Prepared by
Jeffrey M. Dambacher'
Mark W. Buktenica 2
Gary L Larson3
Oregon Department of Fish and Wildlife
8500 15th Street
Corvallis, Oregon, 97333
2National Park Service-
Pacific Northwest Region
Crater Lake National Park
Crater Lake, Oregon, 97604
3National Biological Survey
Cooperative Park Studies Unit
College of Forestry
Oregon State University.
Corvallis, Oregon, 97331
December 1993
National Park Service
Pacific Northwest Region
909 First Avenue
Seattle, WA 98104-1060
Table of Contents
Introduction
Materials and Methods
Habitat Survey
Fish Population Estimates
Results
Sun Creek
Habitat Characteristics
Fish Distribution and Abundance
Habitat Utilization
Fish Length and Weight
Annie Creek
Habitat Characteristics
Fish Distribution and Abundance
Sand Creek
Habitat Characteristics
Fish Distribution and Abundance
Bear Creek
Habitat Characteristics
Fish Distribution and Abundance.
Densities and Habitat Electivity in Sun, Annie,
Sand and Bear Creeks
Habitat Characteristics at Two Different Flows
Discussion
Acknowledgements
Literature Cited
List of Tables
Table 1. Number, area, and volume of habitat unit types in three reaches of Sun
Creek, Crater Lake National Park, summer 1989.
Table 2. Numbers, by habitat type, of brook and bull trout and brook x bull
trout
hybrids estimated by snorkel diving in the three reaches of Sun Creek,
Crater Lake National Park, summer 1989.
Table 3. Density of brook trout and bull trout by habitat type in streams of
Crater
Lake National Park, summer 1989.
Table 4. Habitat electivity E of brook trout and bull trout in streams of Crater
Lake
National Park, summer 1989.
Table 5. Number, area, and volume of habitat unit types in seven reaches of
Annie
Creek, Crater Lake National Park summer 1989.
Table 6. Estimated numbers of brook trout in surveyed portions of three streams
of
Crater Lake National Park summer 1989.
Table 7. Number, area, and volume of habitat unit types in two reaches of Sand
Creek, Crater Lake National Park, summer 1989.
Table 8. Number, area, and volume of habitat unit types in three reaches of Bear
Creek, Crater Lake National Park, summer 1989.
Table 9. Habitat characteristics of a 0.3-km reach of lower Sun Creek, Crater
Lake
National Park, Oregon at different flows.
Table 10. Habitat characteristics of a 0.5-km reach of Annie Creek, Crater Lake
National Park, Oregon at different flows.
List of Figures
Figure 1. Locations of the four surveyed streams in Crater Lake National Park,
Oregon
Figure 2. Limits of habitat, channel morphology, and snorkel surveys (summer
1989)
and location of electrofishing sites (summer 1989 and 1990) in Klamath
River tributaries in Crater Lake National Park.
Figure 3. Longitudinal profile and map of each study reach in Sun Creek, Crater
lake National Park, Oregon.
Figure 4. Dominant substrate in the three main study reaches of Sun Creek,
carter
lake National Park, Oregon, 1989.
Figure 5. Density of woody debris pieces in three reaches of Sun Creek, Crater
Lake
National Park, Oregon, 1989.
Figure 6. Conductivity and alkalinity of three locations in Sun Creek, Crater
lake
National Park, August 31, 1989.
Figure 7. Distribution of brook trout and bull trout in Crater Lake National
Park for
four Klamath River tributaries, summer 1989.
Figure 8. Frequency of microhabitat choice by bull and brook trout in Sun Creek,
Crater Lake National Park, Oregon, as observed by snorkel diving, summer
1989.
Figure 9. Length versus weight of bull trout, brook trout, and brook and bull
trout
hybrids in Sun Creek, Crater Lake National Park, summer 1989.
Figure 10. Longitudinal profile of Annie Creek, Crater Lake National Park.
Figure 11. Dominant substrate in seven reaches of Annie Creek, Crater Lake
National
Park, 1989.
Figure 12. Density of wood debris pieces in seven reaches of Sun Creek, Crater
Lake
National Park, 1989.
Figure 13. Longitudinal profile of Sand Creek, Crater Lake National Park.
Figure 14. Dominant substrate in two reaches of Sand Creek, Crater Lake National
Park, 1989.
Figure 15.
Density of woody debris pieces in two reaches of Sand Creek, Carter lake
National Park, 1989.
Figure 16.
Longitudinal profile of Bear Creek, Crater Lake National Park, Oregon.
Figure 17.
Dominant substrate in three reaches of Bear Creek, Crater Lake National
Park, 1989.
Figure 18.
Density of woody debris pieces in three reaches of Bear Creek, Crater lake
National Park, 1989.
Figure 19.
History of trout introductions into Sun Meadow of Sun Creek, Crater lake
National Park, 1931 to 1947.
Introduction
Four salmonid species reside in streams of Crater Lake National Park. Non-native
brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) and
exotic
brown trout (SalmQ trutta) were introduced to park streams between 1926 to 1971.
Bull
trout (Salvelinus confluentus) are considered to be the only fish species native
to the park
within the Klamath Basin. These four species were also collected during the
first
comprehensive survey of stream fishes in the park in the summer of 1947 (Wallis
1948).
This study was part of a water-rights adjudication program of the Klamath River.
Distribution and abundance of fish in the Klamath River system were considered
in the
adjudication process. Sun, Annie, Bear and Sand Creeks, which drain the southern
and
eastern slopes of Mount Mazama in Crater Lake National Park, are tributaries of
the
Klamath River (Fig. 1). The Sun Creek channel incises a 25,000-year-old glacial
valley
which was filled with pumice and ash from the eruption of Mount Mazama 6,800
years ago
(Bacon 1983). The channel actively erodes the base of the adjacent pumice slopes
which
supply large amounts of sediment to the stream. Objectives of this study were
to:
1. identify the summer distribution and abundance of fishes in Annie Creek, Bear
Creek, Sand Creek, and Sun Creek in Crater Lake National Park;
2. define habitats used by the fishes relative to total area and general
physical
characteristics of stream habitats; and
3. compare channel morphology and the habitat utilized by the fishes at
different
stream flows.
Figure 1. Locations of the four surveyed streams in Crater Lake National Park,
Oregon.
Materials and Methods
Habitat Survey
A stream habitat survey was conducted from July through late September, 1989
(Fig.
2) using methods of Hankin and Reeves (1988). Stream channels were divided into
three
types of habitat units, pools, glides, and riffles (Bisson et al. 1982). In
general, pools were
relatively deep and had slow current velocities, glides were shallow with even
flow, and
riffles were shallow with swift, turbulent flow. Length, mean width, and mean
depth of each
habitat unit was visually estimated. Measurements were made of length, width,
and depth
in approximately one tenth of all habitat units. These measurements were used to
calculate
calibration factors to correct visual estimates of habitat area. Lengths were
measured along
an upstream-downstream transect through the middle of each habitat unit. Widths
were
measured at three transects across a habitat unit and located at positions that
were
considered to represent the general variability of the unit. These values were
averaged for
each unit. Depths were measured across the stream channels at three or more
points
equally spaced along these transects. Reaches were distinguished based on fish
distribution
and differences in channel morphology, such as channel gradient, roughness, and
composition of habitat units.
Figure 2. Limits of habitat, channel
morphology, and snorkel surveys (summer 1989), and location of electrofishing
sites (summer 1989 and 1990) in Klamath River tributaries in Crater Lake
National Park. CC: Cavern Creek, EF: East Fork Annie Creek, MF: Middle Fork
Annie Creek, MC: Munson Creek, GC: Goodbye Creek, PB: Pole Bridge Creek, VC:
Vidae Creek, WC: Wheeler Creek.
Substrate in all habitat units was characterized by the sediment sizes that
dominated
the wetted channel. The most abundant size class by area was called the
dominant; the next
most abundant was called the co-dominant. Size classes were: massive boulder
(>200 cm),
large boulder (> 100 cm), medium boulder (>50 cm), small boulder (Ž25 cm), large
cobble
(Ž12 cm), small cobble (Ž6 cm), very coarse gravel (>3 cm), course gravel (Ž1.5
cm),
medium gravel (>0.8 cm), fine gravel (Ž0.4 cm), very fine gravel (>0.2 cm), sand
and silt
(<0.2 cm) and bedrock ( Lane 1947). For dominant and co-dominant size classes,
the area
of each habitat unit assigned to these sediment size class was summed. The total
area
(dominant plus co-dominant) for each size class was then averaged and expressed
as percent
dominance (D):
For example, a channel with coarse gravel substrate dominating 2 percent and
co-dominating
in 18 percent of the total unit area received a dominance value of 10 percent
Dominance
values were not synonymous with percent area of the stream channel but
represented an
average of two sets of proportions drawn from the same channel area.
The number of pieces of woody debris in each habitat were recorded. Woody debris
was assigned to the following size categories: < 0.1 Di, 0.1 to 0.19 m, 0.2 to
0.29 m, 0.3 to
039 m, 0.4 to 0. 79 m, and > 0.79 m.
Fish Population Estimates
Each stream survey began at the park boundary and progressed upstream into the
tributaries until fish were judged to be in low abundance or absent (Fig. 2).
Estimates of
fish abundance were made by direct observation by a single snorkel diver in 10
percent
(every tenth unit of a habitat type) of all habitat types, except in Sun Creek
where 20
percent of the pools (every fifth pool) were surveyed. These counts were
extrapolated to
estimate the total number of fish in each stream (Hankin & Reeves 1988). A
flashlight was
used to illuminate shaded areas beneath undercut banks and woody debris.
Age classes of fish based on measured body length were: < 60 mm, age 0; 60 - 100
mm, age 1; > 100 mm, age 2 and older. Brook and bull trout hybrids were
identified by
spots on dorsal fins and often by small vermiculation patterns on dorsal flanks
and weak tri-coloration on pectoral and pelvic fins (fins with slight or no orange cast and a
black stripe
next to a white leading edge). Bull trout had solid-colored fins and lacked body
vermiculations. Brook trout as small as 50 mm were distinguished from bull trout
by dorsal
fin vermiculations.
In Sun Creek, the position of each fish in the channel was assigned to one of
three
locations: (1) mid-channel without cover; (2) mid-channel in lee of cover; (3)
and channel
edge. Cover was considered to be any obstruction to stream flow, e.g., woody
debris and
larger than average substrate.
Fish collected using electroshocking were compared with the number of fish
counted
during snorkel counts in Sun Creek. Ideally, ten or more comparisons were needed
to
calculate reliable correction factors for abundance estimates based on snorkel
counts
(Hankin & Reeves 1988). Only a single 70 m section of stream channel was
successfully
electroshocked in a rigorous manner. Other electroshocking efforts met with
failure due in
part to logistical problems and equipment failure. In the 70 m section, three
brook trout
and eight bull trout were estimated from electroshocking, whereas two brook
trout and nine
bull trout were estimated from diving. Other less-precise electroshocking
comparisons were
in general agreement with the dive counts, although in some instances, abundance
of age-1
brook trout were underestimated. Because there were no reliable estimates of
dive count
errors, visual estimates of fish numbers in all streams were not adjusted and
should only be
considered as relative estimates of population size.
Electroshocking was used to sample selected sites to verify presence or absence
of
fish and to give a general impression of fish abundance in reaches not surveyed
by snorkel
diving. Three categories were used to describe fish abundance from snorkel
diving and
electroshocking surveys: high abundance - > 5 fish per habitat unit; moderate
abundance -
2-5 fish per habitat unit; and low abundance - <2 fish per habitat unit.
Ivlev's electivity index (Ivlev 1961) was used to describe habitat utilization
by the
fishes. The index in this application was defined as:
where E was the value of electivity, r was the proportion of fish in a habitat
type i and p
was the proportion of the area in habitat type i The index had a possible range
of -1 to + 1
and was asymptotic towards its extremes. Negative values indicated avoidance,
positive
values indicated preference, and values near zero indicated no selection.
Results
SUN CREEK
Habitat Characteristics
The lower 11 km of Sun Creek were divided into lower (6.6 Iom), middle (1.9 Im),
and upper reaches (2.4 km) based on the distributions of brook trout and bull
trout (Figure
3). These three reaches received complete habitat and fish population
inventories. Channel
substrate was coarser in the middle and upper reaches (Figure 4). The mean size
of
dominant substrate increased from medium gravel in the lower reach to small
cobble in the
middle and upper reaches. Sand and finer sediments were actively transported at
all flow
levels observed from June to October, and all crevices in the channel were
embedded with
fine sediments.
Figure 3. Longitudinal profile and map of each study reach in Sun Creek, Crater
Lake
National Park, Oregon. Filled circles denote reach boundaries, and the cross
lines denote the area of impassable falls.
Figure 4. Dominant substrate in the three main study reaches of Sun Creek,
Crater Lake
National Park, Oregon, 1989. Sediment size classes from Lane (1947).
Of the 49,760 m2 of habitat inventoried in Sun Creek, 72 percent occurred in the
lower, 13 percent in the middle, and 15 percent in the upper reach (Table 1).
Riffle habitat
increased in area as the channel gradient increased from the lower to the upper
reach. The
three reaches contained relatively high densities of woody debris (Figure 5).
The smallest
pieces (0.1 m) occurred in the greatest density. The middle reach contained the
highest
densities of pieces less than 0.4 m in diameter.
Table 1. Number, area, and volume of habitat unit types in three reaches of Sun
Creek,
Crater Lake National Park, summer 1989.
Figure 5. Density of woody debris pieces in three reaches of Sun Creek, Crater
Lake
National Park, Oregon, 1989.
Woody debris supplied by fallen trees in the active channel controlled the
majority of channel structure in Sun Creek. Most breaks in channel gradient were
controlled by woody debris pieces, and practically all pools and scour pockets
were formed
by flow that was either constricted, diverted, or pooled by the debris.
Undercuts were a
major feature along the banks of the stream and these were supported by either
woody
debris or tree roots. This wood material appeared to be stationary after it
entered the
stream.
Figure 6. Conductivity and alkalinity of three locations in Sun Creek, Crater
Lake National
Park, August 31, 1989.
Alkalinity and conductivity were similar in the middle and lower reaches but
substantially lower in the upper reach of Sun Creek (Figure 6). This was likely
a result of
proportionately more flow from deep pumice aquifers in the middle and lower
reaches. The
majority of water in the upper reach originated from surface snowmelt or
groundwater
flowing through the thin soils which overlay the flanks of Mount Mazana. Ferric
hydroxide
flocculent (orange colored) covered the banks near spring seeps and the stream
bottom for
a distance of 1.6 kin, which spanned the upper 1.1 km of the lower reach and the
first 0.5
km of the middle reach. Water in this section, and a few kilometers downstream,
had a
strong metallic taste.
Fish Distribution and Abundance
The upper, middle and lower reaches of Sun Creek received complete fish
population inventories. Fish populations in reaches further upstream were
sampled by
electroshocking. Brook trout and a few brook x bull trout hybrids were found in
the first
6.6 km of stream (lower reach). Bull trout, brook trout, and hybrids were
collected from
6.6 km to 8.5 km (middle reach). Only a few brook trout and hybrids were
observed in the
upper 2.4 km of the surveyed channel (upper reach). No fish were found in Vidae
Creek
and adjoining tributaries (Figure 7). Brook trout were in moderate abundance in
the
uppermost portion of Sun Creek, known as Sun Meadow, from approximately 03 km
downstream and 0.8 km upstream from a road crossing a picnic area. Only a few
brook
trout were found from the confluence of Vidae Creek and Sun Creek to within 0.31
km
downstream from the road crossing in Sun Meadow.
Based on snorkel dive counts, there were 2,265 age-1 and age-2+ fish in the
three
surveyed reaches of Sun Creek (Table 2). Brook trout made up approximately 93
percent
(2,101 fish), bull trout 6 percent (133 fish), and brook x bull trout hybrids 1
percent (31 fish)
of the total number. Hybrids totaled about 19 percent of bull trout and hybrids
combined
(164 fish).
Figure 7. Distribution of brook trout (thick lines) and bull trout (see note for
Sun Creek)
in Crater Lake National Park, for four Klamath River tributaries, summer 1989.
Table 2. Numbers, by habitat type, of brook and bull trout, and brook x bull
trout hybrids estimated by
snorkel diving in the three reaches of Sun Creek, Crater Lake National Park,
summer 1989.
Table 3. Density (number/lO00m2 ) of brook trout and bull trout by habitat type
in streams of
Crater Lake National Park, summer 1989.
The density of brook trout in the lower reach (5.8 fish/lOOm2) was about 2.5
times
greater than those of both bull and brook trout combined in the middle reach (23
fish/lOOm2; Table 3). The density of age-1 and age-2+ bull trout in the middle
reach was
about 10 times that of brook trout. The highest densities of fish in all reaches
occurred in
pools, intermediate densities occurred in glides, and lowest densities were in
riffles.
Estimates of the densities of small fish in low abundance from a subsample of
less
than 20 percent of the habitat units in a reach should be regarded with caution.
For
example, only one hybrid was counted while snorkel diving in the middle reach,
whereas
hybrids made up about 24 percent of the total number of bull trout and hybrids
in the 0.5-km reach sampled by electroshocking. Similarly, in the same 0.5-km section the
number of
brook trout was half the number of bull trout based on electroshocking sample,
whereas
based on the snorkel diving, brook trout were approximately one tenth as
abundant as bull
trout. The estimated numbers of age-O and age-I brook trout in the lower reach
were
suspiciously low in comparison to age-2+ brook trout (Table 2). This result
might indicate
an inverted age class structure. However, it is likely that many fish of age 0
and 1 were
missed during snorkel counts, and their actual abundances were probably greater
than
estimated. The relative differences in the number of fish among the reaches and
between
fish species were quite large and not likely the result of estimation error.
Habitat Utilization
Bull trout and brook trout utilized similar habitats in Sun Creek. At the
level of the habitat unit, both species preferred pools (Table 4). Age-2+ brook
trout
utilized pool habitat more than did age-1 fish. At the micro-habitat level, the
majority of
all age classes of both species maintained positions at the channel edge (Figure
8).
Utilization of the mid-channel increased with age. Age-O brook trout positioned
themselves
exclusively at the channel edge. When brook and bull trout were observed in the
same pool,
brook trout occupied the center of the pool, and bull trout occupied the
downstream end
and the margins of the pools. Under allopatric conditions, the largest (age-2+)
fish of
either species were observed to occupy the center of pools.
Table 4. Habitat electivity E (Ivlev 1968) of brook trout and bull trout in
streams of
Crater Lake National Park, summer 1989. E has a possible range of -1 to
+ 1; negative values indicate avoidance, positive values indicate preference,
values near zero indicate neutral selection.
Figure 8. Frequency of microhabitat choice by bull and brook trout in Sun Creek,
Crater
Lake National Park, Oregon, as observed by snorkel diving, summer 1989;
number of fish in parentheses.
Fish Length and Weight
Bull trout weighed less than brook trout of the same length (Figure 9). Bull x
brook trout hybrids were similar in weight to bull trout of the same length.
Brook trout in
the middle reach attained the same weight for a given length as those in the
lower reach.
Thus, even though fish densities were six times less in the middle reach than in
the lower
reach, brook trout attained the same level of condition in both reaches.
Figure 9. Length versus weight of bull trout, brook trout, and brook and bull
trout hybrids
in Sun Creek, Crater Lake National Park, summer 1989.
ANNIE CREEK
Habitat Characteristics
The mainstem of Annie Creek, from the park boundary to its confluence with
Munson Creek, was divided into seven reaches based on differences in channel
morphology
(Table 5, Figures 10 and 11). All reaches had channel profiles that were
controlled in part
by large fallen trees. All reaches generally contained equal densities of woody
pieces
(Figure 12).
The first three reaches occurred within a transition zone from a narrow canyon
to the broad Wood River Valley known as the "panhandle". Reaches 1 and 3 were
Table 5. Number, area, and volume of
habitat unit types in seven reaches of Annie Creek, Crater Lake National Park,
summer 1989.
Figure 10. Longitudinal profile of Annie Creek, Crater Lake National Park; from
1:24,000
scale USGS map. Filled circles denote reach boundaries.
Figure 11. Dominant substrate in seven reaches of Annie Creek, Crater Lake
National
Park, 1989. Sediment size classes after Lane (1947).
Figure 12. Density of wood debris pieces in seven reaches of Sun Creek, Crater
Lake
National Park, 1989.
dominated by glide habitat and gravel substrate (Table 5). Reach 2 was dominated
by riffle
habitat and boulder substrate. The stream channel in these three reaches
meandered across
a terraced valley floor bounded by forested hillslopes. The width of the valley
floor
decreased from about 60 m in reach 1 to about 20 m in reach 3. Upstream from
reach 3,
the stream was relatively straight, being confined by steep hillslopes and
canyon walls. In
reach 4, the stream was confined to a 10-m-wide valley floor by sheer rock
walls. This was
the steepest reach surveyed in Annie Creek, and it was dominated by riffle
habitat and
boulder and cobble substrate. Reach 5 also was narrowly confined by the rock
canyon, but
it had less channel gradient than reach 4. Reach 5 was dominated by glide
habitat and
cobble and gravel substrate. In reach 6, the valley floor was bounded by
forested hillslopes
and bedrock outcrops, and it varied in width between 20 m and 40 m. Major breaks
in
gradient were controlled by bedrock falls; Annie Falls was the largest of these.
The seventh
reach was dominated by glide habitat and gravel substrate. The valley floor
varied in width
between 20 m and 60 m and was confined between steep forested hillslopes. Fallen
trees
had a major influence on the channel profile in reach 7.
Fish Distribution and Abundance
The estimated number of age-1 and age-2+ brook trout in the mainstem of
Annie Creek was 768 (Table 6). One rainbow trout was observed 0.42 km upstream
from
the park boundary and four brown trout were observed in the lower 13 km of the
stream
within the park. Only a few age-0 brook trout were observed by snorkel diving.
Sixty-eight
percent of the observed fish were in pools.
Based upon electroshocking results, no fish were found in Pole Bridge Creek,
and Goodbye Creek Creek (Figures 2 and 7). The middle and east forks of Annie
Creek
and Munson Creek near the headquarters of Crater Lake National Park could not be
electrofished in September because the electroshocking unit was not working
properly.
Thus, additional electrofishing was conducted in these sections of Annie Creek
drainage in
the summer of 1990. Munson Creek was found to be sparsely populated by brook
trout,
whereas the lower half of the middle fork of Annie Creek had a moderately
abundant
population of brook trout (Figure 7). No fish were found in the East Fork of
Annie Creek
in 1990. An absence of fish near the mouth of the East Fork of Annie was also
noted in
the summer of 1989 while snorkel diving the lower 0.5 km of stream. A water
Table 6. Estimated numbers of brook trout in surveyed portions of three streams
of
Crater Lake National Park, summer 1989.
fall approximately 10 m high just upstream of the mouth of the east fork of
Annie Creek
was a barrier to fish migration. Furthermore, there was no record of fish
stocking in the
East Fork of Annie Creek (Wallis 1948).
SAND CREEK
Habitat Characteristics
Sand Creek was surveyed most intensively for approximately 5.5 km from the park
boundary to the base of a 360-m-long cascade and less intensively upstream from
the
cascade (Figure 13). Two reaches were identified below the cascade on Sand Creek
and
two reaches were identified upstream from above the cascade (Figure 13). Reach 1
was
dominated by glide habitat and fine and medium gravel size substrate (Table 7,
Figure 14).
The substrate was not large enough to control the channel profile. All channel
units and
all controls of channel profile were formed by pieces of fallen trees (Figure
15). Riffles in
this reach were formed by many small steps created by pieces of fallen trees
across the
channel. The valley floor was 40 m to 80 m wide and confined by steep slopes,
which were
either forested or covered by exposed pumice soil and isolated spires of
pinnacle formations.
The stream meandered across the valley floor and created eroding cut-banks that
supplied
large amounts of fine sediments to the channel.
Figure 13. Longitudinal profile of Sand Creek, Crater Lake National Park; from
1:24,000
scale USGS map. Filled circled denote reach boundaries.
Reach 2 was dominated by riffle habitat and substrate was small cobble to very
coarse gravel (Table 7, Figure 14). Channel structure in this reach was
controlled by fallen
trees and cobble substrate (Figure 15). The valley floor was 10 to 15 m wide.
Adjacent
hillslopes were forested, but compared to reach 1, exposed pumice soil and
pinnacle spires
were more prevalent. Many of the pinnacle spires had fallen into the stream
channel and
created scour pools, dam pools, and cascades. This reach ended at the base of
the 360-mlong
cascade.
Upstream from the cascade, reach 3 was incised into a narrow canyon of welded
tuft.
Although there was no extensive habitat survey, this reach was generally
dominated by riffle
habitat and cobble-and-gravel-sized substrate. Only a few fallen trees were in
the channel.
The channel profile was predominantly controlled by bedrock, large boulders, and
cobbles
composed of welded tuft.
Reach 4 was in a broad plane of mounded terraces above the canyon formed by
pinnacle formations. The stream channel was dominated equally by riffle and pool
habitat
and the substrates were primarily gravel sized. Fallen trees formed the majority
of pools,
whereas riffles were composed of a mix of cobble and gravel-size substrate.
Table 7. Number, area, and volume of habitat unit types in two reaches of Sand
Creek,
Crater Lake National Park, summer 1989.
Figure 14. Dominant substrate in two reaches of Sand Creek, Crater Lake National
Park,
1989. Sediment size classes after Lane (1947).
Figure 15. Density of woody debris pieces in two reaches of Sand Creek, Crater
Lake
National Park, 1989.
Fish Distribution and Abundance
A total of 25 age-1 and 467 age-2+ brook trout were estimated to be in Sand
Creek
in the lower two reaches that were surveyed (Table 6). The majority of these
fish were
observed in pools. Based on electroshocking, brook trout were present 5.5 km
upstream
from the 360-m-long cascade. Brook trout in Wheeler Creek and Cavern Creek
(Figure 7)
were restricted to reaches downstream from steep, and what appeared to be,
impassable
channels. Presumably these brook trout immigrated from Sand Creek because there
were
no records of stocking in these streams. Numerous brook trout were found in Lost
Creek.
This stream has surface flow for approximately 2 km before flowing subsurface.
BEAR CREEK
Habitat Characteristics
Bear Creek, from the park boundary to approximately 3.5 km upstream was divided
into three reaches (Figure 16). Glide and riffle habitat dominated the three
reaches and
the stream bed was composed of sand and gravel-sized substrate (Table 8, Figure
17). The
channel was incised into a small "V"-shaped valley of loose pumice soil.
Adjacent hillslopes
were covered by lodge-pole pine, which were largely dead and fallen from an
infestation of
bark beetles. The channel profile and morphology were controlled by pieces of
the fallen
trees (Figure 18). All breaks in gradient were associated with limbs and trunks
of fallen
trees.
Figure 16. Longitudinal profile of Bear Creek, Crater Lake National Park; from
1:24,000
scale USGS map. Filled circles denote reach boundaries.
Table
8. Number, area, and volume of habitat unit types in three reaches of Bear
Creek, Crater
Lake National Park, summer 1989.
Figure 17. Dominant substrate in three reaches of Bear Creek, Crater Lake
National Park,
1989. Sediment size classes after Lane (1947).
Figure 18. Density of woody debris pieces in three reaches of Bear Creek, Crater
Lake National
Park, 1989.
Fish Distribution and Abundance
Brook trout in Bear Creek were confined within 0.4 km of channel (reach 2),
starting 1.0
km from the park boundary (Figure 7). The population was constrained by
intermittent flow in
reach 1 and by a small dam located 90 m upstream in reach 3. The 3-m-high
woodplank dam was
backfiled with sediment.
The estimated number of age-I and age-2 brook trout in Bear Creek was 91 (Table
6). This
population estimate was based on adding the total fish captured from two passes
with an
electroshocker (blocknets were not used) in 10 percent of the habitat units
because the stream was
too small for effective snorkeling. Fish abundance determined from this crude
method should be
considered as a minimum population estimate. Most fish were captured in riffle
habitat
Densities and Habitat Electivity in Sun, Annie, Sand and Bear Creeks
Bear Creek had the highest fish density of all streams surveyed (Table 3),
whereas the
density of fish in Sand Creek was more than twice that of either Annie Creek or
Sun Creek. Brook
trout in Sun Creek, Annie Creek, Sand Creek, and Bear Creek generally exhibited
a high
preference for pool habitat (Table 4). Compared to age 2+ fish, however, age-1
brook trout
showed a greater utilization of glide and riffle habitat.
Habitat Characteristics at Two Different Flows
Changes in channel morphology relative to stream discharge were evaluated along
a 0.3 km
reach of lower Sun Creek on July 20 and September 19, 1989 (Figure 2). The
survey included
measurements of water surface slope and the dimensions of the habitat units
(Table 9). The
substrate was dominated by gravel-sized sediments with all major breaks in
gradient controlled by
fallen pieces of wood. On July 17 while the stream was still receiving snowmelt,
the flow was 0.62
m 3/s. On September 19, the flow had decreased by 50% to 031 m 3/s. Total
habitat area
decreased 5.4 percent and total habitat volume decreased 26 percent between the
two surveys. There were small decreases in the mean and maximum depths and maximum widths of
all habitat
types. Glides emerged from riffles; none were present in July and eight were
present in September.
Riffles decreased from nine to three units. On a percentage basis, pool area and
volume remained
relatively constant, riffle area and volume decreased, and glide habitat
increased. The slope of the
water surface in pools decreased greatly, whereas the slope of riffles increased
between July and
September.
Table 9. Habitat characteristics of a 0.3-kn reach of lower Sun Creek, Crater
Lake National
Park, Oregon at different flows. Flow on July 17 was 0.62 m 3/s and flow on
September 19 was 0.31 m 3/s. The July flow was measured 3 days before the
habitat
measurements were recorded.
Additional surveys of channel morphology and stream flow were conducted in 1989
on a
0.5- km-long section of Annie Creek just upstream from its confluence with the
East Fork (Figure
7) on July 21 when the streamflow was 2.6 m 3/s, and on September 16 when the
streamflow was
1.6 m 3/s. This stream section was dominated by gravel substrate, but cobble and
boulder size
sediment also were present and controlled many breaks in the channel profile.
From July to
September the wetted channel area decreased by 9 percent and channel volume by
25 percent,
whereas there were only small decreases in mean and maximum depth and maximum
width (Table
10). The classification of habitat types between surveys remained the same, as
did the proportion
of wetted area and volume attributed to each habitat type.
Table 10. Habitat characteristics of a 0.5-km reach of Annie Creek, Crater Lake
National Park,
Oregon at different flows. Flow on July 17 was 2.6 m3/s, and flow was 1.6 m 3/s
on
September 15. Flows were determined 1-4 days prior to habitat measurements.
Discussion
One objective was to compare the habitat utilized by fish relative to stream
channel
morphology and discharge. Although the range of stream flows during these
studies was
probably too narrow to assess all of the important flow-related changes in
stream habitat
characteristics, some initial results were obtained. Pools, which were the
preferred habitat
of both brook trout and bull trout, did not appear to change in availability and
general
dimensions under the two flow regimes. In Sun Creek, however, the net increase
in the
number of glides was balanced by a loss of riffles. This change in habitat may
have favored
brook trout slightly because glides were preferred over riffles. In contrast,
bull trout
exhibited nearly neutral selection of glides and riffles. The survey techniques
employed,
however, only addressed changes in the characteristics and composition of
habitat at the unit
level. Habitat as expressed by stream volume, decreased by 25 percent from July
to
September.
Park stocking records reported by Wallis (1948) indicate that approximately
45,000
brook trout fry and 7,000 rainbow trout fry were introduced into Sun Creek
(Figure 19).
Wallis (1948) overlooked the rainbow trout stocking record and mistakenly
concluded that
rainbow trout were native to the park (see Wallis 1948, pages 40, 55, and 104).
Sand Creek,
Bear Creek, and Annie Creek may have been fishless prior to the introduction of
non-native
salmonids into park streams (Wallis 1948).
Figure 19. History of trout introductions into Sun Meadow of Sun Creek, Crater
Lake
National Park, 1931 to 1947. Fish released at lengths of 50 to 75 mm.
Wallis (1948) noted that bull trout were "well distributed" in Sun Creek
downstream
from a falls located about 0.7 km downstream from the confluence of Vidae Creek
and Sun
Creek in 1947. The bull trout population was restricted to a 1.9-km-long reach
in 1989.
Interspecific competitive interactions and hybridization with brook trout are
probably the
principal mechanisms that have restricted distribution and reduced abundance of
bull trout
in Sun Creek (Ratliff 1992). Hybridization with brook trout is likely a great
detriment to
the reproductive capacity of the bull trout population in Sun Creek because
previous
research found that brook x bull hybrids were infertile males (Leary et al.
1983). Hence,
a hybrid is a loss to the gene pool of the population. However, a hybrid female
with
developed ovaries (Markle 1991) was collected from the middle reach of Sun Creek
in 1989.
It is not known if the hybrids in Sun Creek are capable of producing viable
offspring.
Survival of bull trout to emergence in Sun Creek is probably low owing to the
great
amount of fine pumice sediment in the stream bed (Shepard et al. 1984). Bull
trout
recruitment in the middle reach of Sun Creek may also be limited owing to a lack
of
spawning gravel.
The status of the bull trout population in Sun Creek should be considered
precarious
at best. In addition to the noted impacts caused by competitive interactions and
hybridization between bull trout and brook trout, variation in population
abundance as great
as 500 percent from random perturbations in the environment are common among
stream
fishes (Hall and Knight 1981). It seems reasonable to be concerned about the
long-term
well being of the Sun Creek bull trout population owing to its restricted
distribution, low
abundance (133 fish), and sympatry with brook trout.
Acknowledgements
The authors sincerely thank Warren Griffin for his dedicated field work. This
study
was supported by funding from the Water Rights Branch of the National Park
Service Water
Resources Division. Cindy Alexander and Becca Nightingale typed and Ruth Jacobs
edited
the manuscript.
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