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MOVEMENT AND DISTRIBUTION OF TROUT FOLLOWING
HYPOLIMNETIC OXYGENATION IN
TWIN LAKES, WASHINGTON
By
EMILY M. CLEGG
A thesis submitted in partial fulfillment of
the requirements for the degree of
MASTER OF SCIENCE IN NATURAL RESOURCE SCIENCES
WASHINGTON STATE UNIVERSITY
Department of Natural Resource Sciences
MAY 2010
ii
To the Faculty of Washington State University:
The members of the Committee appointed to examine the thesis of EMILY M. CLEGG
find it satisfactory and recommend that it be accepted.
_________________________________
Barry C. Moore, Ph.D., Chair
_________________________________
Marc W. Beutel, Ph.D.
_________________________________
Gary H. Thorgaard, Ph.D.
iii
ACKNOWLEDGMENT
I would like to thank my committee, Barry Moore, Marc Beutel, and Gary Thorgaard for
their guidance. I would also like to thank Dave Christensen and Mike Biggs for laying the
groundwork for which this study is based on. I also owe a big thanks to Ellen Preece for being
the devil‟s advocate and for all of her help whether it is studying, field work or moral support. To
the hard working members of our lab, Sandra Mead, Brian Lanouette, and Amy Martin, who
helped with many hours of field work and preparation. I would like to recognize the Colville
Confederated Tribes for the lodging, equipment and boats used to complete this work, especially
Ed Shallenberger, Allen Hammond, and Bernie Abrahamson. To the members of Marc Beutel‟s
lab, Stephen, Victoria, Piper, Jen and Brandon, thank you for all of the really great food themed
field trips, who would have thought we could eat so good!
I want to thank my family, Mom and Dad who encouraged me to go for my dreams and
Danny for always making me laugh with a crazy song. I want to especially thank my mom, dad
and grandpa for staying up those late nights with me trying to find just the right wording. Finally,
I would like to thank my husband Kevin for putting up with my craziness through the highs and
the lows of my work, you truly inspire me with your patience.
iv
MOVEMENT AND DISTRIBUTION OF TROUT FOLLOWING
HYPOLIMNETIC OXYGENATION IN
TWIN LAKES, WASHINGTON
Abstract
by Emily M. Clegg, M.S.
Washington State University
May 2010
Chair: Barry C. Moore
Twin Lakes are popular trout fishing lakes on the Colville Confederated Tribes
Reservation in Washington. Thermal stratification and hypolimnetic oxygen demand have led to
anoxic conditions in the hypolimnion of both lakes, therefore restricting rainbow trout, brook
trout and Columbia Basin redband trout to a narrow band of suitable habitat. In North Twin Lake
in 2009, a line diffuser hypolimnetic oxygenation system was installed to increase trout habitat.
We assessed trout distributions with and without hypolimnetic oxygenation using ultrasonic
telemetry, gillnetting, and hydroacoustics in North and South Twin Lakes. Hypolimnetic
oxygenation increased minimum usable trout habitat in North Twin from about 8% to 49% of
total lake volume. Ultrasonic telemetry observations of redband trout below the average
thermocline at a depth of 6 m had a significantly higher percent of total observations during
hypolimnetic oxygenation. Furthermore, redband trout swimming speeds were significantly
decreased during oxygenation. Gillnets captured high numbers of trout in the metalimnion nets
(5 to 8 m) of both lakes. However, significantly more trout were captured in the oxygenated
hypolimnion in North Twin Lake. Population estimates based on hydroacoustic soundings
v
showed no significant difference in total numbers of fish in North Twin Lake before versus
during oxygenation. However, hydroacoustic data from deep layers was excluded due to large
swarms of Chaoborus sp. that obscured fish targets at the available frequencies. Overall,
hypolimnetic oxygenation has established a thermal refuge for trout in North Twin Lake. Fishery
managers should consider the new productive capacity of trout during hypolimnetic oxygenation
when stocking North Twin Lake for a put-grow-take fishery.
vi
TABLE OF CONTENTS
ACKNOWLEDGEMENTS……………………………………………………………... iv
ABSTRACT……………………………………………………………………………... v
LIST OF TABLES………………………………………………………………………. ix
LIST OF FIGURES……………………………………………………………………... x
CHAPTER
1. INTRODUCTION………………………………………………………….. 1
Overview………………………………………………………………... 1
Study Site Description………………………………………………….. 3
Species of Interest………………………………………………………. 7
Goals and Objectives…………………………………………………… 10
2. METHODS…………………………………………………………………. 11
Physical Parameters ……………………………………………………. 11
Ultrasonic Telemetry…………………………………………………… 11
Gillnets…………………………………………………………………. 13
Hydroacoustics…………………………………………………………. 14
3. RESULTS………………………………………………………………….. 17
Physical Parameters……………………………………………………. 17
Ultrasonic Telemetry…………………………………………………… 20
Gillnets…………………………………………………………………. 23
Hydroacoustics…………………………………………………………. 27
4. DISCUSSION……………………………………………………………… 29
vii
5. MANAGEMENT IMPLICATIONS……………………………………… 34
BIBLIOGRAPHY…………………………………………………………………….. 38
APPENDIX
A. Volume Calculations Using Hydroacoustics and GIS Techniques…....... 41
B. Temperature, Dissolved Oxygen, and Usable Trout Habitat……………. 53
viii
LIST OF TABLES
1. Physical dimensions of North and South Twin Lakes…………………………… 6
2. Least amount of usable trout habitat volumes………………………………….... 17
3. Gillnetting catch per unit effort with and without oxygenation ………………..... 25
ix
LIST OF FIGURES
1. Map of Twin Lakes Location and Watershed………………………………………. 4
2. Twin Lakes Watershed……………………………………………………………… 4
3. Bathymetric Map of North and South Twin Lakes…………………………………. 5
4. Map of North Twin‟s hypolimnetic oxygenation system…………………………… 8
5. Suitable trout habitat in North Twin Lake…………………………………………... 18
6. Suitable trout habitat in South Twin Lake…………………………………………... 19
7. Percent of redband trout observations at each depth ……………………………….. 21
8. Percent of redband trout observations at each depth due to time of day……………. 22
9. Redband trout average swimming speeds…………………………………………... 24
10. Trout caught at each depth using gillnets…………………………………………… 26
11. Average percent of fish using hydroacoustics………………………………………. 28
12. Echogram example of Chaoborus……………………………………………………. 33
1
CHAPTER ONE
INTRODUCTION
Overview
Twin Lakes are located on the Colville Confederated Tribes (CCT) Reservation in north
central Washington and are popular freshwater lakes known for their trout and bass fishery.
Thermal stratification and hypolimnetic oxygen demand have led to anoxic conditions in the
summer hypolimnia of both lakes, therefore restricting suitable habitat for rainbow
(Oncorhynchus mykiss Walbaum), brook (Salvelinus fontinalis Mitchill), and Columbia Basin
redband (O. mykiss gairdneri Richardson) trout. Monitoring in 2006 and 2007 showed only a
narrow band of water with suitable temperature and dissolved oxygen (DO) remains for trout to
live during stratification. Ultrasonic tracking has shown that fish congregate in this layer (Biggs
2007, Christensen and Moore 2009). Coutant‟s (1985) temperature-oxygen hypothesis states that
when this narrow band or “squeeze” occurs, fish experience thermal or respiratory stress,
crowding stress, and decreased fecundity. Therefore maintaining suitable temperature and
dissolved oxygen throughout the water column is essential for fish health. To improve trout
habitat and reduce habitat “squeeze,” the CCT installed a hypolimnetic oxygenation system in
North Twin Lake in August 2008 and initiated seasonal operation in 2009.
Aeration and oxygenation systems are used in lake restoration to raise dissolved oxygen
levels, increase habitat and food for cold water fish, and to reduce the phosphorus release from
sediment (Cook et al. 2005, Beutel and Horne 1999). Hypolimnetic oxygenation and aeration
have been shown to improve and increase cold water fish habitat since the 1970s (Fast 1973,
Overholtz 1977). Ultrasonic telemetry, gillnetting and hydroacoustics have been used to
determine fish habitat and these methods can be used to measure changes before and during
hypolimnetic oxygenation.
2
Ultrasonic telemetry was used to find vertical depth preferences and swimming speeds by
Barwick et al. (2004) and Baldwin et al. (2002) without oxygenation. Fast (1973), Overholtz et
al. (1977) and Aku et al. (1997) used gillnetting to find the vertical distribution of trout following
the installation of a hypolimnetic oxygenation or aeration system. Busch and Mehner (2009),
Mehner and Schulz (2002), and Burczynski et al. (1987) used hydroacoustics to assess
population and distribution of cold water fish without oxygenation.
Telemetry has been used to find trout depth, temperature, and DO preferences in several
lakes and reservoirs. Temperature sensing transmitters showed rainbow trout preferred
temperatures from 8.3 to 13.4°C, DO from 2.9 to 8.7 mg/L, and depths from 30 to 52 m in
Jocassee Reservoir, South Carolina (Barwick et al. 2004). In Strawberry Reservoir, Utah,
ultrasonic telemetry was used to track cutthroat trout horizontal and vertical diel movement, and
seasonal migrations (Baldwin et al. 2002). Vertically, the cutthroat trout were restricted to the
metalimnion in late summer due to hypoxic hypolimnion and warm epilimnetic temperatures
(Baldwin et al. 2002). Horizontally, swimming speeds were greatest during the day and less at
night (Baldwin et al. 2002).
In Twin Lakes, as well as other sites, there have been apparent high mortality rates while
using telemetry. Mortalities following transmitter implantation are most likely due to surgery
recovery stress and exacerbated by high water temperatures (Bunnell and Isely 1999). However,
transmitters have been recovered from sediments, suggesting that they were expelled by the fish
rather than attributable to supposed mortalities (Bunnell and Isely 1999). Indeed, transmitter
expulsion rates in some cases have exceeded mortality rates (Bunnell and Isely 1999).
Gillnetting has been used in several cases to assess vertical distribution of trout during
hypolimnetic aeration and oxygenation (Fast 1973, Overholtz et al. 1977, Aku et al. 1997). In
3
Hemlock Lake, Michigan and Ottoville Quarry, Ohio, trout were caught in gillnets at all depths
following hypolimnetic oxygenation or aeration, inferring that trout were really only limited by
temperature (Fast 1973, Overholtz et al. 1977). Similarly, during hypolimnetic oxygenation in
Amisk Lake, Alberta, trout habitat was increased by 9 meter strata (Aku et al. 1997). Gillnet
surveys in the same lake showed that cisco were found 8 meters deeper in the basin with
oxygenation (Aku et al. 1997).
Hydroacoustics surveys have been used to measure distribution and abundance of fish
since the 1950s (Thorne and Lahore 1969). Several studies have used hydroacoustics to find
vertical distribution of fish in freshwater lakes. Seasonal responses to temperature and diel
vertical migrations are thought to cause variability among density estimates (Busch and Mehner
2009). There was correspondence between hydroacoustic estimates and gillnet catches for
average length and age groups in the same German lake (Mehner and Schulz 2002). A
hydroacoustic assessment of Lake Oahe, South Dakota indicated that vertical distribution of
rainbow smelt was controlled by temperature and fish were restricted to strata immediately
below the epilimnion (Burczynski et al. 1987).
Study Site Description
North and South Twin Lakes are similar size lakes at the same elevation (784 m) located
in north central Washington (Table 1, Figure 1). They are about 8.5 miles west of Inchelium in
Ferry County on the Colville Confederated Tribes Reservation. The Twin Lakes watershed is
approximately 9,776 ha, and the whole Twin Lakes drainage, including the lake watershed and
Stranger Creek outflow watershed, is approximately 19,537 ha (Figure 2) (Frazer 2009). Figure 3
4
Figure 1. North and South Twin Lakes are located in the Colville Confederated Tribes
Reservation in north central Washington.
Figure 2. A map of the Twin Lakes Watershed (indicated by the lighter line) and the
Twin Lakes outflow watershed (indicated by the darker line) to the confluence
with Lake Roosevelt.
5
Figure 3. A bathymetric map of North and South Twin including tributaries and
outflows with contour intervals of 5 ft.
6
shows the lake bathymetry. The lakes are connected by a shallow channel (1-2 m) that is heavily
vegetated with macrophytes. Past studies have detected no trout movement between the lakes
through the channel (Biggs 2007). North Twin Lake has five tributaries and South Twin has
seven tributaries, all of which are relatively small. Two regulated outflow creeks drain into Lake
Roosevelt, from North and South Twin Lakes.
Maximum
Depth (m)
Mean
Depth (m)
Volume
(m3)
Surface
area (ha)
North Twin
Lake 15.4 9.7 32,371,943 316
South Twin
Lake 17.0 10.4 35,380,988 387
Activities in the watershed that may impact internal and external nutrient loading into the
lakes include timber harvest, livestock grazing, and development. The lakes are surrounded by
conifer forest and past timber harvests can be seen from the lakes. Most of the developments on
the lakes are located on the eastern sides of both lakes, where there are resorts, trailers and
cabins. There are two resorts, a tribal owned one on North Twin Lake and a private resort on
South Twin Lake.
The lakes serve as a popular recreation destination, for tribal and non-tribal members.
Twin Lakes has a recreational fishery composed of warm water and cold water species. Warm
water species include largemouth bass (Micropterus dolomeui) and golden shiners (Notemigonus
crysoleucas). The cold water species in the lakes are Columbia Basin redband trout, rainbow
trout, and brook trout. Redband trout are the only fish historically native to Twin Lakes, however
it is unknown if there are any remnant populations. Redbands are currently being stocked from
the tribal hatchery. Brook and rainbow trout were introduced in the 1950‟s and are still being
Table 1. Physical parameters of North and South Twin Lakes. All
parameters were found using hydroacoustic data and GIS (Appendix A).
7
raised and stocked. Illegal introductions of largemouth bass and golden shiners have created a
warm water fishery. Originally, it was thought that the illegally introduced largemouth bass and
golden shiners could be competing for the same food sources as the trout and adversely affecting
the trout populations (Biggs 2007). Christensen and Moore (2009) used stable isotopes and gut
content analyses to characterize the lakes food webs and found that largemouth bass fed on
recently stocked brook trout diminishing their populations at first, but there was also resource
partitioning between species.
To improve the trout fishery in North Twin Lake, a line diffuser hypolimnetic
oxygenation system was installed in the deepest part of the lake in August 2008 (Figure 4). The
line diffuser system consists of a liquid oxygen storage tank and evaporator on shore, with a line
running from the evaporator to the deepest part of the lake where oxygen gas flows through a
porous hose. As oxygen percolates into the water and as the small bubbles rise, the oxygen gas
dissolves into the water. As the gas dissolves it also spreads out horizontally circulating well
oxygenated water through more of the hypolimnion (Beutel and Horne 1999, Singleton and Little
2006).
Species of Interest
While there are several species of fish in North and South Twin Lakes, this study focused
on the three cold water species. Gillnet collections seemed to favor rainbow and brook trout,
ultrasonic telemetry was used to track Columbia Basin redband trout, and hydroacoustics
potentially showed all species in the lake.
Rainbow trout is in the family Salmonidae. They can be anadromous (steelhead) or
resident form (such as redband trout). Color variation depends on life histories and surroundings;
lake-dwelling individuals are typically dark greenish to blue with irregular spots above and
8
Figure 4. The hypolimnetic oxygenation line diffuser system installed in North Twin in
August 2008 is located in the deepest part of the lake.
9
below the lateral line (Behnke 2002). Their native range extends from southwestern Alaska to
northern Mexico in any river, stream or lake that has access to the Pacific Ocean (Behnke 2002).
However, rainbow trout have been introduced world wide as an important sport fish and food
source. Rainbow trout prefer water with temperatures < 20°C and > 5 mg/L DO (Behnke 1992,
Fast 1973). They can withstand temperatures up to 26°C, however prolonged temperatures above
24°C leads to increased mortality (Fast 1973).
Columbia Basin redband trout are a resident subspecies of rainbow trout. Redband trout
of the Columbia Basin are found east of the Cascade Range in any tributary to the Columbia
River up to barrier falls (Behnke 2002). They have a large distinctive spots on their bodies and a
bright red lateral line (Behnke 2002). There are several strains of redband trout including the
Gerrard strain of Kamloops trout that live in lakes (Behnke 1992). The Gerrard strain of
Kamloops trout are more silvery with less pronounced spotted pattern and lateral line (Behnke
2002). Kamloops trout are piscivorous and do not reach maturity until they are four to six years
old and can live up to ten years (Behnke 2002). Some redband trout have been found to
withstand temperatures up to 29°C and also that at high water temperatures, and metabolic rates
have a positive correlation with swimming behaviors (Rodnick et al. 2004).
Brook trout are also members of the family Salmonidae. Brook trout have green dorsal
vermiculation. Their sides have red spots with blue rings, and pelvic and anal fins have white
edges. They are native to the eastern United States and Canada, from Hudson Bay to the Great
Lakes and south through the Appalachian Mountains (Page and Burr 1991). Brook trout have
been introduced worldwide to lakes and rivers outside their native range. Like rainbow trout they
require habitat with temperatures <20°C and DO >5 mg/L (Wydoski and Whitney 2003).
10
Goals and Objectives
The goal of this study was to determine the distribution of trout following hypolimnetic
oxygenation. To complete this goal, we used the following objectives:
Objective 1: Determine horizontal and vertical movement of hatchery redband trout using
ultrasonic telemetry in North Twin Lake.
Objective 2: Determine depth distributions of rainbow trout and brook trout by gillnet
collections.
Objective 3: Determine fish abundance and vertical distribution using hydroacoustics.
Objective 4: Statistically compare telemetry, gillnetting and hydroacoustic results for significant
difference between oxygenated and non-oxygenated hypolimnion.
11
CHAPTER TWO
METHODS
Physical Parameters
We recorded temperature and DO profiles for North and South Twin from 2006 to 2009
using Hydrolab MiniSonde 4a (HACH Environmental), or in a few instances, a YSI Model 55
DO Meter (YSI Inc., Yellow Springs, Ohio). In 2006, profiles were taken during six sampling
events in North Twin from June to November and in 2007 profiles were taken during five
sampling events in North Twin from June to September. Profiles were taken during eight
sampling events from May to October in North and South Twin Lakes in 2008. Finally, we took
profiles during twelve sampling events from May to October in North and South Twin Lakes in
2009.
Ultrasonic Telemetry
On May 1, 2009, fourteen female brood stock redband trout were tagged with ultrasonic
transmitters (Model IBT-96-9-I, Sonotronics, Inc., Tucson, Arizona) at the CCT hatchery in
Bridgeport, Washington using implant techniques from Summerfelt and Smith (1990). Tags were
47 mm long, with a diameter of 10.5 mm, and a wet weight of 3.8 g and did not exceed 2% of the
fish total weight. The transmitters were calibrated for temperature prior to implantation. Prior to
surgery, trout were anesthetized in a knockout tank in 80 mg/L of tricaine methanesulfonate
(MS-222). When fully anesthetized, fish were placed in a surgery cradle dorsal side down and
their gills were oxygenated with 40 mg/L of MS-222 during the procedure. The incision site was
located anterior to the pelvic fins and slightly to the side of the ventral midline and sterilized
with iodine. The transmitter was then inserted into the peritoneal cavity. Incisions were closed
with 3 to 4 monofilament nylon sutures using a non-interrupted suture pattern. Finally, the fish
12
were placed in the recovery tank and held until it began swimming on its own. The whole
surgery process lasted less than seven minutes. There was one mortality during recovery and the
remaining thirteen of the fish were stocked into North Twin on May 26, 2009.
Ultrasonic tracking was also performed in 2006 and 2007. The same implantation
methods were used as in 2009. In 2006, redband trout were tagged at the CCT hatchery, 11 with
coded identification transmitters (Sonotronics, Inc., Tucson, Arizona), and 6 with pressure
sensitive transmitters (Sonotronics, Inc., Tucson, Arizona) (Biggs 2007). On May 23, 2007, ten
hatchery redband trout were implanted with cycled (5 days on, 21 days off) pressure sensitive
transmitters (Sonotronics, Inc., Tucson, Arizona) (Christensen and Moore 2008).
In 2009, we actively tracked redband trout using a USR-96 narrow band receiver and
DH-4 directional hydrophone (Sonotronics, Inc., Tucson, Arizona). We used signal direction and
strength to find and follow each fish. Tracking took place once a month from May through
September for three days each month. The hydrophone was lowered into the lake and we listened
for the transmitters for 3 to 5 minutes at each site which was sufficient to scan through every
frequency 4 to 6 times. If a transmitter was detected, we tracked it for at least one hour with
observations recorded every minute or until the fish was lost. We recorded time, fish
identification, temperature, and GPS location (in NAD 83) every minute the fish was being
tracked. We took temperature and DO profiles on the second day of tracking. The temperature
was then used to infer depth.
Tracking methods were similar in 2006 and 2007. In 2006, tracking events took place in
June, July, August and November. Trout with pressure tags were tracked for at least an hour with
observations recorded every minute, and coded tags were recorded when found, but not followed
(Biggs 2007). Tracking events took place June through September in 2007. Trout were followed
13
for five hours or until signal was lost, with observations recorded every minute (Christensen and
Moore 2008).
Statistical analysis was performed on vertical redband trout distribution using Minitab 15
(Minitab, Inc. 2009). A one-way ANOVA with Dunnett‟s test was used to determine if there was
a difference between the average depths of each fish tracked for each year (α = 0.05). To
determine differences between years with and without hypolimnetic oxygenation, I used a
student t-test (α = 0.05). A student t-test was also performed to find if there was a difference with
and without oxygenation of the number of observations of redband trout utilizing the
hypolimnion depth greater than or equal to 6 m (α = 0.05). Horizontal distribution of redband
trout was measured using swimming speeds. To determine if there was a difference between
mean swimming speeds during 2006, 2007 and 2009 (α = 0.05) I used a one-way ANOVA with
Dunnett‟s test. Finally, I performed a one-way ANOVA to determine if there was a difference in
average swimming speed in North Twin Lake with and without hypolimnetic oxygenation (α =
0.05).
Gillnets
In 2009, we used six monofilament gillnets, 3 x 30 m, of two different mesh sizes, 1 and
1.5 inch knot to knot not stretched (Memphis Net and Twine, Memphis, Tennessee). We placed
the nets perpendicular to the shore in North and South Twin Lakes. A 1 inch mesh net and a 1.5
inch mesh net were placed at 2 to 5 meters deep representing the epilimnion, 5 to 8 meters deep
representing the metalimnion, and 8 to 11 meters deep representing the hypolimnion. Gillnets
were left over night for approximately 12 hours about once a month from May to October in
North Twin Lake, and in May, July, August and October in South Twin Lake. We recorded the
14
net depth of captured rainbow and brook trout, as well as length measured to the nearest
millimeter, weight to the nearest gram, and the trout was checked for any hatchery tags.
The number of trout caught in each net, shallow (2 to 5 m), mid (5 to 8 m) and deep (8 to
11 m) was determined for each sampling month in North and South Twin Lakes. A two-way
ANOVA was used to test differences and an interaction between depth with and without
hypolimnetic oxygenation (Minitab, Inc. 2009). If there was interaction, a Tukey test was
performed on factors that had a significant difference (α = 0.05). One-way ANOVAs were used
to determine if there was a difference between the number of trout caught in the epilimnion,
metalimnion and hypolimnion in nets between North Twin and South Twin (α = 0.05).
Hydroacoustics
Hydroacoustic data was collected once a month from May through November in 2008
and 2009 in North and South Twin Lakes using a DT-X digital scientific echosounder with a 10°
split-beam 420 kHz transducer (BioSonics, Seattle, Washington). The transducer was mounted to
a 16 ft aluminum boat traveling at about 3 miles per hour (5 pings/s). Four transects were used in
North Twin and six transects in South Twin.
We used both echo counting and echo integration techniques to analyze hydroacoustic
data. Echo counting detects echoes from individual fish and determines the density of the fish
within the acoustic beam by taking into account the size distribution of the population being
measured (Simmonds and MacLennan 2005). Due to hatchery stocking in Twin Lakes, there are
several different size classes, which makes echo counting a viable analysis option. Echo counting
could underestimate fish densities, but would not affect fish distribution (Luecke and
Wurtsbaugh 1993). Echo integration is used for high densities of fish, such as schools and can
estimate the quantity of fish in the acoustic beam whether or not there are overlapping echoes
15
(Simmonds and MacLennan 2005). Echo integration does not take into account the different size
classes of trout at Twin Lakes, but rather looks for the echo that best fits the specified parameters
and backscattering cross section.
Hydroacoustic files were analyzed using BioSonics Visual Analyzer 4.1 software
(Seattle, Washington). The display was set to -60 dB and prepared a bottom tracking file for each
transect using an above bottom blanking zone of 50 cm. The file was checked to make sure there
was no vegetation or bottom located in the zone. Next, the strata was set to 1 m intervals to give
in depth vertical distribution of fish. Strata with Chaoborus (in the family Chaobridae) were
noted. For echo counting, to limit the distance off the beam axis, beam pattern threshold was
narrowed from -4 dB to -24 dB, meaning that the fish has to be closer to the beam to be counted
(BioSonics, Inc. 2004). For echo integration, the echo threshold (minimum echo strength to be
accepted as a target), max pulse width (maximum number of pulse widths an echo can have to be
accepted as a target), and end point criteria (where on the echo signature the pulse width was
measured) were set to -60 dB, 1.5 and -6 dB respectively (BioSonics, Inc. 2004). The number of
fish per cubic meter was calculated for each meter strata for each transect using both echo
counting and echo integration for every sampling event. Strata containing Chaoborus were
discarded because Chaoborid air sacs are strong acoustic reflectors and may resemble small fish
(Knudson et al. 2006). Fish per cubic meter of each of the transects for a sampling event were
added to provide the number of fish per cubic meter in each strata. Then the number of fish per
cubic meter was multiplied by the volume of each depth strata for each individual lake to
determine the total number of fish per meter strata. The total number of fish per strata was added
together and a total number of fish was calculated for that sampling date.
16
The statistical analysis using differences in echo counting versus echo integration
estimates for hydroacoustic data began with finding out if there was a significant difference
between echo counting and echo integration mean total number of fish calculated for each
sampling date using a paired t-test (α = 0.05) (Minitab, Inc. 2009). If no significant difference
was found, echo counting would be used for the rest of the analysis. Once this was determined, a
paired t-test was performed to determine if the total number of fish calculated for echo counting
in North Twin in 2008 without hypolimnetic oxygenation differed from 2009 with hypolimnetic
oxygenation (α = 0.05). Another paired t-test was used to determine if there was a difference
using echo counting in the number of fish at each depth with and without hypolimnetic
oxygenation (α = 0.05). Finally, a paired t-test to determine if there was a difference in the
number of fish found at each depth greater than or equal to 6 m (α = 0.05).
17
CHAPTER THREE
RESULTS
Physical Properties
Suitable trout habitat was defined as < 20°C and > 5 mg/L DO for each month (Appendix
B). North and South Twin Lakes are relatively similar in temperature, DO, and habitat volume
for all years, except 2009 in North Twin Lake. With the hypolimnetic oxygenation system
operating, minimum volume of suitable habitat for trout was 18,234,729 m3, or 49% of total
volume, compared to 2006 and 2008, when the minimum volume of suitable habitat was
3,021,219 m3, or 8 % of the lake‟s total volume as seen in Table 2 and Figures 5 and 6.
North Twin Lake
Year Date
Minimum Habitat
Volume (m3) Depth Strata
2006 August 16 3,021,219 5 - 6 m
2007 August 7 5,949,250 5 - 7 m
2008 July 22 to August 12 3,021,219 5 - 6 m
2009 August 13 18,234,729 6 - 15 m
South Twin Lake
Year Date
Minimum Habitat
Volume (m3) Depth Strata
2008 July 31 to August 12 3,177,412 6 - 7 m
2009 September 3 2,903,914 7 m
Table 2. Minimum of usable trout habitat volume defined as temperature <20°C and
DO >4 mg/L, the date, and the strata for 2006 to 2009 in North Twin and
2008 and 2009 in South Twin.
54
25
178
46
98
0
10
20
30
40
50
60
70
80
90
100
June 16 June 28 July 24 Aug. 16 Sept. 27 Nov. 16
Per
cen
t o
f L
ak
e V
olu
me
Su
ita
ble
fo
r T
rou
t
2006
a.
62
25
16
62
54
0
10
20
30
40
50
60
70
80
90
100
June 14 July 10 Aug. 7 Aug. 30 Sept. 27
Per
cen
t o
f L
ak
e V
olu
me
Su
ita
ble
fo
r T
rou
t
2007
b.
76
46
8 8 8
5462
69
0
10
20
30
40
50
60
70
80
90
100
Per
cen
t o
f L
ak
e V
olu
me
Su
ita
ble
fo
r T
rou
t
2008
c.98 95 95 95
5849
5449
92 9295 95
0
10
20
30
40
50
60
70
80
90
100
Per
cen
t o
f L
ak
e V
olu
me
Su
ita
ble
fo
r T
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t
2009
d.
Figure 5. Suitable trout habitat (temperature of < 20 ° C and > 5 mg/L DO) as percent of total lake volume in North
Twin Lake in a.) 2006, b.) 2007, c.) 2008, and d.) 2009.
18
63
7 7 7
42
63
75
0
10
20
30
40
50
60
70
80
90
100
June 24 July 22 July 31 Aug. 12 Aug. 30 Sept. 13 Oct. 21
Per
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t o
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Su
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t
2008
a.
85
69 69
49
2214
7
6975 75
0
10
20
30
40
50
60
70
80
90
100
Per
cen
t o
f L
ak
e V
olu
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Su
ita
ble
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r T
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t
2009
b.
Figure 6. Suitable trout habitat (temperature of < 20 ° C and > 5 mg/L DO) as percent of total lake volume in South Twin
Lake in a.) 2008, and b.) 2009.
19
20
Ultrasonic Telemetry
Vertical distribution of each tagged redband trout observation was averaged for the years
2006, 2007, and 2009. An ANOVA showed that there was no significant difference in the
average depths of each tracked trout for each year (p = 0.267). A t-test found no significant
difference in the average depths in 2006 and 2007 without hypolimnetic oxygenation and 2009
with hypolimnetic oxygenation (p = 0.633). However, we were more interested in whether or not
the redband trout were using more of the newly available hypolimnion habitat following
hypolimnetic oxygenation. The percent of observations below 6 meters increased from 27% and
28% in 2006 and 2007 respectively to 35% in 2009. Figure 7 shows that there was a higher
percent of observations below 6 m in 2009 during hypolimnetic oxygenation than in the previous
years, 2006 and 2007. A t-test found that there was a significant difference in the number of
occurrences below 6 m before (2006 and 2007) and during (2009) hypolimnetic oxygenation (p =
0.015).
The percent of observations were also categorized by time of day before and during
hypolimnetic oxygenation (Figure 8). Prior to hypolimnetic oxygenation, the largest percent of
daylight observations occurred between 5 and 6 m (max depth 10 m). During oxygenation, the
largest percent of daylight observations occurred between 6 and 7 m (max depth 10 m). During
the crepuscular period, which was defined as 4 am to 6 am and 8 pm to 10 pm for late May to
August, prior to oxygenation trout were detected between 3 and 4 m (max depth 10 m), whereas
during oxygenation the fish were detected between 5 and 6 m (max depth 13 m). Finally, the
greatest percent of night observations before oxygenation were detected between 5 and 6 m (max
depth 8 m) and during oxygenation observations were between 4 and 5 m (max depth 8 m).
21
0 5 10 15 20 25 30 35 40
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0 5 10 15 20 25
Percent of Observations
Dep
th (
m)
Temperature (°C)
a. Percent of Observations Average Temperature
0 5 10 15 20 25 30 35 40
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0 5 10 15 20 25
Percent of Observations
Dep
th (
m)
Temperature (°C)
b.Percent of Observations Average Temperature
Figure 7. Depth distribution of tagged redband trout in North Twin Lake a.) before
oxygenation in 2006 and 2007, and b.) during oxygenation in 2009.
22
0 10 20 30 40 50 60 70
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0 5 10 15 20 25
Percent of Observations
Dep
th (
m)
Temperature (°C)
Percent of Observations Average Temperaturea.
0 10 20 30 40 50 60 70
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th (
m)
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Percent of Observations Average Temperatureb.
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th (
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0 10 20 30 40 50 60 70
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th (
m)
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Percent of Observations Average Temperaturee.
0 10 20 30 40 50 60 70
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Percent of Observations
Dep
th (
m)
Temperature (°C)
Percent of Observations Average Temperaturef.
Figure 8. The percent of redband trout observations with the average temperature
profile a. and b.)during the day, c. and d.) crepuscular period, and e. and f.)
night, a., c., and e.) before and b., d., and f.) during hypolimnetic oxygenation.
Before Hypolimnetic Oxygenation
North Twin 2006 and 2007
During Hypolimnetic Oxygenation
North Twin 2009
23
Horizontal movement of the redband trout was calculated as average swimming speed
(cm/s) for each redband trout tracked in 2006, 2007 and 2009. The total average for the time of
day was found before and during hypolimnetic oxygenation (Figure 9). The trout were more
active during the day and crepuscular periods. A one-way ANOVA showed that there was a
significant difference between all three years (p < 0.001). I used a Dunnett‟s test and found that
average swimming speed in 2006 (40.70 ± 25.88 cm/s) and 2007 (38.93 ± 16.75 cm/s) before
hypolimnetic oxygenation were significantly different than 2009 (14.90 ± 9.23 cm/s) during
hypolimnetic oxygenation. Using a one-way ANOVA, I also found that there was a significant
difference in swimming speed before and during hypolimnetic oxygen (p < 0.001).
Gillnets
CCT deployed gillnets for the epilimnion, metalimnion and hypolimnion in 2009 in
North and South Twin Lakes. The number of trout caught using the nets by depths were
compared between lakes. Gillnet data was used to calculate catch per unit effort (CPUE) (# of
fish/ hour) for trout where the unit effort was two nets deployed at each depth per sampling event
as seen in Table 3. For both North and South Twin Lakes, most trout were caught in the
metalimnion between 5 and 8 m deep. In North Twin when the hypolimnetic oxygenation system
was active, hypolimnion nets, 8 to 11 m, had more fish than in South Twin hypolimnion nets
without a hypolimnetic oxygenation system.
24
15.94
16.22
13.06
43.8
51.2
23.34
0 10 20 30 40 50 60
Day
Crepuscular
Night
Swimming Speed (cm/s)
Before Oxygenation During Oxygenation
Figure 9. Redband Trout average swimming speed (cm/s) by photo period during (2009) and
before (2006 and 2007) hypolimnetic oxygenation.
25
North Twin
With Oxygenation
South Twin
Without Oxygenation
2 - 5 m 5 - 8 m 8 - 11m 2 - 5 m 5 - 8 m 8 - 11m
May 2 0 1 19 24 0
June 14 32 7 - - -
July 2 31 14 0 10 0
August 0 4 4 0 6 0
September 0 15 8 - - -
October 2 1 1 3 0 1
Total number of fish caught at each depth was added then was plotted against the average
temperature for gillnet sampling dates (Figure 10). The greatest numbers of fish caught were in
metalimnion nets for both North and South Twin. In North Twin the hypolimnion nets caught
more fish than the same deep nets in South Twin.
No interaction was found using a two-way ANOVA, so only one-way ANOVAs were
used to determine significance for each net depth with and without hypolimnetic oxygenation.
The number of trout caught in the nets representing the epilimnion (2 to 5 m) showed no
significant difference between North Twin with hypolimnetic oxygenation and South Twin
without hypolimnetic oxygenation (p = 0.644) using a one-way ANOVA. Similarly, a one-way
ANOVA of the number of trout caught in the nets representing the metalimnion (5 to 8 m) also
showed no significant difference between North and South Twin (p = 0.657). In contrast, the
number of trout caught in the nets representing the hypolimnion (8 to 11 m) showed a significant
difference using a one-way ANOVA (p = 0.047). This shows that statistically, more fish are
using the new habitat because they were caught in the hypolimnion net in North Twin during
hypolimnetic oxygenation.
Table 3. Catch per unit effort (# fish/12 hour) caught in two nets at each depth in the
epilimnion, metalimnion and hypolimnion in North and South Twin during 2009.
26
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m)
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Total # fish Caught Average Temperature
a.
0 10 20 30 40 50 60 70 80 90 100
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0.0 5.0 10.0 15.0 20.0
Number of Trout Caught
Dep
th (
m)
Temperature (°C)
Total # fish Caught Average Temperature
b.
Figure 10. The total number of trout caught in three depth strata (2 – 5 m, 5 – 8m, and 8 –
11m) a.) in South Twin in 4 months without hypolimnetic oxygenation and b.) in
North Twin in 6 months with hypolimnetic oxygenation (bars) and average summer
temperature profile (lines).
27
Hydroacoustics
Hydroacoustic data was analyzed using two different methods, echo counting and echo
integration in North Twin Lake. The total number of fish for echo counting and integration was
calculated by the sum of fish per cubic meter in each strata multiplied by the volume of each lake
strata. A paired t-test found that there was no significant difference in the total number of fish
using echo counting and echo integration (p = 0.436). Because no significant difference was
found, echo counting and echo integration were assumed to have the same validity, so echo
counting was used to calculate the total number of fish in Twin Lakes. The difference in the total
number of fish in North Twin between 2008 without hypolimnetic oxygenation and 2009 with
hypolimnetic oxygenation was not significant (p = 0.374). A paired t-test showed no significant
difference between the number of fish in each meter depth strata (p=0.151). Finally, a paired t-
test found that there was also no significant difference between the number of fish in each strata
below 6 m (p=0.700).
The average percent of fish found at each depth was calculated (Figure 11) using echo
counting for North and South Twin in 2008 and 2009. The highest average percent for South
Twin without hypolimnetic oxygenation in 2008 and 2009 were at depths of 3 to 4 m and 5 to 6
m respectively. The highest average percent for North Twin without hypolimnetic oxygenation
in 2008 was 3 to 4 m. The highest average percent for North Twin during hypolimnetic
oxygenation in 2009 was still 3 to 4 m. However, the echo counting average percents in North
Twin in 2009 are more evenly distributed than in 2008, for example in 2008, there were only
four 1 m strata (1 to 2 m and 3 to 6 m) that had an average percent greater than 10%, where as in
2009, there were six 1 m strata (1 to 7 m). Much of the data in 2008 and 2009 below the
thermocline was eliminated due to chaoborus interference.
0 5 10 15 20 25 30
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Dep
th S
tra
ta (
m)
Temperature (°C)
a. Average Percent of Fish Average Temperature
0 5 10 15 20 25 30
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Dep
th S
tra
ta (
m)
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c. Average Percent of Fish Average Temperature
0 5 10 15 20 25 30
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th S
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ta (
m)
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b. Average Percent of Fish Average Temperature
0 5 10 15 20 25 30
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0 5 10 15 20
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Dep
th S
tra
ta (
m)
Temperature (°C)
d. Average Percent of Fish Average Temperature
Figure 11. Average percent of fish distribution estimates detected by hydroacoustics echo counting at each depth in b.
and d.) North and a. and c.) South Twin Lakes in a. and b.) 2008 and c. and d.) 2009. In North Twin 2009, the
hypolimnetic oxygenation system was operating.
28
29
CHAPTER FOUR
DISCUSSION
Hypolimnetic oxygenation greatly increased suitable trout habitat in North Twin in 2009.
In Amisk Lake (zmax = 34m and 60m), Alberta, hypolimnetic oxygenation increased summer DO
concentrations from 1 mg/L to 4.6 mg/L (Prepas and Burke 1997). Whereas the hypolimnetic
oxygen system in North Twin Lake was able to increase the DO from an average of 2.8 mg/L to
8.8 mg/L below 6 m, and increased the minimum usable habitat volume from 8% to 49%.
Temperature and DO appeared to be the main factor influencing trout distributions (Biggs 2007).
However, there are other important habitat factors such as light and prey ability (Nowak and
Quinn 2002). Redband trout in North Twin Lake follow diel vertical migration, following prey of
zooplankton and chaoborus, which are the trout‟s main food source in Twin Lakes (Christensen
and Moore 2005). Redband trout are also known to be piscivorous (Behnke 2002) suggesting
that they may also prey on golden shiners when their habitats overlap (Christensen and Moore
2005). Tagged redband trout in 2009 were consistent with those in 2006 and 2007 in that they
were found to have no home range and assumed no movement between North and South Twin
Lakes (Biggs 2007, Christensen and Moore 2008). The tagged trout were found at deeper depths
during the day and crepuscular periods which is consistent with light availability for hunting prey
at deeper depths. Ultrasonic telemetry, gillnetting and hydroacoustics with and without
hypolimnetic oxygenation all showed that the trout prefer the metalimnion habitat which was
about 3 to 6 m. However, when hypolimnetic waters became available during oxygenation, trout
also utilized the deeper habitat from 6 to 12 m.
During oxygenation the hypolimnion can be thought of as a thermal refuge. In rivers and
streams, cold water refuges are created by tributaries, seeps, springs and stratification (Erbersole
30
et al. 2001). In lakes, refuges are primarily created by thermal stratification. In streams, cold
water patches studied by Erbersole et al. (2001) were 3 to 10°C colder than the surrounding
stream flow. Similarly, in North Twin Lake, the epilimnion was 2 to 17°C warmer than the
hypolimnion during stratification. Ebersole et al. (2001) found that rainbow trout tended to move
into thermal refuges in streams during the afternoons when the streams reached their daily peak
temperatures. We also found that redband trout observations in the hypolimnion increased during
the day and crepuscular periods when the epilimnion is warmer. Finally, Ebersole et al. (2001)
found that 10% to 40% of individuals in a stream reach used the thermal refuges during times of
thermal stress. Similarly, using the gillnet data from North Twin in 2009 showed that 13% to
50% of the total number of trout caught each month were in the thermal refuge of the
hypolimnion.
Horizontal movement of redband trout showed that they were more active during the day
and crepuscular periods and less active at night both with and without hypolimnetic oxygenation.
However, with hypolimnetic oxygenation, there was less variation between time of day and
swimming speeds. Nowak and Quinn (2002) found that the average swimming speed of cutthroat
trout in Lake Washington, in natural low DO conditions without hypolimnetic oxygenation, was
22 cm/s. Baldwin et al. (2002) also found the average swimming speed of cutthroat trout in
natural low DO concentrations in Strawberry Reservoir, Utah was 21 cm/s. Prior to hypolimnetic
oxygenation, the average swimming speed of tagged redband trout in North Twin Lake was 39
cm/s, and during oxygenation, the average swimming speed dropped to 15 cm/s. We hypothesize
that prior to oxygenation, in the habitat squeeze, the suitable strata that the trout were occupying
had higher temperatures which increased metabolic rates so they had to eat more, and also that
trout swam farther in search of zooplankton prey that was below the trout‟s suitable habitat.
31
Whereas following oxygenation, trout had more access to more suitable habitat with lower
temperatures to lower metabolic rates, and also contained prey, so the trout would not have to
swim as far.
Tagged redband trout in our studies have had high mortality rates. When fish locations
did not change over long periods of time, we considered the fish a mortality, but this could also
be due to expulsion of the transmitter, which is possible when temperatures are increased
(Bunnell and Isely 1999). In 2006, of seventeen tagged hatchery redband trout, three died
between stocking and the first tracking event, two tags were returned by anglers and six died in
late July or early August (Biggs 2007). In 2007, ten hatchery redband trout were tagged, of those
three died and two were caught by anglers (Christensen and Moore 2008). In 2009, fourteen
redband trout were tagged, one fish died while recovering in the hatchery and thirteen were
stocked into North Twin. Three of the tagged trout were caught by anglers, one was never found,
and four others were assumed as mortalities or expulsions.
The number of observations of tagged redband trout was less in 2009 than in the previous
years. It is possible that it is due to a difference in the type of transmitters. In 2006, six redband
trout were implanted with pressure sensitive transmitters, and eleven were implanted with coded
wire transmitters (Biggs 2007). In 2007, pressure sensitive transmitters that cycled were
implanted into twelve redband trout (Christensen and Moore 2008). There was some
complication with tags not giving depth data, so only horizontal data could be recorded
(Christensen and Moore 2008). In 2009, fourteen redband trout were implanted with temperature
transmitters rather than pressure sensitive transmitters. In 2006 and 2007, we were able to hear
redband trout transmitters from the center of the lake all the way to the edges. In 2009, the
temperature transmitters did not seem to broadcast as far as the pressure sensitive transmitters,
32
making it much harder to locate fish and easier to lose the signal. We also presume that there was
interference because of density differences in the water column, making it difficult to locate fish
below the thermocline. When the signal went in and out, temperature readings were few and far
between, decreasing the total number of observations in 2009. Recommendations for future
telemetry projects would be to use pressure sensitive transmitters for active tracking, or to use
archival tags.
In the Ottoville Quarry, Ohio, Overholtz et al. (1977) also found that when oxygenated,
rainbow trout were caught in gillnets at all depths, but in July, August, and September were
primarily found at or below the thermocline. Likewise, in North Twin during oxygenation, most
rainbow and brook trout were at or below the thermocline in July, August, September and
October. The results for North Twin with hypolimnetic oxygenation and South Twin without
hypolimnetic oxygenation in 2009 showed that rainbow and brook trout still prefer the habitat
around the thermocline with the majority of trout caught in each lake being in the net
representing the metalimnion at a depth of 5 to 8 m. However, with hypolimnetic oxygenation
and deeper habitat available, the trout also used and were caught in the deeper net representing
the hypolimnion at 8 to 11 m in North Twin. The number of trout caught in the hypolimnion nets
in North Twin during oxygenation were significantly higher than the number of trout caught in
South Twin throughout 2009.
Twin Lakes has an abundance of larval Chaoborus sp., or phantom midges, which are an
important food source for trout. Chaoborus have air sacs for buoyancy regulation and exhibit a
diel vertical migration pattern. These air sacs create a strong acoustic target, and have been found
to be a source of acoustic scattering (Knudsen et al. 2006). Using a 200 kHz transducer, Knudsen
et al. (2006) found that target strengths of Chaoborus around – 60 dB can resemble target
33
strength of a very small fish. So with transducers of higher frequencies, such as the one used at
Twin Lakes, Chaoborus can be a source of error in fish density estimates (Knudsen et al. 2006).
To correct for this, we noted at what depths the Chaoborus were located at and discarded that
strata. However, the best way to retain more data and have better accuracy in the future would be
to obtain a lower frequency transducer that would not reflect off of Chaoborus air sacs.
Figure 12. Echogram of South Twin Lake on August 25, 2009 with an opaque swarm
of Chaoborus occurring below 7 m.
34
CHAPTER FIVE
MANAGEMENT IMPLICATIONS
Available trout habitat has been increased with hypolimnetic oxygenation of North Twin
Lake. Ecologically, we have opened more preferred habitat to trout; with that we would expect a
higher productivity capacity. Jones (1996) suggests that productivity capacity is a combination of
production and carrying capacity. Management objectives also play a role in maintaining and
increasing productive capacity at Twin Lakes. Based on the installation of the hypolimnetic
oxygenation system, management goals should include maintaining or increasing fish yield, and
restoring the degraded system to a healthier state (Jones 1996). Productive capacity studies can
be costly, so surrogate indicators like water quality, and fish growth, can serve as linkages for the
population or carrying capacity (Jones 1996). Physical, chemical and biological parameters have
been measured at Twin Lakes in the past and should continue as they are the surrogate indicators
that will help define the productive capacity of Twin Lakes. However, as Twin Lakes is a put-
grow-take fishery, a full trout carrying capacity study would benefit managers to know how
many fish to stock into the lakes.
As the management goal of maintaining or increasing the yield of fish, controlling
biological parameters can help trout survival. Managers should consider the size, amount and
stocking time of the trout into Twin Lakes to ensure growth and survival based on habitat
availability. By installing the hypolimnetic oxygenation system, we have opened up new habitat
and have seen use of that habitat. Stocking juvenile trout early in the spring can give them the
advantage of less time to become accustomed to hatchery life, may be able to avoid bass
predation, and they can acclimatize to the lake temperatures and feeding before summer
stratification and habitat reduction occurs. Stocking juveniles rather than adult trout will also
35
reduce the cost to the hatchery. Fishing regulations should also be considered to reduce
unnecessary mortality rates in trout, such as increasing limits on piscivorous bass over 300 mm.
In conjunction with hypolimnetic oxygenation, we also need to continue to reduce
internal and external nutrient loading. Reducing external and internal nutrient loading can lead to
a decreased sediment oxygen demand, and an increase in hypolimnetic oxygen (Doke et al.
1995). This is a way to naturally increase hypolimnetic oxygen and decrease dependence on the
hypolimnetic oxygenation system and reduce costs of operation.
While hypolimnetic oxygenation increases trout habitat availability, carrying capacity
also depends on the food source. Along with improving fish habitat, hypolimnetic oxygenation
may improve and increase habitat suitable for zooplankton and benthic invertebrates (Aku and
Tonn 1999, Dolk et al. 1995, Fast 1973). However, trout can now also exploit hypolimnetic food
sources that were not available prior to hypolimnetic oxygenation and increase their food
consumption (Aku and Tonn 1999). Zooplankton such as Daphnia and Chaoborus, which make
up the main diet of brook and rainbow trout in Twin Lakes (Christensen and Moore 2005),
would normally have a refuge from trout predators below the thermocline in lower DO habitat
(Aku and Tonn 1999, Shapiro 1990). So managers should also consider continuing to monitor
zooplankton and benthic invertebrates as a food source that we can also use as a surrogate
indicator which can influence carrying capacity.
We have observed infestations of copepods Lernea spp. on rainbow and redband trout in
Twin Lakes (Biggs 2007, Christensen and Moore 2008). It was thought that the trout stress from
habitat reduction may have enabled the infestations of parasitic copepods (Biggs 2007,
Christensen and Moore 2008). However, copepods were observed on rainbow trout in North
Twin in 2009 during hypolimnetic oxygenation as well. It is still unknown how much the
36
copepods actually influence trout stress and possibly mortality. This issue requires further
investigation.
Twin Lakes is a popular fishing destination, and as such the anglers should be considered
stake holders in the future of the Twin Lakes system. They need to be informed and educated
about the ecological relationships in the lake, as well as the benefits of hypolimnetic
oxygenation, its effects on the lakes populations of rainbow, redband, and brook trout. Continued
creel surveys will give managers valuable information about what anglers are catching, along
with what sizes and species of fish they desire in the lakes.
Ultrasonic telemetry has provided us with two years of horizontal and vertical redband
trout distribution data prior to hypolimnetic oxygenation in North Twin Lake and one year
during hypolimnetic oxygenation. However, in all three years, there were a small number of
tagged trout and high mortality rates. Also, only the distribution of trout in North Twin Lake was
studied for all three years. Another year of distribution data would benefit the whole Twin Lakes
Project and help increase the sample size and statistically enhance the validity of depth
distribution estimates. It would also benefit the project to look into distribution of the trout in
South Twin Lake to compare to North Twin Lake.
Hydroacoustics should continue to be used in Twin Lakes. Hydroacoustics can provide a
cost effective long term way to estimate density and distribution of all species of fish within
Twin Lakes by supplementing and eventually replacing gillnetting and telemetry. It can also be
used to estimate zooplankton distribution and abundance while using the 420 kHz transducer to
monitor the effects of hypolimnetic oxygenation on zooplankton communities. For fish
distribution and densities, we would recommend obtaining a 70 kHz or lower transducer to
exclude invertebrates such as Chaoborus which have strong acoustic signal.
37
In conclusion, a summary of recommendations for the future of Twin Lakes management
include:
The continuation of hypolimnetic oxygenation in North Twin with the expansion
of oxygenation into South Twin Lake to increase trout habitat.
Monitoring of physical, chemical and biological surrogate indicators, such as
temperature, DO profiles, nutrient concentrations, zooplankton and invertebrate
abundance counts, and fish health, distribution and density monitoring.
Determining the size, timing and amount of trout to be stocked into North and
South Twin Lakes.
Educating the public on the benefits of oxygenation and the reduction of external
nutrient loading.
38
LITERATURE CITED
Aku, P.M.K., L.G. Rudstam and W.M. Tonn. 1997. Impact of hypolimnetic oxygenation on the
vertical distribution of cisco (Coregonus artedi) in Amisk Lake, Alberta. Canadian
Journal of Fisheries and Aquatic Sciences. 54:2182-2195.
Aku, P.M.K. and W.M. Tonn. 1999. Effects of hypolimnetic oxygenation on the food resources
and feeding ecology of cisco in Amisk Lake, Alberta. Transactions of the American
Fisheries Society 128:17-30.
Baldwin, C.M., D.A. Beauchamp and C.P. Gubala. 2002. Seasonal and diel distribution and
movement of cutthroat trout from ultrasonic telemetry. Transactions of the American
Fisheries Society 131:143-158.
Barwick, D.H., J.W. Foltz and D.M. Rankin. 2004. Summer habitat use by rainbow trout and
brown trout in Jocassee Reservoir. North American Journal of Fisheries Management
24:735-740.
Behnke, R.J. 1992. Native trout of western North America. American Fisheries Society,
Monograph 6. Bethesda (MD): American Fisheries Society. p. 161-178.
Behnke, R.J. 2002. Trout and salmon of North America. New York (NY): The Free Press. p. 67-
86.
Beutel, M.W. and A.J. Horne. 1999. A review of the effects of hypolimnetic oxygenation on lake
and reservoir water quality. Lake and Reservoir Management 15(4):285-297.
Biggs, M.J. 2007. Seasonal habitat use and movement by Columbia River redband trout in Twin
Lake, Washington. MS Thesis. Pullman (WA):Washington State University.
BioSonics, Inc. 2004. User guide Visual Analyzer 4. BioSonics Inc., Seattle (WA). p. 35- 40
Bunnell, D.B. and J.J. Isley. 1999. Influence of temperature on mortality and retention of
simulated transmitters in rainbow trout. North American Journal of Fisheries
Management 19:152-154.
Burczynski, J.J., P.H. Michaletz and G.M. Marrone. 1987. Hydroacoustic assessment of the
abundance and distribution of rainbow smelt in Lake Oahe. North American Journal of
Fisheries Management 7:106-116.
Busch, S. and T. Mehner. 2009. Hydroacoustic estimates of fish population depths and densities
at increasingly longer time scales. International Review of Hydrobiology 94:91-102.
Christensen, D.R. and B.C. Moore. 2009. Using stable isotope and a multiple-source mixing
model to evaluate fish dietary niches in a mesotrophic lake. Lake and Reservoir
Management 25:2:167-175.
39
Christensen, D.R. and B.C. Moore. 2008. A report to the Colville Confederated Tribes: Summer
habitat use and prey selection of hatchery rainbow trout in Twin Lakes, Washington.
Christensen, D.R. and B.C. Moore. 2005. Prey selectivity and population dynamics of a lentic
fish community, Twin Lakes, Washington: A report to the Colville Confederated Tribes.
Pullman (WA): Washington State University Department of Natural Resource Sciences.
Cooke, G.D., E.B. Welch, S.A. Peterson and S.A. Nichols. 2005. Restoration and management of
lakes and reservoirs. 3rd
ed. Boca Raton (FL): Taylor and Francis Group. p. 459 – 474.
Courtant, C.C. 1985. Striped bass, temperature, and dissolved oxygen: a speculative hypothesis
for environmental risk. Transactions of the American Fisheries Society 114:31-61.
Doke, J.L., W.H. Funk, S.T.J. Juul and B.C. Moore. 1995. Habitat availability and benthic
invertebrate population changes following alum treatment and hypolimnetic oxygenation
in Newman Lake, Washington. Journal of Freshwater Ecology 10:87-102.
Ebersole, J.L., W.J. Liss and C.A. Frissell. 2001. Relationship between stream temperature,
thermal refugia and rainbow trout Oncorhynchus mykiss abundance in arid-land streams
in the northwestern United States. Ecology of Freshwater Fish 10:1-10.
Fast, A.W. 1973. Effects of artificial hypolimnion aeration on rainbow trout (Salmo gairdneri
richardson) depth distribution. Transactions of the American Fisheries Society 4:715-
721.
Frazier, S. 2009. Watershed boundaries Washington. Portland, (OR): Bureau of Land
Management, Oregon/Washington State Office. http://hydro.reo.gov/hu.html. Accessed
10 Sept 2009.
Jones, M.L., R.G. Randall, D. Hayes, W. Dunlop, J. Imhof, G. Lacroix and N.J.R. Ward. 1996.
Assessing the ecological effects of habitat change: moving beyond productive capacity.
Canadian Journal of Fisheries and Aquatic Sciences 53(S1):446-457.
Knudsen, F.R., P. Larsson and P.J. Jakobsen. Acoustic scattering from a larval insect
(Chaoborus flavicans) at six echosounder frequencies: Implication for acoustic estimates
of fish abundance. Fisheries Research 79:84-89.
Luecke, C. and W.A. Wurtsbaugh. 1993. Effects of moonlight and daylight on hydroacoustic
estimates of pelagic fish abundance. Transactions of the American Fisheries Society
122:112-120.
Mehner, T. and M. Schulz. 2002. Monthly variability of hydroacoustic fish stock estimates in a
deep lake and its correlation to gillnet catches. Journal of Fish Biology 61: 1109-1121.
Minitab, Inc. 2009. Minitab 15 Statistical Software. State College, Pennsylvania.
40
Nowak, G.M. and T.P. Quinn. 2002. Diel and seasonal patterns of horizontal and vertical
movement of telemetered cutthroat trout in Lake Washington, Washington. Transactions
of the American Fisheries Society 131 (3):452-462.
Overholtz, WJ, AW Fast, RA Tubb and R Miller. 1977. Hypolimnion oxygenation and its effects
on the depth distribution of rainbow trout (Salmo gairdneri) and gizzard shad (Dorosoma
cepedianum). Transactions of the American Fisheries Society 106(4):371-375.
Page, L.M. and B.M. Burr. 1991. A Field Guide to freshwater fishes, North America, north of
Mexico. Boston (MA): Joughton Mifflin Company. p. 66-67 and 263-264.
Prepas, E.E. and J.M. Burke. 1997. Effects of hypolimnetic oxygenation on water quality in
Amisk Lake, Alberta, a deep eutrophic lake with high internal phosphorus loading rates.
Canadian Journal of Fisheries and Aquatic Sciences 54:2111-2120.
Rodnick, K.J., A.K. Gamperl, K.R. Lizars, M.T. Bennett, R.N. Rausch and E.R. Keeley. 2004.
Thermal tolerance and metabolic physiology among redband trout populations in south-
eastern Oregon. Journal of Fish Biology 64:310-335.
Shapiro, J. 1990. Biomanipulation: the next phase – making it stable. Hydrobiologia 200:13-27.
Simmonds, J. and D. MacLennan. 2005. Observation and measurement of fish. In Fisheries
acoustics theory and practice. 2nd
ed. Oxford (UK): Blackwell Science, Oxford, United
Kingdom. p. 163 – 216.
Singleton, V.L. and J.C. Little. 2006. Designing hypolimnetic aeration and oxygenation systems
– A review. Environmental Science & Technology 40:7512-7520.
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CB and Moyle PB editors. Methods for Fish Biology. Bethesda (MD): American
Fisheries Society. p. 213-272.
Thorne, R.E. and H.W. Lahore. 1969. Acoustic techniques of fish population estimation with
special reference to echo integration. Circular No. 69-10. Seattle (WA): Fisheries
Research Institute, University of Washington.
Wydoski, R.S. and R.R. Whitney. 2003. Inland fishes of Washington. 2nd
ed. Bethesda (MD):
American Fisheries Society.
APPENDIX A
Volume Calculations Using Hydroacoustic and GIS Techniques
42
Methods
Hydroacoustic surveys were performed not only to analyze fish densities, but also to
obtain more accurate bathymetry and volumes of North and South Twin Lakes. Hydroacoustic
files were analyzed in Visual Analyzer 4.2 (BioSonics, Inc. Seattle, WA). Display settings were
set to a threshold of -60 dB. Bottom tracking parameters were set to a peak threshold of -30 to -
40 dB, depending on signal strength of the leading edge of the bottom and on the amount of
aquatic vegetation present in the echogram. The tracking window was 100 cm and the peak
width was 10 cm. Above bottom blanking threshold was set to -60 db and the zone was 25 cm.
The lost bottom was set to re-initialize after 10 pings. Then the bottom was drawn and manually
inspected for inconsistencies. The number of strata was set to 1 and the number of reports was
set to the number of pings in the file. The Visual Analyzer program was set to give GIS friendly
outputs using the function supplied at C://Biosonics/Analyzer/Execs, in the Analyzer.ini file; the
GIS output line was changed to 1. Then, the file was analyzed to obtain an excel output. This
process was followed for each hydroacoustic file, including the ones in between transects. All
excel outputs were combined into one excel worksheet, making sure that the columns
representing latitude, longitude, and depth were consistent throughout.
Digital elevation model (DEM) data for the Twin Lakes was downloaded from the USGS
National Map Seamless Server website (http://seamless.usgs.gov/) by accessing „View &
Download United States Data,‟ zooming to the Twin Lakes area, under the download tab
selecting „Elevation 1/3” NED‟ which is the 10 m elevation dataset, and finally using the
download tool to select the Twin Lakes area. The DEM was imported into ArcGIS 9.3.1
(ArcEditor edition, ESRI, Redlands, CA). The polygons of North and South Twin that were
drawn from satellite imagery were also added. The projection of the data frame was set to a
43
projected coordinate system of NAD 1983 UTM zone 11N. Surface elevation of the lakes were
determined with the identify tool to be 785.2 m. A point shapefile was created to represent the
outline or surface of the lake, using the North and South Twin Lakes polygons. Points were
placed approximately 10 m or less apart along the shore. In the attribute table a field labeled
„Elevation‟ was added (Float, Precision 15, Scale 15). Then by right clicking the field and
selecting the „field calculator,‟ the statement “Elevation = 785.2” was entered. The excel
worksheet was added to the ArcGIS project and the layer was right clicked and „Display XY
data‟ was activated creating a temporary events file with a geographic coordinate projection of
WGS 1984, because the hydroacoustic coordinates were taken with a GPS. A new field was
created in the attribute table labeled „Elevation‟ (Float, Precision 15, Scale 15). Then the
statement “Elevation = 785.2 + „Depth‟” was entered to yield the elevation of each hydroacoustic
point. The lake outline point files were then merged to the hydroacoustic events file creating an
“All Points” file using „Merge‟ Tool from ArcToolbox.
After the “All Points” file was created, the 3D Analyst extension was activated. The 3D
analyst tool bar was used to create triangular irregular networks (TIN) using 3D Analyst
Create/Modify TIN Create TIN from features. The dialog box parameters were set to:
Check “All points” file‟s box
Height source: Elevation
Triangulate as: mass points
Tag field value: <None>.
The output TIN was then converted to a DEM using 3D Analyst Convert TIN to Raster.
The dialog box parameters were set to:
Check the Input TIN
Attribute: Elevation
Z factor: 1
44
The DEM was then clipped to the polygon of the lake using the „Extract by mask‟ in
ArcToolbox.
Volume calculations were extracted from the lake DEMs using 3D Analyst via 3D
Analyst Surface Analysis Area and Volume. The area and volume statistics dialog box
parameters were set to:
Input surface was the lake DEM
Height of plane: was selected for every meter (i.e. 785.2, 784.2, 783.2 …)
Check the calculate statistics below plane
Z factor: 1
Surface area of the plane and the volume below the plane were recorded into an excel worksheet.
Finally, the volume for each meter strata was calculated by subtracting the volume below the
plane from the plane below it.
The DEMs were added to ArcScene and changed into 3D data sources by adding the
DEM layers right clicking the layer Properties click the Base Heights tab check
obtain heights for layer from surface. Then, right click on Scene Layers Scene properties
General tab Calculate from extent. This turned the 2D DEMs into 3D. I then created 2 m
contours by going to 3D Analyst Surface analysis Contours Contour interval: 2 m. Then
converted them to 3D layers by going to 3D Analyst Convert Features to 3D.
The process was also repeated using existing bathymetry data that was downloaded from
the Washington Department of Ecology‟s GIS website titled „Lake Bathymetry‟
(http://www.ecy.wa.gov/services/gis/data/data.htm). The “lakebath_arc” file was added to
ArcGIS. This file only contained data for North Twin, so the North Twin bathymetry was
selected and exported to create its own line shapefile. Following the process above the volume
was also calculated from the existing Washington Department of Ecology bathymetry layer.
45
Results
North Twin‟s volume was analyzed using three data sets; points from hydroacoustics data
in GIS, contour lines from an existing bathymetry file from the Washington Department of
Ecology in GIS, and a hypsographic curve created in excel (Moore, BC unpublished data). South
Twin Volumes were calculated using points from hydroacoustics in GIS and the hypsographic
curve in excel. There was no existing GIS bathymetry data for South Twin. In North Twin, we
found that there was a difference in the total volume of all three methods. However in the
volume below 6 m, which is the seasonal average thermocline, the two datasets that were
calculated using GIS were similar, and the hypsographic curve calculated a much higher volume.
The volume below 6 m greatly affects the amount of oxygen that managers put into North Twin
through the hypolimnetic oxygenation system. Prior to this work, we had been using the
hypsographic curves to determine the amount of oxygen needed in the hypolimnion North Twin
Lake. We believe that the hydroacoustic volume estimates are the most accurate because of the
amount of points that went into creating the DEMs.
46
North Twin Volume Calculations Method Total Volume (m
3) Volume below 6 m (m
3)
Hydroacoustics* 32,371,943
15,625,767
Existing
Bathymetry** 30,008,382
15,236,026
Hypsographic Curve 36,872,856
19,926,727
South Twin Volume Calculations Method Total Volume (m
3) Volume below 6 m (m
3)
Hydroacoustics 35,380,989
15,683,680
Hypsographic Curve 44,134,867
19,719,866
* Includes areas with aquatic vegetation, but not the channel
**Does not include areas with aquatic vegetation
A summary of volume calculations for hydroacoustic bathymetry using points in
GIS, existing bathymetry from WA Department of Ecology using contours
in GIS, and from a hypsographic curve (Moore, BC unpublished data).
47
Hydroacoustic Points in GIS
North Twin Lake Volume Calculation
Lake Depth (m) Surface Area of Plane (m2) Volume Below Plane (m
3) Volume per 1 m strata (m
3)
0 3,155,645.19 32,371,943.00 3,102,650.55
1 3,034,020.30 29,269,292.45 2,951,090.35
2 2,880,568.89 26,318,202.10 2,816,423.70
3 2,760,817.63 23,501,778.40 2,711,328.20
4 2,669,159.83 20,790,450.20 2,624,315.30
5 2,584,195.58 18,166,134.90 2,540,368.14
6 2,501,737.77 15,625,766.76 2,458,213.84
7 2,417,153.30 13,167,552.92 2,366,080.46
8 2,313,680.41 10,801,472.46 2,246,576.65
9 2,179,936.11 8,554,895.81 2,108,601.84
10 2,035,861.44 6,446,293.97 1,945,289.63
11 1,845,931.26 4,501,004.34 1,707,656.83
12 1,552,674.79 2,793,347.51 1,367,811.94
13 1,168,329.41 1,425,535.57 962,654.81
14 741,658.89 462,880.76 449,626.31
15 122,012.08 13,254.45 13,254.45
15.4
Total Volume 32,371,943.00 m
3
Surface Area 3,155,645.19 m
2
**Includes Aquatic vegetation but not channel
South Twin Lake Volume Calculations
Lake Depth (m) Surface Area of Plane (m2) Volume Below Plane (m
3) Volume per 1 m strata (m
3)
0 3,867,056.91 35,380,988.61 3,791,448.29
1 3,690,662.04 31,589,540.32 3,571,962.21
2 3,460,610.11 28,017,578.11 3,352,845.17
3 3,256,648.50 24,664,732.94 3,164,162.19
4 3,073,674.07 21,500,570.75 2,984,095.07
5 2,911,014.63 18,516,475.68 2,832,795.26
6 2,759,607.82 15,683,680.42 2,678,263.78
7 2,593,865.13 13,005,416.64 2,478,316.37
8 2,360,168.21 10,527,100.27 2,252,584.09
9 2,145,565.76 8,274,516.18 2,041,120.67
10 1,940,188.83 6,233,395.51 1,833,616.96
11 1,722,522.62 4,399,778.55 1,585,412.22
12 1,431,148.63 2,814,366.33 1,230,702.85
13 1,002,119.28 1,583,663.48 805,197.46
14 635,091.49 778,466.02 495,271.63
15 352,156.10 283,194.39 229,547.91
16 123,478.46 53,646.48 53,646.48
17
Total Volume 35,380,988.61 m
3
Surface Area 3,867,056.91 m
2
North and South Twin Lakes volume calculations using hydroacoustic points by 1 m strata.
48
Existing Lake Bathymetry Contour Lines from WA Dept of Ecology in GIS
North Twin Lake Volume Calculations
Lake Depth (m) Surface Area of Plane (m2) Volume Below Plane (m
3)
Volume per 1 m
strata (m3)
0 2,998,346.34 30,008,381.93 2,815,179.21
1 2,689,624.39 27,193,202.72 2,579,895.30
2 2,508,996.05 24,613,307.41 2,459,945.05
3 2,419,515.37 22,153,362.37 2,374,696.29
4 2,337,354.85 19,778,666.07 2,298,456.59
5 2,269,065.86 17,480,209.48 2,244,183.66
6 2,210,339.21 15,236,025.82 2,177,715.20
7 2,148,986.64 13,058,310.62 2,110,090.76
8 2,066,321.43 10,948,219.86 2,009,980.47
9 1,956,782.44 8,938,239.39 1,901,120.25
10 1,848,605.21 7,037,119.14 1,774,923.96
11 1,654,945.75 5,262,195.18 1,501,932.43
12 1,357,008.10 3,760,262.75 1,224,665.74
13 1,100,142.10 2,535,597.01 983,543.79
14 859,010.77 1,552,053.22 737,972.43
15 625,003.46 814,080.79 526,523.58
16 435,897.50 287,557.21 287,557.21
16.76
Total Volume 30,008,381.93 m
3
Surface Area 2,998,346.34 m
2
**Does not include aquatic vegetation or channel
North Twin Lake volume calculations using existing bathymetry contour lines by 1 m
strata.
49
y = -1.0884x6 + 10.673x5 + 934.36x4 - 19361x3 + 190710x2 - 4E+06x + 4E+07
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
35,000,000
40,000,000
45,000,000
50,000,000
0 5 10 15
Vo
lum
e (
m3
)
Depth (m)
North Twin Volume Hypsographic Curve
y = 136,749x2 - 4,955,149x + 44,527,796
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
35,000,000
40,000,000
45,000,000
50,000,000
0 5 10 15 20
Vo
lum
e B
elo
w D
ep
th (
m3
)
Depth (m)
South Twin Volume Hypsographic Curve
North and South Twin Lakes hypsographic curves used to calculate volume (Moore, BC
unpublished data).
50
Hypsographic Curve
North Twin Lake Volume Calculations
Lake Depth (m) Volume Below Plane (m3) Volume per 1 m strata (m
3)
0 36,872,855 700,562
1 36,172,292 3,549,119
2 32,623,173 3,352,047
3 29,271,126 3,213,203
4 26,057,923 3,109,976
5 22,947,946 3,021,219
6 19,926,727 2,928,030
7 16,998,697 2,814,535
8 14,184,161 2,668,675
9 11,515,486 2,482,986
10 9,032,500 2,255,385
11 6,777,114 1,989,954
12 4,787,159 1,697,719
13 3,089,440 1,397,441
14 1,691,998 1,116,395
15 575,603 575,603
Total Volume 36,872,855.69 m
3
South Twin Lake Volume Calculations
Lake Depth (m) Volume Below Plane (m3) Volume per 1 m strata (m
3)
0 44,134,867 4,425,471
1 39,709,396 4,544,902
2 35,164,494 4,271,404
3 30,893,090 3,997,906
4 26,895,184 3,724,408
5 23,170,776 3,450,910
6 19,719,866 3,177,412
7 16,542,454 2,903,914
8 13,638,540 2,630,416
9 11,008,124 2,356,918
10 8,651,206 2,083,420
11 6,567,786 1,809,922
12 4,757,864 1,536,424
13 3,221,440 1,262,926
14 1,958,514 989,428
15 969,086 715,930
16 253,156 253,156
17
Total Volume 44,134,867 m
3
North and South Twin Lakes volumes calculated by hypsographic curves by 1 m strata
(Moore, BC unpublished data).
51
North and South Twin Lakes bathymetry from hydroacoustic points with 1 m contour
intervals represented by lines.
52
North and South Twin Lakes profiles created from hydroacoustic points with 2 m
contour intervals represented by lines.
A 3D representation of North and South Twin Lakes profiles from hydroacoustic points
with 2 m contour intervals represented by lines.
APPENDIX B
Temperature, Dissolved Oxygen and Usable Habitat
Temperature and DO profiles with trout habitat ( temperature < 20 °C and DO > 5 mg/L) represented by
shaded the area for North Twin in May a.) 2008 and b.) 2009.
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
54
Temperature and DO profiles with trout habitat ( temperature < 20 °C and DO > 5 mg/L) represented by
shaded the area for North Twin in June a.) 2006, b.) 2007, c.) 2008, and d.) 2009.
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
c. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
d. Temperature DO55
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for North Twin in July a.) 2006, b.) 2007 c.) 2008 and d.) 2009.
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
c. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
d. Temperature DO
56
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for North Twin in August a.) 2006, b.) 2007, c.) 2008 and d.) 2009.
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
c. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
d. Temperature DO57
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for North Twin in September a.) 2006, b.) 2007, c.) 2008, and d.) 2009.
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
c. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
d. Temperature DO58
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for North Twin in October a.) 2008 and b.) 2009.
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0123456789
101112131415
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
59
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for South Twin in June a.) 2008 and b.) 2009.
0 5 10 15 20
0
1
2
3
4
5
67
8
9
10
11
1213
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0
1
2
3
4
56
7
8
9
1011
12
13
14
1516
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
60
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for South Twin in July a.) 2008 and b.) 2009.
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0.0 5.0 10.0 15.0 20.0
0
12
3
45
6
78
9
1011
12
1314
15
1617
0.0 5.0 10.0 15.0 20.0 25.0 30.0
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
61
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for South Twin in August a.) 2008 and b.) 2009.
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
62
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for South Twin in September a.) 2008 and b.) 2009.
0 5 10 15 20
0123456789
1011121314151617
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
63
Temperature and DO profiles with trout habitat (temperature < 20 °C and DO > 5 mg/L) represented by shaded
the area for South Twin in October a.) 2008 and b.) 2009.
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
a. Temperature DO
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0 5 10 15 20 25 30
Dissolved Oxygen (mg/L)
Dep
th (
m)
Temperature (°C)
b. Temperature DO
64