Some ecological relationships between the yellow perch, trout, and other fish in Thompson Lakes,
Montana
by John B Echo
A THESIS Submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree
of Master of Science in Fish and Wildlife Management
Montana State University
© Copyright by John B Echo (1954)
Abstract:
An investigation was made on the relationships between yellow perch and cutthroat trout in Thompson
Lakes, Montana, in the summers of 1952 and 1953. These lakes originally contained cutthroat trout and
were later planted with yellow perch. The spawning time of yellow perch was in early May, and for the
cutthroat trout in late May. The population of yellow perch was large and growth was very slow. While
the number of cutthroat trout was small, the growth rate for this species was about average. The food of
yellow perch was largely immature aquatic insects and plankton while that of cutthroat trout was
mostly mature aquatic insects and small perch. Yellow perch were commonly distributed along the lake
margins and concentrations of perch fry and adults were found in these areas in the spring. During this
same period the salmonid fishes were predominately in the deep water. Poisoning of the yellow perch
concentrations was very effective. Management suggestions are given.
O O coLj.1== Introduction TfilhIle many studies of the yellow perch (Perca flavescens Mitchill) have
been made, only a few concern the relationships between yellow perch and trout = Swynnerton and
Worthington (l9ko) examined the food of perch and trout in Haweswater (lifestmoreland) and found
little competition. Worthington (l9ii9) studied the fishes of hake Wendermere, a perch infested trout
lake, and concluded that a reduction, of perch would be beneficial to the trout fishery. Ho studies of
this kind are known in the United States. In western Montana there are many trout lakes which have
been contaminated by the introduction of yellow perch, Zn most cases the trout fishery has apparently
suffered from this introduction.
An Investigation on the ecological relationships of yellow perch, trout, and other fishes in the
Thompson Lakes, Lincoln County, Montana (Fig. l), was initiated in the summer of 1952. Work was
renewed in the spring of 1953, and continued through the following summer.
The three lakes selected represent perch infested trout lakes which are readily accessible to fishermen.
They are approximately 5>0 miles west of Kalispell, on U. S. Highway Ho. 2. These lakes are
connected by short channels and comprise the headwaters of the Thompson River. Their approximate
areas and depths ares Lake Area-acres Maximum depth-feet
Upper Thompson ' 375 5o
Middle Thompson 730 160
Lower Thompson 2ltO i5o 
O;iM i
SOME ECOLOGICAL RELATIONSHIPS BETWEEN THE YELLOW PERCH, 
TROUT, AND OTHER FISH IN THOMPSON LAKES, MONTANA
Z 1'1'
^  / , V
by
JOHN Bo ECHO
o
A THESIS
Submitted to the Graduate Faculty 
in
partial fulfillment of the requirements 
for the degree of
Master of Science in Fish and Wildlife Management
at
Montana State College
Approved
¥R
/" “ 7 - A
Head, Major Department
Chairman, Examining Committee
Dean, Graduate Division
Bozeman, Montana 
March, 195h
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Table of Contents
Abstract .......... ................ ..................
Introduction ........................ ................
Description of the area ......................
Species of fish present .......................
Acknowledgements .... ..........................
Life history ..........................................
Yellow perch spawning ..........................
Cutthroat trout spawning .... ................ .
Age and growth ................... ..............
Food relationships ............... ...................
Fish distribution .................................
An experiment to reduce the numbers of yellow perch 
Suggested management recommendations ..............
Page
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Literature cited a o o o o e o o o o o e o e o o o o o e o o o o o A o o e o o o e o o o o o o o o o a f t o o 19
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Abstract
An investigation was made on the relationships between yellow perch 
and cutthroat trout in Thompson Lakes5 Montana, in the summers of 195>2 
and 1933» These lakes originally contained cutthroat trout and were 
later planted with yellow perch. The spawning time of yellow perch was 
in early May,, and for the cutthroat trout in late May. The population 
of yellow perch was large and growth was very slow. Ihiie the number of 
cutthroat trout was small, the growth rate for this species was about 
average. The food of yellow perch was largely immature aquatic insects' 
and plankton while that of cutthroat trout was mostly mature aquatic 
insects and small perch. Yellow perch were commonly distributed along 
the lake margins and concentrations of perch fry and adults were found 
in these areas in the spring. During this same period the salmonid 
fishes were predominately in the deep water. Poisoning of the yellow 
perch concentrations was very effective. Management suggestions are 
given.
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Jntroduction ■
1Hhile many studies of the yellow perch (Perca flaveseens Mitchill) 
have 'been made=, .only a few concern the relationships between .yellow perch ■ 
and trout = Swynnertbn arid Worthington (19U6) examined the food of perch 
and trout in Haweswater (Mestmoreland) and' found little Competition. . 
Worthington (l9ir9l studied the fishes of lake Wendermere) a perch in­
fested trout lake, and concluded that a reduction, of perch, would be 
beneficial to the trout fishery. Ho studies of this kind are known in 
the United States. Jn western Montana there are .many trout lakes which 
have been contaminated by the introduction of yellow perch. Jn most 
cases the trout fishery has apparently suffered from this introduction. . 
An investigation on the ecological relationships of yellow perch, trout, 
and other fishes in the Thompson Lakes, Lincoln County, Montana (Fig.- I),
' was initiated in the summer of 1 9 E > 2 W o r k  was renewed in the spring of
195>3, and continued through the following summer.
The three lakes selected represent perch Infested trout lakes which 
are readily accessible to fishermen. They are approximately 50 miles 
west of Kalispell, on U„ S. Highway Mo. 2. These lakes are connected by 
short channels and comprise the headwaters of the Thompson Hiver. Their 
approximate areas and-depths ares
Lake • Area-acres Maximum depth-feet
Upper Thompson . ■ 375 50
Middle Thompson 730 . 160
■Lower Thompson .2h0 - 150 '
G
Introduction
IiZhile many studies of the yellow perch (Perca flavescens Mitchill) 
have been made, only a few concern the relationships between yellow perch 
and trout. Swynnerton and Worthington (l9ltO) examined the food of perch 
and trout in Haweswater (Iifestmoreland) and found little competition. 
Worthington (l9lt9) studied the fishes of Lake Wendermere, a perch in­
fested trout lake, and concluded that a reduction of perch would be 
beneficial to the trout fishery. No studies of this kind are known in 
the United States. In western Montana there are many trout lakes which 
have been contaminated by the introduction of yellow perch. In most 
cases the trout fishery has apparently suffered from this introduction.
An investigation on the ecological relationships of yellow perch, trout, 
and other fishes in the Thompson Lakes, Lincoln County, Montana (Fig. l), 
was initiated in the summer of 1952. Work was renewed in the spring of 
1953j and continued through the following summer.
The three lakes selected represent perch infested trout lakes which 
are readily accessible to fishermen. They are approximately 50 miles 
west of Kalispell, on U. S. Highway No. 2. These lakes are connected by 
short channels and comprise the headwaters of the Thompson River. Their
approximate areas and 
Lake
Upper Thompson 
Middle Thompson 
Lower Thompson
depths are:
Area-acres
375
730
2liO
Maximum depth-feet 
5o 
160 
i5o
Fig» I. Thompson Lakes, Lincoln County, Montana
Upper
Thompson
U. S. Highway No. 2
Davis Creek
Middle
Thompson
Boiling Springs
Creek
Lower
Thompson
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About 25 percent of the Lower and Middle Thompson Lakes and nearly 90 
percent of the Upper Thompson Lake is shoal. The maximum surface tem­
perature near the middle of Lower Thompson Lake was 75°F. (July 11,
1953). Lower and Middle Thompson Lakes were found thermally stratified 
in each year studied. Additional physical and chemical data are given 
in Table I.
The game fish (Montana designation) found in the Thompson Lakes 
weret kokanee (Oncorhynchus nerka), cutthroat trout (Salmo elarkii), 
rainbow trout (Salmo gairdnerii), eastern brook trout (Salvellnus fon- 
tinalis), dolly varden (Salvelinus malma), mountain whitefish (Pro- 
■ sopium williamsoni), and. Iargemouth bass (Micropterus salmoides). The 
most abundant of these was the mountain whitefish with kokanee second 
and cutthroat trout third. Yellow perch (Perea flavescens) was the most 
abundant non-game fish. Pumpldnseed sunfish (Lepomis gibbosus) and 
squawfish (Ptychocheilus oregonensis) were common while longnose sucker 
" (Catostomas catostomus) and Columbia large scale sucker (Catostomas 
macrocheilus) were abundant. The red-side shiner (Richardsonius bal- 
teatus) was scarce.
Acknowledgements
The writer is indebted to Dr. C. J. D. Brown who directed this study 
and assisted in the preparation of the manuscript. Mr. Frank Stefanich 
and Mr. Charles Phenicie gave valuable suggestions and assistance in the 
field. The Montana Department of Fish and Game provided much of the 
equipment. The project was financed by Federal Aid to Fish Restoration
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Table I 0 Physical and chemical data for Thompson Lakes in 1952 and 1953°
Date Depth
feet
Lower
Thompson
Lake
Middle
Thompson
Lake
Upper ’ 
Thompson 
Lake
6/16/52 .0 59.0 59.0 60:5 .
.15 59.0 59.0 60.5
36 . 12,0 I11.5 53.09/1/52 O 65.0 65.0 66=0
25 5%,5 58,0 62.0
Temperature °F. 35 5^.5 5^.o 5o.6
6/26/53 2 60=0 . 60.0
18 5Lo 59.5
30 13.5 W = O
9/1/53 2 6L.5 66.0
22 .63.5 65.0
35 ' U5°o k6;5
Methyl orange 9/V52 2 236 220 228
Alkalinity p,p.m. 7/21/53 2 230 232
pH ■ 9/V52 0 8.U 8.h 8.3
7/21/52 15 8.5 8.0 . . 8.5
35 3°5 I1=O 2.5
Dissolved . 9A/52 15 8.0 . 8=0 8.0
Oxygen p.p.m. 35 1.8 . &.3: 6.1
7/21/53. 35 3.6 • lt.2
9/1/53 35 2.0 3.5
6/16/52 28 23 17
Sedohi disc 9A/52 32 30' 23
. ft. ' 7/21/53 - ' 18 18.
- 9/1/53 2li 25
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Table I. Physical and chemical data for Thompson Lakes in 1952 and 1953.
Date Depth
feet
Lower
Thompson
Lake
Middle
Thompson
Lake
Upper
Thompson
Lake
Temperature 0F.
6/16/52
W52
6/26/53
9/1/53
0
15
36
0
25
35
2
18
30
2
22
35
59.0
59.0 
lt2.0
65.0 
5k.5 
1;5.5 
60.0 
5k.o 
k3o5 
6ko5 
63-5 
k5.o
59.0
59.0
kl.5
65.0 
58.0 
k5.o 
60.0 
59.5 
kk.o 
66.0 
65.0 
k6.5
60.5
60.5
k3.0
66.0
62.0
50.0
Methyl orange 
Alkalinity p.p.m.
9/h/$2
7/21/53
2
2
236
230
220
232
228
pH 9/V52 0 8.k 8.k 8.3
Dissolved 
Oxygen p.p.m.
7/21/52
9/V52
7/21/53
9/1/53
15
35
15
35
35
35
8.5
3.5 
8.0 
1.8
3.0
2.0
8.0
k.O
8.0
k.3
k.2
3.5
8,k
2.5
8.0
6.1
Secchi disc 
ft.
6/16/52
9A/52
7/21/53
9/1/53
28
32
18
2k
23
30
18
25
17
23
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ftinds under Dingle-Johnson Project Number F7R.
Life History
An attempt was made to determine the relationships of yellow perch 
and cutthroat trout at each stage of their life cycles. If yellow perch 
proved to be vulnerable to control at some life history stage then they 
might be reduced in favor of the trout„'
Yellow perch spawning
The first ripe males and nearly ripe females of yellow perch were 
caught near a known spawning area in Lower Thompson Lake in late April, 
1953« Specimens taken here on May 2 were all males. On May 5, several 
ribbons of eggs were found on the branches of a submerged pine tree in 
this area (surface water temp, 57° F-1« On May 6 , eggs were found to be 
common in the littoral zones of all three lakes. Clusters were observed 
from the surface to a depth of about five feet; usually near three feet. 
Yellow perch deposited their eggs on the following substrata in the 
Thompson Lakess conifers (Pirns ponderosa and Pseudotsuga taxifoila), 
birch (Betula fontinalis), bulrush (Scirpiis validus), and stonewort 
(Chara) , Ba the order named, the largest number of egg clusters was 
found on the submerged conifers and the smallest on Chara. A few eggs 
were seen directly on the bottom in areas without vegetation.
An experiment was conducted to determine whether female yellow 
perch showed preference in the type of substrata used. Two likely areas 
were selected in Lower Thompson Lake and three structures: an 8-foot fir
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tree, a 10-foot birch tree; withput Ieaves5 and a 2 by. 8 foot chicken wire 
grid w r e  placed in each=' These structures were located in a favorable 
spot near the bottom. Egg clusters were removed daily. The experiment 
continued from May 2 to May 29, and in this interval the conifers 
received 19 egg masses, the birches S5- and the chicken wire none.
Eggs containing well developed' embryos were first noticed on May 10, 
EFo new egg deposits were found after May 17,. and all eggs had hatched by 
May 29o EIewly hatched yellow perch were about 0.29-inch in total length, 
"When they reached a length of about 0 o6-inch they appeared near the sur­
face in schools of a few to several hundred. These schools appeared over 
the spawning areas (depth 3 to 6 feet) and moved in short spurts which 
gave a shimmer to the water. Schools of fry were first seen on June 12, 
1992, in Lower Thompson Late and on June 29, 195>3, in Middle Thompson. 
Lake, On July 6, 1992, a large school estimated to have an area of 20 
by 300 feet and containing many thousands of fry was observed over the 
shoal area in Lower Thompson Lake, What was believed to be this same 
school remained intact for three days. On July 23, 1953, an almost 
continuous band of yellow perch fry estimated to be approximately four 
feet wide and extending nearly a mile along the margin of Middle Thompson 
Lake was seen. On the following day this school had dispersed into the 
littoral vegetation.
Cutthroat.trout spawning
. A nearly ripe (13,2-inch) female cutthroat trout was caught in 
Lower Thompson Lake on April 16, 1993° Qn May 7, what was presumed to
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tree  ^ a 10"foot birch tree without leaves, and a 2 by 8 foot chicken wire 
grid were placed in each. These structures were located in a favorable 
spot near the bottom. Egg clusters were removed daily. The experiment 
continued from May 2 to May 29, and in this interval the conifers 
received 19 egg masses, the birches 2, and the chicken wire none.
Eggs containing well developed embryos were first noticed on May 10. 
No new egg deposits were found after May I7, and all eggs had hatched by 
May 29. Newly hatched yellow perch were about 0.25-inch in total length. 
When they reached a length of about 0.6-inch they appeared near the sur­
face in schools of a few to several hundred. These schools appeared over 
the spawning areas (depth 3 to 6 feet) and moved in short spurts which 
gave a shimmer to the water. Schools of fry were first seen on June 12, 
1952, in Lower Thompson Lake and on June 29, 1953, in Middle Thompson 
Lake. On July 6, 1952, a large school estimated to have an area of 20 
by 300 feet and containing many thousands of fry was observed over the 
shoal area in Lower Thompson Lake. VJhat was believed to be this same 
school remained intact for three days. On July 23, 1953, an almost 
continuous band of yellow perch fry estimated to be approximately four 
feet wide and extending nearly a mile along the margin of Middle Thompson
Lake was seen. On the following day this school had dispersed into the 
littoral vegetation.
Cutthroat trout spawning
A nearly ripe (13.2-inch) female cutthroat trout was caught in 
Lower Thompson Lake on April 16, 1953. On May ?, what was presumed to
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he a pair of -spawning enitl^oat trout .was observed ou a small' riffle :.
.
about three miles up Bavis Creek9 a tributary to M d d l e  Thompson lake. : 
One sas captured; a ripe male 13»? inches in total length* Gn JpriJ I? 
and 18. 11 cutthroat trout were seen in this area, M e y  were estimated 
to average about 13 inches ..in total length, ' In the previous year on 
July 29» a l^G-foot section of this area was censused by the electric 
shock method and lkO cutthroat trout averaging 3 ,8 inches in total 
length were taken, io other species were found, Brom May 21 to June Il9 
1953s 21 adult cutthroat trout were removed from a sucker, trap at the 
mouth of Boiling Springs Creek9 a tributary to lower Thompson lake.
Hiese were spent spanners and averaged approximately 13 inches in length.- 
Qn Mhy l 69 1953 s numerous fingerling trout were seen approximately one 
mile up Boiling Springs Creek and on June. I? and 189 about 2f> to 5C 
fingerling trout were observed in the vicinity of the sucker trap. They ■ 
disappeared from this area on June 19. Mo trout fry or ydung-of-the-year 
were found .in the lakes.
During May9 19539 schools, of approximately 20 to 70 suckers 9 either 
Catostomas maeroeheilus or G l catostomus gresius or both9 were seen in 
the spawning area used by the perch. Smaller schools of squawfish were 
here'also. Mo. aggressive behavior on the part of one species toward? 
another was observed. Suckers-were trapped in the tributary streams. be­
ginning -May" 20 9' '1953. The largest number was taken on June- S9 ^ after which 
their number, declined-.' Gravid;-squawfish were '.caught.: In' the lake'around? 
the stream mouths during ,this period M t  were.-.never'takenl-ln the traps.
O"Hs*
lb; apparent competition Ier apawiing sites betEgen the.;,^ l l o u  per eh s 
cutthroat trout or any of the. other fishes %as found in .Thompson Likes» 
T e H o w  perch, eggs x-aere distributed, very widely over the- entire shoal 
•areas-*." Cutthroat -trout .undoubtedly confine their spawning to suitable
areas of the tributary streams*
O'
- teliow perchg Scale samples from 1^ 0 yellow perch were taken during the 
study period. #ge was determined fey the usual method and calculations 
assumed a straight line relationship between the length of scale a M  that 
of fish (fable" 2-) „ fhe average calculated mean total lengths in inches 
for - the year classes I through ? were a la%  3»hj, !>«,6, 6»6» The
average total length of 960 yellow perch taken by hook and line was 6*2 
inches »• The grand average of 3200 fish captured by dll means (angling 5 
gill nets, poison) was 6.h Inches, and only one percent was over i :S  
Inches. -. There Is Httle • question that this population is slow growing 
and stunted. Carlander (l9$0), Hile (Ip&g), and Esehmeyer (1938), in
their studies of yellow perch, report few instances of such poor growth. '
. ■ ' '
Cutthroat trout s ,Scale samples from Chtfhroat treat ,caught fey
.. . /-• . ... • . . . .
trolling, in the Middle and, lower Thompson lakes during the summer of
1933 were analysed. Calculations 'assumed a straight line relationship 
feetween the. length of. scale' and that of fish (fable 3)= The average 
calculated mean-total lengths in inches for the year classes' I through 
.BT were#; 3*1, Ib.S-, 12.3.- Ihe largest ■ filh eaptmred'was 23.-7 inches 
in total length, ■ and the - average of ail cutthroat trout taken was 10.6
/
Ho apparent competition for spawning sites between the ,yellow perch, 
cutthroat trout or any of the other fishes was found in lhonpson Lakes. 
Yellow perch eggs were distributed very widely over the entire shoal 
areas. Cutthroat trout undoubtedly confine their spawning to suitable 
areas of the tributary streams.
Age and growth
Yellow Berchs Scale samples from 1 #  yellow perch were taken during the 
study period. Age was determined by the usual method and calculations 
assumed a straight line relationship between the length of scale and that 
of fish (Table 2). The average calculated mean total lengths in inches 
for the year classes I through V were.* 1.9, 3*1*, I*.!*, 2.6, 6.6. The 
average total length of 900 yellow perch taken by hook and line was 6.2 
inches. The grand average of 3200 fish captured by all means (angling, 
gill nets, poison) was 6.1* inches, and only one percent was over 7.2 
inches. There is little question that this population is slow growing 
and stunted. Carlander (1920), Hile (l9l*2), and Eschmeyer (1938), in 
their studies of yellow perch, report few instances of such poor growth. 
Cutthroat trout? Scale samples from hi cutthroat trout caught by 
trolling in the Middle and Lower Thompson Lakes during the summer of 
1953 were analyzed. Calculations assumed a straight line relationship 
between the length of scale and that of fish (Table 3). The average 
calculated mean total lengths in inches for the year classes I through 
IV were? 2.1, 7*8, 10.3, 12.2. The largest fish captured was 23.7 inches 
in total length, and the average of all cutthroat trout taken was 10,6
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Table 2 <, Summary of the mean total lengths and annual length increments 
in inches calculated from scales of yellow perch at lower 
Thompson Lake in 195>2 and 1953«
Age Number of fish
Calculated mean total lengths
I 2 3 ' h ' 5
I 35 1.8
U 30 ■ 2 .0 3.6,
H I 11 1.9 3«2 it-3
H 32 . . 1.8 3.2 h'.k 5.6
-V i|2 2;0 3.3 U«5. .. .5.6 '6.6
Average mean 
’length 1.9 3.U k*h 5.6 6.6
Increment 1.9 1.5 1.0 i.i 1.0
Table 3« Summary of the mean-total lengths and annual length increments 
in inches calculated from scales of cutthroat trout at Middle 
Thompson Lake in 1953«
Age Number of fish Calculated mean total lengths
I 2 3 Ii-
I 6 5.3
II 18 h'9 7.7
III 10 li.9 7.7 10.lt
'I? - 7 5.3 7.9 10.3 12.5
Average mean 
length 5.1 7.8 10 .3 ■12.5 „ .. .
Iherement ■ 5.1 2.7 2.5 2 .2__________
O
O-13-
inches. This growth is as good or better than that found for other lakes 
within the drainage, and slightly less than that reported by Calhoun •
(Ipliit) in Blue Lake, California.
Food relationships '
A total of 900 yellow perch stomachs was examined from specimens 
collected by hook and line in the areas of greatest adult concentration 
in Lower Thompson Lake. A sample of 50 fish was taken approximately 
every 10 days during the period from June'to September in 1952, and from 
May to September in 1953° Captured fish were immediately preserved in 
formalin and stomach analyses were made at a later time. The stomachs 
of 83. cutthroat trout were examined at the time of capture. Specimens 
were taken by trolling in the Middle and Lower Thompson Lakes during 
the summers of 1952 and 1953°
Only those food items ’occurring in more than one percent of the 
specimens were considered. Ninety percent o f  the yellow perch and 98. 
percent of the cutthroat trout had eaten some identifiable food organism. 
Small fish were eaten by 2 percent of the yellow perch and by I4O percent 
of the cutthroat trout. Yellow perch fry made up.99 percent of these 
while the remaining one percent consisted of sucker fry and unidentified 
fish. The maximum number of yellow perch fry found in the cutthroat 
trout stomachs was 21, with an average of 7«5° The smallest cutthroat 
trout containing these fry was 6 .5  inches in total length and the largest 
specimen examined contained three yellow p$rch and one sunfish all of 
which were over It inches in length.
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f
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inches . This growth is as good or better than that found for other lakes 
within the drainage, and slightly less than that reported by Calhoun 
(19I4I1) in Blue Lake, California.
Food relationships
A total of 900 yellow perch stomachs was examined from specimens 
collected by hook and line in the areas of greatest adult concentration 
in Lower Thompson Lake. A sample of $0 fish was taken approximately 
every 10 days during the period from June to September in 1952, and from 
May to September in 1953« Captured fish were immediately preserved in 
formalin and stomach analyses were made at a later time. The stomachs 
of 83. cutthroat trout were examined at the time of capture. Specimens 
mere taken by trolling in the Middle and Lower Thompson Lakes during 
the summers of 1952 and 1953«
Only those food items occurring in more than one percent of the 
specimens were considered. Ninety percent of the yellow perch and 98 
percent of the cutthroat trout had. eaten some identifiable food organism.
Small fish were eaten by 2 percent of the yellow perch and by ItO percent 
of the cutthroat trout. Yellow perch fry made up 99 percent of these 
while the remaining one percent consisted of sucker fry and unidentified 
fish. The maximum number of yellow perch fry found in the cutthroat 
trout stomachs was 21, with an average of 7«f>« The smallest cutthroat 
trout containing these fry was 6.5 inches in total length and the largest 
specimen examined contained three yellow perch and one sunfish all of 
which were over h inches in length.
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Jmmature aquatic insects were' present in 28 percent and adults in 
Il percent of the yellow perch stomachs. Cutthroat trout had immature 
aquatic insects in 2k percent and adults in IiJ percent of their stomachs. 
About one-half of the aquatic insects were dipterans. Damselflies were 
second in abundance and mayflies third. Yellow perch apparently showed 
preference for immature forms while the cutthroat trout ate more adults. 
Crustacea (Daphnia3 Leptodora3 and Gammarus} were found in 82 percent of 
the yellow perch stomachs and in 23 percent of the cutthroat trout.
Snails .appeared in only two percent of the yellow perch stomachs and in 
none of the cutthroat trout.
Moffett and Hunt (l9li3) reported that Perea flavescens showed a 
change in diet from plankton and insects to forage fish after reaching 
about five inches in length. Allen (1935) had previously recognized 
this for Perea fluviatilis. The yellow perch in Lower Thompson Lake 
showed no marked shift to a diet of fish as evidenced by the fact that 
only two percent had fish in their stomachs.
The stomach contents of mountain whitefish and kokanee was ex­
clusively plankton. Thirty suckers taken from tributary streams had 
empty stomachs while 25 specimens captured in the lake contained only 
detritus.
Fish Distribution
Graded experimental gill nets and trolling were used to determine 
fish distribution. Gill net sets pe're made in Lower Thompson Lake during 
the periods from June to August 1952., and from March to July 1953« These
f-Tfv-.!';-. ’ Iil 
■V- V, ' ' - J  .
were of 2l).-hours duration and were m a d e 'In' the following areas '('Tatild uIif •' 
26 sets in deep water (35> to 70 f e e t ) 22 on open shoals (5 to-'lO.feet)-> 
and 2k in weed beds (io to V? feet)„ Yellow perch were caught predomin­
ately in deep water in March and April= Beginning April 293 195)3, heavy 
catches were made in shoal and weed bed areas' in Bower Thompson Lake and 
continued throughout the.summer= Cutthroat trout were never taken by 
gill nets in deep water or on the open shoal areas. Three specimens 
were captured in the weed beds' in April.
Additional information on distribution was secured by 28 gill net 
sets' made over deep water. In this area surface catches of kokanee 
and cutthroat trout were common during May, and gradually declined -until 
June 10, when the last kokanee was caught. Trolling catches of kokanee 
and cutthroat trout also declined in June. Gill nets set from the sur­
face. to 30 feet failed to catch any of these fish during July and August.
An Experiment to Reduce the Uumbers'of Yellow Perch 
•Schools of yellow perch fry along the shoals were treated with 
poison•(Derris root or FishmTox) using a liquid solution and power pump 
or towing the sack of the dry powdered poison behind a boat. The towed 
sack method created too much disturbance to be effective and was dis- ■ 
continued. A tank of solution and'a power pump was carried by boat to 
a position out beyond (lakeward) a school of yellow perch fry. Poison 
was introduced slightly below the surface in a line parallel to the 
school of fry. When this barrier of poison was complete the entire 
area containing fry was sprayed. The minimum amount of poison necessary
were of 2it-hours duration and vtere made in the following areas (Table h) 
26 sets in deep water (35 to 70 feet), 22 on open shoals (5 to 10 feet), 
and 2h in weed beds (10 to 15 feet). Yellow perch were caught predomin­
ately in deep water in March and April. Beginning April 29, 1953, heavy 
catches were made in shoal and weed bed areas in Lower Thompson Lake and 
continued throughout the summer« Cutthroat trout were never taken by 
gill nets in deep water or on the open shoal areas. Three specimens 
were captured in the weed beds in April.
Additional information on distribution was secured by 28 gill net 
sets made over deep water. In this area surface catches of kokanee 
and cutthroat trout were common during May, and gradually declined until 
June 10, when the last kokanee was caught. Trolling catches of kokanee 
and cutthroat trout also declined in June. Gill nets set from the sur­
face to 30 ieet failed to catch any of these fish during July and August.
An Experiment to Reduce the Numbers of Yellovr Perch
Schools of yellow perch fry along the shoals were treated with 
poison (Derris root or Fish-Tox) using a liquid solution and power pump 
or towing the sack of the dry powdered poison behind a boat. The towed 
sack method created too much disturbance to be effective and was dis­
continued. A tank of solution and a power pump was carried by boat to 
a position out beyond (lakeward) a school of yellow perch fry. Poison 
was introduced slightly below the surface in a line parallel to the 
school of fry. When this barrier of poison was complete the entire 
area containing fry was sprayed. The minimum amount of poison necessary
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Table I;,, Summary of the catch of 72 gill net sets from Lower Thompson 
Lake during the summers of 19^2 and 1953 (Expressed as catch 
per gill net day for species and area).
Species Area Number of fish caught per gill net day
March-April May-June July-August
Deep
water 13 8 3
Yellow ' . 
perch
Tfeed 
beds 2 Ip U6 Il
Open 
shoals 3 8 19 6
Deep
water 0 0 0
Cutthroat 
• trout
feed
beds I 0 0
Open
shoals 0 0 0
Deep
water 7 8 8
Mountain 
tihitefish .
Weed
beds 2 7 3
Open
shoals . I- ' 0 3 ■
Deep
water 2 2 3
Suckers feed
beds - '6 7 I
Open
shoals 11 6 3
Deep water sets 35-70.feet. 
^ Weed bed sets 10-15 feet.'
3 Open shoal sets 5-10 feet.
O O
to get good results in Thompson Lakes was about 8 parts per million of 
Derris root (£ percent rotenone) or I4 parts per million, of Fish-Tox for 
the immediate areas treated. These high concentrations were necessary 
to maintain effective levels because of dilution by (Surrounding water. 
Fifty pounds of Fish-Tox or -100 pounds of .Derris root was sufficient to 
treat about 1000 feet of lake margin, .
Yellow perch fry usually showed distress within 1$ minutes. Al­
though some fish swam through the poison barrier out into clear water 
most of these died. Dead fry were seen as far as 5>00 feet from the 
toxic area. Practically all of the fry in the schools treated were 
destroyed,
A method was developed for poisoning schools of adult yellow perch. 
A concentrated solution of Derris root or Fish-Tox was taken by boat to 
the poison area. The boat was anchored and chum (chopped fish or ham- ■ 
burger) was distributed until a large number of yellow perch had accumu­
lated in the area. Poison was then gently poured into the water over 
the school of yellow perch. This solution was also poured into the 
wake of the boat as it slowly Oircled the yellow perch concentration.
Ten pounds of Derris root or £ pounds of Fish-fox was sufficient to"kill 
yellow perch' in a 100-foot circle over l3> feet of water. Approximately ■ 
one-half of the solution was used in the chum area and the other^ half to 
form a b airier.
The kill of fish in the treated areas was almost complete. Swingle 
(1953) evaluated partial poisoning on known populations of bluegills and
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-17-
r >
to get good results in Thompson Lakes was about 8 parts per million of 
Derris root (S percent rotenone) or I parts per million of Fish-Tox for 
the immediate areas treated. These high concentrations were necessary 
to maintain effective levels because of dilution by .surrounding water. 
Fifty pounds of Fish-Tox or 100 pounds of Derris root was sufficient to
treat about 1000 feet of lake margin*
Yellow perch fry usually showed distress within 1$ minutes. Al­
though some fish swam through the poison barrier out into clear water 
most of these died. Dead fry were seen as far as # 0  feet from the 
toxic area. Practically all of the fry in the schools treated.were
destroyed.
A method was developed for poisoning schools of adult yellow perch.
A concentrated solution of Derris root or Fish-Tox was taken by boat to 
the poison area. The boat was anchored and chum (chopped fish or ham­
burger) was distributed until a large number of yellow perch had accumu­
lated in the area. Poison was then gently poured into the water over 
the school of yellow perch. This solution was also poured into the 
wake of the boat as it slowly circled the yellow perch concentration.
Ten pounds of Derris root or £ pounds of Fish-Tox was sufficient to kill 
yellow perch in a 100-foot circle over 15 feet of water. Approximately 
one-half of the solution was used in the chum area and the other half to
form a barrier.
The kill of fish in the treated areas was almost complete. Svdngle 
(1953) evaluated partial poisoning on known populations of bluegills and
(D)
- 18-
largemouth bass in small ponds« He concluded that this was effective in 
eliminating fish of small or intermediate size-. It is believed that In­
tensive partial poisoning in Thompson Lakes would be effective in reduc­
ing the yellow perch population to more favorable numbers.
Suggested Management Recommendations 
■ Total poisoning of the entire Thompson Lake chain is not economical­
ly feasible. During the spring months yellow perch are concentrated on 
the shoal areas and kokanee and.cutthroat trout are in deep water. .Par­
tial poisoning along the lake margins and in the bays at this time should 
be very effective in reducing the yellow perch population. The aim of 
such a program should be to reduce the yellow perch population to a level 
where this species will show good growth and attain useful size. Such a 
reduction should also make conditions more favorable for an increase in 
the number of salmonids. A combination method of poisoning yellow perch 
fry and chumming and poisoning the larger perch is•recommended for Lower 
Thompson Lake. This should be initiated about June 20 and be continued 
.as long as concentrations of yellow perch are found. It is believed that 
with further study an effective method might be developed for the reduc­
tion of yellow perch by concentration and destruction of spawn. An age 
and growth study should be made at the end of the first year to check the 
effectiveness of this, program.
As soon as the treated areas in Lower Thompson Lake are non-toxic =, 
cutthroat trout fry at the rate of 300 or more per surface acre should be 
planted along the littoral zone.
I
O-19- '
Since the cutthroat trout are known'to feed rather extensively on 
yellow perch fry it is recommended that tjeavy plantings of this'species - 
7 inches or over in length - he made in Middle Thompson Lake* In order 
to prevent fish movement between M d d l e  and Lower Thompson Lake a screen 
harrier should be installed in the connecting channel.
A careful check should be made on all plantings in both lake's by 
creel census and gill netting.
fishermen should be encouraged to harvest yellow perch by furnishing 
them with all information available on effective fishing methods and 
perch distribution. Means should also be developed whereby' the. mountain 
Whitefish5 which is relatively abundant and very poorly utilized, can be 
harvested.
Literature Cited
Allen, K. R.
1935- The food and migration of the perch (Ferea f-Iuviatllis) in 
Mendermere. Jour. Animal Ecol., Vol. k (1935) 5 pp. 265-273- 
Calhoun, A. J. .
1955- Black-spotted trout in Blue Lake, California. Calif. Fish 
and Game, Vol. 30 (1955), pp. 22-52.
Carlander, K,. B .
1950'o Handbook of freshwater fisheries biology, tin. C, Brown Co., 
Dubuque, Iowa. 28l pp.
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I
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Since the cutthroat trout are known to feed rather extensively on 
yellow perch fry it is recommended that heavy plantings of this species - 
7 inches or over in length - he made in Middle Thompson Lake. Bi order 
to prevent fish movement between Middle and Lower Thompson Lake a screen 
barrier should be installed in the connecting channel.
A careful check should be made on all plantings in both lakes by
creel census and gill netting.
Fishermen should be encouraged to harvest yellow perch by furnishing 
them with all information available on effective fishing methods and 
perch distribution. Means should also be developed whereby the mountain 
whitefish, which is relatively abundant and very poorly utilized, can be
harvested.
Literature Cited
Allen, K. H •
!935. The food and migration of the perch (Perea fluviatilis) in 
Tfendermere. Jour. Animal Ecol., Vol. It (1935)> PP• 273»
Calhoun, A. Jo
19ltU. Black-spotted trout in Blue Lake, California. Calif. Fish 
and Game, Vol. 30 (l9Wi), PP• 22-12.
Carlander, K. D.
1950. Handbook of freshwater fisheries biology. Wn. C. Brom Co., 
Dubuque, lowa. 2 81 pp•
O O V
X
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\
1938c Further studies of perch populations« Pap, Mich. Acad, Sci., 
Arts, and Letters, Vol.- 23 (1937), pp. 611-630. - Xi
Hile, R., and F. ¥. Jobes
T-
\
19iil- Age and growth of the yellow perch, Perea flavescens
(Mitchill), in the Wisconsin waters of Green Bay and northern 
Lake Michigan. Pap. Mich6 Acad6 Sci., Arts, and Letters, Vol. 
27 (I9hl), pp. 2I4I-266.
Moffett, J. W-., and B. P 6 Hunt
19h3o Winter feeding habits of Bluegills, Lepomis maeroehirus
(Rafinesque), and yellow perch, Perea•flavescens (MitchiXl), in •
Swynnerton, G 6 H., and E. B. Worthington
19liO. Note on the food of fish in Haweswater (Westmoreland). Jour. 
Animal Ecol.,Vol6 9 (19U0.), pp. 183-187.
Worthington, E. B.
19l(.9. An experiment with populations of fish in Wendermere, 1939= 
U8 . Proc6 Zool6 Soc6 Lond6, Vol6 120 (I9ii9), pp. 113“lh9.
Cedar Lake, Washtenaw County, Michigan. Trans. Am. Fish. Soc., 
Volo 73 (I9'h3), PPo 231-2&2.
Swingle, H,. S., E. E. Prather, and J. M 6 Lawrence
1933. Partial poisoning of overcrowded fish populations. Agr.
Experiment Sta. Ala. Polytechnic Ihst. Circular No. 113. 15, pp.