GROWTH AND DISPERSAL OF RECENTLY STOCKED EAGLE LAKE RAINBOW
TROUT IN THE LAKE DAVIS WATERSHED
Daniel Lewis Worth
B.S., University of Nevada, Reno, 2003
THESIS
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE
in
BIOLOGICAL SCIENCES
(Biological Conservation)
at
CALIFORNIA STATE UNIVERSITY, SACRAMENTO
FALL
2010
 2010
Daniel Lewis Worth
ALL RIGHT RESERVED
ii
GROWTH AND DISPERSAL OF RECENTLY STOCKED EAGLE LAKE RAINBOW
TROUT IN THE LAKE DAVIS WATERSHED
A Thesis
by
Daniel Lewis Worth
Approved by:
__________________________________, Committee Chair
Ronald M. Coleman, Ph.D.
__________________________________, Second Reader
Ben Sacks, Ph.D.
__________________________________, Third Reader
Brett Holland, Ph.D.
Date: ___________________________
iii
Student: Daniel Lewis Worth
I certify that this student has met the requirements for format contained in the
University format manual, and that this thesis is suitable for shelving in the Library and
credit is to be awarded for the thesis.
__________________________, Graduate Coordinator
Susanne Lindgren, Ph.D.
Department of Biological Sciences
iv
___________________
Date
Abstract
of
GROWTH AND DISPERSAL OF RECENTLY STOCKED EAGLE LAKE RAINBOW
TROUT IN THE LAKE DAVIS WATERSHED
by
Daniel Lewis Worth
There are many reasons why resource managers move plants and animals from
one location to another. Understanding how the organisms disperse after relocation is an
important aspect to any relocation action. This study was done to evaluate the poststocking movement of Eagle Lake rainbow trout (Oncorhynchus mykiss aquilarum). This
trout is endemic to Eagle Lake, California and has many characteristics that no other
rainbow trout have. The unique traits of these fish are thought to be a result of the
complete isolation that these fish historically enjoyed in the terminal Eagle Lake
watershed. To study the post-stocking behavior of this strain of trout, eggs and sperm
were collected from wild fish spawning at Eagle Lake, California. The offspring were
raised in a hatchery for about one year and then transported to the nearby Lake Davis
watershed, which had recently been treated with a piscicide by the California Department
of Fish and Game in an attempt to rid the lake of northern pike (Esox lucius). Eight
hundred of these wild strain Eagle Lake rainbow trout were tagged and stocked into Cow,
Big Grizzly, Freeman, and Old House creeks, which are the four main tributaries of Lake
Davis. The tags used were Floy T-bar anchor tags that each had a unique number used to
identify individual fish. The location and size of each stocked fish were recorded at the
v
time of stocking. After the fish were stocked in May of 2008, the tributaries were
sampled for fish approximately once per month, ending in September of 2008. Each time
a tagged fish was captured, the GPS location and size of the fish were recorded. These
data were used to evaluate post-stocking growth and movement patterns of Eagle Lake
rainbow trout in the Lake Davis Watershed. Additionally, the effect that the tags and
electrofishing had on the condition of fish was evaluated.
Rainbow trout are often observed moving downstream after being stocked into a
stream or river, but other types of trout have been observed to move upstream following
stocking. This study evaluated whether the unique Eagle Lake strain of rainbow trout
moved downstream like many other strains of rainbow trout after stocking. The average
post-stocking movement of fish in three of the creeks was 365 meters in the downstream
direction. The fish that were stocked in the fourth creek moved an average of 178 meters
upstream, but it is thought that this was caused by a barrier to downstream movement.
On average, the Eagle Lake rainbow trout in this study moved in a downstream direction
shortly after being stocked. A few fish moved long distances, up to 3000 meters, but the
majority moved slightly downstream. The downstream movement appeared to be shortlived because the fish remained relatively stationary following the first sampling event,
which was 27 day after stocking.
It is often postulated that trout populations include static individuals and mobile
individuals, and that mobile trout are presumably those that are unable to establish
territories, and static trout are those that can establish territories. Additionally, after trout
vi
are stocked it is often noted that some individuals stay near the stocking location, and
others move great distances away from the stocking location. Because stream-dwelling
salmonids compete for space in streams, some of the variation in movements may be
attributed to competitive ability. To evaluate the influence that competitive interactions
have on post-stocking movement, size at stocking was compared to dispersal distance.
The results of this study did not indicate that relative size at stocking was related to poststocking movement; however, design limitations may have led to the uncertainty.
The creeks in this study were electrofished once a month for five straight months.
The main driving force for this electrofishing effort was to monitor for pike. While
conducting these pike surveys, the recently stocked trout were captured and data was
collected from them. The effects of electrofishing and handling on the trout were
evaluated by comparing the condition of fish that had previously been captured to fish
that had been captured for the first time during each sampling event. The results of this
study indicate that repeated electrofishing and handling significantly reduced the
condition of the trout.
This research also evaluated the effect that the Floy T-bar anchor tags had on the
condition of the Eagle Lake rainbow trout. During each of the sampling periods, the
condition of tagged fish was compared to the condition of non-tagged fish from the same
size range. There was no significant difference in the condition of tagged versus
untagged.
_____________________, Committee Chair
Ronald M Coleman, Ph.D.
vii
ACKNOWLEDGMENTS
I would like to thank the entire department of Biological Sciences at California
State University, Sacramento, with a special thanks to my Supervisory Committee (Dr.
Ronald M. Coleman, Dr. Ben Sacks, and Dr. Brett Holland), Dr. Ewing, and Dr.
Lindgren. I would especially like to thank Dr. Ronald M. Coleman for his support and
guidance through this journey. From the California Department of Fish and Game I
would like to thank Joe Johnson, Robert Vincik, Robert G. Titus, Chris Ball, Sarah
Rains, Farhat Bajjaliya, Taylor Call, Frances Ross, Nicholas Miguel, Amber Rossi and
the Portola crew, Jim Adams, Jay Rowan, Michael J. Harris, Phil Mohler, and all of the
others who helped me along the way. I would like to give a special thanks to Joe
Johnson and Robert Vincik for the incredible opportunities and support that they
provided. Lastly, I would like to thank my wife Kristen, my parents, and my long-time
friends for all of their love and support through very difficult times.
viii
TABLE OF CONTENTS
Acknowledgements ....................................................................................................... viii
List of Tables ................................................................................................................ xiii
List of Figures ................................................................................................................ xv
Chapter
1. GENERAL INTRODUCTION.................................................................................... 1
Distribution of Organisms....................................................................................... 1
Distribution of Fish ................................................................................................. 3
Diadromous Fish ..................................................................................................... 3
Salmonidae.............................................................................................................. 4
Movement of Trout ................................................................................................. 5
Background of Lake Davis ..................................................................................... 7
Eagle Lake Rainbow Trout ................................................................................... 11
Objectives ............................................................................................................. 12
Hypotheses ............................................................................................................ 13
2. STOCKING THE LAKE DAVIS WATERSHED WITH RAINBOW TROUT AND
THE POST-STOCKING MOVEMENT OF THE FISH ............................................ 14
Introduction ........................................................................................................... 14
Methods................................................................................................................. 16
Stocking The Lake ..................................................................................... 16
Initial Survey Of The Creeks ..................................................................... 17
Stocking The Creeks .................................................................................. 18
ix
Post-Stocking Electrofishing Surveys ....................................................... 23
Analysis Of Creek Movement .................................................................... 24
Results ................................................................................................................... 26
Initial Creek Survey .................................................................................. 26
Post-Stocking Electrofishing Surveys ....................................................... 29
Initial Post-Stocking Movement Of Tagged Fish ...................................... 41
Movement Of Tagged Fish Between Captures.......................................... 47
Movement Of Fish Between The Lake And The Creeks ............................ 48
Conclusions ........................................................................................................... 50
Initial Creek Surveys ................................................................................. 50
Initial Post-Stocking Movement Of Tagged Fish ...................................... 51
Movement Of Tagged Fish Between Captures.......................................... 54
Movement Of Fish Between The Lake And The Creeks ............................ 56
3. SIZE AT STOCKING VERSUS DISPERSAL DISTANCE .................................... 58
Introduction ........................................................................................................... 58
Methods................................................................................................................. 59
Results ................................................................................................................... 59
Conclusions ........................................................................................................... 63
4. CONDITION AND GROWTH OF TROUT IN THE CREEKS OF LAKE
DAVIS ........................................................................................................................ 65
Introduction ........................................................................................................... 65
Methods................................................................................................................. 65
x
Condition Of Tagged Fish During The Sampling Season ........................ 65
Comparison Of Condition Of Tagged Fish In Each Creek ...................... 66
Condition Of Tagged Versus Non-Tagged Fish ....................................... 66
Growth Rates of Tagged Fish ................................................................... 68
Growth Rate Of Young Of Young Of The Year Fish ................................. 68
Effect Of Electrofishing And Handling On The Condition Of Fish .......... 69
Condition Of Size Class Three Non-Tagged Fish ..................................... 69
Results ................................................................................................................... 69
Condition Of Tagged Fish During The Sampling Season ........................ 69
Comparison Of Condition Factor Of Tagged Fish In Each Creek ........... 74
Condition Of Tagged Versus Non-Tagged Fish ....................................... 77
Growth Rates of Tagged Fish ................................................................... 79
Growth Rate Of Young Of Young Of The Year Fish ................................. 83
Effect of Electrofishing and Handling On The Condition Of Fish ........... 86
Condition Of Size Class Three Non-Tagged Fish ..................................... 86
Conclusions ........................................................................................................... 88
Condition Of Tagged Fish During The Sampling Season ........................ 88
Comparison Of Condition Factor Of Tagged Fish In Each Creek ........... 88
Condition Of Tagged Versus Non-Tagged Fish ....................................... 89
Growth Rates of Tagged Fish ................................................................... 89
Growth Rate Of Young Of Young Of The Year Fish ................................. 90
xi
Effect of Electrofishing and Handling On The Condition Of Fish ........... 90
Condition Of Size Class Three Non-Tagged Fish ..................................... 90
5. CREEK TEMPERATURES ...................................................................................... 92
Introduction ........................................................................................................... 92
Methods................................................................................................................. 92
Results ................................................................................................................... 94
Conclusions ........................................................................................................... 97
6. FINAL DISCUSSION ............................................................................................... 99
Post-Stocking Movement ...................................................................................... 99
The Creeks of Lake Davis................................................................................... 101
Literature Cited ............................................................................................................ 104
xii
LIST OF TABLES
Page
Table 1. A summary of fish stocked into each grid .......................................................21
Table 2. A summary of fish stocked into each creek, and the density of fish
stocked into the creeks .....................................................................................22
Table 3. A summary of the fish captured during the initial survey on 20, 21, 22,
23 May 2008, in the four main creeks of Lake Davis ......................................28
Table 4. The number of tagged and untagged fish caught during each sampling
period, and the effort for each sampling period ...............................................30
Table 5. A summary of the non-tagged fish captured on 23, 24, 25 June 2008,
in the four main creeks of Lake Davis .............................................................33
Table 6. A summary of the non-tagged fish captured on 14 and 15 July 2008, in
the four main creeks of Lake Davis .................................................................35
Table 7. A summary of the non-tagged fish captured on 4, 5, 6 August 2008, in
the four main creeks of Lake Davis .................................................................37
Table 8. A summary of the non-tagged fish captured on 15, 16, 17 September
2008, in the four main creeks of Lake Davis ...................................................39
Table 9. A size summary for all tagged fish released (May) and then captured
(all other months) during 2008 in the four main creeks of Lake Davis ...........40
Table 10. The number of tagged fish caught in each creek and the average
distance moved by tagged fish in each creek between 25 May and 23
June ...............................................................................................................42
Table 11. The capture locations of fish caught in June relative to their stocking
locations ........................................................................................................46
Table 12. An ANOVA table of condition factor of tagged fish caught during
each sampling period ....................................................................................71
Table 13. Combined July and August condition factor of tagged fish by creek ............76
xiii
Table 14. A comparison of the Fulton Condition Factor for tagged and
untagged fish caught during each sampling period.......................................78
Table 15. Length versus time regression for young of the year fish caught
during 2008 ...................................................................................................85
Table 16. The average temperatures measured in each creek location ..........................95
xiv
LIST OF FIGURES
Page
Figure 1. A map of the four creeks being researched in this project ...............................9
Figure 2. A length-frequency distribution of the fish captured during the initial
survey on 20, 21, 22, 23 May 2008, in the four main creeks of Lake
Davis. ...............................................................................................................27
Figure 3. A length-frequency distribution of non-tagged fish captured on 23, 24,
25 June 2008, in the four main creeks of Lake Davis. .....................................32
Figure 4. A length-frequency distribution of non-tagged fish captured on 14 and
15 July 2008, in the four main creeks of Lake Davis. .....................................34
Figure 5. A length-frequency distribution of non-tagged fish captured on 4, 5, 6
August 2008, in the four main creeks of Lake Davis. .....................................36
Figure 6. A length-frequency distribution of non-tagged fish captured on 15, 16,
17 September 2008, in the four main creeks of Lake Davis. ...........................38
Figure 7. The number of fish caught in each creek and the approximate distance
moved by each fish between 25 May and 23 June...........................................44
Figure 8. The initial dispersal distance versus the length at stocking.............................60
Figure 9. Fish grouped into length categories, and the dispersal distance of fish in
each category...................................................................................................62
Figure 10. The condition factor of tagged fish in the four main creeks of Lake
Davis versus the time (days) after stocking. .................................................73
Figure 11. Combined July and August condition factor of tagged fish by creek ..........75
Figure 12. Growth rates of tagged fish measured from the time they were
released to the time of first capture (average 0.25 mm/day, sd=0.22,
n=119). ..........................................................................................................80
Figure 13. The length of fish caught during each of the sampling periods ...................82
xv
Figure 14. Length versus time regression for young of the year fish caught during
2008...............................................................................................................84
Figure 15. The condition factor of size class three fish versus days after the initial
survey. ...........................................................................................................87
xvi
1
Chapter 1
GENERAL INTRODUCTION
Distribution of Organisms
The success of all organisms is ultimately defined by their ability to survive,
grow, and reproduce. The factors that limit the success of organisms can be classified
as either biotic or abiotic. The biotic factors that limit the success of organisms are
those such as food availability, intraspecific competition, and interspecific competition.
The abiotic factors that limit organisms are those such as temperature, pH, and
moisture. Together these factors control population numbers and geographic
distributions. Additionally, it appears that physical barriers, such as oceans, mountain
ranges, or deserts play an important role in limiting the distribution of organisms
(Krebs 1994). With current transportation technologies, humans are able to move
species great distances, across historically physical barriers in a matter of hours or days.
Gordon and Thomas (1996) reported that in one year (1990) 333 million plants were
brought into Florida. Nilsson (1981) reported that between 1977 and 1980, nearly
400,000 finches and other seed-eating birds representing 67 species were imported into
the United States. These species, which are moved around by humans, are often
released or escape into areas where the native species are poorly adapted to deal with
the intruders. Wilcove et al. (1998) reported that approximately 400 of the 958 species
that were currently listed as threatened or endangered, under the Endangered Species
Act, were considered to be at risk primarily because of competition with or predation
2
by non-indigenous species. Primentel et al. (2000) estimated that the current annual
economic damage caused by biological invaders in the United States alone was around
US$137 billion. This estimate only accounted for the economic losses and control
costs, but did not take the damaging environmental effects into account. Currently,
there is a conscious effort being made to slow further environmental and economic
damages, and in some cases undo past environmental damage caused by invasive
species introductions. In California, no invasive species has received as much recent
attention as the northern pike (Esox lucius) that were found in Lake Davis. This species
of fish is historically found approximately 1,100 kilometers northeast of California
(Harvey 2009), and the native fish of California do not possess the traits needed to deal
with such an efficient predator. Wildlife managers in California made the decision that
the potential for pike to move from Lake Davis into the Central Valley and negatively
affect the state’s aquatic resources was a significant risk (California Department of Fish
and Game and USDA Forest Service 2007). Like many other invasive species
eradication projects, the non-native northern pike were removed from the project area
to prevent their spread into other parts of the region. Also like other restoration
projects, native species (or as close to native as currently available) were reintroduced
into the restoration site following the invasive species eradication. Understanding how
and why re-introduced species distribute themselves following a restoration project will
be of particular importance to the success of current and future restoration projects.
3
Distribution of Fish
When studying the movement and distribution patterns of organisms, there is
one set of organisms, fish, which are particularly useful to study because they are
confined to an area that is relatively easy to define. For example, the boundaries of a
river are much more clearly identifiable then the boundaries of a chaparral forest.
Additionally, rivers and streams are linear in fashion, and these linear features provide
many benefits over other environmental settings. This makes studying the distribution
patterns of fish more simplistic than something that flies for example. Finally, studying
this set of organisms is particularly important because fish have great cultural,
economical, scientific, and ecological value.
Diadromous Fish
To understand the behavior and distribution patterns observed in migratory fish
populations, we first need to understand the reasons behind the migrations of
diadromous fish species. The behavior and physiology of diadromous fish, those that
migrate between fresh and saltwater, is particularly fascinating because this behavior
has extraordinary energetic costs associated with it (Cooperman et al. 2010). What is
puzzling is why some fish around the world reproduce in freshwater but live and grow
in saltwater, and other fish reproduce in saltwater but live and grown in freshwater.
When this pattern is viewed on a global scale, it appears that relative productivity
between saltwater and freshwater can explain diadromous behavior. In areas were
4
productivity is greater in oceans when compared to the adjacent freshwater
environments, anadromy is predominant. In areas where productivity is greater in
freshwater environments when compared to the adjacent ocean, catadromy is
predominant (Gross et al. 1988). This suggests that the optimal habitats for growth,
survival, and reproduction are separated spatially and/or seasonally (Northcote 1984).
In California, there are many anadromous fish species but no catadromous fish species,
which is evidence of California having a relatively productive ocean compared to its
rivers. Additionally, many freshwater environments in California that support fish go
through seasonal environmental extremes, which certainly influence migratory
behavior. Prior to the current influences of dams, many rivers and streams in California
would have dried up or become too warm for fish during the summers, and during the
winters many small creeks reach near freezing temperatures also creating harsh
conditions for fish. These types of environmental factors most certainly shaped the
timing and need for the migratory behavior of fish observed in California.
Salmonidae
In the Western world, no family of fishes has received as much interest in recent
times as the salmonids (Salmonidae) (Moyle 2002). This family of fishes represent
diverse taxa that display an amazing array of behaviors and life history types. Just
within California there are 31 recognized native salmonid taxa consisting of salmon
(Oncorhynchus spp), steelhead trout (Oncorhynchus mykiss), and trout (Oncorhynchus
spp). Of the 31 native salmon, steelhead trout, and trout taxa currently living in
5
California, 20 are predicted to be in danger of extinction within the next century (Moyle
et al. 2008). One of the most interesting salmonids in California is the steelhead trout,
which are an anadromous form of rainbow trout (Oncorhynchus mykiss) (Moyle 2002).
What makes the steelhead trout so fascinating is that individuals within a population
can show a wide array of life history patterns. Being an iteroparous organism, it has
recently been discovered that steelhead trout may be anadromous one year, but not the
next year, or anadromous offspring may come from mothers who were or were not
anadromous and vise versa (Pascual et al. 2001, Thorpe 2007). The technological
advances in genetic research and the use of highly sophisticated machinery for otolith
microchemistry studies are allowing for an increased understanding of these highly
versatile fish (Heath et al. 2008, Riva-Rossi et al. 2007, Thrower et al. 2004,
Zimmerman et al. 2009). Even after several decades of scientific investigations, there
are still many unanswered questions about salmonid behavior.
Movement of Trout
Rainbow trout are populations of steelhead trout that do not migrate to the ocean
(Moyle 2002). Like steelhead trout, some populations of rainbow trout show a variety
of life history patterns. Rainbow trout are obligate stream spawners but some
populations of rainbow trout have individuals that will migrate to a lake for part of their
lifecycle, essentially making them a landlocked version of the steelhead trout (Meka et
al. 2003). Even within a population of migratory rainbow trout, some individuals may
spend their entire lives within a small reach of stream, which is generally less than tens
6
of meters in length (Northcote 1992, Riley et al. 1992). The behavior of rainbow trout
has been well documented over the past sixty years, and there are several forms of
movement displayed by rainbow trout that are widely accepted, including passive fry
dispersal with flow, active fry dispersal, daily movements from feeding to resting
positions, seasonal movements between summer and winter habitats, and movement
towards and away from spawning grounds (Gowan et al. 1994). Despite extensive
research, there are still many aspects of trout movement that are not well understood.
One of these includes the post-stocking movement of stocked rainbow trout. A general
downstream movement of recently stocked rainbow trout has been noted on several
occasions, but other taxonomic groups, including different strains of rainbow trout,
have shown random or upstream post-stocking movement (Bettinger and Bettoli 2002,
Cresswell 1981, Gowan et al. 1994, Morning and Buchanan 1978). The post-stocking
movement of rainbow trout has often been attributed to environmental factors such as
streamflow, water temperature, physical features of streams, and availability of food
(Morning and Buchanan 1978). The post-stocking dispersal direction of trout fry
appears to be related to whether they came from a lake-inlet spawning population or a
lake-outlet spawning population, which is evidence of genetic control (Bowler 1975,
Raleigh 1971, Raleigh and Chapman 1971). There is a lack of literature that explores
the influence of genetics on the direction of post-stocking movement in older (than fry)
life stages of trout. While genetic and environmental factors may cause some
individuals to swim away from the stocking location, why would other individuals stay
near the stocking location? I speculate that the answer to this may be related to the
7
competitive ability of the fish. Because stream-dwelling salmonids compete for space
in streams (Caron and Beaugrand 1988), some of the variation in movement may be
attributed to competitive ability. It has often been postulated that stream fish
populations contain two components: static individuals and mobile individuals (Funk
1955, Gerking 1959, Solomon and Templeton 1976, Riley et al. 1992). Additionally,
Riley et al. (1992) suggested that the mobile trout are presumably those that are unable
to establish themselves, and static trout are those that can establish themselves. The
purpose of the present research is to document the post-stocking behavior of Eagle
Lake rainbow trout, and to investigate the possible relationship between the relative
size of an individual fish compared to the stocking group, and its post-stocking
movement. In addition, the effects of electrofishing and tagging on the condition of
fish will be examined.
Background of Lake Davis
Lake Davis, located in Plumas County California, is a 1,630-hectare recreational
reservoir that was created by the construction of Big Grizzly Dam in 1967. De Lain
(1983) described Lake Davis as a moderately productive reservoir that has historically
produced high yields of trout. The tributaries of Lake Davis run through open
meadows, and are lined by willows (Salix spp.) in many sections. Lake Davis is unique
when compared to many of the other lakes in the Sierra Nevada because the tributaries
of Lake Davis flow through relatively long flat meadows. Many other lakes found in
the Sierra Nevada are characterized by steep rocky tributaries. Trout are known to use
8
many of the tributaries in the Lake Davis watershed. Lake Davis has three major
inputs, Cow, Freeman, and Big Grizzly creeks, which are respectively 6.7, 7.5, and 6.5
kilometers (km) long (Schatz 1989). Big Grizzly creek has a tributary named Old
House creek, which joins it 2.5 km upstream of the lake, and Old House creek is also
considered a significant water input to Lake Davis (Figure 1).
9
Figure 1. A map of the four creeks being researched in this project. A variety of lake
levels are shown on this map.
10
The creeks of Lake Davis are spring fed (subsurface influences) and rain/snow
fed creeks that are characterized by high flows in the spring season, and extremely low
flows in the late summer season. Many sections of the creeks dry up during certain
times of the year. The four main creeks of Lake Davis produce fingerling trout that are
known to swim downstream into the lake (Schatz 1989).
This study took place during the first spring/summer season after the California
Department of Fish and Game (DFG) treated Lake Davis with rotenone in September
2007, in an attempt to rid the lake of the non-native northern pike. This treatment
theoretically killed all of the trout (Oncorhynchus mykiss, Salvelinus fontinalis, Salmo
trutta) and pike in the lake’s 114 square kilometer drainage area. The pike should have
been completely eliminated from the watershed in 2007, but time will tell if the
treatment was successful. This study will help to document the post-pike eradication
trout stocking efforts at Lake Davis, and this study has documented aspects of the
growth and behavior of recently stocked Eagle Lake rainbow trout (Oncorhynchus
mykiss aquilarum). Additionally, this research will provide information about how
trout are using the different areas in the Lake Davis watershed, which may be important
in the future management of this fishery. The tributaries of Lake Davis (mainly Big
Grizzly creek) are known to have areas that go dry during the summer season, and it is
important that we know if fish are moving into these dry sections and becoming
trapped. If this is the case, then certain sections of these creeks may be acting as sinks
to the population of fish in the watershed. This research has begun to monitor this
aspect of trout management in the Lake Davis watershed.
11
Eagle Lake Rainbow Trout
The species of fish that was researched in this study was Eagle Lake rainbow
trout. The Eagle Lake rainbow trout are endemic to Eagle Lake California, and have
been provided subspecies status (Behnke 1992). Early logging, grazing, road building,
and commercial fishing activities nearly brought the Eagle Lake trout to extinction.
Passage barriers were constructed in the 1950s on the Eagle Lake tributaries to prevent
the fish from attempting to spawn in degraded habitats, denying the Eagle Lake trout
access beyond the first kilometer of the main tributary. Since the 1950s, the lake
fishery has been maintained by artificial spawning from the California Department of
Fish and Game. Adult fish are trapped near the mouth of Pine Creek tributary, and the
eggs and sperm are harvested and taken to hatcheries. Offspring are reared in
hatcheries and then subsequently released into Eagle Lake each year. Recent
management practices have led to improvements to the Eagle Lake watershed, although
the Eagle Lake trout have not been allowed to attempt their natural spawning
migrations beyond the fish barriers. There is not much known about the historic or
current natural life history traits of this fish because they have been artificially spawned
for roughly sixty years. The extent to which the hatchery program has altered the life
history of this fish is unclear, although it is thought that these fish are being selected for
survival in the early life history stages, and perhaps for early spawning (Moyle et al.
2008).
12
The Eagle Lake rainbow trout is a relatively hardy strain of rainbow trout which
is capable of tolerating higher temperatures and alkalinities than other strains of
rainbow trout (Moyle 2002, Myrick and Cech 2000). Another unique characteristic of
this trout is that it possesses 58 chromosomes rather than the 60 that are present in most
other rainbow trout strains (Busack et al. 1980). However, like all other rainbow trout,
the Eagle Lake rainbow trout are obligate stream/river spawners. Some populations of
rainbow trout contain individuals that spend their entire lives in streams and are
considered resident stream trout. These same populations may also contain individuals
that reside in a lake for part of their lives and return to a stream to spawn at the
appropriate time (Meka et al. 2003). It is unclear if the remaining population of Eagle
Lake rainbow trout at Eagle Lake contains a resident stream component (Moyle et al.
2008).
Objectives
The objectives of this project were to study the growth and dispersal patterns of
recently stocked Eagle Lake rainbow trout in the Lake Davis watershed; this included
evaluating the following questions.
1. Will stocked fish stay where they are stocked?
2. Will fish move to a new location, and then establish a small home range?
3. Will creek-stocked fish move to the lake, and will lake-stocked fish move to the
creeks?
4. Will post-stocking dispersal patterns be different for fish in each of the creeks?
13
5. Will the relative size of a fish (compared to the rest of the stocking group) be related
to its dispersal behavior?
6. Will the fish that are living in each of the four main creeks of Lake Davis have
different levels of physical condition?
7. Will tagged fish be in worse physical condition that non-tagged fish?
8. Will electrofishing and handling negatively affect the physical condition of the fish?
Hypotheses
1. The Eagle Lake rainbow trout that are stocked into the creeks will show a general
downstream post-stocking movement.
2. Between sampling periods some fish will stay within a small reach of stream (100
meters) and other fish will continuously move longer distances.
3. Some of the fish stocked into the lake will move into the creeks, and some of the
fish stocked in the creeks will move into the lake during the sampling season.
4. The post-stocking movement patterns will be similar in each of the creeks.
5. On average, larger stocked fish will remain closer to the initial stocking site.
6. Fish stocked in each of the creeks will have similar levels of physical condition.
7. Non-tagged fish will be in better physical condition than tagged fish throughout the
sampling season.
8. Electrofishing and handling will reduce the physical condition level of fish.
14
Chapter 2
STOCKING THE LAKE DAVIS WATERSHED WITH RAINBOW TROUT AND
THE POST-STOCKING MOVEMENT OF THE FISH
Introduction
Prior to the construction of Big Grizzly Dam in 1967, the upper sections of Big
Grizzly creek were surveyed for fish and only rainbow trout (Oncorhynchus mykiss)
were observed. The lower sections of Big Grizzly, below the site of the current dam,
were reported to contained rainbow trout, Sacramento sucker (Catostomus
occidentalis), and speckled dace (Rhinichthys osculus). After Lake Davis was
impounded in 1967, the California Department of Fish and Game stocked the lake with
rainbow trout, brook trout (Salvelinus fontinalis), and cutthroat trout (Oncorhyncus
clarki). The trout fishery was very successful for many years but started to decline
after illegally introduced species began to show up in the lake. By 1978, the non-native
illegally introduced fish in the lake included golden shiners (Notemigonus crysoleucas),
brown bullhead (Ameiurus nebulosus), and largemouth bass (Micropterus salmoides).
After the trout fishery began to significantly decline, the California Department of Fish
and Game (DFG) experimented with many species and strains of salmonids. Eagle
Lake rainbow trout continually had the highest growth and survival rates; therefore
emphasis was placed on stocking this strain in the lake (Powers 2003). By the 1990s,
the illegally introduced non-native species found in the lake included largemouth bass
(Micropterus salmoides), golden shiner (Notemigonus chrysoleucas), pumpkinseed
sunfish (Lepomis gibbosus), brown bullhead (Ameiurus nebulosus), and northern pike
15
(Esox lucius) (California Department of Fish and Game and USDA Forest Service
2007). The illegal introduction of northern pike (which are found no where else in
California) in the early 1990s led to the concern that this fish could escape Lake Davis
and ultimately end up in the California Central Valley and California Delta. Pike in the
Central Valley and Delta would jeopardize the state’s valuable natural resources. The
California Department of Fish and Game treated Lake Davis with a piscicide in 1997
(Powers 2003). Pike reappeared in Lake Davis in May of 1999, and genetic studies
indicate that the fish that reappeared descended from the original Lake Davis
population. It is unclear whether these fish survived the treatment or were illegally
removed before the treatment and then illegally reintroduced after the treatment.
Between 1999 and 2005, DFG investigated strategies to reduce and contain the
population of pike. In September 2005, DFG and the U.S. Forest Service began the
process of preparing joint environmental impact documents for a proposed project to
eradicate pike from Lake Davis. A second treatment of Lake Davis occurred in
September 2007. It was decided by the fisheries managers who planned the 2007
treatment that Lake Davis would be managed as a trout fishery, and would be stocked
only with rainbow trout and primarily Eagle Lake rainbow trout because of their past
success in Lake Davis (California Department of Fish and Game and USDA Forest
Service 2007). In the year following the 2007 treatment at Lake Davis, nearly 845,000
rainbow trout were stocked into the watershed. During the post-pike treatment surveys,
information was collected in the Lake Davis tributaries with regards to the growth and
movement of the recently stocked Eagle Lake rainbow trout.
16
Methods
Stocking The Lake
After the treatment of Lake Davis in September 2007, the lake was first
restocked with Eagle Lake rainbow trout on 11-13 December 2007, before the winter
ice covered the lake. These fish came from the American River Hatchery at 1.3 fish per
pound (or 1.3 fish per 0.453 kilograms), and were year class 2006 fish. Approximately
31,200 total fish of this size were stocked during this event. The stocking of Lake
Davis continued on 17 and 24 April 2008, after the winter ice melted. Approximately
64,080 fish were stocked on these dates in April and they were year class 2007 fish that
were measured by the hatchery at approximately 20 fish per pound (or 20 fish per 0.453
kilograms). Approximately 844,870 trout were stocked into the lake by the end of 2008
(Personal communication with Joe Johnson, DFG Senior Environmental Scientist,
2009). All of the fish put into the lake were rainbow trout, and most were Eagle Lake
rainbow trout. This strain was used because it has been shown to be relatively
successful and hardy when compared to the other strains of rainbow trout stocked in
Lake Davis (Powers 2003), and throughout California (Cordone 1970, Moyle 2002,
Myrick and Cech 2000, Rawstron 1973, Rawstron 1977). Out of the approximately
844,870 trout stocked into the watershed, only about 11,202 were not the Eagle Lake
strain of rainbow trout.
In May 2008, 500 tagged Eagle Lake rainbow trout were stocked in Lake Davis.
These fish came from the Mount Shasta State Fish Hatchery and are considered by the
California Department of Fish and Game to be trophy-sized fish. These tagged fish had
17
an average total length of 447 millimeters (range=258mm - 658 mm, sd=60), and an
average weight of 1,289.9 grams (g) (range=311.8g - 4139.0g, sd=822). All length
measurements reported in this study represent maximum total length with the caudal fin
spread in a “natural” position (see Murphy and Willis 1996). These fish were marked
with $10 reward tags that are used to evaluate angler success. For the purpose of this
report, these tagged fish were used to evaluate the possible movement of these fish into
the creeks. All of the fish stocked into the lake in 2007 and 2008 were stocked at the
dam or at Honker Cove Boat Ramp.
Initial Survey Of The Creeks
During the week of 20 May 2008, the four main tributaries of Lake Davis were
surveyed for fish. This survey was done to determine if fish were present in the creeks
before creek stocking began. The entire lengths of each of the four main tributaries of
Lake Davis were electro-fished in a single upstream pass using Smith-Root
electrofishing backpacks. Output voltage of 400-500V at 60 hertz was used the
majority of the time, although problems with batteries or changing water conditions
occasionally required adjustments outside this voltage range. The backpack settings
were always set at a low voltage (400-425V) to start the surveys, and if this voltage was
not effective at immobilizing fish long enough to be netted, then the voltage was
increased to the point where netting fish was possible. Adjustments were made when
necessary to maximize catch efficiency while minimizing recovery times and visible
injuries to fish.
18
Stocking The Creeks
The tributaries of Lake Davis were stocked with both tagged and non-tagged
fish during the last week of May and the first week of June 2008. The fish stocked into
the tributaries were all a wild strain of Eagle Lake rainbow trout. These fish were the
offspring of wild fish. The eggs and sperm were collected from Pine Creek, a tributary
of Eagle Lake California, and then taken to the Mount Shasta State Fish Hatchery for
rearing. These fish were brood year 2007 Eagle Lake rainbow trout (Personal
communication with James Adams, Mount Shasta State Fish Hatchery Manager, May
2008). On 28 May 2008, 800 of these wild-strain Eagle Lake rainbow trout were
tagged at the Mount Shasta State Fish Hatchery. These fish were tagged with a yellow
FD-94 T-Bar Anchor Tag manufactured by Floy Tag. The tags were a total length of 3
inches (7.62 centimeters), with 2 3/8 inches (6.03 centimeters) tubing, and 5/8 inches
(1.59 centimeters) monofilament. Each of these tags had a unique number used to
identify individual fish. Total lengths of all 800 fish were recorded, and 485 of these
fish were weighed. The average length of these fish was 179 mm (sd=11,
range=151mm-214mm), and the average weight was 62.7 g (sd=14, range 37.0g125.0g). Tagged fish were held overnight at the hatchery to evaluate tagging mortality.
There were no mortalities the following morning. The fish were stocked in Cow,
Freeman, Big Grizzly, and Old House creeks on 29 May 2008. The fish were spread
out in stretches of the creeks that were thought to hold water year round. The locations
were selected by consulting with DFG employees who had worked in the area in the
19
previous years. In addition, a previous Masters Thesis by Schatz (1989) was used to
evaluate suitable locations for trout. The first step of the stocking procedure was to net
individual fish out of the fish transporter. Next, the tag numbers were recorded, and
then groups of fish were taken in a bucket or ice chest (fitted with aerators) to their
destinations. A few of the locations required carrying the fish by foot up to
approximately 350 meters. The watershed of Lake Davis has been previously mapped
and separated into ¼ mile (64.75 hectare) grids as part of the 2007 pike eradication
effort. Using GPS (UTM, NAD 83), the release grid locations were recorded for all of
the tagged fish. The exact location of each fish was not recorded because there was a
requirement that fish would not be stocked in large batches, but would rather be “spread
stocked” (meaning stocking a few fish here and a few fish there). The logistics of
marking the location of each fish was not possible considering the requirement of
spread stocking, because the fish were dispersed in a single day using a small crew to
spread them over approximately 15,000 meters of stream (the sum of creek distances
from the highest stocking location to the lake, for each creek). Instead of recording the
exact location of each stocked fish, the grid number that each fish was stocked into was
recorded. The center point along the stream within each grid was recorded as the
stocking location for all fish stocked in each of the grids. Overall, fish went into 16
separate grids. Other grids on each of the creeks received no fish because these
locations are known to dry up completely or to become extremely shallow in the
summer months. Once a grid was identified as one that would be stocked, fish were
stocked by staff members who started on one side of the grid and then worked towards
20
the other side of that grid. The fish were stocked in a leapfrog approach; meaning that
one staff member would take a bucket of fish and stock them into a pool(s), and the
next staff member would take another bucket of fish and stocked them in the next
pool(s) until one entire grid had been covered. Large pools often received multiple
buckets of fish, and small pools often received only one fish. The number of fish put
into each pool was based on a rough estimate of what that pool could support. The
average number of fish per grid, in the grids that received fish, was 49. The grid that
received the most fish was grid 734, which contains the intersection of Old House and
Big Grizzly creeks. In grid 734, Old House creek received 120 fish and Big Grizzly
creek received 100 fish. Grids 735 (Big Grizzly creek), 1125 (Cow creek), and 957
(Freeman creek) received the least amount of fish with 15 each. Overall, the average
number of fish per meter was 0.099. This was calculated by using the lengths of stream
within each of the grids that received fish (7904 meters of stream were stocked within
the grids that received fish). The average stocking density equaled approximately 1
fish for every ten meters of stream in the grids that received fish. Twenty tagged fish
were stocked into Little Summit Lake and were never sampled; therefore, these fish
were left out of all discussion in this paper. Tables 1 and 2 summarize the stocking
locations and numbers of tagged creek fish stocked into the creeks of Lake Davis.
21
Table 1. A summary of fish stocked into each grid. The table includes the number of
fish stocked into each grid, the length of stream within each grid, and the GPS
point of the middle stream location of each grid. GPS points are measured in
UTM, NAD 83.
Grid
1070
1124
1125
956
957
1011
1175
795
683
734
735
736
737
684
630
678
734
Length of
Stream Within
Creek
Grid (m)
Cow
664
Cow
402
Cow
109
Freeman
174
Freeman
550
Freeman
538
Freeman
445
Freeman
281
Big Grizzly
595
Big Grizzly
476
Big Grizzly
492
Big Grizzly
571
Big Grizzly
437
Big Grizzly
402
Big Grizzly
503
Old House
704
Old House
561
Total
7904
Fish
20
70
15
45
15
70
30
30
50
100
15
30
40
50
60
20
120
Northing
709396
709081
709230
707919
708036
707764
707428
709533
708622
706960
707396
707814
708192
708993
709406
706607
706998
780
Easting
4420188
4419740
4419961
4420870
4420936
4420621
4419376
4422055
4423068
4422488
4422605
4422666
4422708
4423165
4423294
4423016
4422601
22
Table 2. A summary of fish stocked into each creek, and the density of fish stocked
into the creeks. The table includes the total length of stream within stocked
grids for each creek, and the length of each creek measured from furthest
upstream stocking location to the lake (lake elevation of 1761 meters). *The
Old House creek stocking location furthest from the lake was measured from its
intersection with Big Grizzly creek not the lake.
Creek
Fish
Cow
Freeman
Big Grizzly
Old House
Total
Average
105
190
345
140
780
Total
Length of
Stream
Within
Stocked
Grids (m)
1175
1988
3476
1265
7904
Stocking
Average
Location
Density
Stream
Furthest
(Fish per Total Grids Length (m) Average From Lake
Meter)
Stocked
Per Grid Fish / Grid (in meters)
0.089
0.096
0.099
0.110
3
5
7
2
391.7
397.6
496.6
632.5
35
38
49
70
3407
5629
4814
1265*
15035
17
0.0985
479.6
48
23
One week after the tagged fish were stocked into the creeks, 1,300 non-tagged fish
were stocked into similar locations as the tagged fish (4 June 2008). The approximate
number of fish stocked in each location was recorded. These non-tagged fish were
stocked in roughly the same locations as the tagged fish with two exceptions. First,
approximately 120 non-tagged fish were stocked above the second bridge on Big
Grizzly creek. All tagged fish stocked in Big Grizzly creek were stocked at or below
the first bridge. Second, approximately 60 non-tagged fish were stocked into each of
the Old House ponds. The lengths and weights of non-tagged fish were not recorded,
but they came from the same raceway at the hatchery as the 800 non-reward tagged fish
that were released the week prior.
Post-Stocking Electrofishing Surveys
After the initial survey and creek stockings occurred, the creeks were not
sampled until the week of 23 June 2008. Additional samplings occurred during the
weeks of 14 July, 4 August, and 15 September 2008. The creeks were electrofished
using Smith-Root electrofishing backpacks walking upstream in a single pass while
using reliable techniques and backpack settings. Adjustments were made to the
techniques and backpack settings when needed in order to maximize catch efficiency
while minimizing injury to fish. Length and weight measurements were taken on every
tagged, and untagged fish caught. Using GPS (UTM, NAD 83), the grid number and
exact location were recorded for each tagged fish that was caught. The end of the 2008
sampling period for this study was on 15 September.
24
Analysis Of Creek Movement
The exact location of all captured tagged fish was recorded throughout the
sampling season. Each tag recovery location was then converted into Environmental
Systems Research Institute, Inc. (ESRI) Shape Files. The files were merged into a
master file of all tags and sampling events. Stream channels were digitized using aerial
photos of the study area (National Agriculture Imagery Program 2005) and “Routes”
were created using Linear Referencing tools in ArcGIS. The upper end of each stream
route was used as the reference point for measurements along a stream. The relative
location of each tag along the route (stream) was generated via the ArcGIS “Locate
Feature Along Route” tool. A search radius of 15 meters was used to locate the points
to the stream because not all data points are exactly on the stream. This search feature
only allows data points that are within a set distance (15 meters for this analysis) of the
stream to be counted as valid. Any point outside of this radius was determined to be
invalid and was discarded. The result was a table that listed each tag capture, capture
date, and capture distance. The capture distance was measured from the origin (upper
end of the route) to the point of capture. To generate a distance that an individual fish
moved between captures, the current location along the route was subtracted from the
last known location along the same route to give an exact stream distance between the
two known locations of that fish. Fish that moved in a downstream direction were
indicated by a negative number, and fish that moved in an upstream direction were
indicated by a positive number.
25
Measuring movement between captures was straightforward because there were
two exact known locations. Measuring movement between the stocking point and first
capture was not as precise because the exact stocking location was not recorded. Only
the grid number that each fish was stocked into was recorded. To estimate where fish
were stocked, the center point along the stream within a grid was used as the stocking
location for all fish in that grid. It is assumed that the error was minimized because fish
were randomly stocked above and below the center point of each grid. Therefore some
fish moving in the downstream direction would have been calculated as moving farther
than they actually did, and other fish would have been calculated as moving less than
they actually did. On average, it is assumed that the calculated error for initial fish
movement for fish that were stocked above the center grid location and below the
center grid location would cancel out. The maximum amount of average error for this
method is 239.8 meters, which is half of the average length of stream within each grid.
This error would occur if all of the fish that were stocked into a grid were stocked at
either the upstream border or downstream border of that grid. Because fish were
distributed throughout the entire grid it is assumed that the initial movement error was
minimized. Initial movement was also evaluated by comparing initial grid location to
the grid location during the first sampling event to verify the general trend in initial
post-stocking fish movement.
26
Results
Initial Creek Survey
During the week of 20 May 2008, the four main tributaries of Lake Davis were
surveyed for fish using electrofishing backpacks. Four days of electrofishing with
multiple crews produced the capture of 63 rainbow trout. The effort of electrofishing
was 13.99 hours (the time that electrical current was being sent to the water), and two
size classes of fish were captured (Figure 2 and Table 3).
Number of Fish Caught
27
8
6
4
2
0
0
50 100 150 200 250 300 350 400 450 500
Length (mm)
Figure 2. A length-frequency distribution of the fish captured during the initial survey
on 20, 21, 22, 23 May 2008, in the four main creeks of Lake Davis.
28
Table 3. Fish captured during the initial survey on 20, 21, 22, 23 May 2008, in the four
main creeks of Lake Davis (a summary of the data presented in Figure 2). Size
class one is used to describe the fish that hatched in the Lake Davis creeks in the
spring of 2008, and were captured in later surveys. Size class two and three are
used to describe the fish that were stocked into the lake and were found in the
creeks during this initial creek survey.
May
Size Class One
Size Class Two
Size Class Three
Count
0
28
35
Length Range (mm) Average Length (mm)
NA
NA
110-188
150
285-425
334
Standard
Deviation
NA
18.7
34.4
29
Post-Stocking Electrofishing Surveys
After the initial survey and creek stocking occurred, the creeks were sampled
the weeks of 23 June, 14 July, 4 August, and 15 September 2008. A summary of all
sampling data is provided in Table 4.
30
Table 4. The number of tagged and untagged fish caught during each sampling period,
and the effort for each sampling period. Effort is read from the electrofishing
backpack display. This displays the actual time that the electrical current had
been sent into the stream. CPUE refers to Catch Per Unit Effort, and this
represents how many fish were caught per hour.
Month
May (Initial
Survey)
June
July
August
September
Total
Average
NonTagged
Tagged
Total
Captures
Effort
(Hours)
63
177
68
124
67
499
NA
83
25
34
20
162
63
260
93
158
87
661
13.99
13.88
6.62
6.12
4.30
44.91
CPUE
Tagged/Non
-Tagged
4.50
18.73
14.05
25.82
20.23
NA
16.67
NA
0.47
0.37
0.27
0.30
NA
0.32
31
The following length-frequency distributions show the number of non-tagged fish
caught at different lengths for each of the sampling months (Figures 3-6 and Tables 58). Size class one fish represent fish that hatched in the creeks during the spring of
2008. Size class two fish represent both creek and lake-stocked fish that were found in
the creeks during these surveys. Size class three fish represent lake-stocked fish that
had moved into the creeks. Monthly lengths of tagged fish are summarized in Table 9,
and no graph is shown because each month there was a normal distribution around the
average.
Number of Fish Caught
32
20
16
12
8
4
0
0
100
200
300
400
500
Length (mm)
Figure 3. A length-frequency distribution of non-tagged fish captured on 23, 24, 25
June 2008, in the four main creeks of Lake Davis.
33
Table 5. Non-tagged fish captured on 23, 24, 25 June 2008, in the four main creeks of
Lake Davis (a summary of the data presented in Figure 3). Size class one fish
represent fish that hatched in the creeks during the spring of 2008. Size class
two fish represent both creek and lake-stocked fish that were found in the creeks
during these surveys. Size class three fish represent lake-stocked fish that had
moved into the creeks.
June Non-Tagged
Size Class One
Size Class Two
Size Class Three
Count
2
129
25
Length Range (mm) Average Length (mm)
30-31
30
70-206
159
281-399
345
Standard
Deviation
0.7
31.6
32.9
Number of Fish Caught
34
10
8
6
4
2
0
0
100
200
300
400
Length (mm)
Figure 4. A length-frequency distribution of non-tagged fish captured on 14 and 15
July 2008, in the four main creeks of Lake Davis.
35
Table 6. Non-tagged fish captured on 14 and 15 July 2008, in the four main creeks of
Lake Davis (a summary of the data presented in Figure 4). Size class one fish
represent fish that hatched in the creeks during the spring of 2008. Size class
two fish represent both creek and lake-stocked fish that were found in the creeks
during these surveys. Size class three fish represent lake-stocked fish that had
moved into the creeks.
July Non-Tagged
Count Length Range (mm)
Size Class One
0
NA
Size Class Two
54
108-225
Size Class Three 14
325-383
Average Length (mm)
NA
174
356
Standard
Deviation
NA
26.9
17.9
Number of Fish Caught
36
12
10
8
6
4
2
0
0
100
200
300
400
Length (mm)
Figure 5. A length-frequency distribution of non-tagged fish captured on 4, 5, 6 August
2008, in the four main creeks of Lake Davis.
37
Table 7. Non-tagged fish captured on 4, 5, 6 August 2008, in the four main creeks of
Lake Davis (a summary of the data presented in Figure 5). Size class one fish
represent fish that hatched in the creeks during the spring of 2008. Size class
two fish represent both creek and lake-stocked fish that were found in the creeks
during these surveys. Size class three fish represent lake-stocked fish that had
moved into the creeks.
August Non-Tagged Fish
Count
Size Class One
20
Size Class Two
100
Size Class Three
3
Length Range (mm) Average Length (mm)
51-83
63
100-227
168
266-360
316
Standard
Deviation
9.0
32.4
47.4
Number of Fish Caught
38
10
8
6
4
2
0
0
100
200
300
400
Length (mm)
Figure 6. A length-frequency distribution of non-tagged fish captured on 15, 16, 17
September 2008, in the four main creeks of Lake Davis.
39
Table 8. Non-tagged fish captured on 15, 16, 17 September 2008, in the four main
creeks of Lake Davis (a summary of the data presented in Figure 6). Size class
one fish represent fish that hatched in the creeks during the spring of 2008. Size
class two fish represent both creek and lake-stocked fish that were found in the
creeks during these surveys. Size class three fish represent lake-stocked fish
that had moved into the creeks.
September Non-Tagged
Size Class One
Size Class Two
Size Class Three
Count Length Range (mm) Average Length (mm)
7
75-120
98
55
130-235
181
5
275-380
340
Standard
Deviation
15.9
29.1
40.3
40
Table 9. A size summary for all tagged fish released (May) and then captured (all other
months) during 2008 in the four main creeks of Lake Davis.
Month
May (Release)
June
July
August
September
Count
800
83
25
34
20
Average
Length (mm)
179
184
193
198
204
Standard
Deviation
11.2
12.2
11.1
15.5
15.6
Average
Weight (g)
63
58
59
62
66
Standard
deviation
13.8
13.8
14.6
17.8
24.3
41
Initial Post-Stocking Movement Of Tagged Fish
Fish that were stocked into the creeks of Lake Davis showed a range of initial
movement patterns. Initial movement was measured from the time of stocking to the
first sampling, which was 27 days later (23 June). Fish that were stocked into Big
Grizzly, Freeman, and Cow creeks showed an average downstream movement, while
fish that were stocked into Old House creek showed an average upstream movement
(Table 10).
42
Table 10. The number of tagged fish caught in each creek and the average distance
moved by tagged fish in each creek between 25 May and 23 June 2008.
Upstream movement is denoted by positive numbers, and downstream
movement is denoted by negative numbers. Movement is measured in meters.
Standard
Deviation
Farthest
Downstream
Movement (m)
Farthest
Upstream
Movement
(m)
-496
710
-1698
56
22
-273
695
-2996
191
Big Grizzly
12
-478
444
-1573
-63
Old House
43
178
297
-218
828
Count
Average
Movement
(m)
Cow
5
Freeman
Creek
43
To determine if movement was different between the creeks, a One-Way
ANOVA was performed. There is a statistically significant difference between the
mean movements between creeks (F-ratio=11.40, p<0.01, df=3). A Multiple Range
Test using Fisher’s Least Significant Difference (95.0 percent LSD) procedure was
used to determine which means are significantly different from the others. Old House
creek was significantly different than each of the other three creeks (95.0 percent LSD
procedure, F-ratio=11.40, p<0.05). Fish movement in the other three creeks was not
significantly different (95.0 percent LSD procedure, F-ratio=11.40, p>0.05). The
average combined movement of fish in Cow, Big Grizzly, and Freeman creeks was 365
meters in the downstream direction, furthest movement upstream was 191 meters,
furthest movement downstream was 2991 meters (n=39, sd=623). The average
movement of fish in Old House creek was 178 meters in the upstream direction,
furthest movement upstream was 828 meters, furthest movement downstream was 218
meters (n=43, sd=297) (Figure 7).
Movement (meters)
44
1000
0
-1000
-2000
-3000
Cow
Freeman
Grizzly Old House
Fish Caught In Each Creek
Figure 7. The number of fish caught in each creek and the approximate distance moved
by each fish between 25 May and 23 June 2008. Upstream movement is
denoted by positive numbers, and downstream movement is denoted by
negative numbers.
45
The initial movement pattern was also evaluated by comparing the stocking grid
of each fish relative to the grid that each fish was captured in during the first sampling
period. Table 11 shows where fish were captured during June, and it shows if fish were
caught in the same grid that they started in, or if they were captured in grids upstream
or downstream relative to the starting grid.
46
Table 11. The capture locations of fish caught in June relative to their stocking
locations. Upstream and downstream grid categories represent fish caught one
or more grids away from the starting grid.
Creek
Cow
Freeman
Big Grizzly
Old House
Number of Fish
Caught in
Downstream
Grids
3
14
9
0
Number of Fish
Number of Fish
Caught in the Same Caught in Upstream
Grid
Grids
2
1
8
0
3
0
36
7
47
The results of Table 11 show that the measured fish data is consistent with the relative
grid location that fish were found in.
Movement Of Tagged Fish Between Captures
There were a total of 40 fish that were captured more than once in 2008, but
because of a problem with one of the GPS units only 36 of the recaptures will be used
for the between-capture movement analysis. There were 18 recaptures in Old House
creek, 13 recaptures in Freeman creek, 3 recaptures in Cow creek, and 2 recaptures in
Big Grizzly creek. Because sample sizes were low for between-capture movements,
there was no comparison made between each of the creeks. Movement data from Cow,
Freeman, and Big Grizzly creeks were combined to compare initial movements to
between-capture movements in these creeks. Old House creek was analyzed separately
because average initial fish movement was shown to be significantly different than the
other creeks. Fish that were captured in Big Grizzly, Freeman, and Cow creeks during
the June sampling period (first post-stocking sample) were found on average 364.6
meters downstream of the stocking site (sd 623.3, n=39). Fish that were captured on 14
July or later and had previously been captured (on 23 June, 14 July, 16 August) had an
average movement of 1.6 meters downstream (sd 34.8, n=18). A t-test was performed
to determine if the average post-stocking movement was significantly different than
average between-capture movement. There is a statistically significant difference
between the mean initial movement and mean between-capture movement in these
three creeks (unpaired t-test, t=2.46, p=0.017, df=2). The same analysis was performed
48
for the fish that were released and then caught in Old House creek. Fish that were
captured during the June sampling period moved on average 178.5 meters upstream (sd
296.6, n=43). Fish that where captured on 14 July or later and had previously been
captured (on 23 June, 14 July, 16 August) moved on average 6.7 meters downstream
(sd 18.0, n=18). The average post-stocking initial movement of fish in Old House
creek was significantly different than the average between-capture movement of fish in
Old House creek (unpaired t-test, t=2.63, p=0.01, df=1). To determine if betweencapture movement was different between Old House creek and the other three creeks a
t-test was performed. Average between-capture movement of fish in Cow, Big Grizzly,
and Freeman creeks was 1.6 meters downstream (sd 34.8, n=18). Average betweencapture movement of fish in Old House creek was 6.7 meters downstream (sd 18.0,
n=18). There was no statistically significant difference of between-capture movements
of fish in Old House creek versus fish in the other three creeks (unpaired t-test, t=0.55,
p=0.58, df=1).
Movement Of Fish Between The Lake And The Creeks
During the creek samplings no tagged fish that were released into the lake were
recovered in the creeks. During the initial creek survey however, 63 untagged trout that
were stocked into the lake were found in the creeks. These fish were assumed to come
from the lake stockings because they matched the two size ranges of fish that had been
stocked into the lake up to that point following the rotenone treatment of the watershed.
These fish came from the December stocking (1.3 fish per pound, 31,200 total fish),
49
and the April stocking (20 fish per pound, approximately 60,000 total fish). These fish
had moved up the creeks in some cases as much as approximately 7 kilometers. The
water level in the creeks dropped rapidly by 23 June, making connection to the lake
very shallow, and it is unknown if any additional untagged fish had moved from the
lake into the creeks after the first sampling period.
Many tagged fish that were stocked high up in the creeks were found in the
lower portions of the creeks (near the lake) by the June sampling period. There were
not any tagged creek fish captured in the lake by boat electrofishing, and only one creek
tagged fish was caught in the lake by a fisherman who returned the tag by mail. This
fish was caught in the north end of Lake Davis by an ice-fisherman on 31 January 2009.
This fish had originally been stocked into the lower portion of Big Grizzly creek , close
to the lake (grid# 630). Additionally, a tag from one of the creek fish was found by
Gary Scoppettone of the United States Geological Survey (USGS) on Anaho Island at
Pyramid Lake, Nevada (Approximately 75 kilometers to the east of Lake Davis). This
tag was apparently on a creek tagged fish that was eaten by an American white pelican
(Pelecanus erythrorhynchos) at Lake Davis. The pelicans are known to stop at Lake
Davis on their migratory path to Pyramid Lake Nevada where they breed. This tagged
creek fish was most likely eaten while swimming in the lake, because there were no
pelicans observed in the creeks of Lake Davis during this sampling season. In addition
to the one creek released tag that was found on Anaho Island, four lake-stocked reward
tags (out of 500 total) were found by Gary Scoppettone between 20 October 2008, and
31 January 2009, on Anaho Island.
50
Conclusions
Initial Creek Surveys
The initial creek survey conducted in May 2008 showed that many fish that
were previously stocked into the lake had moved into the creeks. High spring seasonal
flows made backpack electrofishing difficult because creek depths were often over two
meters, and many visual sightings of trout were made without capture. The low initial
survey CPUE presented in Table 3 is thought to represent difficult sampling conditions
in addition to fewer fish being present in the creeks at that time. It is assumed that the
fish caught during the initial survey came from two lake stockings: the first stocking
was the December 2007 lake stocking (n=31,200, average length at initial survey 334
mm), and the second stocking was the April 2008 lake stocking (n=60,000, average
length at initial survey 150 mm). The fish that were caught during the initial survey
had lengths consistent with the fish stocked in December and April. Only one other
lake stocking occurred prior to the initial survey. This stocking occurred during the
week prior to the initial survey and these fish were a larger class fish (average length
442 mm, average weight = 1290 grams), plus a small amount of fingerling-sized fish.
The sizes of the fish released during the week prior to the initial survey are not
consistent with the fish caught during the initial survey.
Many sightings were reported of the size class three fish (average 334 mm)
displaying spawning behavior in the four main creeks of Lake Davis. Additionally,
observations of spawning behavior were made in the smaller named and unnamed
51
creeks around Lake Davis during the month of May. Around the middle of June a
fisherman reported that the male fish that he had caught were still milting at this time,
and that the female fish that he caught and kept to eat did not have any eggs left in
them. These observations are consistent with the observations Schatz (1989) made in
the Lake Davis creeks. He reported that peak spawning observations were noted in the
last week of May and tapered off quickly during the first week of June. It is also
interesting to note that the size class 2 fish (average 150mm) moved into the creeks in a
short period of time after being stocked into the lake. These fish were approximately
one year old at the time of stocking, and rainbow trout generally do not reach sexually
maturity until age 2 or 3. It is unknown if these fish were attempting to spawn in the
creeks, because no sightings of spawning behavior of this size class fish were reported.
Initial Post-Stocking Movement Of Tagged Fish
The Eagle Lake rainbow trout that were stocked in the four main creeks of Lake
Davis showed a general downstream post-stocking movement pattern. This was
determined by comparing release grid location and capture grid location, and by
measuring the distance moved from an approximate stocking location to the capture
location. This pattern is generally consistent with other strains of rainbow trout
(Cresswell 1981, Morning and Buchanan 1978). The average post-stocking movement
of fish in Cow, Big Grizzly, and Freeman creeks was 365 meters in the downstream
direction (n=39, sd=623, furthest upstream 191 meters, furthest downstream 2991
meters). The fish stocked into Old House creek moved on average 178 meters
52
upstream (n=43, sd=297, furthest upstream 828, furthest downstream 218). A shallow
section of Old House creek likely caused the movement in the downstream direction to
be blocked. This section is the last stretch of Old House creek before it enters Big
Grizzly creek. In this stretch, Old House creek fans out into a grassy meadow and
becomes extremely shallow. During high spring flows, movement through this section
does occur based on the fact that many fish that were stocked into the lake had moved
into Big Grizzly creek and then into Old House creek past the shallow section in the
spring of 2008. After the high spring flows subside, this section appears to be
impassible, and this is what likely caused fish that were stocked into Old House creek
to move in an upstream direction after they encountered the downstream barrier. By
July 2008, surface flows of Old House creek were entirely disconnected from Big
Grizzly creek.
In Cow, Freeman, and Big Grizzly creeks, many fish were captured well
downstream of their original stocking location, and it is suspected that many more had
moved into the lake and were never recaptured. This assumption is made because there
were several fish that were stocked in the upper reaches of the streams and were found
very close to the lake on the first sampling event. Other fish that were not stocked as
high in the creeks likely made it to the lake within the first month. This type of study
may actually under estimate downstream movement because fish that moved the
furthest downstream and into the lake were effectively out of the sampling area. It was
originally thought that the electrofishing efforts in the lake would yield more captures
of rainbow trout. These lake efforts were relatively ineffective at catching large
53
numbers of rainbow trout, primarily because boat electrofishing occurred during the
daytime hours. As seen during the recent Caples Lake fish rescue (a dam repair caused
the need to drain Caples Lake) made by the California Department of Fish and Game
(DFG), electrofishing for trout in a large mountain lake is far more productive at night.
In approximately 72 hours of around-the-clock work (26-29 August 2008), DFG caught
approximately 6,000 adult trout from Caples Lake and transplanted them into nearby
lakes. All but a few hundred of these fish were caught at night with electrofishing boats
(a variety of net types were also tried). These same electrofishing boats were run nonstop during the daylight hours of this 72-hour event, and only a handful of fish were
caught (personal experience). The Lake Davis electrofishing sampling effort ran during
the daytime hours because the primary objective of the effort was to survey for pike,
which in the past have been caught relatively successfully during the daytime. Only
one tagged trout out of 1,300 (800 non-reward creek-stocked fish and 500 reward lakestocked fish) was captured by electrofishing boat in Lake Davis in 2008. This fish was
one of the reward fish that was stocked in the lake. The lack of efficiency of the
electrofishing boats at catching trout in the surveys of the lake effectively made creekstocked fish disappear if they entered the lake. Perhaps a better way of capturing the
movement of creek stocked fish swimming downstream and ultimately into the lake
would be to use PIT (Passive Integrated Transponder) tags with data recorders placed in
strategic locations. This would allow for an accurate estimate of how many tagged fish
migrated to the lake after stocking. Another way to capture post-stocking movement is
to use a weir type trap similar to the ones used by Schatz (1989). This type of trap has
54
some benefits and draw backs when compared to using PIT tags. The benefits of this
type of trap are that it potentially catches all age classes of fish without the requirement
of tagging fish. This type of trap would be good for catching stocked fish and wild fish,
including young of the year fish. The problem with this type of trap at Lake Davis is
that the high spring flows in the creeks of Lake Davis often flood the meadows and
flow through many alternative channels. Placement of this type of trap early enough in
the season to capture spring time movement would require knowledge of spring flows
from previous years. One area that a two-way weir type trap would be useful is at the
first bridge on Big Grizzly creek. A trap at this location would help to determine if the
adult trout and their offspring produced above the first bridge are moving downstream
in time to avoid becoming stranded in the section between the two bridges on Big
Grizzly creek. This section of creek became mostly dry by the end of the summer,
although there were spots that held a small amount of water and fish all year. Many
stretches along this section of creek dried out and ultimately killed fish. A trap located
at the first bridge on Big Grizzly creek would help to determine if the upper section of
this creek is acting as a sink to the trout population in the Lake Davis watershed.
Movement Of Tagged Fish Between Captures
It has often been postulated that stream fish populations contain two
components: static individuals and mobile individuals (Funk 1955, Gerking 1959,
Solomon and Templeton 1976, Riley et al. 1992). Additionally, Riley et al. (1992)
suggested that the mobile trout are presumably those that are unable to establish
55
themselves, and static trout are those that can establish themselves. Fish that were
captured more than once during the present study were found on average to be 4.16
meters downstream from the previous capture location (n= 36, sd = 27.43). The
farthest that an individual fish had moved between capture events was 94.82 meters
downstream and another fish had moved 69.95 meters upstream. Northcote (1992)
stated that home ranges of salmonids are usually a few tens of meters. Riley et al.
(1992) and Young (1995), reported that mobile segments of trout populations
continuously move throughout the summer season, and that some fish may move tens
or hundreds of kilometers. The present research indicated that trout within the creeks
of Lake Davis did not continue to move throughout the summer season, therefore, these
fish would fit best into the classification of static individuals under the definitions
presented by Funk (1955), Gerking (1959), Solomon and Templeton (1976), Riley et al.
(1992). It is possible that a segment of the population is a mobile segment, and these
fish may have moved to the lake during the initial movement period (first 27 days), and
were essentially out of the research area for the remainder of the year. Although many
fish may have moved to the lake shortly after stocking, it is not likely that fish were
moving into the lake after the first sampling period because the connections to the lake
had become extremely shallow. By the July sampling period, the lower section of Big
Grizzly creek had become intermittent and was no longer connected to the lake. The
dry stretch between the lake and the first signs of water on Big Grizzly creek was
approximately 800 meters long. Cow and Freeman creeks remained connected but
were shallow to the point that trout passage would be unlikely. Because the creeks
56
essentially lost their connectivity to the lake, the movement data collected after the first
sampling period should not have any bias (i.e., fish did not move out of the effective
sampling area). It is possible, but unlikely, that all mobile fish would have made it to
the lake during the initial movement period. The data indicates that there were few or
no mobile fish present in the creeks of Lake Davis during the sampling period, though
these results would be expected to change during spawning or seasonal movements, and
could possibly change with different strains, species, or age class of trout.
Movement Of Fish Between The Lake And The Creeks
The results of this study show that some of the sexually mature fish that were
stocked into the lake in December 2007 moved into the creeks to spawn in the spring of
2008. In addition, some of the approximately one-year-old fish that were stocked in
Lake Davis in April 2008 moved across the lake and swam into the creeks over a period
of one month. The December stocked fish were observed displaying spawning
behavior in many of the named and unnamed creeks all around Lake Davis. It is
unclear if any of the one-year-old fish were attempting to spawn. After the high spring
flows had dropped off around June, it is thought that additional fish were not moving
from the lake into the creeks, because the creek-lake connections were extremely
shallow or nonexistent.
It is suspected that some of the fish that were stocked into the creeks moved into the
lake shortly after stocking. The approximate number of fish that moved from the
creeks into the lake is unknown because the 2008 lake surveys were relatively
57
ineffective at catching large amounts of trout. In addition, many sections of the creeks
are so densely lined with willows that surveying for fish is extremely difficult, and this
may have led to some uncertainty of how many tagged fish remained in the creeks.
There are a few pieces of evidence that lead to the conclusion that fish stocked into the
creeks moved into the lake. First, there was one creek tagged fish caught in the north
end of Lake Davis by an ice-fisherman on 31 January 2009. This fish was stocked into
the lower portion of Big Grizzly creek, close to the lake (grid# 630). Second, the one
creek tag that was found by Gary Scoppettone on Anaho Island at Pyramid Lake is
suspected to have been eaten by a pelican while the tagged fish was swimming in the
lake because that is where the pelicans were observed feeding throughout the sampling
season. Finally, there were tagged fish in Cow, Freeman, and Big Grizzly creeks that
were observed moving over 1,500 meters in the downstream direction during the first
month after release. These fish were stocked in the higher portions of each of the
creeks and were found in the lower portions of the creeks during the first sampling
event. This led to the assumption that fish stocked in the lower portions of the creeks
could have moved downstream into the lake. Although there was substantial
downstream movement displayed by some of the fish, other fish remained within the
same grid that they were stocked in for the entire sampling season.
58
Chapter 3
SIZE AT STOCKING VERSUS DISPERSAL DISTANCE
Introduction
To evaluate the influence that competitive interactions have on post-stocking
movements of trout, relative size at stocking was compared to dispersal distance.
Movement of trout away from the stocking site may be caused by competitive
interactions, because trout are generally stocked in high densities and this may lead to
competition for resources. If competitive interactions are the sole cause for poststocking movement, then a pattern could emerge where smaller subdominant fish
(Abbott et al. 1985, Caron and Beaugrand 1988, Gotceitas and Godin 1992, Jenkins
1969) are forced to move farther than larger fish because of these interactions. If
something else is causing post-stocking movement, like the level of anadromous (or
limadromous, used interchangeably) instinct, then movement should be random with
respect to size, unless all fish have an equally anadromous instinct. If all fish have an
equal level of anadromous instinct then larger fish may move the furthest away from
the stocking site because they generally have a greater swimming capacity (Ojanguren
and Brana 2003). The general concepts of animal competition for resources, led to the
hypothesis that when fish are stocked in the creeks of Lake Davis, the larger fish will
gain access to the most profitable locations nearest the stocking point, requiring smaller
fish to move greater distances in search of a suitable habitat that they can dominate. It
was thought that relatively large fish would stay near stocking locations because they
59
have incomplete information about the rest of the stream. This does not mean that
small fish will not be found near the stocking location. Small subdominants may be
found in the stocking location, but they along with the dominant fish will be larger on
average than the fish that were forced to move.
Methods
The size of a fish at stocking was compared to its initial movement to determine
if there is a relationship between relative size and post-stocking dispersal. A
regression was used to determine if dispersal distance was related to the length at
stocking. The results of the regression suggested that medium length fish might have
moved longer distances than short or long fish. To test if medium sized fish dispersal
was different than long or short fish dispersal, the fish were sorted by size and then split
into three categories; short (155-172mm, n=27), medium (173-184mm, n=27) and long
(185-210mm, n=26). A One-Way ANOVA was use to compare the distance that fish
moved in each of the three length categories.
Results
The size of a fish at stocking was compared to its initial movement to determine
if there is a relationship between size and post-stocking dispersal. A regression
analysis was used to determine if dispersal distance was related to the length at stocking
(Figure 8). There was no significant relationship between dispersal distance and length
at stocking (p=0.53, slope= -2.65, R-squared=0.50%).
Dispersal Distance (m)
60
3000
2500
2000
1500
1000
500
0
150
160
170
180
190
200
210
Length (mm)
Figure 8. The initial dispersal distance versus the length at stocking.
61
Although the regression did not indicate a linear relationship between dispersal distance
and size at stocking, it appears that medium length fish may have moved longer
distances than short or long fish. To test if medium sized fish dispersal was different
than long or short fish dispersal, the fish were sorted by size and then split into three
categories; short (155-172mm, n=27), medium (173-184mm, n=27) and long (185210mm, n=26). A One-Way ANOVA was use to compare the distance that fish moved
in each of the three length categories. The average distance that fish moved was not
significantly different for each of the three categories (95.0 percent LSD procedure, Fratio=0.78, p=0.46, df=2) (Figure 9).
Dispersial Distance (m)
62
3000
2500
2000
1500
1000
500
0
1
2
3
Length Group
Figure 9. Fish grouped into length categories, and the dispersal distance of fish in each
category. These fish were grouped because the regression (Figure 8) suggested
that medium size fish moved further. This analysis also suggest that medium
sized fish moved slightly further but this result was not significant.
63
Conclusions
Originally it was thought that a pattern would emerge where larger fish would
defend territories closest to the stocking location requiring smaller fish to disperse
further. The results of this study do not indicate that the relative size at stocking of an
individual fish was linked to its post-stocking dispersal. There are several theories that
could explain these results. First, post-stocking dispersal may be caused by something
other than competitive interactions. For example, the variation in downstream dispersal
may be caused by individual variations in the response to stress and changing
environmental conditions. It is suspected that conditions such as low water level or
high water temperature have historically influenced migratory behavior. These types of
conditions may be an instinctive cue for fish to move to safer waters, which in the case
of Eagle Lake rainbow trout from Eagle Lake, is in the downstream direction. The
stocking procedure certainly causes stress in trout and involves changes to
environmental conditions, and this may lead to the genetically influenced movement.
As with most behavior, trout populations may contain variation in behavioral responses
related to post-stocking movement, and this variation may be independent of growth
rate or size. Second, the design and limitations of this study may have led to the
appearance of random movement with respect to relative size at stocking. Because
there was some error built into this study with regards to the exact stocking location for
each fish (see Methods section in Chapter 2), comparisons between size and initial
movement may have been inaccurate. Also, it is thought that many fish swam
downstream and into the lake and were effectively out of the sampling area creating an
64
uncertainty of size related movements. In addition, if larger fish are stocked into areas
that do not suite their habitat requirements, then the larger fish may be forced to search
out alternative habitats suitable for their requirements. Smaller fish on the other hand
may require fewer resources, and may find a suitable habitat closer to their stocking
location. Stocking some fish in suitable habitats, and stocking others in non-suitable
habitat may lead to a random movement with respect to size. Another design limitation
of this study with respect to post-stocking movement was that the fish in this study
were stocked in a relatively low density because of the spread-stocking approach. With
this approach, fish may not compete for resources as intensely as they would have if
stocked in large batches. If fish are stocked in higher densities, as often occurs in
stocking efforts, then competition for resources may lead to size-related dispersal.
Finally, the fish in this study were all relatively similar in size, and the level of
aggression may have out weighed small differences in size for determining control of
resources. If a greater variety of lengths were used and fish were stocked at higher
densities, then a size-influenced movement pattern may have been observed.
65
Chapter 4
CONDITION AND GROWTH OF TROUT IN THE CREEKS OF LAKE DAVIS
Introduction
The post stocking condition of tagged fish was evaluated throughout the 2008
sampling season at Lake Davis. The effect that the tags had on fish was also evaluated
by comparing the condition of tagged fish to the condition of non-tagged fish of the
same size range. Additionally, the condition of lake-stocked fish that had moved into
the creeks to spawn was measured throughout the year. Finally, the effects of
electrofishing and handling were evaluated by comparing the condition of tagged fish
that were caught for the first time to tagged fish that had previously been captured.
Methods
Condition Of Tagged Fish During The Sampling Season
The condition factor of fish caught in the creeks was calculated using the Fulton
Condition Factor, K=(W/L3)*100,000 (Murphy and Willis 1996). In this equation, K
represents the Fulton Condition Factor, W represents the weight in grams, and L
represents the total length in millimeters. First, a One-Way ANOVA was used to
determine if the condition factor of fish changed from month to month on average.
Then, a regression analysis was used to show the trend of changing condition factor for
all tagged creek fish during 2008. A problem with one of weighing devices in June led
to some of the fish not being weighed, therefore, not all of the tagged fish caught in
June could be used in the condition factor analysis. Additionally, length measurements
66
were taken for all 800 tagged fish during tagging, but only 485 were measured for
weight. Therefore initial condition measurements represent 485 fish rather than 800.
Comparison Of Condition Of Tagged Fish In Each Creek
To compare the condition factor of fish in each of the creeks, a time period had
to first be determined. June was excluded because it was relatively close to the
stocking time. That left July, August, and September. Sample sizes were low for some
of the creeks during each of the months, so it was determined that combining months
was necessary to increase sample size. To determine if the condition factor of fish for
each month was significantly different from the other months, a One-Way ANOVA
was performed. The results of the One-Way ANOVA from the monthly comparison
indicated that the average condition factor of tagged fish caught in September was
significantly different than the fish caught in July and August (see Table 12) (95.0
percent LSD procedure, F-ratio=217.30, p<0.05, df=4). The average condition factor
of fish caught in July was not significantly different than the average condition factor of
fish caught in August (see Table 12) (95.0 percent LSD procedure, F-ratio=217.30,
p>0.05, df=4), so these two months were combined to compare conditions factors of
fish in each of the creeks.
Condition Of Tagged Versus Non-Tagged Fish
A comparison of the condition of tagged fish and non-tagged fish of the same
size range was performed. Non-tagged size class one and three fish were not used for
the comparison with tagged fish, because the tagged fish were only size class two fish
67
(see Chapter 2 and Figure 5 for a description of size classes). The non-tagged size class
two fish had a slightly wider range of lengths than the tagged fish each month. To
compensate for this, only non-tagged fish that fell within the range of the tagged fish
for each month were used for comparison. This wider range of non-tagged fish found
in the creeks was a result of two factors. First, the smallest fish found in the hatchery
raceway during the tagging effort were excluded from being tagged because they were
not large enough for the tags. Second, the fish stocked into the lake in April were Eagle
Lake rainbow trout, but did not come from the Mount Shasta Hatchery and therefore
represented slightly different sizes than the fish that were stocked into the creeks. For
example, the tagged fish caught in June had total lengths ranging from 210 mm to
163mm. The non-tagged fish in the same size class (as determined from Figure 3) had
total lengths ranging from 206 mm to 70 mm. To compare the condition factor of the
non-tagged fish to the tagged fish, only non-tagged fish that were within the length
range of the tagged fish were used. For June, non-tagged fish that were used for this
comparison measured between 206 mm to 164 mm. These fish were within the 210
mm to 163mm range of the tagged fish captured in June. Table 14 shows the size range
and sample size of tagged and non-tagged fish used to compare condition factor. A ttest was used to compare the condition factor of tagged and non-tagged fish for each
month.
68
Growth Rates of Tagged Fish
Individual growth rates for tagged fish were measured from the time that they
were released to the time of first capture. There were a total of 119 first capture events
that occurred during the 2008 sampling season. The equation to measure change in
growth over time was: (capture length – release length)/ days between.
A population growth rate for tagged fish was also measured by plotting the
length of each tagged fish caught versus the day it was caught. Initial measurements
were also used in this method, and initial measurements were assigned day zero. For
this analysis, all 800 fish initially measured and all 163 captures (including first time
captures and recaptures) were used. A regression analysis was performed for the
population growth rate.
Growth Rate Of Young Of Young Of The Year Fish
During the 2008 sampling season, juvenile (young of the year) trout were
captured in the creeks of Lake Davis. These fish had hatched in the Lake Davis creeks
in the spring of 2008, and were the offspring of the late 2007 and early 2008 lakestocked rainbow trout. The growth rate of these young of the year fish that were caught
during the June, August, and September sampling periods was evaluated. There were
no young of the year fish caught in May or July. A regression of length versus time
was plotted for these size class one fish.
69
Effect Of Electrofishing And Handling On The Condition Of Fish
The effects of electrofishing and handling were evaluated by comparing the
condition factor of fish that had previously been captured by electrofishing, to fish that
had not been previously captured by electrofishing. Because sample sizes were low, all
months were combined for this comparison. Fish in the two groups were not captured
in equal numbers each month, so for each month, fish in the larger group were
randomly discarded until both groups were equal. This was done to remove the bias
caused by the change in condition factor over time. After previously electrofished and
not-previously electrofished groups were randomly equalized for each month, all
months were combined then compared using a t-test.
Condition Of Size Class Three Non-Tagged Fish
The condition of the size class three fish was evaluated throughout the season.
These fish were all likely from the December lake stocking and had moved into the
creeks to spawn. The condition of these fish was evaluated to determine if a different
stocking group showed a trend similar to the tagged creek fish.
Results
Condition Of Tagged Fish During The Sampling Season
A comparison of the condition factors between each sampling periods was done.
A One-Way ANOVA was used to determine that condition factor changed from month
to month. Fish caught in June were found to have a significantly higher condition
70
factor than fish caught during July, August, and September (95.0 percent LSD
procedure, F-ratio=217.30, p<0.05, df=4). The fish caught during September had
significantly lower condition factors than fish caught during the all of the other months
(95.0 percent LSD procedure, F-ratio=217.30, p<0.05, df=4) (Table 12).
71
Table 12. An ANOVA table of condition factor of tagged fish caught during each
sampling period. The condition factor of tagged fish progressively got worse
during the sampling season. Length measurements were taken for all 800
tagged fish during tagging, but only 485 were measured for weight.
Month
May (Release)
June
July
August
September
Count
485
29
24
33
20
Average
Condition Factor
1.08
0.89
0.81
0.79
0.73
sd
0.08
0.10
0.11
0.14
0.15
Homogeneous Groups
X
X
X
X
X
72
A regression analysis (Figure 10) of condition factor versus time shows that condition
factor significantly declined after tagged fish were stocked into the creeks of Lake
Davis (n=591, p<0.01, R-squared 54.8%, Condition Factor = 1.08156-0.0039496*Day).
73
ConditionFactor
1.5
1.25
June 23
July 14
August 4
September 15
1
0.75
May 28
0.5
0
20
40
60
80
100
120
Days After Stocking
Figure 10. The condition factor of tagged fish in the four main creeks of Lake Davis
versus the time (days) after stocking.
74
Comparison Of Condition Factor Of Tagged Fish In Each Creek
The average condition factor of fish caught in Old House creek during the
combined July and August period was significantly lower than fish caught in any of the
other creeks (95.0 percent LSD procedure, F-ratio=11.16, p<0.05, df=3). The other
three creeks were not significantly different from each other during this same time
period (Figure 11 and Table 13).
Condition Factor
75
1.17
1.07
0.97
0.87
0.77
0.67
0.57
Cow
Freeman
Grizzly Old House
Creek
Figure 11. Combined July and August condition factor of tagged fish by creek. The
average condition factor of fish caught in Old House creek during the combined
July and August period was significantly lower than fish caught in any of the
other creeks. The other three creeks were not significantly different from each
other during this same time period.
76
Table 13. A summary of the data presented in Figure 9. Combined July and August
condition factor of tagged fish by creek. The average condition factor of fish
caught in Old House creek during the combined July and August period was
significantly lower than fish caught in any of the other creeks. The other three
creeks were not significantly different from each other during this same time
period.
Count
Average Condition
Factor
Cow
6
0.92
Freeman
18
0.85
Big Grizzly
12
0.81
Old House
21
0.70
Creek
P-value
0.000
77
Condition Of Tagged Versus Non-Tagged Fish
To test if there was a difference in the condition of tagged and non-tagged fish
of the same size range for each of the sampling events, a t-test was performed. For
each of the sampling events there was not a significant difference between the average
condition factor (Fulton’s) for tagged fish and non-tagged fish of the same size range
(Table 14).
78
Table 14. A comparison of the Fulton Condition Factor for tagged and untagged fish
caught during each sampling period.
June
Tagged
Count
Length
Range
(mm)
29
July
Nontagged
19
Tagged
24
August
Nontagged
20
Tagged
33
Nontagged
37
September
Tagged
20
Nontagged
23
163-210 164-206 174-215 174-210 170-225 170-221 184-240 187-235
Average
Condition
Factor
0.90
0.85
0.81
0.80
0.79
0.82
0.75
0.72
sd
0.13
0.16
0.11
0.21
0.14
0.11
0.19
0.19
p-value
0.21
0.86
0.30
0.54
t
1.26
0.18
1.05
0.61
79
Growth Rates of Tagged Fish
Individual growth rates for tagged fish were measured from the time that they
were released to the time of first capture. There were a total of 119 first capture events
that occurred during the 2008-sampling season. The change in growth over time
(capture length – release length/ days between) was on average 0.25 mm/day (sd=0.22,
n=119) (Figure 12).
80
Frequency
16
12
8
4
0
-0.5
-0.25
0
0.25
0.5
0.75
1
1.25
Growth Rate
Figure 12. Growth rates of tagged fish measured from the time they were released to
the time of first capture.
81
Growth rates were also measured by plotting the length of each fish caught versus the
day it was caught (all first captures and recaptures included). Initial measurements
were also used in this method, and initial measurements were assigned day zero. For
this analysis all 800 fish initially measured and all 163 captures were used. This
method measured the growth rate of the entire tagged group and not individual fish. A
regression analysis was performed (Figure 13) (n= 963, p<0.01, R-squared=17.65%,
Total Length = 178.83 + 0.24 * Days Post Stocking). This method produced similar
results to the measurements taken from individual growth.
Total Length (mm)
82
250
230
August 4
May 28
July 14
June 23
210
190
170
September 15
150
0
20
40
60
80
100
120
Days After Stocking
Figure 13. The length of fish caught during each of the sampling periods. Day zero is
the day when the fish were tagged and measured.
83
Growth Rate Of Young Of Young Of The Year Fish
During the 2008 sampling season, juvenile (young of the year) trout were
captured in the creeks of Lake Davis. These fish had hatched in the Lake Davis creeks
in the spring of 2008, and were the offspring of the late 2007 and possibly early 2008
lake-stocked rainbow trout. The growth rate of young of the year fish that were caught
during the June, August, and September sampling periods was evaluated. There were
no young of the year fish caught in May or July. A regression of length versus time
was plotted for the young of the year data (Figure 14 and Table 15, n=29, p<0.01, Rsquared=75.93%, Total Length= 7.74 + 0.80*Day).
84
Length (mm)
140
September 15
120
100
August 4
80
60
June 23
40
20
0
0
20
40
60
80
100
120
Days After May 28
Figure 14. Length versus time regression for young of the year fish caught during
2008.
85
Table 15. A summary of the data presented in Figure 12. Length versus time
regression for young of the year fish caught during 2008.
Month
June
July
August
September
Count
2
0
20
7
Length Range (mm)
30-30
NA
51-83
75-120
Average Length (mm)
30
NA
63
98
sd
0
NA
9
16
86
Effect of Electrofishing and Handling On The Condition Of Fish
Tagged fish that were previously electrofished and handled in this study had an
average condition factor of 0.76 (sd=0.13, n=30), and tagged fish that had not been
previously electrofished and handled in this study had an average condition factor of
0.84 (sd=0.13, n=30). A t-test was used to determine that fish captured for the first
time were in significantly better condition than fish that had previously been captured
(unpaired t-test, t=2.42, p<0.02, df=1).
Condition Of Size Class Three Non-Tagged Fish
The condition of 62 size class three fish was measured during the 2008
sampling season. In June, only 5 fish were used because one of the scales was not
working properly (20 size class three fish went un-weighed). The regression for size
class three fish was: Condition Factor = 1.04019 – 0.00367124 * Day (p<0.01, Rsquared=28.55%)(Figure 15).
Condition Factor
87
1.8
1.5
July 14
1.2
August 4
June 23
September 15
0.9
0.6
May 20
0.3
0
0
20
40
60
80
100
120
Days After May 20
Figure 15. The condition factor of size class three fish versus days after the initial
survey. Note that all of the other graphs represent days after stocking (28 May
2008) and this graph represents days after the initial survey (20 May 2009).
88
Conclusions
Condition Of Tagged Fish During The Sampling Season
On average, the condition of each tagged creek fish was significantly worse
after 27 days of its release. The condition of all fish continued to decline throughout
the 2008 season. It is suspected that the change in food supply from the hatchery to the
creeks of Lake Davis caused an initial drop in condition (see Ersbak and Haase 1983).
The water quality is also suspected to have played a role in the declining condition of
these fish. The flows of the creeks slowed down after June and water quality appeared
to be poor in some sections of the creeks. The water quality of the creeks will be
discussed further in the Chapter Five.
Comparison Of Condition Factor Of Tagged Fish In Each Creek
The condition factor of the fish in this study appeared to be influenced by the
creek temperatures, because the creeks that maintained the lowest summer time
temperatures had fish with the highest condition factors (see Chapter 5 for more
information on the creek temperatures). Myrick and Cech (2000), reported that Eagle
Lake trout consumed less food and grew less at temperatures above 19 C when
compared to temperatures between 14C and 19 C. Growth rates also slowed down as
temperatures approached 10 C. Temperatures in Old House creek and upper and
lower Big Grizzly creek reached above 19 C on a daily basis for much of the time
89
recorded. These daily fluctuations above 19 C may have led to the lower condition
factors of these creeks.
Condition Of Tagged Versus Non-Tagged Fish
The average condition factor of tagged fish and non-tagged fish of the same size
range was not significantly different in this study. It was thought that the tags might
adversely affect these fish, because these fish were on the lower size limit of trout that
can be tagged with this size tag (personal communication with Floy Tag & Mfg. Inc.).
The fish were tagged and then held overnight at the hatchery, and the following
morning there were no mortalities. There was only one mortality noted after
transporting the fish by truck and then by bucket to the stocking locations, which was
an all day event for the last of the fish that were stocked. Overall, the tagged fish
appeared to be in similar condition compared to the non-tagged fish throughout the
entire sampling season. There was a significant trend for all fish caught in the creeks to
have a lower condition factor over the course of the summer. It is suspected that a
change in diet for these hatchery raised fish, and declining water quality throughout the
season led to the decline in condition.
Growth Rates of Tagged Fish
Measuring the growth rates of individual fish and the growth rate of the entire
tagged population both produced similar average growth rates. The tagged fish stocked
90
in the creeks of Lake Davis grew approximately 0.24 mm per day during the 2008
sampling season.
Growth Rate Of Young Of Young Of The Year Fish
Young of the year fish grew faster than did the tagged fish. The young of the
year fish grew on average 0.80 mm per day during the 2008 sampling season. With the
assumption that growth is linear, the y-intercept of the regression analysis estimated
that the young of the year fish were 7.74 mm on 28 May 2008.
Effect of Electrofishing and Handling On The Condition Of Fish
Electrofishing and handling, significantly affected the condition of fish in this
study. Many fish in this study were caught on multiple occasions. There were 11 fish
that were caught three times in this study, 19 fish that were caught two times, and 0 fish
that were caught all four times. Past studies that have shocked fish multiple times have
shown similar results (Gatz et al. 1986).
Condition Of Size Class Three Non-Tagged Fish
The non-tagged size class three fish were stocked in Lake Davis in December of
2007, and were captured in the creeks of Lake Davis during the 2008 creek surveys.
The condition of size class three fish found in the creeks declined over the course of the
2008 sampling season. This trend (slope= -0.00367124) was similar to the trend
(slope= -0.00394962) that was observed in the size class two fish found in the creeks.
91
These size class three fish were stocked in the lake in December and were in relatively
good condition during the initial May creek survey. This indicates that they adapted
well to the conditions in Lake Davis shortly after being stocked in December. The
condition of size class three fish was not measured at the time of stocking, but the
condition of the creek tagged fish and reward tagged lake fish were 1.08 and 1.13
respectively as measured during tagging at the hatchery. The size class three fish that
were captured during the initial creek survey in May had an average condition factor of
1.04, which was approximately five months after being stocked. This suggests that the
conditions that these fish experienced between December and May were better than the
conditions that they experienced between May and September. By September, the
average condition factor for these fish was 0.53 (n=5, sd=0.14). With that being said it
is unclear when these fish made the transition from the lake into the creeks, and it is
unclear the influence that spawning had on the measured condition of these fish. In
addition, the effects of competition may have increased as more fish were stocking into
the watershed during 2008.
92
Chapter 5
CREEK TEMPERATURES
Introduction
Myrick and Chech (2000) reported that Eagle Lake and Mount Shasta strain
rainbow trout (often used in California for stocking) had optimal growth rates between
14 C to 19 C. At temperatures above 19 C and near 10 C, both strains consumed
less food and grew less. The upper reported incipient lethal limit for rainbow trout is
generally 25 C to 26 C (Cherry et al. 1977, Hokanson et al. 1977). However, the
results of Myrick and Chech (2000) showed that these two strains of rainbow trout
could maintain weight at 25 C for 30 days. Temperature loggers were placed in the
four main creeks of Lake Davis in the summer of 2008 to evaluate the suitability for
rainbow trout during the summer season.
Methods
On 26 June 2008, seven temperature loggers were placed into the four study
creeks. Loggers were placed in locations on the creeks that met several requirements:
1) the location needed to have a strong anchoring point, 2) the location had to provide
shade to the logger, 3) the location needed to be in a relatively deep spot of the creek,
4) the logger and cable needed to be out of sight, 5) the location needed to hold water
all year. All of the loggers were secured to trees except the logger that was placed in
upper Big Grizzly creek. This logger was secured to a piece of concrete found in the
93
stream. The loggers used were HOBO U22 Water Temp Pro v2 loggers (Onset
Computer Corporation). The loggers were set to record temperature every 15 minutes.
Two loggers went into each of the main tributaries, Big Grizzly, Cow, and Freeman
creeks. Only one logger was placed into Old House creek because this creek is
relatively short and there are not many locations that fit the specific requirements of
logger placement. On 14 July 2008, a third temperature logger was placed into Big
Grizzly creek. This logger was not placed originally because there were reports that the
entire lower section of Big Grizzly creek would go dry. During the electrofishing
surveys it appeared that one area in particular would remain wet because of the many
deep pools. The logger was placed in lower Big Grizzly creek on 14 July, and by 4
August the pool was almost dry (the pool level dropped about 1 meter). This logger
was then moved approximately 75 meters upstream to another pool that was
maintaining a constant water level. The final location of this logger was in a deep pool
that appeared to be influenced by subsurface water because the creek was dry both
upstream and downstream. All of the temperature loggers were taken out of the
streams on 15 September 2008. They were not left over winter, because snow in the
wintertime makes them inaccessible, and spring flows and beaver activity made it likely
that they would not be recovered. These loggers were used to evaluate summertime
temperatures.
94
Results
The average temperatures, date ranges measured, locations, and approximate
depths of creeks where each logger was deployed are summarized in Table 16.
95
Table 16. The average temperatures measured in each creek location. Temperature
was measured every fifteen minutes during the indicated 2008 date range. 1
July is represented as 7/1, 15 August is represented as 8/15, and 1 September is
represented as 9/1.
Stream
Upper Cow
Lower Cow
Upper Freeman
Lower Freeman
Upper Big Grizzly
Middle Big Grizzly
Lower Big Grizzly
Old House
Average
Standard Date
Temperature (C) Deviation Range
12.6
13.0
14.9
15.5
17.3
12.9
19.1
16.2
3.0
1.6
3.4
1.6
3.0
1.0
2.3
4.2
7/1-9/1
7/1-9/1
7/1-9/1
7/1-9/1
7/1-8/15
7/1-9/1
7/15-9/1
7/1-9/1
Approximate
UTM Location (NAD Depth of Water
83)
(meters)
0708971 4418407
0709267 4420059
0707591 4419886
0709350 4421983
0702818 4423003
0707136 4422491
0709274 4423293
0706796 4422780
0.5
0.5
0.5
1.0
1.0 - 0.0
1.2
1.5
0.5
96
The upper Cow creek data logger and middle Big Grizzly creek data logger had the
lowest average temperatures between 1 July and 1 September 2008. The upper and
lower sections of Big Grizzly creek had the warmest average temperatures. When the
upper Big Grizzly creek data logger was recovered on 18 September 2008, the section
of creek (entire meadow above the second bridge) it was placed in was dry. The data
used to determine an average for this section was therefore cut off on 15 August 2008,
because that is when the temperature graph appeared to be showing air temperature
rather than water temperatures. The temperature logger placed on lower Big Grizzly
creek was placed there on 15 July 2008, and then it had to be moved on 4 August 2008
because the pool it was in was close to becoming completely dry. This pool had gone
from over a meter deep to less than a third of a meter in 20 days. The logger was
moved upstream approximately 75 meters to its final location (shown in Table 16). The
pool at this location remained full for the remainder of the year and appeared to be
influenced by subsurface flows, because the sections of creek above and below this
pool were dry. Lower Big Grizzly creek had the warmest average temperature despite
the temperature logger being placed in the deepest pool of any of the loggers. Although
this pool was the deepest that a temperature logger was placed in, the pool lacked
substantial shade. The data listed in Table 16 for lower Big Grizzly creek represents
combined data from both locations that the logger was placed in. If only the
temperatures from the second location are averaged, then the average temperature in
lower Big Grizzly creek at the second location is 18.5 C (sd=1.73, 4 August through 1
September 2008), which is still higher than any of the other creeks. The section of Big
97
Grizzly creek just below the first bridge (middle temperature logger), maintained the
most constant temperatures through the summer months that were measured. This
consistency in water temperatures is likely due to the influences of subsurface flows,
substantial shade (willows), and the water inputs from Old House creek. Most sections
of Big Grizzly creek above the first bridge crossing (bridge closest to the lake) were
completely dry, but had intermittent pools here and there. It is thought that the sections
that held water were influenced by subsurface water. The dry sections of Big Grizzly
creek did result in some fish becoming stranded in shallow pools and ultimately dying.
Attempts were made, when possible, to move these trout to deeper water. The other
streams did not have dry sections. However, Cow and Freeman creeks became
extremely shallow before entering the lake, and Old House creek lost surface
connection to Big Grizzly creek around the end of June. The other three creeks had
lower average temperatures than upper and lower Big Grizzly creek despite being
relatively shallow all year long. Overall, daily water temperatures fluctuated widely.
The temperatures in Old House creek usually fluctuated over 10 C daily during late
summer. It is thought that this is result of the creek being shallow and lacking much
shade. The other creeks generally fluctuated by 1 C to 5 C daily.
Conclusions
The temperatures measured in Old House creek had the highest daily
temperature fluctuations of any of the creeks, and this was likely caused by the lack of
shade and shallow water found on most of this creek. Big Grizzly creek appeared to be
98
the creek with the most variation in water quality and temperature along its length.
This creek had many sections that remained deep and cool all summer long, and other
sections that dried up completely. Dry sections on Big Grizzly creek were found all
along the creek from where it enters the lake to the upper sections of the creek above
the second bridge. Additionally, Big Grizzly creek had a large number of cattle that
were grazed in the meadows along its banks. There were many areas along Big Grizzly
creek that had recently been visited by cattle, and it was observed that the banks were
deteriorated and the water quality appeared to be poor based on the brownish-orangish
color of the water. It was noted on a few occasions that isolated pools that were filled
near the tops of the banks before cattle had visited them for water, were nothing but
mud after the visit. It seemed as though the large number of cattle had the ability to
drink most of the water in some of the isolated pools. Based on observations made
during this study and the results of Schatz’s experimental cattle enclosures (1989), it
appears that from a water quality and fisheries standpoint the cattle are negatively
affecting the creeks of Lake Davis and possibly the lake fishery. The creeks of Lake
Davis could be better fenced from cattle, while still allowing cattle to drink at strategic
locations. Future fisheries studies that mapped areas where fish are spawning, and
areas where the creeks are drying up during the summer could help to determine where
cattle should be allowed to access the creeks.
99
Chapter 6
FINAL DISCUSSION
Post-Stocking Movement
Understanding the post-stocking movement of trout is an important aspect of
trout fishery management. This study showed that Eagle Lake rainbow trout that were
stocked into Lake Davis moved into the creeks shortly after stocking. Additionally,
many of the Eagle Lake rainbow trout stocked into the creeks of Lake Davis moved in a
downstream direction and it is suspected that many of them moved into the lake shortly
after stocking. It would be interesting to know if fish that were simultaneously stocked
in the lake and the creeks moved in opposite directions, meaning that fish stocked into
the lake may move into the creeks, and fish stocked into the creeks may move into the
lake. The results of this study confirm that the Eagle Lake strain of rainbow trout, like
many other strains of rainbow trout, generally move in the downstream direction after
being stocked into a creek. However, it is unknown if alternative environmental
conditions or seasonal timing would cause a general upstream movement. It is
suspected that these fish have a genetic trigger that directs them to move towards safer
areas during stressful conditions or during changing environmental conditions, and
safer areas are generally downstream with regards to Eagle Lake rainbow trout from
Eagle Lake California. There are lotic ecosystems, however, where the opposite could
be true. For example, spring fed rivers and streams may possess a relatively stable
habitat closer to the mouth of the spring than farther away from it, which may cause
100
trout to swim upstream during harsh environmental conditions. Additionally, it is
possible to have trout that migrate downstream out of a lake to spawn, and then return
to the lake for refuge during harsh environmental conditions. There is little research
available on trout movement in these types of systems, and it is unknown how these
fish react to changing or stressful environmental conditions. A review paper that
compares historic migration patterns to movements caused by environmental stress
and/or post-stocking movements would be useful.
Although many of the creek stocked fish in this study moved in the downstream
direction, other creek stocked fish stayed relatively close to the original stocking
location. The reason for this variation is not entirely clear. Past research has shown
that within a population of rainbow trout, different life history types may exist. Life
history types could include lake-river migrating fish, river-river migrating fish, and
river non-migrating fish (Meka et al. 2003). For example, rainbow trout are obligate
stream spawners, but a segment of the population may live in a lake until the spawning
season arrives at which time they will migrate into the river to spawn. Following
spawning these fish will return to the lake. This type of spawning movement would be
classified as a lake-river migrating fish. Other fish in the population may live in an area
of the river not suitable for spawning and may have to migrate to another location in the
river to spawn. These fish would be classified as river-river migrating fish. To further
complicate matters, Riva-Rossi et al. (2007) demonstrated that female steelhead trout
that migrated to the ocean could produce offspring that did or did not migrate to the
ocean, and female steelhead trout that did not migrate to the ocean could produce
101
migratory or non-migratory offspring. It is currently unclear the extent that genetics
influence the behavioral differences observed in trout populations (Cresswell 1981,
Heath et al. 2008, Raleigh and Chapman 1971, Riva-Rossi et al. 2007). In addition to
genetic factors influencing post-stocking behavior, it is suspected that competitive
interactions may also contribute to post-stocking movement because fish are generally
stocked in high densities and territorial disputes are inevitable. However, if stocking
density were the only cause for post-stocking movement, then it would be expected that
movement would be in both the upstream and downstream directions. Post-stocking
movement is most likely caused by a combination of stress, environmental factors,
genetics factors, and competitive interactions. Although this study did not provide
additional information on the causes for the post-stocking downstream movement often
observed in rainbow trout, it did document the downstream movement of Eagle Lake
rainbow trout shortly after stocking.
The Creeks of Lake Davis
The creeks of Lake Davis are extremely influenced by the seasons. They are
covered in ice during the winter season, and overtop the banks in the spring season
often flooding large areas of meadows. By late summer, the creeks are extremely
shallow and dry in some sections, and daily water temperatures fluctuate widely. The
temperatures in Old House creek usually fluctuated over 10 C daily during late
summer. The other creeks generally fluctuated between 1 C and 5 C daily. Although
there is extreme variation in the condition and water quality of these streams, there are
102
many areas of these creeks that provide excellent habitat for trout. These creeks
provide important spawning habitat that helps to maintain a trout fishery in the lake,
which has historically been one of the better lake-based trout-fisheries in California. It
is thought that habitat improvement projects and cattle exclusion projects along the
tributaries of Lake Davis could help to make the lake-fishery less reliant on annual trout
stockings. Future research could be aimed at identifying and improving areas in the
creeks that trout use for spawning. This would include excluding cattle from spawning
areas, and excluding cattle from upstream areas that could lead to the siltation of the
spawning areas. Additionally, Big Grizzly creek was observed to be almost entirely dry
from the first bridge all the way to the upper limits of the creek. Many fish that had
migrated from the lake into this stretch of creek became stranded in increasingly
shallow-isolated pools. There were several instances where remains of dead fish were
found in completely dry stretches of Big Grizzly creek. Future research could be aimed
at excluding fish from swimming from the lake into the upper sections of Big Grizzly
creek; however, it is not known if the benefits of spawning habitat provided by this
section outweigh a few fish becoming stranded and perishing in this section. It would
be worthwhile to know how many lake-fish move above the first bridge to spawn, and
then how many of these fish and how many of their offspring return downstream below
the first bridge before the upper section of this creek dries up in the summer. This
research could be accomplished by placing a two-way fish trap near the first bridge on
Big Grizzly creek.
103
The Lake Davis watershed is unique when compared to many of the other lakes
in the Sierra Nevada because the tributaries flow through relatively long flat meadows.
Many other lakes found in the Sierra Nevada are characterized by having steep rocky
tributaries. The long flat meadows of Lake Davis provide for a unique habitat that is
used by a wide variety of wildlife, including many state and federally protected plants
and animals. Within these meadows there are many vernal pool and spring habitats,
that like the creeks, deserve enhanced protection from cattle grazing. It is thought that
slightly modified management strategies could provide much greater protection to the
beneficial uses of the water resources in the Lake Davis watershed.
104
LITERATURE CITED
Abbott JC, Dunbrack RL, Orr CD. 1985. The interaction of size and experience in
dominance relationships of juvenile steelhead trout (Salmo gairdneri).
Behaviour. 92:241-253.
Behnke RJ. 1992. Native trout of western North America. American Fisheries Society.
Monograph 6: 275pp.
Bettinger JM, Bettoli PW. 2002. Fate, dispersal, and persistence of recently stocked and
resident rainbow trout in a Tennessee tailwater. North American Journal of
Fisheries Management. 22:425-432.
Bowler B. 1975. Factors influencing genetic control in lakeward migrations of cutthroat
trout fry. Transactions of the American Fisheries Society. 104:474-482.
Busack CA, Thorgaard GH, Bannon MP. 1980. An electrophoretic, karyotypic and
meristic characterization of the Eagle Lake trout, Salmo gairdneri aquilarum.
Copeia 1980:418-424.
California Department of Fish and Game, USDA Forest Service. 2007. Final
Environmental Impact Report/Environmental Impact Statement for the Lake
Davis Pike Eradication Project. California Department of Fish and Game,
Sacramento CA and USDA Forest Service, Plumas National Forest, Quincy CA.
Caron J, Beaugrand JP. 1988. Social and spatial structure in brook chars (Salvelinus
fontinalis) under competition for food and shelter/shade. Behavioural Processes.
16:173-191.
105
Cherry DS, Dickson KL, and Cairns J. 1977. Preferred, avoided and lethal temperatures
of fish during rising temperature conditions. Journal of the Fisheries Research
Board of Canada. 34: 239-246.
Cooperman MS, Hinch SG, Crossin GT. 2010. Effects of experimental manipulations
of salinity and maturation status on the physiological condition and mortality of
homing adult sockeye salmon held in a laboratory. Physiological and
Biochemical Zoology. 83:459-472.
Cordone AJ. 1970. Harvest of 4 strains of rainbow trout, Salmo-gairdnerii, from
Beardsley-Reservoir, California. California Fish and Game. 56:271.
Cresswell RC. 1981. Post-stocking movements and recapture of hatchery-reared trout
released into flowing waters—a review. Journal of Fish Biology. 18:429-442.
De Lain LI. 1983. Limnological conditions of Lake Davis, California with emphasis on
habitat suitability for salmonids. Masters Thesis. University of California,
Berkeley.
Ersbak K, Haase BL. 1983. Nutritional deprivation after stocking as a possible
mechanism leading to mortality in stream-stocked brook trout. North American
Journal of Fisheries Management. 3:142-151.
Funk JL. 1955. Movement of stream fishes in Missouri. Transactions of the American
Fisheries Society. 85:39-57.
Gatz JA, Loar JM, Cada GF. 1986. Effects of repeated electrofishing on instantaneous
growth of trout. North American Journal of Fisheries Management. 6:176-182.
106
Gerking SD. 1959. The restricted movement of fish populations. Biological Review.
34:221-242.
Gordon DR, Thomas KP. 1996. Florida’s invasion by nonindigenous plants: history,
screening and regulation. In: Lockwood JL, Simberloff D, McKinney ML.
2001. How many, and which, plants will invade natural areas? Biological
Invasions. 3:1-8.
Gotceitas V, Godin JG. 1992. Effect of location of food delivery and social status on
foraging-site selection by juvenile Atlantic salmon. Environmental Biology of
Fishes. 35:291-300.
Gowan C, Young MK, Fausch KD. 1994. Restricted movement in resident stream
salmonids: A paradigm lost? Canadian Journal of Fisheries and Aquatic
Sciences. 51:2626-2637.
Gross MR, Coleman RM, McDowall RM. 1988. Aquatic productivity and the evolution
of diadromous fish migration. Science. 239:1291-1293.
Harvey B. 2009. A biological synopsis of Northern pike (Esox Lucius). Canadian
Manuscript Report of Fisheries and Aquatic Sciences 2885.
Heath DD, Bettles CM, Jamieson S. 2008 Genetic differentiation among sympatric
migratory and resident life history forms of rainbow trout in British Columbia.
Transactions of the American Fisheries Society. 137:1268-1277.
Hokanson KEF, Keliner CF, and Thorslund TW. 1977. Effects of constant temperatures
and diel temperature fluctuations on specific growth and mortality rates and
107
yield of juvenile rainbow trout, Salmo gairdneri. Journal of the Fisheries
Research Board of Canada. 34: 639-648.
Jenkins TM. 1969. Social structure, position choice and micro-distribution of two trout
species (Salmo trutta and Salmo gairdneri) resident in mountain streams.
Animal Behavior Monographs. 2:57-123.
Knouft JH, Spotila JR. 2002. Assessment of movements of resident stream brown trout,
Salmo trutta L., among contiguous sections of stream. Ecology of Freshwater
Fish. 11:85-92.
Krebs CJ. 1994. Ecology, Fourth Edition. Harper Collins College Publishers, Menlo
Park, CA.
Lockwood JL, Simberloff D, McKinney ML. 2001. How many, and which, plants will
invade natural areas? Biological Invasions. 3:1-8.
Meka JM, Knudsen EE, Douglas DC. 2003. Variable migratory patterns of different
adult rainbow trout life history types in a southwest Alaska watershed.
Transactions of the American Fisheries Society. 132:717-732.
Moring JR, Buchanan DV. 1978. Downstream movement and catches of two strains of
stocked trout. Journal of Wildlife Management. 42:329-333.
Moyle PB. 2002. Inland fishes of California. Revised and expanded edition. University
of California Press, Berkeley, CA.
Moyle PB, Israel JA, Purdy SE. 2008. Salmon, steelhead, and trout in California, status
of an emblematic fauna. Center For Watershed Sciences. Davis, CA. A report
commissioned by California Trout.
108
Murphy BR, Willis DW. 1996. Fisheries Techniques. Second Edition. American
Fisheries Society, Bethesda, Maryland.
Myrick CA, Cech JJ. 2000. Temperature influences on California rainbow trout
physiological performance. Fish Physiology and Biochemistry. 22:245-254.
Nilsson G. 1981. This Bird Business: A study of the commercial cage bird trade.
Animal Welfare Institute, Washington, DC. In: Lockwood JL, Simberloff D,
McKinney ML. 2001. How many, and which, plants will invade natural areas?
Biological Invasions. 3:1-8.
Northcote TG. 1984. Mechanisms of fish migration in rivers. Pages 317-355 in
McCleave JD, Arnold GP, Dodson JJ. Mechanisms of migration in fishes.
Plenum Press. New York. From Northcote TG. 1997. Potamodromy in
Salmonidae-living and moving in the fast lane. North American Journal of
Fisheries Management. 17:1029-1045.
Northcote TG. 1992. Migration and residency in stream salmonids: some ecological
considerations and evolutionary consequences. Nordic Journal of Freshwater
Resources. 67:5-17. From Young MK. 1995. Resident trout and movement:
consequences of a new paradigm. Fish Habitat Relationships Technical Bulletin.
18:1-5.
Northcote TG. 1997. Potamodromy in Salmonidae-living and moving in the fast lane.
North American Journal of Fisheries Management. 17:1029-1045.
109
Ojanguren AF, Brana F. 2003. Effects of size and morphology on swimming
performance in juvenile brown trout (Salmo trutta). Ecology of Freshwater Fish.
12:241-246.
Pascual M, Bentzen P, Rossi CR. 2001. First documented case of anadromy in a
population of introduced rainbow trout in Patagonia, Argentina. Transactions of
the American Fisheries Society. 130:53-67.
Pimentel D, Lach L, Zuniga R. 2000. Environmental and economics costs of
nonindigenous species in the United States. BioScience. 50:53-65.
Powers L. 2003. History of the Lake Davis fishery and management. Unpublished file
paper. In: California Department of Fish and Game, USDA Forest Service.
2007. Final Environmental Impact Report/Environmental Impact Statement for
the Lake Davis Pike Eradication Project. California Department of Fish and
Game, Sacramento CA and USDA Forest Service, Plumas National Forest,
Quincy CA.
Raleigh RF. 1971. Innate control of migrations of salmon and trout fry from natal
gravels to rearing areas. Ecology. 52:291-297.
Raleigh RF, Chapman DW. 1971. Genetic control in lakeward migrations of cutthroat
trout fry. Transactions of the American Fisheries Society. 100:33-40.
Rawstron RR. 1973. Harvest, mortality, and cost of 3 domestic stains of tagged
rainbow-trout stocked in large California impoundments. California Fish and
Game. 59:245.
110
Rawstron RR. 1977. Harvest, survival, and weight returns of tagged Eagle Lake and
Coleman rainbow-trout stocked in Lake Berryessa in 1972. California Fish and
Game. 63:274-276.
Riley SC, Fausch KD, Gowan C. 1992. Movement of brook trout (Salvelinus fontinalis)
in four small subalpine streams in northern Colorado. Ecology of Freshwater
Fish. 1:112-122.
Riva-Rossi C, Pascual MA, Babaluk JA, Garcia-Asorey M, Halden NM. 2007. Intrapopulation variation in anadromy and reproductive life span in rainbow trout
introduced in the Santa Cruz River, Argentina. Journal of Fish Biology.
70:1780-1797.
Schatz JA. 1989. Stream habitat and trout population relationship in Lake Davis
tributaries. Masters Thesis. Humboldt State University, California.
Solomon DJ, Templeton RG. 1976. Movements of brown trout Salmo trutta L. in a
chalk stream. Journal of Fish Biology. 9:411-423.
Thorpe JE. 2007. Maturation responses of salmonids to changing developmental
opportunities. Marine Ecology Progress Series. 335:285-288.
Thrower FP, Hard JJ, Joyce JE. 2004. Genetic architecture of growth and early lifehistory transitions in anadromous and derived freshwater populations of
steelhead. Journal of Fish Biology. 65:286-307.
Wilcove DS, Rothstein D, Bubow J. 1998. Quantifying threats to imperiled species in
the United States. Bioscience. 48:607-615.
111
Young MK. 1995. Resident trout and movement: consequences of a new paradigm.
Fish Habitat Relationships Technical Bulletin. 18:1-5.
Zimmerman CE, Edwards GW, Perry K. 2009. Maternal origin and migratory history
of steelhead and rainbow trout captured in rivers of the Central Valley,
California. Transactions of the American Fisheries Society. 138:280-291.