroat trout in the upper basin, and for
coho salmon in the middle portions of the basin (Figure 3). Fish
abundance varied seasonally between species and between ageclasses within species, and reaches with the greatest numbers of
fish were often located where transitions between species and
age-classes occurred.
Longitudinal distribution of the salmonid assemblage did not
differ from habitat distribution seasonally or between years (P
> 0.10; Figure 3). However, longitudinal distribution of individual species and age-classes varied from habitat distribution
in some sampling periods. Age-0 coho salmon distribution was
significantly different from habitat distribution in each sampling
period except August and October 1988 (P < 0.05; Figure 3).
Age-0 coho salmon were concentrated in reaches 5–7 (Figure
3) in April of both years.
The relative distribution of age-1 steelhead varied with the
longitudinal distribution of habitat throughout the study (P >
0.10; Figure 3) except for the presmolts sampled in April 1988,
June 1988, and April 1989. Both steelhead presmolts and coho
salmon presmolts were most abundant in pool habitats within
the lower reaches during spring of both years (Table 2; Figure 3).
Mean pool area and volume were significantly larger in reaches
1–4 than in reaches 5–8 (P < 0.01) during April of both years,
and reaches 1–4 contained 65–72% of the total pool volume
(Figure 3). In April 1989, the amount of pool area with surface
velocities less than 0.5 m/s was strongly correlated with total
pool area (r = 0.73, df = 183, P < 0.01), and approximately
70% of the streamwide slow-velocity area in pools was located
in reaches 1–4.
Abundances of coho salmon presmolts and steelhead presmolts were significantly correlated with the area of slow surface
velocity (<0.5 m/s) in pools in April 1989 (coho salmon: r =
0.66, df = 45, P < 0.01; steelhead: r = 0.57, df = 47, P < 0.01)
and with pool volume in April 1988 (r = 0.62, df = 46, P <
0.01) and April 1989 (r > 0.67, df > 24, P < 0.01).
Age-0 trout were distributed in proportion to longitudinal
habitat during all sampling periods (P > 0.10; Figure 3). Coastal
cutthroat trout distribution was significantly different from longitudinal habitat distribution in each sampling period (P < 0.10)
except August 1988. In all sampling periods except April 1988,
coastal cutthroat trout were most abundant in upper reaches,
typically just upstream from areas of high coho salmon abundance.
Fish abundance appeared to have a strong influence on longitudinal distribution. Total salmonid abundance was 50–60%
greater in 1988–1989 than in 1987–1988, primarily because of
greater coho salmon numbers (Figure 2). Fish were distributed
more widely when abundance was high than when abundance
was low. The relatively high fish abundance in August and Oc-
FIGURE 4. Longitudinal distribution of the salmonid assemblage (steelhead,
coho salmon, and coastal cutthroat trout combined) during the fall (September
1987 = solid line; October 1988 = dashed line) and spring (April 1988 = solid
line; April 1989 = dashed line) in Cummins Creek, Oregon.
tober 1988 resulted in large increases in fish abundance within
downstream reaches, whereas upstream reaches had similar
numbers between years (Figure 4). The opposite pattern was
observed in spring. Higher abundance in April 1989 was associated with expanded fish distribution upstream (particularly for
coastal cutthroat trout and age-0 coho salmon) in comparison
with April 1988 (Figure 4). There was a large increase in fish
abundance in upstream reaches, whereas downstream reaches
had similar numbers between years. The result was that certain
reaches had consistent numbers of fish between years, while the
number of fish in other reaches varied widely.
DISCUSSION
The relative distribution of fish in Cummins Creek changed
both longitudinally and by habitat type over the course of the
study. We found that there were continuous temporal shifts in
salmonid distribution throughout the basin and that gradual,
relatively minor shifts influenced the basinwide distribution of
salmonids. Other studies have focused on major changes in distribution that occur with the emergence of fry in spring (Hartman
et al. 1982), the establishment of territories (Chapman 1962),
and the onset of large freshets in fall (Cederholm and Scarlett
1982). Most studies on juvenile salmonid distribution and habitat use in Pacific Northwest streams have focused on a particular
season (Roper et al. 1994) or life history event (Hartman et al.
1982). This study emphasizes that the basinwide distribution
of juvenile salmonids can vary temporally among species and
age-classes.
Species-specific distribution patterns have been observed at
most spatial scales ranging from microhabitats (Everest and
Chapman 1972) to longitudinal reaches (Frissell 1992; Scarnecchia and Roper 2000). In Cummins Creek, there was a general longitudinal pattern wherein reaches with highest steelhead
abundance were located in the lower basin, reaches with the
highest coastal cutthroat trout abundance were found in the upper basin, and reaches with the highest coho salmon abundance
Downloaded By: [Reeves, Gordon H.][National Forest Service] At: 16:35 1 June 2011
SEASONAL CHANGES IN SALMONID DISTRIBUTION
were intermediate. Schwartz (1991) found a similar pattern in
Drift Creek, Oregon, where the highest abundance of Chinook
salmon O. tshawytscha was in the lower basin, the highest abundance of coastal cutthroat trout was in the upper basin, and
the highest abundance of coho salmon was in an intermediate
area; steelhead in Drift Creek were more evenly distributed.
Similar species segregation has been observed among steelhead, coho salmon, and Chinook salmon in the Umpqua River
basin (Roper et al. 1994; Scarnecchia and Roper 2000). However, we also observed temporal changes in the distribution of
species throughout Cummins Creek. The relative importance of
individual factors that influence distribution often depends on
interrelationships among factors (Bilby and Bisson 1987) and
on temporal changes in life history characteristics and habitat
conditions.
Initially, the distribution of the juvenile salmonid assemblage
in Cummins Creek was probably influenced by spawning habitats for adult fish (Kocik and Ferreri 1998) and the timing of
spawning. Coho salmon fry were most abundant in the middle reaches during the spring of both years. These reaches were
highly influenced by tributary confluences and by log jams from
debris torrents, which resulted in ideal habitats (Montgomery et
al. 2003; Benda et al. 2004) with low gradients, abundant LWD,
off-channel floodplains, and medium to large gravels that are
excellent for coho salmon spawning (Reeves et al. 2002). Reach
5 contained two large debris deposits that accumulated a large
concentration of spawning gravels and created a relatively open
canopy and abundant floodplain rearing habitats. Similar conditions existed in reach 7, although to a lesser extent, where three
large tributaries enter Cummins Creek. Coastal cutthroat trout
spawning and rearing areas were generally located immediately
upstream from those of coho salmon and steelhead, and age-1
coastal cutthroat trout were most abundant in the upper reaches
during spring. Large coastal cutthroat trout (>20 cm) were the
least abundant group throughout the basin at this time, probably
because they migrated into the uppermost tributaries to spawn
(Trotter 1989). Age-0 steelhead (which included age-0 coastal
cutthroat trout; see Methods) were absent from the surveys in
April of each year. Adults of each species spawn in the late
winter and early spring, and the age-0 fish had not yet emerged
by the April sampling period. Although age-0 steelhead were
evenly distributed when they began to emerge in June 1988,
by late summer they were most abundant in the lower basin
during both years. This result suggests that steelhead spawn
throughout the system but that juveniles disperse quickly into
the lower river because of competition (Chapman 1962; Bohlin
1978).
Habitat type preferences, species interactions, and the distribution of habitat types probably modify the initial distribution
established by spawning adults. Disproportionate use of floodplain habitats by coho salmon fry in spring and the concentration of those habitats within reaches 4–7 limited the dispersal
of these fish from spawning areas. Coho salmon were generally
most abundant in those reaches; the exception was for presmolts,
545
which were found in the lower reaches during the spring prior to
out-migration. The wide range of habitat types used by steelhead
suggests that most reaches contained suitable habitat for these
fish. Coastal cutthroat trout were found in greater abundance in
the upper part of the basin. The use of these reaches by coastal
cutthroat trout may be more attributable to competition with
the other species than to selection (Glova 1987; Hicks 1990).
These small streams and tributaries are important habitats for
coastal cutthroat trout in Pacific coastal streams (Rosenfeld et al.
2000).
Not surprisingly, pool habitats contained the majority of
salmonids and became increasingly important during low-flow
conditions. This result is similar to the findings reported by
other investigators (Bisson et al. 1988; Frissell 1992; Nickelson
et al. 1992). For the most part, salmonid abundance was directly
related to pool size (Sleeper 1993). In comparison with small
pools, large pools are more likely to maintain the slow-velocity
areas that are suitable for salmonids during winter fluctuations in
streamflow. The major component in pool formation was LWD;
this result is consistent with the importance of LWD for influencing fish abundance (Johnston et al. 2005), and it exemplifies
the role of natural disturbances (e.g., debris torrents and log
jams) in creating quality fish habitat in coastal Oregon streams
(Reeves et al. 1995; Montgomery et al. 2003; Bigelow et al.
2007).
Use of riffle habitats by age-0 steelhead in Cummins Creek
appeared to be directly related to total fish abundance in summer,
when riffles were extremely shallow. We assumed that competition for food and space was more intense in 1988 because of
higher fish abundance, and therefore species interactions stimulated age-0 salmonids to increase their use of riffle habitats
in 1988 relative to 1987. Other investigators have found that
riffle habitats are used extensively by age-0 trout in summer
(Bisson et al. 1982; Schwartz 1991). In Drift Creek, age-0 and
age-1 coastal cutthroat trout and steelhead used riffle habitats
in greater proportion than their availability in the main stem
during summer, but these fish were more concentrated in pool
and glide habitats within tributaries, where the riffles were shallow (Schwartz 1991). The extent of riffle use seems to depend
on riffle depth (Reeves et al. 2002), species composition (Hartman 1965; Glova 1987), season (Glova 1986), and total fish
abundance.
Floodplain habitats, such as side channels and valley floor
tributaries, were important habitats for juvenile coho salmon,
particularly in the spring. These habitats provide relatively persistent low-velocity areas for small fish at this time of year, when
main-channel fluctuations are common. Often, such habitats are
also slightly warmer than the main channel, and this greater temperature can accelerate growth (Murphy et al. 1989). Use of side
channels by juvenile coho salmon and other salmonids has been
observed elsewhere (e.g., Cederholm and Scarlett 1982; Nickelson et al. 1992). Floodplain areas can also provide overwintering habitat (Cederholm and Scarlett 1982; Hartman and Brown
1987; Rosenfeld et al. 2008). However, the below-average flows
Downloaded By: [Reeves, Gordon H.][National Forest Service] At: 16:35 1 June 2011
546
REEVES ET AL.
during the study may have reduced the availability of these habitats.
Although certain species were not distributed in proportion
to habitat availability, the overall salmonid assemblage distribution was proportional to habitat availability during all sampling periods; this observation suggests that longitudinal segregation of species is a mechanism that allows for full utilization of available habitat. A relatively even distribution of highquality pool habitat occurs throughout Cummins Creek, which
probably facilitates the even distribution of the salmonid assemblage. If habitat conditions had been more variable among
reaches (e.g., several reaches dominated by riffle habitat), the
longitudinal distribution of the fish assemblage might not have
been as consistently proportional.
Some researchers highlight the fact that on a seasonal
basis, stream salmonids exhibit little movement and maintain
relatively permanent positions in the stream network (Gowan
et al. 1994). However, this conclusion is often associated with
resident fish and is based on recaptures or observations of
marked fish when the percentage of fish recaptured is low and
decreases through time (Gowan et al. 1994). Within a given
population, there are fish that exhibit little movement and
others that show more wide-ranging movement (Armstrong et
al. 1997; Rodrı́guez 2004; Gresswell and Hendricks 2007).
In our study, the distribution of fish in the basin changed
constantly through time, implying a significant amount of movement in the fish populations. Our results are more consistent with
the idea that a large proportion of the salmonids in a given system are not station holders (Pucket and Dill 1985; Decker and
Erman 1992). Certainly, some of the movement we observed
was attributable to the fish being anadromous and migratory at
various life history stages. However, the seasonal movements
could also have been undertaken for additional reasons. Movement by juvenile salmonids can be advantageous, such as when
fish move into food-rich seasonal habitats (e.g., ephemeral tributaries, side channels, and floodplains; Ebersole et al. 2006;
Lang et al. 2006). Juvenile fish that move could achieve better
growth rates than those that maintain a more stationary existence
(Kahler et al. 2001). Fish probably occupy a preferred position
or habitat only temporarily and then change positions in response to changes in fish size (Bisson et al. 1988), fish density
(Close and Anderson 1992), and habitat conditions (Cederholm
and Scarlett 1982; Frissell 1992).
Although our study was limited to the period from September 1987 to April 1989, the results emphasize that the basinwide distribution of juvenile salmonids in Cummins Creek
varied among species, age-classes, seasons, and years. Reaches
and habitat types that in some seasons contained the bulk of a
given species or age-class had relatively few fish at other times.
Species-specific patterns in longitudinal distribution and habitat
type use suggest that our understanding of salmonid distribution
and abundance could be greatly enhanced by adopting a basinwide, year-round, community perspective. Seasonal changes in
habitat use by salmonids in Cummins Creek emphasize the lim-
ited nature of data that single (“snap-shot”) surveys provide and
suggest that multiple surveys are needed annually to understand
the dynamics of habitat use by anadromous salmonids. As was
noted by Fausch et al. (2002), a more continuous view of a
river is necessary for understanding the complex relationships
between stream fishes and their habitat. The modified Hankin
and Reeves (1988) method employed in this study offers a relatively quick, inexpensive, nondestructive approach to assess the
seasonal changes in the basinwide distribution and abundance
of fish and their habitats within small coastal Oregon systems
and similar systems.
ACKNOWLEDGMENTS
We thank J. Sedell and F. Everest, who provided valuable
support for this project from the beginning. S. Gregory, W. Liss,
R. Beschta, H. Li, D. Bateman, and an anonymous reviewer
provided comments on early drafts of the manuscript and helped
to improve it. K. Ronnenberg copyedited the manuscript and
produced the graphics. Special thanks to B. Lovatt, C. Dewberry,
T. Mendenhall, D. Price, M. Raugh, and D. Tickner for field
work. Financial support was provided by the Aquatic and Land
Interactions Program of the U.S. Department of Agriculture,
Forest Service, Pacific Northwest Research Station, Corvallis,
Oregon.
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