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

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90

100

Per

cen

t o

f L

ak

e V

olu

me

Su

ita

ble

fo

r T

rou

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

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June 24 July 22 July 31 Aug. 12 Aug. 30 Sept. 13 Oct. 21

Per

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2008

a.

85

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49

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10

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90

100

Per

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olu

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Su

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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

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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

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m)

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Percent of Observations Average Temperaturea.

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0 10 20 30 40 50 60 70

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0 10 20 30 40 50 60 70

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Dep

th (

m)

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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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Total # fish Caught Average Temperature

a.

0 10 20 30 40 50 60 70 80 90 100

0

1

2

3

4

5

6

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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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0 5 10 15 20 25 30

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Dep

th S

tra

ta (

m)

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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.

Summerfelt, R.C. and L.S. Smith. 1990. Anesthesia, surgery, and related techniques. In Schreck

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