A LIMNOLOGICAL SURVEY OF PAXSON AND SUMMIT LAKES
IN INTERIOR
ALASKAY
With Special Reference t o t h e Lake Trout and Lake Whitefish
.
George L Van Whye
and
James W . Peck
Alaska Department of Fish and Game
Division of Sport Fish
Fairbanks, Alaska
INTRODUCTION
A survey of Summit and Paxson Lakes w a s initiated by the Alaska
Department of Fish and Game, Sport Fish Division, in 1962. The objectives
of the survey were: (1) evaluate t h e potential lake trout (Salvelinus namaycush)
sport fishery, ( 2 ) determine the possibility of a commercial whitefish fishery,
(3) gather information on growth r a t e s and a g e of maturity for t h e s e fish in
Interior Alaska, and (4) provide limnologica 1 information for management of
t h e s e populations.
Lake trout and whitefish populations a r e found scattered throughout
Interior Alaska l a k e s . The importance of t h e Lake trout a s a trophy sport fish
has become very evident in the past five y e a r s while t h e economic value of
t h e whitefish has not a s y e t been determined.
Little prior information of t h e s e f i s h e s is available for t h i s region.
Additional data on the life history of the round whitefish (Prosopium cylindraceum)
w a s collected in conjunction with, but not presented in t h i s study and w a s
reported in t h e form of a t h e s i s written a s partial fulfillment of t h e require-
1/ This work w a s carried out under Dingle-Johnson Federal Aid t o Fish Restoration,
Project No. F-5-R-3 Job B between the d a t e s of June 1 , 1962 and May 1 , 19 64.
ments for a Master of Science Degree from the University of ~ i c h i ~ a & / .
LOCATION AND DESCRIPTION OF THE STUDY AREA
Paxson and Summit Lakes lie a t the head of the Gulkana River in t h e
Copper River Basin. This b a s i n i s located in southcentral Alaska a t approximately i a t i t u d e 63O N and longitude 145' W , between the 2,600 and 3,300
foot e l e v a t i o n s , and drains into the Gulf of Alaska, Figure 1 .
Historically, both Paxson and Summit Lakes were formed a s a result of
Pleistocene glaciation. Glaciers in t h e Chugach Mountains dammed t h e Copper
River forming a large l a k e within the Copper River Basin. The present l a k e s
and river valleys were carved out of deposited sediment after retreat of t h e
i c e and drainage of t h e Copper River Basin. Between the river v a l l e y s , muskeg
and marshes occupy depressions in t h e poorly drained, permanently frozen old
l a k e floor. The s o i l type surrounding both lakes i s glacial moraine. The rock
type is sedimentary in origin which, in many c a s e s , h a s become metamorphosed.
Paxson and Summit Lakes drain a n area of approximately 3 ,000 square miles in
the southern foothills of the Alaska Range. Tributaries a r e short, clearwater
streams. Summit Lake i s drained by the Gulkana River which flows into Paxson
Lake 15 miles downstream.
LIMNOLOGY OF THE LAKES
Physical Characteristics
Morphometry of Paxson Lake. Paxson Lake has a surface area of 6 . 0 8
square miles, i s 1 0 . 3 miles long, and has a maximum width of 0 . 9 miles. The
maximum depth i s 89 f e e t , and the mean depth is 35 f e e t .
Paxson Lake exhibits a regular basin type bottom (Figure 2). The total
a r e a between shore and the outer extreme of the 40-foot depth zone i s 3 . 6 8
square miles or 60 percent of t h e total surface a r e a . The greater part of the
shoal area l i e s in the southern portion 01 t h e l a k e toward t h e outlet.
2/ Peck, James W. A comparative study of the growth of t h e round whitefish,
Prosopium cylindraceum, in the Copper River Drainage, Alaska . 53 pages.
F I G U R E 1.
PORTION O F STATE OF ALASKA SHOWING STUDY AREA.
Figure 2 . Paxson L a k e contour map. Roman numerals indicate
sampling s t a t i o n s .
The shore line of Paxson Lake i s quite regular and c o n s i s t s of sedimentary rocks which, in many c a s e s , have become metamorphosed. The
substrate above 20 feet i s composed principally of sedimentary rocks t o 2
inches in diameter, interspersed with sand and some organic debris. Below
2 0 f e e t , the substrate i s chiefly c l a y with traces of organic debris.
Morphometry of Summit Lake. Summit Lake h a s a s u r f a c e area of 6.38
square miles, i s 7 . 1 miles Long, and h a s a nlaximum width of 1.1 miles. The
maximum depth i s 214 feet and the mean depth i s 70 f e e t .
Summit Lake has both a n irregular shoreline and very irregular bottom
a s shown in Figure 3. The total area between shore and t h e outer extreme of
t h e 40-foot depth zone is 3.50 square miles or 55 percent of the total surface
a r e a . The greater part of the shoal a r e a s a r e in the southern portion of the
l a k e . Diversion of glacial streams in 1 9 2 9 , fed by the Gulkana glacier out
of Gunn Creek, resulted in a clearing of the l a k e waters.
The drainage basin has a typical a r c t i c continental weather regime
with mild t o warm summers and s e v e r e winters. The mean maximum temperature
is 3 7.3O F , and the mean minimum i s 1 6 . SO F The mean a r p u a 1 temperature i s
27.2' F. Ice i s usually present on both l a k e s from early November until early
June and may obtain a thickness of 36 inches ( U . S Weather Bureau records).
Mean annual precipitation i s 11 . 7 inches and the mean annual snowfall i s 48.6
i n c h e s . Seasonal variation in the amount of daylight varies from 20 hours in
June to l e s s than 5 hours in December, giving a general frost-free period of
about 67 d a y s . Paxson Lake, which i s below tfee l i n e , p o s s e s s e s a brushy
t o wooded shoreline with alder and willow being the dominant brush forms and
spruce and a s p e n being the dominant tree forms.
.
.
Summit dake is above t h e tree l i n e , which for t h i s area i s about the
3 ,000-foot elevation. The shoreline vegetation is restricted t o willow and
a lder brush with tundra-type ground cover. Part of the e a s t shore i s formed
by t h e Richardson Highway road bed and l a c k s vegetation entirely.
Most of the exposed shoreline i s composed of racks ranging in s i z e
from 2 inches t o 2 feet in diameter. The substrate above 20 f e e t i s chiefly
composed of large1 rubble. Some sand and rocks t o 2 inches in diameter a r e
present. Organic material i s present in only small quantities in the very shallow
waters of t h e north and s o u t h e a s t e n d s . Generally, the substrate below 20 feet
i s rock or c l a y deposited by glacial outwash.
A s shown in Table I,, Summit and Paxson Lakes a r e very similar, t h e
Figure 3 . Summit Lake contour map. Roman numerals indicate sampling stations.
TABLE 1.
LAXE MORPHOMETRY DATA, PAXSON AND SUMMIT LAKES.
P a x s o n Lake
Summit Lake
Elevation
2,600 f t ,
3,300 f t .
Area
6 . 0 8 sq. m i .
6.38 sq.mi.
M a x i m u m width
0.9 mi.
1.1 m i .
Maximum l e n g t k
10.3 m i .
7.1 m i .
Maximum d e p t h
89 f t .
214 f t .
Mean d e p t h
35 f t .
70 f t .
P e r c e n t bottom area l e s s t h a n :
20 f t . d e p t h
3 2%
40 f t . d e p t h
5 5%
60 f t . depth
64%
80 f t . depth
8 5%
100 f t . d e p t h
9 1%
120 f t . d e p t h
9 4%
140 f t . d e p t h
9 7%
160 f t . d e p t h
98%
180 f t . d e p t h
99%
200 f t . d e p t h
99%
main differences being in total volume of water and depths, Summit Lake
being t h e greater of t h e two. Summit Lake h a s a mean depth of twice that
01 Paxson Lake, but the percent of shoal a r e a s i s practically the same.
.
Temperature - Paxson Lake Two temperature s t a t i o n s were maintained
in 1963. Data were collected s i x times between June 30 and August 9 , 1 9 6 3 .
Temperature profiles a r e shown in Figures 4 and 5 . The data indicated that
this l a k e does not distinctly stratify during t h e summer months. However, on
July 4, a distinguishable thermocline w a s present a t Station 11, but not a t
Station I. This thermocline disappeared three d a y s later and may reflect a
temporary abatement of prevailing winds. The a b s e n c e of stratification a t
Station I on July 4 may be due t o the proximity of t h i s station t o the Gulkana
River inlet. Warmer temperatures penetrated t o greater depths later in t h e
s ummer .
,
Paxson Lake, due t o i t s location, s h a p e and orientation t o prevailing
w i n d s , is subject t o continual turnover during i t s ice-free period. Based on
o b s e d a t i o n s by local r e s i d e n t s , ice forms about the first of November and
t h e break-up occurs during the first or second week of June. In 1962, freezeup occurred between November 4 and 9 . The d a t e of freeze-up in 1963 i s not
known.
Temperature - Summit Lake. Two temperature stations were maintained
in 1963. Data were collected five times between July 2 and August 1 3 . Temperature profiles a r e shown in Figures 6 and 7. Data collected on July 2
immediately following spring break-up implied the presence of inverse stratification. The data a r e insufficient t o be conclusive and no winter temperature
data were collected t o support t h i s implication. However, it is quite probable,
based on studies of l a k e s a t t h i s and other latitudes with similar climatic
conditions, that both Paxson and Summit Lakes experience some degree of
inverse stratification during their periods of i c e cover. A weak thermocline
w a s evident on July 9 a t Station 11. This thermocline disappeared prior t o July 2 1 .
Prevailing winds blow along the long a x i s of Summit Lake. Although i t s
fetch i s l e s s than that of Paxson Lake, Summit Lake is located above the tree
line and i s more exposed; therefore, it should experience vertical mixing of a t
l e a s t the magnitude found in Paxson Lake.
Transparency. Light penetration w a s measured with the standard Secchi
d i s c and w a s made in conjunction with plankton sampling. Readings in Paxson
F I G U R E 4.
WATER TEMPERATURES I N PAXSON LAKE, 1963
Station I
T e m p e r a t u r e (OF)
FIGURE 5.
WATER 'IEMPERATURES I N PAXSON LAKE, 1963
Station I1
Temperature
3 50
400
450
(OF)
500
550
0
10
20
-
30
C,
w
V
C
C,
2 40
R
50
. ..-
- - - -6/30/63
60
7/4/63
7/20/63
70
80
.......8/9/63
FIGURE 6.
WATER TEMPERATURES I N SUMMIT LAKE, 1963
Station 1
30°
Temperature (OF)
40°
45O
55O
FIGURE 7.
WATER TEMPERATURES IN SUMMIT LAKE, 1963
Station IT
Temperature
(OF)
Lake ranged from 1 0 t o 1 4 f e e t . Summit Lake w a s more variable, with readings
ranging from 5 t o 18 f e e t . Decreased transparency resulted from turbidity
fluctuations, a s no correlation w a s observed between Secchi d i s c values and
the quantity of plankton c o l i e c t e d . The highest turbidity in Summit Lake w a s
observed following a period of high winds which could have produced sufficient
mixing t o bring up the fine bottom sediments. In addition, Gunn Creek, the
principal inlet, brings variable amounts of melt water from Gulkana Glacier
into Summit Lake.
Chemical Characteristics
To obtain a quantitative chemical a n a l y s i s of Paxson and Summit Lake
w a t e r s , samples were s e n t t o t h e University of Alaska for a n a l y s i s . Samples
were collected a t t h e five-foot depth in the center of both lakes on October 2 3 ,
1963 and a t that time, it was believed both lakes had experienced complete
mixing. Therefore, t h e data a s shown in Table 2 should be representative of
t h e entire lake
.
The chemical characteristics indicated that both l a k e s a r e soft water
lakes; both experiencing slow buffering. The lack of sufficient carbonate in
Paxson Lake is the probable c a u s e of the high C 0 2 content which may have been
a temporary condition due t o the f a c t that the pH was alkaline. Both Lakes
exhibited the high bicarbonate content which i s characteristic of soft water
Lakes.
Biological Characteris t i c s
Plankton. Table 3 presents t h e results of plankton sampling conducted
in both Paxson and Summit Lakes during the summer of 1 9 6 3 . Plankton w a s
collected in 40-foot vertical h a u l s , using a Wisconsin type plankton net with
Number 25 s i l k boiting cloth mesh. Plankton coliections were made in conjunction
with temperature data collections in both l a k e s . The specific location of sampling
stations a r e noted in Figures 2 and 3 . The mean settled volume of plankton per
samples from Paxson Lake w a s twice that of t h o s e examined from Summit Lake.
Two types of phytopiankton, Ceratium and Dinobryon, were found in
Paxson Lake, but not in Summit Lake. The zooplankter Polyarthra was poorly
represented in the Paxson Lake s a n ~ p l e sand w a s not found in samples from
Summit Lake. It w a s observed that each organism present in both l a k e s w a s
represented by a larger number of individuals in Paxson Lake.
TABLE 2.
WATER A N A L Y S I S OF PAXSON AND SUMMIT LAKES, O G M B E R ,
Summit
--Pa%son
02
9.4 ppm
8.1 p p m
C02
0.0 ppm
5.5
pH-th a l k a l i n i t y
9 . 0 ppm
0 . 0 pprn
M.O.
50.0 pprn
6 4 . 0 pprn
Total alkalinity
59.0 pprn
6 4 . 8 pprn
pprn
PH
7.8
7.4
ME4 N i t r o g e n
0.07 pprn
0 . 0 7 pprn
NO2 -t- NOj N i t r o g e n
0.00 pprn
0.02 pprn
PO4
0.12 ppm
0.10 pprn
0 - 0 0 pprn
0.46 pprn
SO4
3.00 ppm
0 . 0 9 ppm
Tannin
0.10 ppm
0 . 0 0 ppm
Turbidity
0.00 ppm
2.00 ppm
I
1963
TABU 3 .
P A X S O N
Dsite
----
Station
7/20
7/20
ITI
I1
-
TOTAL
PLANKTON SAMPLE ANALYSIS, PAXSON AND SUMMIT LAKES,
L A K E
Mean S e t t l e d
Volume ( c c )
0.95
0.73
4.89
Most a b u n d a n t f o r m s .
-
S U M M I T
Forms P r e s e n t
Phytoplankton
~sterionelg*
Ulothr ix*
Coe l o s p h a e r i u m
Microcystis
Ceratium
Dinobryon
Aphanizomenon
Anabaena
Zooplanktoq
Copepoda*
Nauplius larvae*
Polyart h r a
Kellicottia
Keratella
1 Each s a m p l e b a s e d o n two, 4 0 - f o o t v e r t i c a l h a u l s .
*
1963~
Date
7/8
7
-- / 2 1
7/21.
7129
7/29
8/13
8/13
Mean S e t t l e d
Volume ( c c )
--
Station
L A K E
I1
0.40
0.20
0.15
0 . 45
0.70
0.17
0.35
TOTAL
2.42
V
I1
V
V
I1
V
-
Forms P r e s e n t
7
-
Phytoplankton
Aster ionella*
U l o t h r ix*
Microcys t i s *
Coelosphaerium
Anabaena
A c t i n a s trum
Zooplankton
Keratella
Kellicottia
Copepoda*
Nauplius l a r v a e
Benthic Fauna. A total of 40 bottom samples w a s taken in the two
lakes using a n Ekman dredge 22.8 cm by 22.8 cm in c r o s s section. Samples
were obtained from various depths in the north, e a s t , and w e s t portions of
Summit Lake and the north, south, and e a s t portions of Paxson Lake. Table 4
and 5 present results of the dredgings in t h e two l a k e s .
Chironomidae larvae were the most abundant forms in both l a k e s . In
Summit Lake, Trichoptera and a clam, Pisidium s p . , were a l s o abundant. In
Paxson Lake, other abundant: forms were various oligochaetes, t h e gastropod
Gyralus s p . , and Pisidium sp.
Compared t o Summit Lake, t h e benthic fauna of Paxson Lake was richer
in numbers and types of organisms. The only exception w a s the relative abundance of Trichoptera in Summit Lake. The greater abundance of oligochaeta and
the presence of hirudinea and amphipods in Paxson Lake reflected t h e more
organic nature of i t s substrate, a s opposed t o the fine c l a y in Summit Lake.
Although not confirmed by measurement, individual organisms were
observed t o be larger Fn Paxson Lake than in Summit Lake. This difference
in s i z e w a s b e s t illustrated by the mollusks where s h e l l s of Paxson Lake
mollusks were heavier than those in Summit, indicating a greater supply of
carbonates .
Except for Chironomidae larvae In Paxson Lake, the majority of organisms
occurred a t depths of 20 feet or l e s s . Chironomidae iarvae in Paxson Lake were
most abundant a t 60 f e e t , while maximum abundance in Summit Lake occurred a t
1 0 f e e t . In both temperature and substrate type, the sixty-foot depth in Paxson
Lake w a s similar t o the ten-foot depth in Summit Lake.
Rooted Aquatic Vegetation. Potamogeton i s the major plant type in both
l a k e s , being represented by a number of different s p e c i e s . Rooted aquatic
plants a r e very s c a r c e in Summit Lake and a r e restricted to the north and southe a s t shoal a r e a s . Rooted vegetation i s s o s p a r s e in Summit Lake that it should
have almost no affect on the environment.
Paxson Lake has abundant aquatic vegetation on every shoal except
t h o s e which a r e subjected t o severe wave action. Potamogeton and Myriophyllum
a r e the most abundant forms, providing a distinct habitat t y p e .
Although no measurements of piant growth were made, eariy summer
growth w a s extremely slow. Apparent1 y a temperature threshold was reached
in l a t e summer after w h i c h plant growth proceeded rapidly. Accelerated growth
TABLE 5 .
BOTTOM FAUNA, SUMMIT LAKE, AUGUST 1963
G I V I N G ORGANISM T Y P E AND AVERAGED FREQUENCY O F OCCURRENCE
A v e r a g e N u m b e r of O r g a n i s m s P e r S q u a r e M e t e r
Dert h
( f t .)
2-5
TOTALS
Chironomidae
Diptera
41
3 adult
20
3
--
5 pupae
125
45
--
30 pupae
170
--
--
2 0 pupae
LOO
81
58
505
---
3
648
PERCENT
Oligochaeta
---
L m n e
.
G y r a l u s 2. P i s i d i um -s*.
3
33
106
--
--
---
140
93
138
323
2046
--
--
41.4
Trichoptera
4.0
2.8
24.7
Total
Per
Depth
4.5
6.7
15.8
w a s observed during the l a s t week in July, 1963. At that time, water temperatures in the shaal a r e a s ranged f r o m 48.5O t o 52.5' F .
Fish
Sampling Methods. Fish populations were sampled by variable mesh
gill n e t s and by bag s e i n e . The variable mesh gill n e t s were 1 2 5 feet long and
6 f e e t d e e p , consisting of 5 panels 25 feet in length, with mesh s i z e varying
from 1 t o 3 . 5 inches stretch measure.
In a n efIort t o reduce sampling b i a s , net s e t s were made along the
shorelines a t predetermined locations with the small mesh toward shore. A s
a result of differences in bottom contour, t h e Larger mesh sampled a t various
depths. The bag s e i n e w a s 50 feet long and 6 feet d e e p with one-half inch
bar mesh. Sampling w a s done throughout the s e a s o n t o c o l l e c t the young-ofthe-year f i s h .
Because sampling w a s intensive, 7 8 7 hours in Paxson Lake and 6 7 7
hours in Summit Lake, it was doubtful that any s p e c i e s in the two lakes were
not represented in the c a t c h .
Relative Abundance. Red salmon (Oncorhynchus nerka) spawn in the
e a s t fork of t h e Gulkana River and in tributaries above and below Paxson Lake.
There i s a l s o limited red salmon spawning in Gunn Creek, the inlet: of Summit
Lake. Adult salmon first appear in t h e two lakes soon after t h e i c e cover
d i s a p p e a r s . In 19 62, spawning continued into October. Adult red salmon
were taken incidentally in the variable mesh gill net c a t c h e s and were much
more numerous in Paxson Lake than in Summit Lake.
Both Paxson and Summit Lakes have a year-round population of juvenile
red salmon. These fish were abundant and comprised t h e majority of the bag
s e i n e c a t c h e s during August and September. Apparently most of the salmon fry
were too small t o be captured in t h e s e i n e until August.
The slimy sculpin (Cottus cognatus) w a s found t o be equally numerous
in both l a k e s . Although it was larger and darker in Paxson Lake, none longer
than 1 0 0 mm were observed in either lake. This s p e c i e s inhabits shallow waters
and was readily captured with the bag s e i n e .
A single long-nosed sucker (Catostomus catostomus) w a s captured in
Paxson Lake. The resident population 01 this s p e c i e s w a s very s p a r s e .
.
Both l a k e s have small populations of burbot (Lota
-lota) Only small
individua 1s were t a k e n , a s the gear w a s unsuitable for taking t h e larger individuals.
A few grayling (Thymallus arcticus) were taken from t h e shallower waters
of both l a k e s . In Paxson Lake, the catch w a s restricted t o the-south end and
near the outlet. In Summit Lake, the c a t c h w a s more widespread.
The lake whitefish (Coregonus clupeaformis) was not found in Summit
Lake, but w a s abundant in Paxson Lake. The rapid fall of the Gulkana River
between t h e two takes may be a factor preventing t h e e a s y entry of lake whitef i s h into Summit Lake. The young-of-the- lake whitefish were taken in the bag
s e i n e only during the early part of July. Later that month they completely d i s appeared from the c a t c h . This disappearance was apparently due t o a migration
t o deeper water and may be correlated t o a r i s e in surface water temperature.
Larger individuals were taken throughout the summer in gill n e t s . Thls s p e c i e s
is taken occasionally on hook and line and supports a small, Local, s u b s i s t e n c e
net fishery during the l a t e fall and early winter.
The round whitefish (Prosopium cylindraceum) was found in both l a k e s .
Young of the round whitefish were taken by bag s e i n e throughout the summer
with the largest c a t c h e s being made a t night. Individuals of a g e 4 or older
were taken in gill n e t s throughout the summer. This s p e c i e s i s a l s o taken
occasionally by hook and l i n e , and supports a small, l o c a l , s u b s i s t e n c e net
fishery when they move into the streams in the l a t e fall to spawn.
The l a k e trout (Salvelinus namaycush) w a s present in both l a k e s . This
s p e c i e s supports a relatively intense fishery during the summer months. Paxson
Lake receives heavier fishing pressure due t o i t s good reputation and available
boat f a c i l i t i e s . No lake trout were taken by bag s e i n e .
Relative population data were collected for lake trout, two s p e c i e s of
whitefish, grayling, and burbot on a c a t c h per unit effort b a s i s . Table 6 and 7
indicate a summary of gill net sampling in both l a k e s . To reduce fouling of the
variable mesh gill n e t s by adult red salmon, no gill net sampling w a s conducted
in Summit Lake before August 2 0 , or in Paxson Lake before September 6 . B y
t h e s e d a t e s , adult red salmon were no longer present in the l a k e s in a n y appreciable numbers.
The data indicated that lake trout populations in t h e s e l a k e s constituted
a very simi!ar percentage of each l a k e ' s fish population. Catch per unit effort
for l a k e trout in Summit Lake was slightly greater than in Paxson Lake and a
greater catch per unit effort w a s achieved for grayling in Paxson Lake than in
TABLE 6 .
CATCH SUMMUXY
U n i t of g e a r :
-
PAXSON LAKE,
V a r i a b l e mesh g i l l n e t 1 2 5 ' x 6 '
Mesh:
1" - 3-1/2" s t r e t c h mesh
Total hours f i s h e d :
Total f i s h caught:
787
1,084
Total catch/unit e f f o r t :
Species
1.377
Number Taken C a t c h / U n i t E f f o r t S/o Comp.
Lake W h i t e f i s h
(Coreqonus c l u p e a f o r m i s )
5 27
Round FSnitef i s h
(Prosopium c y l i n d r a c e u m )
405
Lake T r o u t
( S a l v e l i n u s namaycush)
101
Grayling
( ~ h ~ m a l l uakr c t i c u s )
1962
45
Burbot
(-Lota l o t a )
One l o n g n o s e s u c k e r ( C a t o s tomus c a t o s t o m u s ) was t a k e n
on S e p t e m b e r 20, 1 9 6 2 , i n P a x s o n L a k e , b u t n o t i n t h e
above s e r i e s o f n e t s e t s .
Red s a l m o n (Oncorhynchus n e r k a ) a n d s l i m y s c u l p i n
( C o t t u s c o q n a t u s ) have been o m i t t e d from b o t h t h e
t a b l e and t h e c a t c h p e r u n i t e f f o r t c o m p u t a t i o n .
NOTE:
C a t c h p e r u n i t e f f o r t d e f i n e d a s number o f
f i s h t a k e n p e r hour o f f i s h i n g w i t h above
d e f i n e d u n i t of g e a r .
TABLE 7 .
CATCH SUMWU?Y
U n i t of g e a r :
-
SUMMIT LAKE,
1962
V a r i a h l e mesh g i l l n e t 1 2 5 ' x 6 '
Mesh:
1" - 3 - 1 / 2 " s t r e t c h mesh
T o t a l hours f i s h e d :
Total f i s h caught:
677.5
995
L .469
Total catch/unit effort:
Number Taken C a t c h / U n i t E f f o r t % Comp.
Species
Round W h i t e f i s h
(Prosopium cylindraceum)
880
Lake T r o u t
( S a l v e l i n u s namaycush)
106
Grayling
(Thymallus a r c t i c u s )
5
Burbot
(-Lota l o t a )
Red s a l m o n ( O n c o r h y n c h u s n e r k a ) and s l i m y s c u l p i n ( C o t t u s
c o q n a t u s ) have been o m i t t e d from b o t h t h e t a b l e and t h e
c a t c h per u n i t e f f o r t c o m p u t a t i o n .
NOTE:
C a t c h per u n i t e f f o r t d e f i n e d a s number
o f f i s h t a k e n per h o u r o f f i s h i n g w i t h
above d e f i n e d u n i t o f g e a r .
Summit Lake. The catch per unit effort of burbot was approximately the s a m e
for both l a k e s , hut sample s i z e s were too small t o afford meaningful camparisons.
The round whitefish population of Summit Lake w a s more than t w i c e A M
of Paxson Lake. This difference i s perhaps a result of competition in Paxson
Lake between the two s p e c i e s of whitefish for food, s p a c e , or other resources. ,
The round whitefish population of Summit Lake w a s approximateIy equal to both
s p e c i e s of whitefish in Paxson Lake.
ECOLOGY OF LAKE TROUT AND WHITEFISH
Age Determination
Methods. Age a n d growth determinations were completed on l a k e trout
and round whitefish from both Paxson and Summit Lakes, and lake whitefish
from ~ ' a x s o nLake.
All captured lake trout were used for a g e determinations. Sample s i z e s
totaled 106 specimens from Summit Lake and 101 specimens from Paxson Lake.
Due t o manpower and budgetary Limitations, it was decided t o limit the study
sample of l a k e whitefish to t h e first 150 specimens captured. Age determinations were completed on 597 round whitefish from Summit Lake and 412 from
Paxson Lake. Larger samples of round whitefish than l a k e whitefish.were used
a s data were a l s o being prepared for a Masters t h e s i s on t h e a g e and growth of
round whitefish. S c a l e s used in t h e growth a n a l y s i s were taken midway between
t h e Lateral line and t h e origin of t h e dorsal fin on the left s i d e of t h e body.
Plastic impressions of whitefish s c a l e s were made using a cold-press technique.
Plastic impressions of l a k e trout s c a l e s were made using both hot-press and
cold-press techniques. Optimum results were obtained using the cold-press
technique.
Four s c a l e s from e a c h f i s h were used a s a sample. Of t h e four, two
s c a l e s of uniform s h a p e and characteristics were chosen. Measurements were
made on both s c a l e s and t h e results were averaged.
A g e determinations were made on a Bausch a n d Lomb model 42-63-58
micro-projector. A 2 . 7 ~l e n s w a s used for the whitefish s c a l e s and a 12x l e n s
was used for t h e l a k e trout scales.
Growth whs calculated by the formuis
(Li/;,.)
Sn, where
Ln
=
fork length of fish a: ltk: yez:
bt
=
fork length of fish a t time cf c q t u r e
St
=
d i s t a n c e from s c a l e Ionus to posterior margin
S,
=
d i s t a n c e from s c a l e foci.1~t o n'h annulus.
9:
life
The u s e of this l:rect proportion formula i s justified hy the s t r a ~ ~ h t - t i n e
relationship which w a s found t o e x i s t between the avelage fork 1ang-i-hand
the average s c a l e radius for each a g e group. Some deviation from t h i s
relationship w a s observed in older a g e groups of l a k e trout, but this daviarlon
included only about 1 0 percent of the f i s h in the s a ~ o l e s .
Year C l a s s Composition. Figures 8 , 9 , ar,d ' .3 present
sulnl-~ary:)I
year c l a s s composition for l a k e trout and both speci?; of w h i t t . ~ i s h . The
selectivity of the gear i s illustrated by the l ~ w
£rec;~f
=,r,cy of t > z y s u n s e r a g e
groups of a l l s p e c i e s .
It is interesting that the frequency of rcund waitefish G i Age-class VI
w a s sharply reduced in both l a k e s (Figure C ) . Since the buik f:. t h e samples
w a s composed of individuals from a g e s IV-IX, gear selectivity can be disregareed.
Therefore, a g e cia ss VL may reflect a spawning year of unusually poor survival.
Growth in Length
The increment of yearly growth for lake trout in Sumniit snc: Pcxson
Lakes i s tabulated in Tables 8 and 9 . In acJdition, a comparison of l a k e troat
growth i s shown in Figure 11 As shown, growth was generally s L w s r in S u m ~ i t
Lake than in Paxson Lake. To a g e V, growth r a t e s were similar, thaugh s1igh:ly
slower in Summit Lake. During t h e s e y e a r s , the young l a k e trcut feed primariiy
on insects and mollusks. The small difference in growth, t o a q e V , m a y be
correlated with the more abundant invertebrate fauna in Pr7sson L a k e .
.
From a g e s V through IX, growth was much more rap i d In Ff3xson L a k e .
This difference in growth, after the lake trout have s!?ifted to a f ~ s hd i e t , is
p' ~ S a b l ycorrelaf2d t o the greater number of small f i s h in F , ~ x s a nLake. A s r~oi-l.!'i
~n t'?e food habits section presented l a t e r , red salmon fry were ut iil;7~3dcxferls:~e ! : ~
by Paxson Lake lake trout; while in Summit Lake, wb-.re red r;almon fly were m I c n
FIGURE 8 .
AGE C O M P O S I T I O N O F LAKE TROUT I N PFXSON AND SUlvlMIT LAKES,
AS CALCULATED FROM G I L L N E T T f N G
Aye group
1962,
FIGURE 9.
AGE COMPOSITIOI'J OF LIA-W WHITE&'ISII IPJ PAXSON,
AS CALCULATdD FROM GILL NET SAMPLING
A g e group
1962,
FIGURE 10.
AGE C O M P O S I T I O N O F RQUND WHITEFISH I N PAXSON AND SUMMIT
LAKES, 1 9 6 2 , AS CALCULATED FROM GILL N E T SAMPW
4
/ \
/
r"/
-
\,------------Su
mmit Lake
\
\
\
Paxson Lake
\
5
6
Age g r o u p
7
TABLE 8.
CALCULATED GROWTH I N F O R K LENGTH (crn.) O F L A K E TROUT
TAKEN FROM SUMMIT LAKE, 1962
AVERAGE LENGTH CALCULATED FROM EACH A G E GROUP A T END O F YEAR OF
LIFE
Number
0
f
Fish
1
Weighted
A v e r a g e 5.6
VII
VIII
XIV
TABLE 9.
CALCULATED GROWTH IN FORK LENGTH (cm.) O F LAKE TROUT TAKEN FROM PAXGON LAKE, 1962
AVEXAGE LENGTH CALCULATED FROM EACH AGE GROUP A T END O F YEAR O F LIFE
Number
of
Fish
I
Weighted
Average 6.Y
II
I11
IV
V
VI
VIJ
VI II
IX
8
a
XI1
XI I
12,2
18.0
23.6
29.0
36.3
42.9
49.3
51.1
59.4
63.5
73.7
78.0
F I G U R E 11.
-
GROWTH O F THE L4KE TROUT ( S a L v e l i n u s namaycush)
OF S U M M I T AND PAXSON LAKES BASED ON AVERAGE
CALCULATED FORK LENGTH F O R EACH AGE GROUP
A,ge g r o u p
- 30 -
less numerous, l a k e trout were forced t o feed on the slimy sculpin. Therefore, after a g e V , production a n d growth of lake trout in t h e s e two l a k e s may
well b e keyed t o the continued availability of red salmon fry. Beyond a g e X
t h e number of f i s h from both l a k e s representing each a g e group w a s 'ioo small
t o be of a n y u s e in depicting a n accurate increment of growth. Growth of the
l a k e trout in Summit Lake may a l s o have been retarded somewhat by low water
temperatures .
Comparing the growth of f i s h in t h e s e two l a k e s with other l a k e s
Generally, growth w a s slower
involves c ~ n s i d e r a t i o nof many variables
in Paxson and Summit Lakes than in l a k e s of lower latitudes. Growth comparison for Iarge Alaskan l a k e s a r e frequently made with Great Slave Lake
and Great Bear Lake in C a n a d a , although t h e s e l a k e s a r e extremely large.
.
Great Slave Lake , located between latitude 61' and 63' north and
longitudes 109O t o 117' e a s t , contains 20,500 square miles of surface and
h a s a northern continental climate with a mean annual temperature of approxirna&ly 23O F. (Rawson, 1950). This temperature i s slightly below the 27.2O
annual mean temperature in the Locality of Summit and Paxson Lak,0 a r e a s .
Kennedy (1954) investigated population dynamics of l a k e trout in G e a t Slave
Lake a n d reported a growth rate that w a s intermediate between that of Paxson
a n d Snmmit Lakes.
Miller and Kennedy (1943) a l s o investigated the l a k e trout in Great
Bear Lake, a v a s t lake of 11,800 square mires located a t latitude 64O - 67O
north and longitude l l g O - 123' w e s t . This l a k e is subjected t o severe
climatic conditions with ice floes on the l a k e until l a t e July. In Great Bear
Lake, the l a k e trout growth reporLed by Miller and Kennedy (1948) was
exceedingly slow when compared t o Summit or Paxson Lakes. Age group XV,
from Great Bear Lake, compared favorably with a g e group X in Summit Lake
and a g e group VIII in Paxson Lake.
Growth of the l a k e whitefish in Paxson Lake i s shown in TaSle 1 0 ,
and i s a l s o graphed for clarity in Figure 12. The annual increment of growth
w a s nearly constant until a g e X. From a g e X through a g e XIII, a reduction in
growth rate w a s evident. After a g e XIII, the sample w a s t o o small t o afford
meaningful conclusions.
In comparison, the growth rate for l a k e whitefish h " ~ r e aSlave
t
Lake
(Kennedy, 1953) w a s somewhat above that of Paxson Lake.
Growth ol: the round whitefish is depicted in Figure 13. Since growth
of this s p e c i e s in Paxson and Siunmit Lakes i s t h e subject of a Masters t h e s i s
TABLE 10.
C A L C U L A T E D GROWTH I N F O R K L E N G T H ( c m . )
O F LAKE W H I T L F I S H T A K E N FROM P A X S O N L A K E , 1 9 6 2
A V E R A G E L E N G T H C A L C U L A T E D FROM E A C H A G E G R O U P A T E N D O F Y E A R O F LIFE
Number
of
Fish I
2
5
11
23
17
20
28
11
3
2
I
-I
0
1
to
' weighted
Average
II
I11
IV
V
VI
VII
VIII
IX
X
XI
XI1
XI11
XIV
xv
XVI
XVII
F I G U R E 12.
1
2
3
GROWTH O F THE LAKE W H I T E F I S H ( C o r e q o n u s c l u p e a f o r m i s ) I N PAXSON
LAKE BASED ON AVERAGE CALCULATED FORK LENGTH FOR EACH AGE GROUP
3
,
7
0
9
10
11
A g e group
12
13
14
15
16
17
18
FIGURE 13.
CALCULATED GROWTH O F THE ROUND W H I T E F I S H (Prosopium c y l i n d r a c e u m ) I N
PAXSON AND SUMMIT LAKES BASED ON AVERAGE CALCULATED FORK LENGTH FOR
EACH AGE GROUP
4
Age group
S i n g l e specimen
by the junior author, discussion of round whitefish growth is only briefly
mentioned in this paper. Figure 1 3 is based on sample s i z e s of 470 specfmens from Paxson Lake, and 572 specimens from Summit Lake. However,
below a g e IV and above a g e X , sample sizes were too small t o provide accurate
comparisons of growth.
Sex Ratio
In Paxson Lake s a m p l e s , the overall fema1e:male ratio for l a k e trout
w a s 48:52. Among the l a k e trout s a m p l e s , males exceeded females only in
a g e c l a s s e s IV-VII. Older a g e c l a s s e s contained a majority of females.
In Summit Lake, the fema1e:male ratio of l a k e trout taken w a s 67:33.
Females dominated a l l a g e c l a s s e s . Among t h e l a k e whitefish, males slightly
dominated a11 a g e c l a s s e s . The fema1e:male ratio of iound whitefish w a s
exactly the s a m e a s in Paxson Lake, 56-:44. Females dominated a l l a g e classes
except a g e I V .
The Paxson Lake fema1e:male ratio of t h e round whitefish was 56:44.
Males dominated a g e c l a s s e s 111-VI; but older a g e c l a s s e s consisted predominately of females.
Size and Age a t Maturity
Most lake trout in Paxson Lake mature a t a g e s VIE-VIII. Almost a l l
lake trout in Paxson Lake were mature when reaching 45 cm in length. Maturity
i s defined here a s either having gonads developed t o s u c h a n extent t h a t spawning will t a k e place within the s a m e summer, or in t h a t gonads show evidence of
prior spawning. By g r o s s examination, female l a k e trout were divided quite
e a s i l y into f i s h containing large e g g s that were held loosely in t h e ovaries and
were about t o spawn, and f i s h containing much smaller ova s t i l l held tightLy in
the ovaries. Males could not be definitely separated into spawning males and
mature males which would not spawn in the current year. I t i s unfortunate t h a t
data w a s not compiled on the ratio of mature l a k e trout spawning e a c h year.
Data similar t o t h a t obtained in Paxson Lake were collected in Summit
Lake, e x c e p t that most l a k e trout matured between a g e s VIII-X instead of VIIVIIL. Numerous individuals were lmmature a t 50 cm, but a l l were mature a t
55 cm.
Gonad development indicated t h a t spawning in Summit Lake would
commence in mid-September and approximately 1 0 d a y s l a t e r in Paxson Lake.
The above results compared favorably with a g e ana s i z e a t rnatu~ity
of l a k e trout in Great Slave Lake. In this l a k e , Kennedy (1954) found that
t h e first fish matured a t a g e VII and 4 3 cm in length, All fish were mature by
a g e XI and 5 7 cm in length. Kennedy a l s o reported that Great Slave L a k e 'imbit
apparently spawned once every two y e a r s after becoming mature.
In contrast, Miller and Kennedy (1948) reported that in Great Bear
Lake t h e first l a k e trout matured a t a g e XI11 a t 42 cm in Length, and a l l rake
trout matured by a g e XVII a t approximately 55 crn in length. These authors
reported that Great Bear Lake trout spawned once every three years after
becoming mature.
All l a k e whitefish from a g e VII were judged t o be sexually m a t w e .
Not a l l individuals appear t o spawn e a c h y e a r , however, no data concerrling
the ratio of ripe spawners t o unripe mature fish was compiled. Therefore,
the frequency of l a k e whitefish spawning in Paxson Lake i s unkr~ovvrx. Aki
individuals were mature a t 29 cm
.
Kennedy (1953) reported that in G-reat Slave Lake t h e lake whitefish
first matured between a g e VLII and 30 crn with a l l fish mature by a g e XI11 and
4 5 cm. The same author reported l a k e whitefish in Great Slave Lake spawned
once every two years after attaining maturity.
In both Paxson and Summit Lakes, a11 observed round whiteiish shorter
than 2 2 cm total length and younger than a g e IV were immature; whereas a l l
f i s h were mature when longer than 29 cm and older than a g e VIII.
In Paxson Lake, more than 50 percent of the males sampled were matfire
a t a smaller s i z e ( 2 4 cm) than a comparable majority of females. However, in
Summit Lake, t h e males attained 2 6 cm in length before more than 50 percent
were mature, whereas the females were similar t o t h o s e from Paxson L,aLe.
The round whitefish from both l a k e s had little difference in a g e at
maturity, with more than 50 percent of both s e x e s maturing a t a g e VT, A
greater percentage of males than females matured a t a g e IV and 11. In Paxson
Lake, a slightly higher percentage of f i s h younger than a g e V were m a t ~ ~ ar te
a n earlier a g e and a t a shorter length than for Summit L a k e f i s h .
Food Habits
A qualitative survey of the summer food habits of t h e iake t l = ~ ) ~ii'd
t.
round whitefish in Paxson a n d Summit L a k e s , and lake v~hltefrskl;r, PEA::^^, L ~ L P
w a s conducted in conjunction with gill n e t sampling.
In both l a k e s , lake trout under 40 cm fed principally on i n s e c t s
and mollusks with some small f i s h being eaten by trout in the 30-40 cm
range. Beyond 40 cm, the diet of lake trout w a s almost entirely f i s h . The
slimy sculpin w a s common in stomachs of lake trout between 45 and 55 cm
in Summit Lake. Sculpins were much l e s s common in the stomachs of comparable
s i z e d Paxson Lake l a k e trout. Salmon fry were utilized by l a k e trout in Paxson
Lake much more extensively than in Summit Lake. In both l a k e s , whitefish were
intensively fed upon by large l a k e trout. In Paxson Lake, where both s p e c i e s
of whitefish a r e present, fish remains were usually too badly digested t o allow
identification a s t o s p e c i e s .
Adult lake whitefish in Paxson Lake were observed feeding on salmon
fry quite extensively during the spring and early summer. However, t h e
predation ended a s the fry grew too big for t h e whitefish. It w a s a l s o observed
that while some adult l a k e whitefish were feeding entirely on salmon fry,
others in the same area would ignore the fry completely, feeding on the usual
d i e t of molltrsks and other invertebrates. Round whitef i s h fed almost entirely
on invertebrates. The principal food items were Trichoptera, Diptera larvae,
, and Gyralus 9 . No fish remains were found; but 40 salmon eggs
Lymnea
were found in t h e stomach of one specimen from Paxson Lake.
z.
Parasites
A total of 55 lake trout from both Lakes were examined for p a r a s i t e s .
Specimens were selected randomly a s t o a g e and s e x and examined by the
Department of Fish and Game parasitologist. The following parasites were
found:
Eubothrium salvelini. This tapeworm i s commonly found in many
trouts and chars and w a s found in 3 6 of the 55 specimens. Nine individuals
contained more than 30 of t h e p a r a s i t e s . Incidence was not correlated t o a g e
or s e x . This parasite has a first larval s t a g e (procercoid) in copepods and a
second larval s t a g e (pleroceroid) in prey f i s h and a r e not noted a s significant
pathogens.
Neoechinorhynchus rutili, a n acanthocephalan, h a s a world-wide d i s tribution and is commonly found in salmonoids, perches, and c a r p s . Twentyfive of t h e 5 5 specimens contained t h i s parasite, with 4 individuals carrying
more than 30 of the p a r a s i t e s . Incidence w a s not correlated t o a g e or s e x .
This parasite u s e s Ostracods or certain s p e c i e s of megalopteran i n s e c t s a s a
host for t h e only larval s t a g e . Heavy infestations of this parasite have been
reported to c a u s e mortality in trout.
Crepidostomum farionis. This fluke i s a parasite of salmonoids
throughout Europe and North America. Only 3 of the 55 specimens examlned
were found t o be infected; none having more than 30 of the parasite. The 3
infected specimens were females and a l l were in the 1 2 year a g e c l a s s . The
larval s t a g e of this parasite develops in s n a i l s and the a q u a t i c l a n ~ a eof some
i n s e c t s . Heavy infestation h a s been suggested a s a source of trout mortality.
Proteocephaius 9 . This tapeworm i s found in a wide variety g r i freshwater f i s h e s throughout the world. Copepods a r e the intermediate h o s t s for
the only larval s t a g e . Twenty-three of the 55 specimens were infected, with
8 of the specimens containing more than 30 of the parasite. Generally, alder
individuals were more heavily parasitized. Both s e x e s were equally infected.
A l l parasitic infestations of l a k e trout were relatively mild. Ira no c a s e
w a s t h e infestation judged t o be of sufficient severity t o appreciably impair the
functions or performance of the iniected individual.
SUMMAKY
.
1
All limnological conditions, including water temperature, indicated
Paxson Lake a s a significantly more productive l a k e than Summit Lake. Factors
such a s elevation and surface-to-volume ratio were considered the main r e a s o n s
for the difference in productivity.
2.
A11 fish s p e c i e s present in Summit Lake were a l s o present in Paxson
Lake. However, Paxson Lake p o s s e s s e d one s p e c i e s , the lake whitefish, nor
found in Summit Lake.
3 . The c a t c h per unit effort of round whitefish in Summit Lake w a s more
than twice t h a t of Paxson Lake, and even exceeded t h e combined c a t c h of both
s p e c i e s of whitefish in Paxson Lake. No significant difference in c a t c h per anit
effort w a s found for lake trout in the two- l a k e s .
Lake trout in Paxson Lake grew f a s t e r than t h o s e in S.umira~tLake,
Difference in growth rates t o a g e V w a s apparently correlated t o the reiatively
greater invertebrate fauna in Paxson Lake. Differential growth r a t e s were
especially pronounced between a g e V and a g e X , and were likely a restit: sf
changes in diet from invertebrates t o small fish.
4.
.
The number of small f i s h suitable for l a k e trout food in Paxson Lake
due chiefly t o the larger numbers of salmon fry and smolts greatly exceeded
t h o s e in Summit Lake. Colder w a t e r temperatures in Summit L a k e during t h e
ice-free period were a l s o partly responsible for slower growth. After age X ,
t h e samples were considered too small t o make valid conclusions.
Growth of lake whitefish appeared t o be constant until a g e X; thereafter
a d e c r e a s e in the growth rate w a s evident.
ACKNOWLEDGEMENTS
The author w i s h e s t o sincerely thank K. Neiland for compiling data
on t y p e s and numbers of parasites; Dr. J . M . Morrow f o r u s e of laboratory
equipment and a s s i s t a n c e ; and Dr. L. L. Hufman and S. Moore for a s s i s t a n c e
and valuable information on the past history of t h e fishery; and Richard Haley ,
Dingle-Johnson Coordinator.
,
LITERATURE CITED
KENNEDY, W . A , 1953. Growth, maturity, fecundity and mortality in t h e
relatively unexploited whitefish, Coresonus clupeaformis , of Great
Slave Lake. J. F i s h . R e s . Bd. Canada 1 0 (7): 413-441.
KENNEDY, W. A . 1954, Growth, maturity and mortality in t h e relatively
unexploited l a k e trout, Cristivomer namaycush, of Great Slave Lake.
J. Fish. Res. Bd. Canada 1 1 (6): 827-852.
MILLER, R, B. and W. A . KENNEDY. 1948. Observations on t h e l a k e trout
of Great Bear L a k e . J . Fish. R e s . Bd. Canada 7 14): 176-1 8 9 ,
RAVVSON , D. S. 1950. T h e physical limnology of Great Slave Lake.
R e s , Bd. Canada 8 (I): 1-66.
J. Fish
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The department administers all programs and activities in compliance with Title VI of the Civil Rights Act
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If you believe you have been discriminated against in any program, activity, or facility, or if you desire
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