HomeMy WebLinkAboutAPA1826Susitna Joint Venture
Document Number
Please Return To
DOCUMENT CONTROL
Studies
of
Alaska
Red
Salmon
EDITED BY
Ted S. Y. Koo
SEATTLE • UNIVERSITY OF WASHINGTON PRESS • 1962
Studies of
Red Salmon
Smolts
from the
Wood River Lakes,
Alaska
BY ROBERT l. BURGNER
Contribution No. 110, College of Fisheries, University of Wash-
ington, Seattle, Washington. This is a revised version of the first
of two installments of the author's. thesis accepted in 1958 by
the University of Washington in partial fulfillment of the require-
ments for the degree of Ph.D.
Abstract
introduction
The Seaward Migration
CONTENTS
Age Groups in the Seaward Migration
Determining the Migration Index
Size and Age of Migrants
Procedure for Processing Samples
Correction for Shrinkage of Fish in Formalin
Preservative
Evidence Regarding Selectivity of the Fyke Nets
Diurnal Changes in Size of Smolts Migrating
Samples Taken for Length Frequency and Age
Composition Studies
Method of Age Determination
Relationship between Parent Escapement and Seaward
Migration
Influence of Climate on Timing of Seaward Migration
Sun1mer Growth of Yearlings Prior to Seaward Migration
Growth as Indicated by Scales
Relationship between Scale-Growth Increments
and Seasonal Climate
249
251
251
253
253
254
256
256
257
258
260
262
264
265
268
271
271
274
t
250
Seasonal Changes in Length Frequency of Smolts
Pattern of Seasonal Changes
Effect of Lake-Ice Breakup and Distance from Outlet
on Pattern of Seasonal Migration
Origin of Size Groups in the 1955 Seaward Migration
Causes of Difference between Lakes in Size of Smolts
Produced
Climate
Level of Basic Nutrients
Competition for Food
Relation of Growth Rate to Survival
Fresh-Water Survival
Marine Survival
Effect of Smolt Size on Adult Population Size
Summary
Acknowledgment
Contents
276
276
278
279
283
283
284
284
288
288
290
291
292
294
Literature Cited
Figures 1-27 inclusive
294
following page 298
6. Studies of Red Salmon Smolts from the Wood River Lakes, Alaska
Robert L. Burgner
ABSTRACT
Red salmon (On.cm·hynchus n.erka) smolts of the Wood River lakes, Bristol
Bay, Alaska, were studied to determine fluctuations in abundance, growth,
and survival and to ascertain causes of the fluctuations.
Indexes of seasonal and annual variation in numbers of smelts migrating
seaward were obtained by fishing fyke nets ~t the outlet of the lake system.
Sampling systems to determine changes in age and growth of smolts were
developed, including a method whereby the majority of fish sampled were
measured alive and released. Diurnal changes in size of smolts migrating
were found.
The relationship between numbers of parent spawners and numbers of
smolts produced was found to be highly variable for the year classes 1949
through 1955. Sources of variability in growth and survival were therefore
sought. Amount of growth attained by yearling srnolts during the early part of
the growing season and timing of seasonal migrations were related to timing
of breakup of la...lte ice and te:r,nperatures following breakup. Scales of smolts
and of returning adults were utilized to show that size at seaward migration
varied with lake of origin. Differences between years and between lake areas
in growth attained during first year of life were associated with differences
in srawning population density. Size of yearlings at time of seaward migration
was shown to influence marine survival and age at return to the spawning
grounds.
INTRODUCTION
THE STUDIES described in this paper are a part of the ::t•'isheries Re-
search Institute program directed toward furthering knowledge of the
causes of fluctuations in abundance of red salmon runs in Bristol Bay,
Alask.a. This report concerns primarily studies of red salmon smolts,
or seaward migrants, of the Wood River system in the Nushagak district
of Bristol Bay.
Sockeye or red salmon (Oncorhynchus nerka Walbaum) spend approxi-
251
252 Alaska Red Salmon
mately half their life in fresh water, enter the marine environment at
an advanced stage and do not come in contact with the coastal fishery
until their return migration. Such distinctive environments allow the con-
venient division of fluctuation in abundance into those which occur in
fresh water, at sea, and as a direct result of the fishery.
The anadromous life history of this species permits detailed study
of spawning and early life. For studies to be effective in evaluating mor-
talities at these stages, adequate systems of observation are needed to
cover the fresh -water history year after year in such a manner as to
be quantitative and comparative. Determination of t..he mortalities causing
fluctuations in abundance is essential to proper management and sus-
tained utilization of the very valuable red salmon resources of Pacific
coast rivers.
Seaward migrants are of key significance, for they have reached the
threshold of the marine phase of their life history. Number of seaward
migrants related to number of parent spawners provides a direct measure
of production of young. This relationship provides a measure of vari-
ability in survival rate resulting from interplay of natural causes and
establishes the existence of possible cyclic patterns in fresh-water sur-
vival. Evaluation of seaward :mlgrants with respect to their later return
as adults in catch and escapement provides a measure of marine sur-
vival. With the latter information as a basis, forecast of adult returns
from seaward migrations of known relative magnitude follows logically.
In this report the procedures used in determining abundance, size,
age, and migration timing of Wood River smolts are described. Evi-
dence is presented to relate differences between years in migration
timing, growth and survival, to factors of climate, population density,
and locale of embryonic and juvenile growth.
The main lakes of the Wood River chain are piedmont lakes of glacial
origin occupying essentially bedrock basins, and lie in a general east-
west axis bordered on the west by the Wood River Range (Fig. 1). They are
joined by short rivers, with the 18-mHe-long Wood River connecting
the lowest lake with Nushagak Bay. Wood River drains a basin of ap-
pro~5.mately 1,415 square miles in which the principal lakes cover 174
square miles (U.S. Army Corps of Engineers, 1957).
The Wood River lakes are deep, temperate, and typically oligotrophic,
with bottom water temperatures varying near that of maximum density.
They are ice ... · covered for approximately 6 months of the year, but show
distinct thermal stratification h'ith formation of a true thermocline in
summer. Average annual precipitation recorded at Dillingham, Nushagak
Bay, over a period of 35 years was 25.86 inches (U.S. Army Corps of
Engineers, 1957). Elevation, dimensions, and depths of the primary
lakes are recorded in Table 1 as seen on the following page.
The Wood River lakes constitute the main spawning area for red salmon
Smolts from Wood River Lakes
TABLE 1. PHYSICAL DATA ON PRINCIPAL LAKES
OF THE WOOD RIVER SYSTEM
Maximum Area Surface Length Name Recorded {Square Elevation (Miles) Depth (Feet) Milas) (Feet)
Aleknagik 20 360 34 34
Nerka 25* 538 78 70
Beverley 22 617 38 100
Kulik 17 525 24 140
*Longest arm only.
So1.1rces: Vertie (193R); U.S. Army Corps of Engiueers
(1957). Maximum soundings furnished by author.
253
in Nushagak district. Spawning is distributed over the lakes in tributary
creeks, spring ponds, rivers between the lakes, and along lake beach
areas. All four spawning area types-creek, spring pond, river, and lake
beach-are of importance in the Wood River lakes; their relative impor-
tance varies considerably from year to year.
The following terms will be used in discussion of the stages of young
red salmon in fresh water:
Fry-stage from time of emergence in spring through first gJtowing
-season in the lakes; synonymous with underyearling, and age 0
fish
Yearling-fish in second year of life; synonymous with age I fish
Age II fish-fish in third year of life
Fingerling-general term applied to young salmon during the second
or third year of fresh -water life prior to seaward rrdgration;
young salmon after fry stage
Smolt-seaward migrant in second or third year of life
THE SEAWARD MIGRATION
Age Groups in the Seaward Migration
The annual seaward migration in the Wood River lakes is comprised of
three age groups of young reds. These age groups are: (1) fry from the
adult spawning of the previous year, (2) yearling smolts, and (3) smolts
in their third year of life, age II. The validity of these age designations
for young red salmon has been established by a combined study of sea-
sonal length-frequency progression and scale structure (Koo, 1962).
Fry migrations from the Wood River lakes were not sampled by the
smolt indexing procedure used at the system outlet. However, wh...tttever
the magnitude of the seaward migration of fry, the numbers of returning
adults with no fresh-water annulus on their scales have been inconse-
254 Alaska Red Salmon
quential in the Nushagak District. The highest percentage :return of this
group was found in adult returns from the 1949 spawning (1950 fry), and
amounted to 6.3 per cent of the return run.
Yearling smolts have constituted the major portion of the seaward
migration in every year. During the season of migration they are readily
distinguished from fry by their size and scale pattern. There is no over-
lap in size between fry in the lakes and migrating yearlings during June
and July (see length-frequency curves prepared by writer in Koo, 1962).
Smolts migrating after two years in fresh water form a smaller pro-
portion of the total migration than do year lings.
Determining the Migration Index
Responsibility for studies of the seaward migration of red salmop. at
Wood River was divided between Dr. Koo and the writer. Dr. Koo's work
was primarily concerned with the enumeration of young salmon in the
seaward migration and with the calculation of an index t;o show the rel-
ative abundance between one year and the other. His work included in
this report covered the years 1951 to 1958; the year 1952 was used as
the base year in the computation of indexes. The method used to ob-
tain an annual index to magnitude of the Wood River seaward migration
will be described briefly, since the data are utilized in discussion of
fresh -water survival and of size and age changes in the migration.
Although fyke nets have long been used to obtain samples of seaward
migrants (Babcock, 1905; Chamberlain, 1907), the Fisheries Research
Institute was first to apply the gear as a means of indexing annual mag-
nitude of smolt migrations in large rivers. This gear, installed at the
outlet of the Wood River lake system in 1951, has been used in the major
river systems in Bristol Bay and in the Chi~£1ik River. At Wood River a
winged fyke net (Fig. 2) was fished annually during the seaward migra-
tion period of approximately two months. The net was set daily for a
fixed period during the evening migration in the same location on the
gravel shoal at Mosquito Point {Fig. 3 ). · The method of fishing was kept
as constant as possible from yea.r to year. Total catch for each season
furnished the annual index to abundance of seaward migrants.
The fyke net used for indexing was set on the river bottom in approx-
imately 4 feet of water. The net intercepted a cross section of the river
approximately 8 feet wide and 4 feet deep. According to calculations
based on river measurements taken by Koo on June 15, 1955, the net
intercepted about 1/75 of L'le river width and 1/145 of the cross-sectional
area across the outlet in line with the net site. Maximum current ve-
locities occur across the shoal where the fyke net was set. Average
current velocities taken at the fyke-net location on the date stated above
exceeded 3 feet per second.
Smolts from Wood River Lakes 255
Most of the smolt migration occurs during evening hours. This was
shown by Koo in studies of the hourly pattern in timing of seaward mi-
gration at Wood River. During 17 days of around-the-clock fishing with
fyke nets in 1951, over 95 per cent of the smolt.s were caught during the
evening period from 2100-0200 hours. Hourly distribution of migration
during this evening period ~or the years 1955 through 1957, based on
data collected by Koo, is shown in Figure 4.
Large fluctuations in smolt indexes have been found from 1951 to 1958
(Table 9, p. 267), but no direct test of the reliability of the smolt index
was made. Evidence as to .reliability of the method has come primarily
from consistency of results:
(1) The seasonal trend of catches of the index net, daily changes in
magnitude with fluctuations in water temperature and wind direction,
and catches in relationship to observed abundance of smolts at the lake
outlet have all shown a pattern of consistency.
(2) The proportion of the catch taken early in the evening has been
consistent from year to year. During the 1955 through 1959 seasons,
the evening fyke-netting period was extended to include the hours 2100-
0200. Catches for the 2100-2300 period, used in former years, have
averaged close to the same percentage of the total catch during the 2100-
0200 period in each of these years (Koo, 1959, 1960):
1955 42.1%
1956 43.4%
1957 39.4%
1958 46.4%
1959 42.0%
(3) Magnitude of adult returns has shown a relation to index of a bun-
dance at time of seaward migration. Deviations to date appear to be
explainable largely on the basis of recognized changes in ocean mor-
tality.
(4) In 1952 a second fyke net identical in structure was fished for 28
days during the season in a position 25-50 feet offshore from the index
net. The total calculated catches of the two nets during the 28-day period
were in very close agreement-147,991 fish in the index net, 160,343 fish
in the offshore net. This was in spite of the fact that two nets could not
be tended as carefully or fished in as favorabls a. location and circum-
stances as a single net.
Comparison of fishing results of the two nets fished simultan~ously is
presented in Table 2 (p. 256). Although differences between days in length
of time the nets were fished somewhat obscure the day-to-day fluctua-
tions in magnitude of migration, high catch of one net was associated with
high catch in the other, and low catch with low. The coefficient ai cor-
relation between the unadjusted catches day by day was +0.84e.
256 Alaska Red Salmon
1'ABLE 2. COMPARISON OF FISHING RESULTS BETWEEN 'tHE
MOSQUITO POINT INDEX NE-T AND A Sii;coNil FYKE NET
SET 25-50 FEET FURTHER OFFSHORE, 1952
Date Time Fished I Catch of R~d Sm0lts
-~ ....
Hmu·s M:i.p,t;i;~B ~.nqt;;ii; N~'t Offahora Net
June }..u 4 40 6,612 13,774
22 3 10 10,780 4,480
24 3 10 51,128 51,216
28 3 30 806 1,096
29 2 30 258 342
30 3 0 13 13
July 1 6 40 0 0
2 6 40 15,960 28,462
6 4 0 2,590 981
7 2 45 34,020 15,660
14 3 25 132 58
15 2 25 33 7
16 3 15 142 90
17 3 20 1,041 77
18 2 45 2:304 25,698
19 3 15 12,722 11,957
21 3 15 140 32
22 2 5 172 114
23 3 20 2,368 536
24 2 0 1,210 350
30 3 15 1,193 1,753
31 3 25 1,751 1,534
Aug. 1 3 0 2,383 1,741
2 2 0 41 23
4 g 45 g7 56
5 1 53 8 18
7 2 0 21 45
10 2 0 136 230
TOTAL 147,991 160,343
RATIO 1 . 1.08 .
Size and Age of Mig·rants
Procedure for Proct~ssing Samples
Preliminary studies were made of seasonal and annual size and age
compositi.cm Qp,an~~g Q£~~rr:iii5 1r1 Wu-oo i'iiver smolt§ during the yeru.·s
i949--53. Beginning 1fi 1954, more complete sampling was initiated, and
the number of samples taken annually was increased severalfold. Length,
rather than weight, was used to measure size of individuals in order that
large samples of smolts could be processed rapidly. All length measure-
ments were from tip of snout to fork of tail.
Samples for study were drawn at the fyke-net site during the ~vening -
Smolts from Wood River Lakes 257
index period, held overnight in live-boxes, and processed the following
day. Care was exercised in taking samples at the fyke-net site to avoid
selection resulting from possible size stratification of fish during the
sampLing procedure. Tests of procedure showed no indication of size
selection in drawing samples.
In 1954 a procedure of measuring fish alive v.ras adopted in order to
increase the number of length-frequency samples without unnecessary
killing and preservation of smolts. The live fish were measured under
anesthesia. Lengths of these fish were not directly comparable with
those of fish measured after preservation in formalin. The measure-
ments of preserved fish were converted to correspond to the live fish
measurements, since by far the greater numbers were processed alive
and released.
Correction for Shrinkage of Fish in Formalin Preservative
Measurements taken of a smolt sample collected on June 2, 1954, il-
lustrate changes in length of red smolts accompanying preservation in
10 per cent formalin. Fish in the sample were measured alive under
anesthesia, remea..c;ured approximately 24 hours after preservation, and
again after 5 months in formalin. Table 3 summarizes the results:
TABLE 3, COMPARISON OF LENGTHS OF SMOLTS MEASURED
UNDER ANESTHESIA AND AFTER PRESERVATION
Anesthetized Preserved
24 Hours 5 Months
Age I--139 fish
Mean length in millimeters 86.3 82.0 81.1
Mean decrease in length 4.3 5.2
Percentage shrinkage 5.0 6.0
Age II--15 fish
Mean length in millimeters 106.3 101.7 100.4
Mean decrease in length 4.6 5.9
Percentage shrinkage 4.3 5.5
Measurements in Table 3 indicate that the major changes in length of
red smolts occurred within a few hours after lr • .illing, in preservative.
Roughly 80 per cent of decrease h1. measured length occurred during the
first 24 hours in both age groups of smolts. While the actual shrinkage
was slightly more in older fish, the percentage shrinkage in terms of
total length was slightly less.
Another sample, taken on June 9, 1954, is used to illustrate shrinkage
in different length classes. The fish were measured under anesthesia,
sorted into 5 mm length groups, preserved, and the sampJe remeasured
over 5 months later. Tabulations by length class are given in Table 4.
Difference in mean length between anesthetized and preserved fish is
around f mm for each length class, percentage difference in length de-
258 Alaska Red Salmon
creasL"'lg with increased size. Hile (1936) likewise found that shrinkage
in length of ciscoes was greater on a per cent basis for smaller fish.
His specimens, ranging from 150-350 mm, were first pre}3erved in
formalin and l~ter transferred to alcohol.
TABLE 4. SHRINKAGE OF RED SALMON FINGERLINGS IN LENGTH DURING
STORAGE IN 10 PER CENT FORMAL!~*
Mean Length (in mm) Difference in
Length Class Number of 5i Months
Mean Length
(in mm) Specimens Measured
Alive under After Mill!-Per Cent
Anesthetic Preserved meters
73-77 4 76.5 71.3 5.2 6.8
78-82 53 80.8 76.0 4.8 5.9
83-87 82 84.6 79.6 5.0 ~.9
88-92 17 89.0 84.2 4.8 5.4
93-97 11 94.8 89.5 5.3 5.6
98-102 6 98.5 93.2 5.3 5.4
108-112 1 108.0 103.0 5.0 4.6
Total Age I 170 84.61 79.61 5.0 5.9
Total Age II 4 100.75 95.50 5.25 5.2
*Measured under anesthetic before killing, remeasured 5i months
later.
other measurements taken of red smolts show that the initial and most
abrupt decrease in length is apparently not due to formalm preservative,
but rather occurs as a result of rigor mortis. Shrinkage in length between
fish measured alive under anesthesia and remeasured upon reaching
a state of rigor mortis without being preserved in formalin averaged
between 2 and 3 per cent. This agrees closely with results reported by
Shetter (1936) for brook and brown trout averaging 6-7 inches in length.
To compensate for total shrinkage of preserved specimens, 5 rom was
added to length measurements of yearling smolts preserved several
months in 10 per cent formalin. A slightly larger correction was needed
for age ll fish which ranged over 100 mm.
Evidence Regarding Selectivity of the Fyke Nets
Since the smolt samples taken at the fyke-net site were to be used for
size and age studies, it was necessary to determine whether the nets
were size selective. This was done by comparing samples with those
taken by other gear.
Indirect evidence did not indicate that index fyke nets, as used at Mos-
quito Point, tended to select small smolts. Sampling within the lake
system by means of beach seines, lake traps, tow nets, and fyke nets
failed to furnish any evidence of an abundance of larger or older finger-
Smolts from Wood River Lakes 259
lings not represented in the samples taken by fyke net at the outlet of
the lake system. The fyke nets used within the lake system were set in
rivers between lakes, usually in swifter water than at Mosquito Point.
Length-frequency study established that fish in samples captured within
the lakes by this gear were similar in size or smaller than those sampled
concurrently by fyke net at Mosquito Point. The differences in length
frequency were those to be expected between Mosquito Point migrants
a"'1d those reds still to migrate.
More direct information regarding possible fyke-net selectivity was
obtained in 1954. It had been observed that beach seines of the type used
for sampling red fingerlings in. the lakes tended to capture a school in
its entirety if the school was surrounded initially by the set of the seine.
The fish were observed to herd toward the beach and to avoid contact
with the seine until they were finally pocketed in the bag in shallow water ..
Size selectivity was believed negligible once the young salmon were sur-
rounded by the set. It was decided, therefore, to obtain samples simul-
taneously by beach seine and standard fyke net at Mosquito Point for
study of fyke-net selectivity.
The seine used was tapered, 200 feet long, with a large bunt made
of 1/8-inch-mesh saran-plastic screen. The sets were made with an
outboard boat a short distance above the fyke-net site and in slower
current than at the site. In order to make catches at the same time,
all fish were removed from the cod end of the fyke net, the cod end re-
placed, and as soon as a sufficient number of fish appeared in the fyke
net, seine set was begun. The moment it was determined that smolts
were caught in the seine, catches from both gear were removed. In this
manner, two pairs of catches by seine and fyke net were obtaine.d on each
of three nights, June 15, 16, and 17. The catches were held overnight in
live-boxes and a 2-pound sample (about 150-170) processed from each
in standard manner the following day.
Runs were relatively light during the three evenings of sru.11pling and in-
dividual samples taken by both beach seine and fyke net were composites
from a few schools. Fyke-net catches were obtained by fishing a con-
siderably longer time, and as a result contained components of more
schools than did seine catches. Fyke-net catches were made during 6-
minute fishing periods on June 15 and 16, and during a 14-minute and
a 29-minute period on June 17. It required less than a minute to set the
seine, and no schools could enter once the seine was set. Length fre-
quencies obtained by the two types of gear were compared with com-
posite frequencies of all samples taken during the same evenings. The
frequencies of June 15 are compared in Figure 5, those of the smaller
smolts running on June 16 and 17 in Figure 6.
The feature at once apparent in both figures is the greater hetero-
geneity in length frequency among samples taken by beach seine. The
results support observations that there are marked differences between
260 Alaska Red Salmon
schools in size composition of the individual fish. The fyke-net samples
were composed of portions of a greater number of schools, hence tended
more toward the average size composition of all schools passing, and
thus showed less variability in size composition between samples.
Comparisons of individual samples obtained simultaneously by the two
types of gear are presented in Figure 7. The over-all mean length of
smolts taken by fyke net was 86.07 mm, by beach seine, 86.95 mm, a
difference of only 0.88 mm. The two seine hauls made on June 15, cap-
tured several very la1:ge age n smolts of a size range not found in the
fyke-net samples. Fewer fish of this length range (over 105 mm) were
captured by either gear the following two nights. It is not known whether
unusually large fish of this size avoided capture by the fyke net on June
15 or whether capture of these fish by beach seine and not by fyke net
was a chance occurrence. It is unlikely that fish of this size range com-
prised a substantial proportion of the run, since they have never been
captured in numbers by any gear used. If selection exists, however,
some error would arise in determining the proportion of age II smolts
in the seaward migration in years when sizes of fish in this age group
run large.
In the size range below 105 mm the samples gave no evidence that the
fyke-net set in the current velocities at Mosquito .Point selected smaller
fish. There was, then, no evidence that the proportion of yearlings re-
tained by the fyke net ·was influenced by the size of yearlings migrating.
Comparison of beach-seine and fyke-net samples did bring out the
heterogeneity in length frequency of smolts among schools. As a result of
these tests, it was decided that when samples for size and age study were
to be drawn from the catch, the fyke net should be fished long enough
before lifting to make the resultant catch a composite of several schools.
Diurnal Changes in Size of Smolts Migrating
During early years of sampling at \Vood River, marked diurnal dif-
ferences between samples were noted in size of smolts taken. The diurnal
differences were first studied in detail in 1954 to determine possible
causes and to evaluate their effect on the sampling schedule adopted.
Hwrly samples of the run were taken on two evenings of heavy migration.
Length frequencies of these samples are presented in Figures 8 and 9. A
pattern of general decrease jn the size of smolts during the evening was
evident in the samples. This was caused by a decrease in the size of
yearlings, since very few older fish were present in the samples.
Evidence that such was a regular feature of the migration in 1954 was
indicated by additional samples taken during regular fyke-netting hours,
which were from 2100-2300 each evening. The mean weight of fish in the
first and last samples taken each evening is shown in Table 5. In 20 of 21
instances, average weight of individual migrants in the first sample was
gr<'ater than that in the last.
Smolts from Wood River Lakes 261
TABLE 5. MEAN WEIGHTS OF SMOLTS TAKEN IN FIRST AND LAST SAMPI.:ZS
DURING ~E 2100-2300 EVENING FYKE-NETTING PERIOD, MOSQUITO
POINT, MAY 30 THROUGH JUNE 19, 1954
-
Time Time Difference Mean Weight of Fish ~n Grams
Date First Last in First Last j S 1 Differenr.e Sample Sample Minutes Sample ampe
May 30 2240 2300 20 7.03 6.55 0.48
31 2117 2300 103 9.65 6.54 3.11
June 1 2113 2300 107 6.72 6.05 0.67 ·-
2 2130 2300 90 7.05 5.89 1.14
3 2140 2300 80 6.05 5_.93 0.12
4 2218 2300 42 6.43 6.01 0.42
5 2200 2300 60 6.61 6.53 0.08
6 2200 2300 60 6.67 6.13 0.54
7 2154 2300 66 7.11 5.04 2.07
8 2106 2300 114 5.97 5.34 0.63
9 2130 2300 90 6.21 5.21 1.00
10 2104 2300 116 6.06 5.34 0.72
11 2105 2300 115 8.10 7.26 0.84
12 2104 2300 116 6.45 5.53 0.92
13 2104 2300 116 5.47 5.24 0.23
14 2107 2300 113 7.32 6.26 1.06
15 2120 2300 100 5.89 5.74 0.15
16 2133 2238 65 5.40 6.20 -0.80
17 2200 2243 43 5,2_7 5.10 0.17
18 2122 2300 98 i'i.'t8 5.50 0.28
19 2107 2300 113 6.05 6.01 0.04
TOTAL 1,827 13,87
MEAN 87 5.54 5.88 0.66
In 1956 and 1957 a substantial fraction of the migration was composed
of age II smolts, and although there appeared to be a slight tendency
for age n smolts to ru:n earlier in the evening, the pattern was far from
consistent. The tendency for larger smolts to run e~lier in the evening
is still under study, for in other years it was not as evident as in 1954.
Possible diurnal change in selective action of the fyke net was dis-
carded as a cause of diurnal change in size of fish in the cai:cho If change
in efficiency of the net occurred, it would be expected in the direction
of increase in efficiency with increasing darkness. This would be ex-
pected to increase rather than decrease the proportion of large fish
caught; however, a decrease in proportion of large fish was established.
Further, as shown in Figures 8 and 9, not only do the proportions of
large fish decrease, but size groups of small smolt s are found in late
evening samples that were not present in samples taken earlier in the
evening. The appearance of small fish in later samples cannot be ex-
plained by either increased or decreased efficiency of gear.
Suggested reasons for the phenomenon of diurnal change in sizes caught
262 Alaska Red Salmon
are (1) that the larger fish reaching the lake outlet have a greater mi-
gration stimulus because of their more advanced development, 1 and there-
fore, show less hesitation in entering the river from the lake; or (2} that
the final distance from the daytime milling area to the lake outlet is
traversed more swiftly by larger fish because they tend to be stronger
swimmers.
Neither alternative can be explained solely on the basis of behavior
of individual fish. Red salmon fingerlings exhibit a marked schooling
habit. It is quite unlikely that the faster swimmers or individuals with
a greater urge to migrate break away from their unit schools to reach
the outlet during evening in advance of their slower members. Further,
fingerlings migrating pa...~ Mosquito Point are in definite schools, cross-
ing the shoal areas in distinct waves. The behavior of the school, made
up of individua· :s, must therefore be considered in any explanation of
the phenomenon of diurnal chanr.e rn size frequency. This requires no
particular modification of the ~11ggested reasons advanced, for it has
been shown repeatedly by sampling in the lakes that length-frequency
composition varies greatly from one school to the next. Schools com-
posed of larger fish may simply begin migration out of the lake earlier in
the evening or may migrate faster than those composed of smaller fish.
Migration of t.he individual is thus apt to be controlled to a considerable
degree by size and impulse of its companions.
The explanations advanced, particularly the latter, require the concept
of a milling area or reservoir in the lake near the outlet where young
tend to congregate during the course of the day or early evening prior
to migration out of the lakes. Observations of the behavior of red smolts
near the outlet o:f Lake Aleknagik, particularly in 1949, support a res-
ervoir hypothesis. Schools of red fingerlings were observed during cer-
tain days feeding and milling in considerable c;:>ncentrJ.tions in the more
shallow lower end of the lake near the outlet. Evening observations were
made from a boat anchored over submerged light-colored panels near
shore about 300 yards above the lake outlet. During the day only occa-
sional schools of fingerlings were observed over the panels. During early
evenL"lg many more schools were observed crossing the panels, but
movement was not decisiveJ.y directional. Schools crossed the panels
moving away from the outlet as well as toward the outlet. However, from
about 2140 on, movement was more decisive and all schools swam de-
finitely and directly towa:r:d the lake outlet.
SampJ es Taken for Length Frequency and Age Composition Studies
Most of the smolt samples taken from 1954 through 1956 were 2-pound
1Svardson (1955, p. 246) suggests that the physiological development
achieved by a fish cannot be measured properly by size or age alone,
and states the need for a better measure of "physiological age.''
Smolts from Wood River Lakes 263
samples, averaging well over 150 fish per pound. In 1957, individual
sample size was reduced to 1 pound, averaging over 100 fish per pound.
Total number of samples and fish used in determining the season's length
frequency and age distribution a..~e given in Table 6.
'l'ABLE 6. TOTAL NUMBER OF SMOLT SAMPLES USED FOR LENGTH-
FREQUENCY AND AGE DETERMINATIONS, 1954-57
Total Season's Number of Number Year Catch of Smo1ts Samples of Fish during Index Period*
1954 745,832 52 8,923
1955 904,236 110 14,419
1956 1,325,910 63 11,134
1957 627,884 94 10,207
*Daily fishing hours: 2100-2300 in 1954, 2100-0200 in
1955 through 1957.
During nights of heavy migration, weighing, recording, and releasing of
the catch occupied the full efforts of the fyke-netting crew. However de-
sirable, it was not at all feasible to draw a uniform fraction ot each catch
as a sample. It was the practice to draw a minimum number of samples
spaced at fixed intervals on a sampling schedule that could be followed
each year. This sampling procedure did not fully take into account di-
urnal changes in size and age composition that may have occurred.
Samples taken at or between 2200 and 2300 were used in the present
study for the 1954 period. The standard evening fyke-netting period was
extended to 0200 beginning in 1955, and three samples were generally
drawn at approximately 2200, 2300, and 2400. All three were proce:.;sed
unles~ the evening catch was light (less than one index point, or 4,000
fish). If the days of light catches continued, a sample was processed
every three days. Some flexibility was exercised, particularly if the
evening run was unusually heavy early or late in the evening. Samples
during an evening were not weighted according to the proportion of the
evening catch they were to represent, since this would have been an
unwarranted refinement beyond the accuracy of the fyke-netting and
sampling procedure. Table 7 (p. 264) gives the proportions of the migra-
tion each season that were represented by daily samples.
In computing seasonal length-frequency curves, daily samples were
weighted by the daily catches they represented to adjust for changes
during the season in the magnitude of catches. From 1954 through 1956
this was done by combining frequencies for adjacent days within five-
day periods in which no significant change in size of migrants was ob-
served, then weighting the frequencies by the total fyke-net index catch
for days included. Since this involved a decision as to which days could
be grouped, the procedure was modified in 1957 so that each daily fre-
quency was simply weighted by magnitude of daily catch.
264 Alaska. Red Salmon
TABLE 7. PROPORTION OF THE WOOD RIVER SMOLT MIGRATION REPRESENTED
BY DAILY LENGI'H-FREQID~CY SAMPLES, 1954-57
No Sample At Least One Sample Two or More
from Daily Catch from Daily Catch Samples Daily
Year Number Per Cent Per Cant Per Cent
of Season Number of Se1son Number of Season of Days Catch of Days Catch of Days Catch
1954 5 1.0 30 99.0 20 73.7
1955 18 ) 12.9 36 87.1 23 78.4
1956 31 ! 4.0 32 96.0 19 86.3
1957 25 2.8 34 97.2 29 88.4
Method of Age Determination
Beginning i~1 1954, nearly ,"'1 samples of smolts drawn during evening
fyke-net sampling were. proc-essed alive and released, necessitating an
age-sampling technique adaptable to this procedure. Groups of age I
and age II smolts could generally be separated by length frequencies at
the beginning of the migration season. Later in the season sizes of the
two age groups overlapped. In order to determine age composition it was
necessary to preserve for scale study those fish which fell in the range
in which lengths of age I and age II fish over lapped. Those fish in the
length frequency well outside this overlapping range needed merely to
be counted if age composition of the sample was the only information
desired.
The zone of overlap in length frequency of the two age groups was
determined in the field at intervals during the season by examination
of smolt scales under a microscope. As shifts in length frequency were
observed, scale samples were examined to detect shifts in the overlap
range. Sample fish in the range of overlap were preserved at the time
the daily live-smolt samples were measur~d. Complete smolt samples,
preserved at frequent intervals during the season, provided a check
against the range of overlap designated in the field. By this method, an
adequate age breakdown of a large number of samples was obtained with
a minimum of preserved specimens.
Scales from fish in the preserved samples were mounted on glass
slides and projected for age reading with methods and equipment de-
scribed by Koo (1962). Age readings of smolt scales for the years 1951-
57 were made by the writer, the 1958 age readings by Koo.
An index to annual age composition of smolts in the Wood Riyer sea-
ward migration was obtained by weighting samples by the magnitude of
the catches which they were to represent. Grouping of daily age samples
and catches was the same as used in weighting length frequencies. Al-
though changes during the season in age composition and in magnitude
of migration were considerable, corrections in the season's age com-
position attained by weighting the samples by magnitude of catch were
Smolts from Wood River Lakes 265
not extreme. This may be illustrated by comparing the per.centages of
age ll fish obtained in this manner with values obtained by giving equal
weight to each day on which samples were taken. This comparison is
made in Table 8 for two years when the percentages of age ll fish were
high.
TABLE 8. EFFECT OF WEIGHTING ON AGE DETERMINATIONS,
1956 AND 1957
Method
Samples weighted by magnitude
of fyke-net catch
Daily samples given aqua!
weight
Percentage of Age II Smolts
1956 1957
21.6 19.3
17.6 20.3
Relationship between Parent Escapement and Seaward Migration
Previous investigators have found considerable variability in fresh-
water survival rates of red salmon under natural conditions. At Karluk
Lake on Kodiak Island this variability was detected by indirect calcula-
tions of fresh-water survival after measures of marine survival had been
determined through fin-clipping experiments (Holmes, 1934; Barnaby,
1944). ?¥lore direct measurements have been ma.de by investigators in
British Columbia lakes, with the most extensive work at Cultus Lake.
From 1925 through 1936 tests of artificial versus natural propagation
were conducted there. In experiments on natural propagation, adult
spawners entering the lake and resultant numbers of seaward migrants
produced were counted, average fecundity was determined from samples
of adult females, and potential number of eggs available for deposition
was calculated for each year. Survival to smolt stage from calculated
numbers of eggs spawned varied from 1. 05 to 3. 23 per cent in three ex-
periments conducted prior to initiation of predator control experiments
(Foerster, 1938). However, natural spawning was permitted only in
certain of the years involved, and eggs were shipped to other watersheds
during the experimental period, which may have disturbed natural con-
ditions in Cultus Lake even prior to predator control (Thompson, 1950,
1951).
At Lakelse Lake, British Columbia, the same procedures as those at
Cultus Lake were used to obtain calculated survivals from natural spawn-
ing (Brett and McConnell, 1950). Range in survival from egg to smolt for
seven brood years is given as between 1.0 and 4.9 per cent (Canada,
Fisheries Research Board, 1957): "There has been no obvious rela-
tionship between the number of eggs laid and the number of smolts pro-
duced .... "
Fresh-water survival rates for a small sockeye population at Port
266 Alaska Red Salmon
John Lake in the central coastal region of British Columbia were studied
by similar methods. Foerster {1955) reported survival values of 0.5,
3.0, 5.0, and 3.0 per cent. The smolt production was reported as having
"·varied between 11,000 and 20,000 from egg depositions of 300,000 to
2,000,000" (Canada, Fisheries Research Board, 1957}.
At Babine Lake in the upper Skeena system the number of smolts was
estimated by marking and recovery methods rather than by means of a
cow1ting fence (Withler, 1952). The calculated ratios of smolts produced
to number of eggs available fur deposition range from 0.49 to 2.49 per
cent for the brood years 1949 through 1954 {Canada, Fisheries Research
Board, 1957a); with regard to the relation between initial population size
and survival, they stated: "Not only did larger runs produce more smolts;
they produced a better percentage survival from eggs to smolts, indi-
cating that still better production J:night be expected from still larger
runs.''
At Lcike Dalnee on the east Kamchatka Peninsula, Krogius and Krokhin
{1956a) reported fresh-water survival of sockeye over 17 brood years
(1935-51) to be highly variable, ranging from 0.04 to 1.3 per cent of eggs
available for deposition. Krogius {1951) gave an even wider range of
values {0. 005-1.04 per cent) for the same lake. Krogius and Krolrnin
(1956) commented that marine mortality was much more constant than
fresh-water mortality, and that there was no correlation between es-
capement and return. Their data do show that the four parent spawning
populations producing the greatest number of smolts per spawner were
well below average in size.
In summary, measurements of fresh-water survival have succeeded
in showing variability between brood years in survival. No consistent
relationship between magnitude ot initial population and percentage sur-
vival to seaward migration has been demonstrated.
At Wood River annual indexes of abundance of smolts, 1951-58, clas-
sified into component indexes of age I and age n smolts (Table 9), provide
a basis for study of the relationship between parent escapement of red
salmon to spawning grounds of the Wood River lakes and relative num-
bers of smolts produced. In the first three years, 1951 through 1953, age
composition values were not based on a,s complete sampling and require
a brief explanation. Both the limited smolt samples taken during the 1951
migration and the age composition in the adult returns of 1953 and 1954
to the Nushagak District indicated that the percentage age II fish in the
smolt migration was less than 20 per cent. The smolt samples and sub-
sequent adult returns of the 1952 seaward migration indicated less than
1 per cent age II smolts. All migrants in these years were assigned as
yearling smolts in the comparisons made. This does not seriously alter
the indicated survival relationships because of the small total migration
in 1951 and the very low percentage oi age n smolts in 1952. The maxi-
mum possible degree of error is trivial (Table 10). Determination of
Smolts from Wood River Lakes 267
age co~;r.>sition in the 1953 seaward migration was more complete, and
the ·v-alue of 4. 7 per cent age II smolts is believed to be a reasonable
approximation.
TABLE 9. INDEXES OF ABUNDANCE OF WOOD RIVER SMOLTS
BY AGE (1952 = 100) -
Year of Per Cent Wood River Smelt
Seaward Abundance Ind<.:!x
Migration Age II Age I Age II Total
1951 <20.0 9.9
1952 < 1.0 100.0
1953 app. 4.7 282.2 13.9 296.1
1954 4.2 420.4 18.4 438.6
1955 2.0 217.3 4.4 221.7
1956 21.6 258.2 71.2 329.4
1957 19.3 133.6 31.9 165.5
1958 35.0 150.0 80.8 230.8
TABLE 10 . WOOD RIVER ESCAPEMENTS AND SMOLTS PRODUCED
Wood River Index Values of Index Units
Year Escapement Smelts Produced per 1,000
Age I Age II
1949 101,000
:nso 452,000 100.0 13.9
1951 458,000 282.2 18.4
1952 227,000 420.4 4.4
1953 516,000 217.3 71.2
1954 571,000 258.2 31.9
1955 1,383,000 133.6 80.8
-
*Using maximum values of 20 per cent
migration and 1 per cent age II smelts
index values would be:
1949 year cla.ss
1950 year class
8.9
11.?. 9
Total Spawners
9.9* .10
113.9* .25
300.6 .66
424.8 1.87
288.5 .56
290.1 .51
214.4 .16
age II smelts in 1951
in ~952, the smelt
During the years 1949-52 Wood River escapement data were obtained
by comprehensive ground sur\reys of the spawning areas, supplemented
by aerial survey estimates. Since 1953 total escapement estimates have
been obtained by the much more accurate method of trunk stream enu-
meration from towers situated on Wood River. The spawning ground
surveys were continued after 1953, and provided a basis for adjusting
the 1949-52 escapement estimates to represent total escapement esti-
mates for the system. Values given in Table 10 were determined and
provided by John R. Gilbert, who has summarized the Fisheries Re ...
search Institute spawning-survey data for this period.
268 Alaska Red Salmon
The relations between values representing parent escapement of red
salmon to the Wood River spawning grounds and smolts produced are
given in Table 10 3..t,d graphed in Figure 10. The rate of reproduction is
represented by the number of smolt-index units per 1,000 pa..t'ent snwn-
ers. While survival values !or the brood years 1951, 1953, and 1954
are closely gr.ouped, values for the remaining four years fail to :fall in
line. The best rate of reproduction, that of 1952, was 19 times that
of the poorest, 1949. No definite reh.tion between size of escapement
and smolt index is seen. The two extremes of escapement provided the
poorest reproduction r-=ale. It appears that conditions for survival were
more important than abundance of spawners in determining abundance
of smolts.
Minor changes in the relation between years would be expected il
survival values were corrected for differences between years ii1 average
fecundity of females and in sex ratio. The primary factor influencing
average fecundity would be marine-age composition of female spawners.
Mathisen (1962) showed an average fecundity of 3,639 eggs for female
red salmon returning to Pick Creek, Lake NeJrlr..a, after two winters in
the ocean, and an average fecundity of 4,290 for those returning after
three Winters. The proportions of the two groups, small and large fe-
males;-in the Wood River escapement varied between 23 and 84 per cent
small females during the years 1949-55. Sex ratio of escapement during
these years could not be determined with accuracy. Values obtained
ranged between 52 and 60 per cent females. Approximated corrections
for se;x ratio and fecundity were applied to the data but were found to
modify only slightly the highly variable relation between parent escape-
ment and smolts produced.
Influence of Climate on Timing of Seaward lr1igratirm
Causes for fluctuations in fresh-water survival rate must be sought
in changes in the ecosystem to which salmon are susceptible. Varia-
bility in seasonal timing of seaward migration and in growth attained
by smolts is a reflection of differences between years in conditions of
fresh-water environment. Foerster (1937) demonstrated that differ-
ences between years in timing of seaward migration at Cultus Lake were
largely associated with water temperatures in months immediately pre-
ceding and during migration. As to lakes that freeze over, it was soon
learned that seaward migration of sockeye followed shortly after breakup
of lake ice (Babcock, 1904; Chamberlain, 1907), so that differences in
timing of migration were associated with differences between years in
dates of breakup of lake ice.
Cessation of seaward migration has also been associated with rising
water temperatures (Chamberlain, 1907; Ward, 1932; Foerster, 1937;
Parker and Vincent [1956]). At Cultus Lake, Foerster found, over a
Smolts from Wood River Lakes 269
period of nine years, a close relationship between rising mean daily
temperatures in Sweitzer Creek and cessation of seaward migration.
He stated: "When surface waters rise above 10° C the passage of young
sockeye appears to be inhibited and consequently, as summer stratifi-
cation is set up and the epilimnial v..-a.ters rapidly increase in tempera-
ture, they form a temperature barrier or ~lanket to terminate the further
migration of sockeye" (Foerster, 1937). This ntemperature barrier"
to seaward migration of red salmon was first d~scribed by Ward in an
attem].X to explai,n the origin af landlocked sockeye in Baker Lake, Wash-
ington. His cornrnent is: ''When the surface water of the lake passes 10° C
the ptigrators which have been continuously at or near the surface appear
to desert that level and withdraw into deeper layers" (Wa,rd, 1932).
Striking differences in seasonal timing of Wood River seaward migra-
tions have occurred during the year~ un9,er study. These differences
were measured by daily changes in magnitude of smolt catches made by
the index iyke net at the outlet of the Wood River lakes. The cumulative-
catch curves of Figure 11 show as much as a month's difference between
years i..tl seasonal timing of pe'ak catches.
At least four influences had a significant effect on timing of migration
in t..~e Wood River lakes. The most influential factor was climate. How-
ever, changes in rel~tive numbers in the component s'ubpopulations of
smelts from the lakes, differences between years in size and age of
smolts, and differences in rate of growth in early summer appeared to
contribute. The last three factors will be discussed i.p a later section.
Changes in smolt behavior associated with changes in water tempera-
ture have been observed since the beginning of these studies in 1949.
The start of substantial seaward migration has been consistently delayed
until lake outlet temperatures reach 38°-39° F following breakup of lake
ice in late May or early June. Timing of initial migration was closely
associated with breakup of ice on Lake Aleknagik in spring. This is
shown in Table 11 where the years are listed in order of date of brea.h.~p
and dates by which time 5, 10, and 20 per cent of the season's index
catch had been made. For the 5 per cent dates, the years fell essen-
tially in the same orde:r as the date of lake ice breakup. This initial
sequence was modified by the continuing influence of weather and other
factors; yet by the time 20 per cent of the .mtgration was over, the re-
lation to date of brea.lrup was still 2Lpparent.
Cessation of seaward migration coincided quite closely with warming
to over 50° F (10° C) of the lake-su.rface waters m.?asured at the Lake
Nerka weather station. Records of lake-surface temperature for the
seasons 1952 through 1957 are graphed in Figure 12. Dates by which
time the lake-surface temperatures at the Lake Nerka. station passed
and remained above 50° F varied over: a month between years, ranging
from June 16 in 1954 to July 21 in 1955. These dat~.s were compared with
dates by which time 90 per cent of the season's cumulative-index catch
270 Alaska Red Salmon
TABLE 11. REI.ATION .bETWEEN DATES OF BREAKu'"P OF LAKE ICE ON
LAKE ALEKN.<\GIK AND EARLY-SEASON SEAWARD MIGRATION OF
RED SALMON SMOLTS AT WOOD RIVER INDEX SITE
Breakup Dt~.te, Date 5% of Date 10% of Date 20% of
Year* Migration Migration Migration Lake Aleknagik O'ver Over Over
1954 May 26 June 1 June 2 June 2
1953 May 27 May 31 June 3 June 11
1957 May 28 June 2 June 7 June 12
1951 May 30 June 4 June 7 June 9
1956 June 1-3 June 10 June 12 June 15
1952 June 7 June 11 June 12 June 14
1955 June 10 June 23 June 26 June 29
*Years listed in order of breakup date.
had been taken at Mosquito Point. The smolt catch each year falls off
rapidly beginning at about this time of year (see Fig. 11). In Table 12
it is demonstrated that in five of the six years, the 90 per cent level
was passed within a very few days of the date the lake-surface temper-
ature reached 50° F. Cessation of migration is probably closely as-
sociated with a general thermal ((!hangs in the lake epilimnion.
TABLE 12. RELATION BETWEE:N' LAKE-SURFACE TEMPERATURES
AT LAKE NERKA WEAT".riER S'l'A'l'ION AND SEASONAL TIMING
OF SMOLT SEAWARD MIGRATION AT WOOD RIVER
Year
1954
1957
1953
1956
1952
1~55
Date Surface TempeJ:-atures
at Cabin Bay, Lake Nerka
First Rose over 50 11 F for
Longer Than One-day Period
Jwte 16
June 16
June 21
July B
July 19
,July 21
Date C"Umu1ative
Smolt Catch Reached
90% at Wood River
Index Site
June 15
June 26
June 23
July 12
July 19
July 16
The relation between a~.nnual timing of smolt migration, breakup of
lake ice, and la..lte temp~r~mres following breakup is shown in Figure 13
for the years 1952 through 1957. For each year, the time interval be-
tween breakup and attainment of 50° Flake-surface temperature is com-
pared with the 5 per cent and 90 per cent levels of migration. Delay in
ice breakup and warming of the lake resulted in delay in smolt migration
from the lakes.
As to sockeye yearlings remaining behind in the lake, Ward (1932)
and Foerster (1937) suggested that rising temperatures create an epi-
limniallayer of warm water through which the fingerlings are reluc-
Smolts from Wood River Lakes 271
tant to pass. No such reluctance on the part of red fingerlings has been
observed in the Wood River lakes, for the greatest concentrations ob-
served inshore and near the surface at Lake Nerka were seen during
the week or ten days after surface temperatures exceeded 50° F (10° C).
The record catch of red fingerlings made in surface lake traps fished
for six years at Lake Nerka was made on a day the surface tempera-
ture at the trap site read 61° F (16.1° C).
Summer Grawth of Yearlings Prior to Seaward Migration
Growth as Indicated by Scales
While temperature has been shown to influence timing of seaward mi-
gration, and is known to affect growth as well, there seems to be no pub-
lished data showing that temperature differences between seasons directly
affect growth of young sockeye in the lakes. Differences between years
in size of smolts are usually associated with differences in population
density or in food level rather than with climate. Indirect evidence of
the effect of climate on growth was given by Krogius and Krokhin (1948,
1956a), who stated that at Lake Dalnee annual fluctuations in abundance
of plankton were closely associated with variations in completeness and
intensity of spring overturn and with depth of thermocline. Biogenic
elements were considered to be more thoroughly circulated in years of
more complete overturn and more available to phytoplankton in the epi-
limnion if the epilimnion was thick. It was suggested further that magni-
tude of the plankton . rop affected the size of smolts, although the evi-
dence given does not appear to be at all clear-cut.
In the preceding section it was shown that seasonal climatic conditions
affected timjng of seaward migration. It will be shown in the discussion
to follow that differences in climatic conditions have a definite bearing
upon the amount of growth gained by red salmon yearlings :in June and
early July prior to seaward migration.
The amount of new summer growth that has occurred prior to seaward
migration is .indicated on a scale of a yearling smolt by the increment of
new growth formed beyond the annulus. As shown by the scales, growth
is negligible in the spring prior to breakup of lake ice, but following
breakup and warming of lake waters a rapid increase in size of yearlings
occurs in the lakes. This is indicated on the scales of yearlings by a
band of wide circuli laid down beyond the broken, narrowly spaced rings
of the annulus (Fig. 14).
Increase in scale radius, measured from the focus of the scale, is
not strictly proportional to increase in length of fish over the size ranges
with which we are concerned. Investigators have found that in juveniles
of many different species of tish there is an extended period after scale
formation when the linear dimensions of the scale increase at a rela-
tively faster rate than does the length of the fish. Dunlop (1924) det.:t;r-
272 Alaska Red Salmon
mined that sockeye of the lower Fraser River show a fairly constant
increase in scale radius relative to length of fish between 35 and 100 mm,
a lessening rate to 115 mm, a.'ld a decreasing ratio above 115 mm. Meas-
urements were presu.mably made from preserved specimens. Clutter and
Whitesel (1956) gave tht: relation between mean scale radius (greatest
scale radius, magnified 200x, measured from focus to edge of scale)
and .mean fork length as established by 12 samples of preserved Fraser
River sockeye smolts with mean lengths ranging from approximately
50-150 mm. Their linear equation for the regression line was:
radius = 1.323 fork length -33.11
The writer has also found a proportionately greater increase in scale
radius than in body length of preserved fish over lengths encountered in
age I and age II groups of fingerlings from Wood .River lakes. The per-
centage increase in scale radius was about one-third greater than the
percentage length increase between fish of 80 and 108 mm fork length.
Smolt samples taken in 1953 at Mosquito Point illustrate changes in
amount of summer growth appearing on scales of smolts at different
times during the season. In each sample, scales were mounted from
two fish of each millimeter length in the sample or of one fish of each
length if two were not available. Several scales were mounted from
each fish. The scales were taken from the area immediately above the
lateral line slightly forward of the adipose fin.
The scales were first projected at high magnification and the most
symmetrical from each fish was chosen for measurem...;nt. This scale
was then projected on line paper and the circuli marked off along a Hne,
beginning at the center of the central plate and extending to the scale
edge along the longest axis of the scale. The amount of new summer
growth in the scale was calculated by measuring the distance from the
narrowest. circulus, assumed to represent the outer edge of the annulus,
to the sca1e edge. Percentage of growth made during the current summer
was computed as 100 times this measurement divided by the total pro-
jected distance from mid-central plate to scale edge.
No measurable amount of summer growth was discernible in the first
four samples, taken on June 1, 3, 6, and 12, 1953. The amounts of
summer growth measured on the scales in samples taken after these
dates are presented in Table 13. Percentages were grouped according
to length of fish since it was conceivable that percentage of summer
growth showing on the scales might vary with fish length. However, the
percentage of summer growth on the anterior scale radius was about
the same for all size groups in each sample (Table 13).
Sample averages show a steady increase in summer growth between
June 16 and July 15, on which date 30.9 per cent of the scale radius
constituted new growti1. Increase in summer growth on the scales and
TABLE 13. SUMMARY TABLE OF AMOUNT OF NEW SUMMER GROW'1\H APPEARING ON SCALES OF RED D:ARLINGS IN
SEAWARD MIGRANT SAMPLES TAKEN AT MOSQU!!O POINT, 4AKE ALEKNAGIK, 1953
Length of June 16 June 22 June 28
~'ish in Number Average Per Cent I Number Average Per Cent Number Average Per Cent
Millimeters of Fish Summ.er Growth of Fish Summer Growth of Fish Summer Growth
73-77 8 3.6 8 10.1 6 15.7
78-82 10 1.9 9 12.3 9 16.8
83-87 8 4.5 9 14.4 9 15.8
88-92 18 2.7 10 11.7 8 14.7
93-97 4 3.4 8 10.2 7 15.3
98-102 1 o.o ----
103-101 - -
----
TOTAL 49 44 39
AVERAGE 3.0 11.8 15.7
Length of July 4 July 9 July 15
Fish in Number Average Per Cent Number Average Per Cent Number Average Per Cent
'Hi1limeters of Fish Summer Growth of Fish Su;mner Growth of Fish Summer Growth
73-77 --1 27.6 --
78-82 8 22.4 2 24.5 5 32.8
83-87 7 19.1 7 28.0 10 30.7
88-92 9 20.0 11 26.7 7 30.4
93-97 5 23.5 7 21.3 2 22.8
98-102 4 23.8 2 22.7 2 30.6
103-107 --1 22.8 9 31.4
108-112 ----1 33.6
113-117 __.. ---1 35.8
TOTAL 33 31 37
AVERAGE 21.4 25.3 30.9
-------~--··-·--·--· ----------------·----------------------"--
I
274 Alaska E!ed Salmon
the dates involved are shown graphically in Figure 15. The delay in first
appearance of summer growth is very similar to that found by Dombroski
(1952) for 1951 Babine Lake smolts.
Measurements of new growth on the scales illustrate summer growth
increments are to be found in smolt samples taken at successive dates
during the migration period. The inc:t'ement pattern is not necessarily the
same as would be obtained by repeated sampling of a single population of
fish within the lakes prior to migration, but does represent growth as ob-
served in successive groups of seaward migrants. As will be discussed
later, main seaward migration is generally completed before substantial
summer growth appears on scales of migrating year lings.
Relationship between Scale-Growth Increments and Seasonal Climate
The time of the appearance of summer growth on scales V'a.ried between
years. Much of the difference in timing could be related to differences
in climate between years, just as the time of seaward migration was in-
fluenced by climatic factors.
The difference between years in time of appearance of summer growth
is illustrated by comparing the average amount of growth beyond the an-
nulus present on scales of yearling smelts sampled on the same date
each season. In this instance July 5 was selected, since by this date
summer growth is normally well differentiated on scal~s, yet some
migraUon is still in progress. Smolt samples which had been preserved
on or very close to July 5 were available for the years 1952 through
1957. Dates of samples, numbers of scales measured, and average
percentages of summer growth found along the longest axis of the scale
radius are given in Table 14.
?ABLE 14. PERCENTAGE OF NEW SEASON GRO~T.H ON SMOLT
SCALES, 1952-57*
Date of l{t•:!nber Per Cent New Season
Year of Scales Growth on Scales Saniple Measured Mean Standard Error
1952 July 7 30 7,9 1.15
1953 July 4 33 21.5 1.13
1954 July 5 55 19.9 0.70
1955 July s). 50 6.0 1.02 July sf
1956 July 5 22 4.5 I 1.26
1957 July 6 32 20.7 0.88
*Samples taken at Wood River fyke-net site on or near
July 5.
Two rather simple measures of late spring climatic differences among
these years are used for compu-ison with scale growth. The first meas-
urement is date of lake-ice breakup at Lake Nerka, central lake in the
Smolts from Wood River Lakes 275
Wood River chain. The second is based on temperature records be• ween
breakup and the time when samples were drawn in earJy July. I.1 this
case, daily mean air temperatures were used rather than water tenper-
atures, first, because daily water temperature records were not avail-
able for all years, and second, because surface temperatures can: 10t be
expected to reflect too closely transfer of heat into the lake. It is prob-
able that mean air temperatures give a more accurate index t >lake
warming than do water surface temperatures. Differences betweell sea-
sons in air temperature were measured by the cumulative number of
air "temperature units" beginning with the date of breakup of lal:e ice.
The number of temperature units per day was set as the differen!e be-
tween the mean temperature for the day and 32° F.
In Table 15 the years 1952-57 are listed in order Df time of l~ke-ice
breakup. Included, in addition, are the date on which the smolt flample
was drawn for scale measurement, average percentage summer ~owth
found on the scales, number of days from breakup to date of sample,
and cumulative number of air temperature units from breakup to date
of sampling. The years 1953, 1954, and 1957 group together a~. years
of early breakup with a large number of cumulative temperatuxe units
and a large amount of new growth on smolt scales by July 5. Convarsely,
the late breakup years 1952, 1955, and 1956 show fewer curr;ulative
temperatm·B-units ;md little summer growth on smelt scales. A closer
linear relation appea:rs to exist between cumulative temperat1re and
scale growth than between length of time after breakup and scale growth
(Figs. 16A, 16B).
Year
1954
1953
1957
1952
1956
].955
TABLE 15. RELATION BETWEEN AMOUNT OF NEW SUMMER GROWTH
ON SMOLT SCALES, TIME OF LAKE-ICE BREAKUP 1 AND
TEMPERATURE FOLLOWING BREAKUP
Date of Per Cent New
Season Growth Sample on Scale Radius
July 5 19.9
July 4 21.5
July 6 20.7
July 7 7.9
July 5 4.5
July 6} 6.0
I July 8
Number of
Days from Lake
Nerka Breakup
40
35
34
30
24
22-24
Cumulat. ve Air
Pate
ple
TU' s to
of Sat\
844
805
863
548
44&
382
The existence of t.l).e relation betweAn spring temperatu:..·es and g·rowth
of red fingerlings should not be regarded as proof of direct camle and
effect. Tempe.t'ature records are simply one measure of gener2.1 dif-
ferences in environment caused by climatic conditions. Prior to spring
breakup in Bristol Bay lakes, the surface layer of snow and ice insttlates
the water below from increasing warmth of spring air, penetrat .on of
light, and mixing action of wind. Following breakup, surface tern .. >era-
276 Alaska Red Salmon
tures rise quickly to 38°-39° F. Spring overturn of the lake occurs ac-
companied by rise of nutrients from fue lake bottom, and the amount of
solar radiation inc:reases steadily toward a maximurn in Jtme. At break-
up, and for about two and ..:me-half weeka, there is no indication of re-
cent growth on fingerling scales. This is to be expected since the plank-
ton bloom associated with sprjng overturn and increased light and tem-
perature is not instantaneous. Lag in abqndance of copepod and cladoceran
feed, combined with reduced metabolism and activUy of the fish until
warming of their environment occurs, results in no growth on finger ling
scales until an accumulation of about 300 temperature units has occurred.
Weather and temperature before breakup have little apparent eifect1
then, on subsequent summer growth and activity of young red salmon in
the lakes except by their influence on time of breakup of lake ice. How-
ever, air temperatures after breakup are shown to bear a relationship
to growth attained by young salmon. The amount of sunshine, the 84'ttent,
direction, and timing of wind action, and the amount of rainfall are ad-
ditional factors known to influence the summer temperature regimen in
the lakes. These also affect to some degree the growth of phytoplankton 1
zooplankton, insect, and fish populations within the lakes.
Seasanal Changes in Length Frequency of Srnolts
Pattern of Seasonal Changes
Seasonal changes in length frequency and age of smolts have been de-
scribed by a number of biologists. In many red salmon populations,
smolts migrating ear li&r in the season tend to be larger than later mi-
grants of the same year. class. Ba't"naby (1944) found a ma.th.ed decrease
in average size of age ill smolts du.t,ing successive weeks of sampling at
Karl;,lk Lake in the years 1925-36. A less marked difference in age IT
smo:ts was attributed to the fact that L'l.ter rrligrants had added new sum-
mer growth. He concluded that "the urge to migrate seaward is related
to the size a.nd growth rate of fingerlings .... " Gilbert (1916, 1918)
also found a consistent seasonal decrease in yearling smolt size of Rivers
Inlet sockeye durl11g the yea.i:'s 1914 through 1916. Clutter and Vlhitesel
(1956) reported that ~ .,_ various sockeye populations of the Fraser River
syr::tem, yearling smolts were of fairly consi.stent size dur]ng the main
migratory period but frequently exhibited some trend towards size de-
crease during the season. An exception to seasonal decrease in size was
reported by Dombroski (1954), who found a definite seasonal trend of in-
crease in length and weight of Babint~ Lake yearlings in the years 1950,
1951, and 1953. The inc.~. eases were probably ascribable to additional
growth gains in the summer shortly before migration, shown by Dom-
broski. (1952) for the later migrants of 1951, or to th,~ contribution to
th.e migration made by Nilkitkwa Lake smolts, which may be first to
appear in numbers in the migration because of close proximity to the
Smolts from Wood River Lakes 277
system outlet, but which tend to be smaller in certain years because
of poplla.tion density (Johnson, 1956, 1958). Parker and Vincent [1956]
hypothesized that differential timing of migration of two different races
was the cause of some of the seasonal changes found in size of smolts
at Lake Kitoi in 1955.
In the Wood River lakes, study of size changes in smolts occurring
during the season revealed that the seaward migration of young red sal-
mon passing Mosquito Point was by no means composed of a homogeneous
stock of fish, and that distinct seasonal patterns of change occurred.
Seasonal patterns of change in numbers of different size and age groups
were of special interest in that they provided an insight into causes of
the marked duferences found, and particularly in that a relation was
indicated between size and survival rates.
Length frequencies of smolt samples taken at Mosquito· Point and
weighted as described previously (p. 263) are graphed by five-day periods
in Figures 17 to 20. These graphs present seasonal changes that oc-
curred in numbers, sizes, and ages of smolts migrating in the years
1954-57. In the graphs, the first period in 1955 and the last period in
all four years have been extended to include more than five days because
of low levels of migration at these times. In Figure 21 the season's fre-
quencies for the four years are presented. The season's frequencies
for 1958 and 1959, provided by Koo, are also included.
Features to be noted in these graphs are differences in timing of mi-
gration (already explained in part by differences between years in cli-
mate), differences in age composition, and seasonal and annual differ-
ences in size of smolts in the migrations. Especially noteworthy is the
bimodal size frequency of age I smolts in 1955, 1957, and 1958.
Migration during the years 1952 through 1957 followed a general pat-
tern. Yearling migrants (age I) passing Mosquito Point during the first
several days of the season were small, and the first waves of large
yearlings reached Mosquito Point several days after migration had be-
gun. Grouped frequencies of 1957 provide the clearest illustration of
this phenomenon (Fig. 20). Particularly in the years when the size
range was great, as in 1955 and 1957, yearling frequencies were dis-
tinctly bimodal. The difference in size cannot be accounted for by dif-
ferences in amount of recent summer growth. Initial appearance of large
yearlings at the lake outlet occurred well before summer growth was
registered on the scales, and the major share of the season's migration
was over before appreciable summer growth on the scales was found.
In the Wood River lakes a tendency was apparent, pronounced in cer-
tain years, for the modal group of large yearling migrants to decrease
in average length during the season until rapid new summer growth re-
versed the trend. However, the modal group of small yearlings was first
to appear at the outlet of the lake system-an apparent reversal of the
pattern that larger smolts tend to migrate first (Barnaby, 1944; Gilbert,
278 Alaska Red Salmon
1916, 1918; Clutter and Whitesel, 1956). Furthermore, smaller smolts
tended to complete migration earlier in the season. This, in addition to
other evidence, led to the hypothesis that the migrations commonly are
comprised of numerous groups of smolts which have experienced dif-
ferent growing conditions in different parts of the several lakes. The
small early migrants were believed to be fl~om Lake Aleknagik, the lower
lake in the system, and the waves of larg:er migrants from Lake Nerka
and other upper lakes. It was of particular interest to test this hypothe-
sis, since it would aid in determining what conditions are responsible
for size achieved by the smolts.
Effect of Lake-Ice Braakup and Distance from
Outlet on Pattern of Seasonal Migration
The timing of ice breakup in the various lakes of the Wood River sys-
tenl suggests that smolts from the upper la#:~'S would be later in reaching
Mosquito Point. Substantial seaward migration has never been observed
during spring fyke-netting operations at Wood River, Little Togiak River,
and Aguluk.pak. River until the lake outlet temperatures have reached at
least 39° F following breakup of the lake ice. This is in agreement with
migration threshold temperatures of approximately 40° F, reported for
sockeye fingerlings in lakes with winter t,emperatures falling below this
level (Chamberlain, 1907; Foerster, 1937, 1952; Parker and Vincent,
[1956)). Any delay in ice breakup of the upper lakes in the Wood River
syste1n might therefore be expected to delay arrival of upper-lake mi-
grants at Mosquito Point. Lake Aleknagik has in every year been the
first to become ice free, although brealrup on Lake Nerka may occur
the same day. The contrast between years in breakup sequence is some-
times rnarked; for example, 1954 versus Jl956 (Table 16).
TABLE 16. SEQUENCE OF LAKE-ICE BREAKUP IN 1954 AND 1956
Lake
Aleknagik
Nerka
Little Togiak
Kulik
Breakup Date
1954 1956
May 26
May 26
Before May 30
(No record)
June 1-3
June 11
June 15
June 20 (approx.)
The colder 1956 season extended the breakup period, and the ice cover on
the lakes delayed the arrival of threshold temperatures for migration in
the upper lakes areas.
The rate of smolt migration between the outlet of Lake Nerka and
the outlet of Lake Aleknagik at Mosquito Point, a distance of 18 miles,
is not known. How.ever, marking and recovery experiments conducted
in 1956 shed some light on possible rates of migration. The maximum
rate of movement of red fingerlings released from the Catherine Cove
.....
Smolts from Wood River Lakes 279
(Lake Nerka) lake trap was recorded on July 23. Seven of these tattooed
fish were observed the following day in Cabin Bay, Lake Nerka, a dis-
t~ce of 5 miles from point of release. Thirteen fish tattooed .in marking
experiments on red fingerlings migrating out of Little Togiak Lake were
subsequently recaptured at the outlet of Aleknagik, 40 miles distant. The
minimum length of time before ,"ecapture was 11 days. The shortest
lapse of time between release of h~ttooed red fingerlings from a Lake
Nerka lake trap and their hrrival at the outlet of Aleknagik, a distance
of 34 miles, was 8 days. Tl:i.3Se experiments indicated a maximum rate
of travel, measured in a direct water route, of 4-5 miles per day.
Although the migration rates should not be taken too seriously because
of the small numbers of !'ecoveries and the possible effect of tattooing
on normal behavior, it is to be expected that fingerlings already in Alek-
nagik before breakup woulcl be first to pass Mosquito Point, and also
that over-all timing of seaward migration durir~ a season would be af-
fected to some degree by relative numbers in 1nigrant populations orig-
inating in different lake areas.
Substantiating evidence that Aleknagik smolts are first to migrate
seaward was presented by Koo (1962), who showed that later-migrating
yearling smolts had more new-season, or ''plus," growth on their scales,
and that the amount of fresh-water plus growth found on scales of re-
turning adults was directly related to distance from their lake of origin
to the outlet of the system at Mosquito Point.
Origin of Size Groups in the 1955 Seaward Migration
In a search for additional evidence of origin of different smolt size
groups in the Wood River lakes, the writer made detailed studies of the
1953 year class of Wood River red salmon. This year class was chosen
because yearlings migrating in 1955 exhibited the most striking bimo-
dality in size frequency (Fig. 21) and hence offered the best chance of
recognition in later life stages available for examination.
In the 1955 yearling migration (1953 year class), small yearlings were
first to appear at Mosquito Point, and during the first 10 days of fyke
netting no other yearling sizes were caught. Although the largest migra-
tion of this small size group did not occur until July 10, fairly late in
the season, there was no evidence that this group had moved down from
upper-lake areas. No small yearlings of the size group in question were
encountered in samples from Lake Nerka lake traps or Little Togiak
River fyke-net samples in 1955. A large contingent of small 1955 year-
lings remained an extra year in the lakes, the survivors ma.ldng up the
particularly heavy migration of small age II smolts at the beginning of
the 1956 season (Fig. 19). These small age II fish also were not encoun-
tered in samples from the upper lakes area~ including Little Togiak Lake,
Lake Nerka, and Lake Kulik. Presumably they grew in Lake Aleknagik.
280 Alaska Red Salmon
To settle the question oi the origin of small smolts migrating in 1955 as
yearlings and in 1956 as age II fish, it was necessary to examine scales
from adults of the 1953 year class returning to spawning grounds in
1957 through 1959. H the small smolts did indeed originate only in Lake
Aleknagik and· the large smolts in the upper lakes of the Wood River
system, the nuGlear area of the scales of adult reds from the 1953 year
class taken on the spawning beds in the different lakes should show dif-
ferences in amount of fresh-water growth because of the strong tendency
of red salmon to return to their original birthplace for spawnifig.
Scales used in this study were taken from the fish just above the lateral
line and between dorsal and adipose fins, shown by Koo (1962) and Clutter
and Whitesel (1956) to be in the area of first :.; .. ;3le formation. The meas-
urement chosen for comparison of scales from 1955 yearling smolts with
scales from returning adults was the anterior radius from focus to outer
edge of the fresh-water annulus. Tfrls measurement was chosen in pref-
erence to the radius from focus to edge of fresh-water growth because
of the possibility that additional growth appearing after the fish migrated
from the lakss may not always be distinguishable from the widening
circuli of summer lacustrine growth. Scale-radius measurements were
used instead of circulus counts because the former are a more direct
index to fish size. For simplicity of procedure the longest radius from
focus to edge of the first annulus was used. To facilitate measurement,
the images of smolt and adult scales were projected onto a table with
the apparatus described by Koo (1962) at a magnification of 230 times.
In the analysjs presented here, scale samples were utilized from the
first returning contingent of the 1953 year class, i.e., four-year-olds
taken on the spawning grounds in 1957 that had Iiligrated seaward as
yearlings in 1955 and returned as adults after two winters in the ocean. 2
Koo (1962) found that the fresh-water growth pattern determined from
scales of adults returning after twc· winters in the ocean does not differ
from that of those returning to the same spawning area after three win-
ters in the ocean, if the scales have been collected from a single year
class migrating seaward in the same year. Therefore, it was assumed
that comparison of the scales of yearling smolts of the two size groups
encountered in 1955 with scales of the single age group of adults that re-
turned in 1957 would provide reliable data. (Analysis of scales of adults
returning in 1958, after three winters in the ocean, has since confirmed
this assumption.) The scale photomicrographs in Figure 22 illustrate dif-
ferences between the two smolt sizes in scale growth and the similarity
to be found in scale pattern of smolts and adults of the same year clasE:i.
The 1957 scale samples from adult reds were collected from dead fish
2 Scale formula 1.2 (Koo, 1962) or 42 (Gilbert and Rich, 1927). This is
one of the two main age groups in the Nushagak District, the other the
five-year-olds, scale formula 1.3, or :>2 •
....
Smolts from Wood River Lakes 281
on the various spawning grounds during spawning area studies under the
supervision of J. R. Gilbert. In most instances, the marginal portions of
adult scales were too resorbed to permit counting the number of marine
annuli. Therefore, individuals that had spent but two winters at sea were
identified by length measurement. This was possible bet~ause length is
influenced by the number of winters the fish remain in the ocean. The
smaller adults of both sexes are those fish that have spent two winters
in the ocean; the larger fish have spent primarily thrue, occasionally
four winters in the ocean (Koo, 1962). Because there is some overlap
in length of the two groups, it was necessary to select fish of lengths
falling well below the intercept of the two modal length-frequency groups
to be reasonably certain that the adults used for scale study had spent
only two winters at sea. Males of lengths between 430 and 510 mm and fe-
males between 400 and 490 mm, mid-eye to tail fork, were used. Scales
of 25 of these fish from each of the spawning ground~ sampled were
measured if available. Sexes were combined in treatment since no ap-
preciable difference in amount of lacustrine scale growth has been found
between sexes of red salmon (Clutter and Whitesel, 1956).
Several samples, collected at intervals throughout the main smolt
migration period, were utilized for measurement of 1955 yearling smolt
scales. Scale measurements were first made without reference to length
of the fish, and were later classified by fish length. Scales from fish
of lengths between 68 and 77 mm, inclusive, were used to represent the
mode of small yearling smolts, and scales from fish of lengths between
83 and 102 mm, inclusive, to represent the mode of large 1955 yearlings
(Fig. 23).
Radius-measurement frequencies of 1955 yearling smolt scales, grouped
to 5-millimeter intervals, are presented in Figure 24. Superimposed on
the frequency of small-yearling scale measurements are corresponding
frequencies taken from returning Aleknagik spawners, and on the fre-
quency of large-yearling scale measurements, corresponding ft~equencies
from returnees to the other Wood River lakes. The close correspondence
in amount of scale growth to the first annulus between small smolts and
returning spawners to Aleknagik and between large smolts and upper-
lakes spawners establishes the fact that the small smolts migrating in
1955 did inhabit Lake Aleknagik during their fresh-water growth.
Radius measurements of adult scales from focus to edge of the fresh-
water armulus are presented classified by spawning ground in Figure 25.
Locations of spawning areas repre3ented are shown in Figure 26. As
will be discussed later, few scales of small adults from Lake Aleknagik
were available so these are grouped 1:ogether in the graph. None of the
adults sampled from Agulowak River, tributary to Lake Aleknagik, fell
in the small size category, the 1957 escapement there being almost en-
tirely of five-year-old Lsh with three years of ocean residence.
The greatest number of scale samples were collected from Lake Nerka
282 Alaska Red Salmon
where the majority of salmon spawned in 1957. Scale measurement data
for samples from this lake were examined to determine whether there
was any relation between type or location of spawning area and amount
of growth achieved during the first year. An F test was first applied to
test homogeneity of the set of scale measurement means of the samples
from the Lake Nerka spawning areas (Table 17). A very large F ratio,
significant at the 1 per cent level, was obtained; hence the hypothesis
of homogeneity was rejected, indicating that one or more of the differ-
ences between means was significant.
TABLE 17. MEASUREMENT* DATA FROM SCALES OF ADULT RED SALMON, SCALE
FORMULA 1.2, LAKE NERKA, 1957, SHOWING ANALYSIS OF VARIANCE TEST
Spawning Area lti :LXii X;. I; x;j
River Bay 25 2,529 101.2 258,649
Fenno Creek 25 2,608 104.3 275,414
Allah Beach 25 2,568 102.7 265,388
Stovall Creek 25 2,725 109.0 298,539
N-4 Beach 25 2,456 98.2 244,430
Pick Creek 25 2,624 105.0 277,088
Anvil Bay 25 2,348 93.9 223,334
Kema Creek 25 2,297 91.9 214,281
Agulukpak River 25 2,234 89.4 201,204
TOTAL 225 22,389 2,258,327
*Measurement: focus to outer edge of first annulus in mm; magnifica-
tion 230x.
Analysis of Variance of Scale Measurements
Source of Degrees of Sum of Mean F
Variation Freedom Squares Square
Between areas 8 21,722 2,715.25 69.23
Within areas 216 8,573 39.22
TOTAL 224 30,295 -
F.99 :::::: 2.60
In order to reach a decision as to which of the differences among the
means could be considered significant and which not, a multiple-range
test proposed by Duncan (1955) was applied. Values from his table of
"special significant studentized ranges" were multiplied by the standard
error to obtain a series of "shortest significant ranges" between means.
The means are ranked in order, and the difference between any two
means is considered significant if it exceeds the corresponding shortest
significant range for the number of means involved in the range under
Smolts from Wood R:iver Lakes 283
consideration. Results of the multiple range test are presented in Table
18.
TABLE 18. St.Jm!ARY SHEE'r OF MULTIPLE RANGE TEST FOR SIGNIFICANCE OF DIFFERENCES llETWEEN SAMPLE
MEANS, SCAL:>: RADIUS TO FIRST ANNULUS, OF RED SALMON IN LAKE NERKA SPAWNING AREAS*
Standard error of mean,
s~ = 1.253
Number of means in range 2 3 4 5 6 7 8 9
Shortest significant range,
5 per cent level 3.17 3.66 3.78 3.87 3.95 4.00 4.05 4.08
U~per Lake Nerka Lower Lake Nerka
Beacn Spawning Creek Spawning
Area nwnbers 11 10 9 6 2 4 3 7 5
Localities Agulukpak Kema Anvil N-4 River Allah Fenno Pick Stovall
River Creek llay Beach Bay Beach Creek Creek Creek
Heanst 89.4 91.9 93.9 98.2 101.2 102.7 104,3 105.0 109.0
*Measurement: focus to first annulus x 230. After Duncan, 1955, Table 4.
tAny two means not und~rscored by the same solid line are significantly different, Any two means
underscored by the same ~olid line are not significantly different.
The underscorings in Table 18 indicate which means are and which are
not significantly different. All six means of Lower La!ce Nerka samples
were significantly larger than the means of samples from the three
spawning populations in Upper Lake Nerka. This suggests that young in
the two sections of the lake remained somewhat segregated during their
first year, and that the Lower Lake Nerka feeding area provided better
growing conditions. Among the six spawning groups of Lower Lake Nerka,
the three beach-spawning groups showed less growth during the first
year than did the three stream groups, but there was no clear demarca-
tion between samples from the two spawning-area types: lake-beach and
stream. For this year class, it is evident that rearing-area conditions
exerted more influence on growth than did conditions for embryonic
development.
In a comparison between lakes (Fig. 27), samples from Lakes Beverley
and Kulik suggest that growth conditions for young during their first year
were similar to those in Lake Nerka. The contrast was very striking,
however, between Lake Aleknagik and the other Wood River lakes. The
scale growth of Aleknagik adults was markedly less for this period of
early life.
Causes of Difference Between Lakes in Size of Smozts Produced
Climate
Yearling smolts migrating in June or July have achieved most of their
284 Alaska Red Salmon
growth during the previous summer. For the 1955 smolts, the pr~yious
growing season, 1954, was characterized by early breakup of the lake
ice and warm lake temperatures. New summer growth appeared early
on the scales of yearlings migrating in 1954 (Table 14). As shown in a
previous section, differenceR between years in climate resulted in dif-
ferences in growth rate of you..1g salmon. However, within a single year
the entire lake system is subjected to much the same climatic conditions,
hence poor grovv-th of fry in one lake area, such as Aleknagik in 1954,
would not be expected unless it was caused by conditions other than eli-
mate. Differences between lakes in level of key nutrients or in degrees
of competition for food are suggested.
Level of Basic Nutrients
It has been proposed that in red-salmon lakes, levels of nitrogen,
phosphorus, or other biogenic elements may be limiting factors in pro-
duction of phytoplankton, hence indirectly of zooplankton and young salmon
(Barnaby, 1944; Nelson and Edmondson, 1955; Nelson, 1958; Goldman,
1958; Krokhin, 1957; Alaska Department of Fish and Game, 1959). No
comparative information on levels of critical nutrients has been collected
for the Wood River chain. The lakes are basically quite similar in mor-
phometric features, but Lake Alel:Jlllgik as the lowest lake in the series
may have the greatest amount of dissolved nutrients flowing through. It
is slightly more turbid in summer and there is no reason to suspect a
lower level of basic nutrients.
Competition for Food
Chamberlain (1907) was first to suggest that differences between years
in population density of young sockeye during lake residence might be
the cause of observed annual differences in yearling smolt sizes. Foer-
stelr {1944) demonstrated the effect of population density on size of mi-
grating smolts. He correlated weights of Cultus Lake yearlings in the
migratio11 years 1927 through 1935 with lake population densities based
on Pumbers and ages of seaward migrants. His conclusions were sup-
ported by the inverse correlation found by Ricker (1937) between zoo-
plankton abundance and population size of sockeye salmon in Cultus Lake,
!"egl.!ctim~ in plankton being assumed to be the result of grazing by young
sockeye. Rounsefell (1958) used additional Cultus Lake data from more
recent ye:a.rs to correlate biomass of smolts versus the logarithm of the
rnJmber pf smolts produced. He concluded that "the closeness of the
semilogarithmic fit suggests-that the increasing competition between
smolt~} as their numbers increase sets an asymptotic level on the bio-
mass." Analyzing Karluk Lake data, he interpreted a linear relation
betwP.en numbers and biomass of the annual smolt migrations as indi-
cating no intraspecific competition for food in the years studied. Krogilis
and Krokhin (1956) stated that in Lake Dalnee, Kamchatka, the correla-
Smolts from Wood River Lakes 285
tion was inverse between size and weight of red smolts and the number
of plankton consumers both intra-and interspecific. No relation between
pop1lation density and size of migrants was found at Lakelse Lake for the
seven brood years beginrJ.ing in 1946 (Canada, Fisheries Research Board,
1957).
Studies at Babine Lake were first to show that unequal distribution of
sockeye in a single lake can result in overcrowding and stunting (Johnson,
1956, 1958). Lake areas adjacent to main spawning concentrations were
found by tow-net sampling to be more densely populated by "underyear-
ling" young. Marked differences between years in size of young sockeye
in these areas were attributed to differences in spawning density and
consequent density of young. Abundance of zooplankton was re!ported to
be reduced in areas where density of young salmon was high (Canada,
Fisheries Research Board, 1958).
With regard to intraspecific competition in the Wood River lakes, there
was evidence that changes between lakes in relative population £i.ze of
young red salmon were correlated with observed changes in length fre-
quency of smolts. In various areas of the Wood River lakes, the only
available measure of population size of young for the years concerned
was magnitude of parent escapement. For this measure to be reliable,
it is necessary that in a given year class, mortality rates. of young reds
be reasonably paralleled between population groups defined by major
divisions of the lake system. It would also be desirable, but not as es-
sential, that difference in mortality rates between year classes during
their first year not be large. Since the relation between magnit1·des of
escapement and seaward migration has been shown to be erratic, definite
differences in mortality rate must exist between year classes during
fresh-water life. However, changes among lakes in relative magnitude
of spawning populations have been large, and it is pertinent to examine
the data on parent escapement and smolt size for indications of a rela-
tion between parent population size and growth attained by young salmon.
The red fry population (age 0) in Lake Aleknagik is assumed to consist
only of fish originating within the lake and its tributaries, including the
Agulowak River connecting Lake Aleknagik with the upper Wood River
lakes. Emerging fry in the Agulowak River spawning area are prevented
by the swift current from migrating upstream into Lake Nerka, and con-
sequently must descend into Lake Aleknagik to feed. No appreciable
downstream fry movements between the major lakes has been found,
so that fry migration from Lake Nerka to Lake Aleknagik is assumed
to be negligible.
Two major area groupings will be used for the upper lakes~ (1) the
Lake Nerka-Little Togiak Lake area, including the Agulukpak River
between Lake Nerka and Lake Beverley, and (2) the Lake Beverle)'-Lake
Kulik area. Data on density of spawning in the separate lakes of the
Wood River system have been compiled by J. R. Gilbert Irom Fisheries
286 Alaska Red Salmon
Research Institute records of aerial and ground surveys conducted an-
nually since 1946.3 Estimates are presented in Table 1 of Report of Op-
erations, 1958 (Fisheries Research Institute, 1959). This information
from 1946 through 195'! is expressed in Table 19 in terms of number
of parent spawners per surface square mile of lake rearing area for
young in the three lake regions. The parent years 1952-57, for which
smolt length frequencies are presented, are indicated below the broken
line in Figure 21.
TABLE 19. ESTIMATED ESCAPEMENT OF RED SALMON PER SURFACE
SQUARE MILE OF LAKE REARING AREA, 1946-57
Escapement Lake Aleknagik Lake Nerka-Lake Beverley-
Year (34 Sqnare Hiles) Little Togiak Lake Lake Kulik
~2 Square Miles) (62 Square Miles)
1946 10,600 25,000 21,100
1947 5,500 10,800 11,400
1948 4,600 11,800 5,900
1949 1,000 700 200
1950 3,800 2,700 1,600
1951 2,700 2,400 2,800 -------------------r---------------------------
1952 2,000 1,600 500
1953* 7,400 2,900 500
1954 3,900 3,000 3:100
1955* 14,500 6,300 6,000
1956* 7,400 5,300 1,400
1957 2,700 I 2,400 200
-
*Escapements producing bimodality in yearling smolt length fre-
quencies.
The heaviest spawning density shown in Table 19 for the years 1952-
57 occurred in the Aleknagik-Agulovtak rearing area in 1953, 1955, and
1956. These were parent years of the yearling smolt groups that ex-
hibited the most pronounced bimodality in length frequency. The small
yearlings were offspring of heavy spawning populations in Lake Alek-
nagik and tributaries.
The greatest contrast between growth of Aleknagik smolts and those
from. upper lakes occurred in the 1953 year class (Fig. 21) when the
escapement reached the highest percentage of the Wood Hiver lakes
total. Although spawning was particularly heavy in all three lake areas in
3 Each seaso.1' s escapement estiniates were based on aerial estimates
and ground coWlts taken at or near peak of spawning. Data most directly
comparable were used to determine differences between lakes and be-
tween years. Estimates since 1953 are considered more accurate, since
trunk stream enumeration of the runs by use of towers in Wood River
was begun in that year and provided a more accurate annual estimate
of total escapement to the system.
Smolts from Wood River Lakes 287
1955 alld the over-all size of smolts in the 1957 migration was reduced,
distinct bimodality of yearling smolt sizes in 1957 was still present be-
cause of the much greater parent spawning density in Lake Aleknagik.
Thus, the smallest Aleknagik smolts observed in any year were pro-
duced by the largest escapement, that of 1955. The large escapements
of the same magnitude in 1953 and 1956 produced stunted smolts similar
in average size. The parent populations of the other recent year classes
in the Aleknagik-Agulowa,k area had been at a lower level, and there was
not as much contrast in size between the small, early migrants, when
evident, and the large migrants. The consistency of these results is
strong evidence that the capacity of Lake Aleknagik nursery area was
taxed by the progeny of large spawning populations. It will be shown in
another paper that stunting occurs in other lakes of the system under
similar parent spawning densities.
There is danger in attempting to assign marked differences in smolt
size simply to population pressures of fry alone. If intraspecific com-
petition caused differences in growth, older age groups may well have
played an important part. The largest migration of smolts measured
by the fyke-net index method occurred in 1954 and 1956 (see Table 9).
If early season feeding of these fish prior to migration seriously affected
the lake\s food supplies, the lower lake in the system would presumably
be most affected, since all migrants must either originate in or pass
through it. The fry in this area migrating as yearlings the following
years, 1955 and 1957, would thus be affected. Also yearlings remaining
an additional year in L.'lese lake C'..reas and migrating at age n would com-
pete to some extent with the fry for food. On this latter point, however,
there is no consistent relation between yearling holdover and fry stunt-
ing since the yearling holdover in 1954 was very slight, that in 1956
moderate, that in 1957 heavy. The competition between year classes may
not be as heavy as within year classes because of differences in food and
feeding area, particularly early in the summer when fry utilize the lit-
toral areas more heavily.
There is additional evidence supporting the hypothesis that smolt size
differences are the result of intraspecific competition within the year
group. This evidence is provided by a comparison between areas in
amount of fresh-water growth associated with relative magnitude of
parent spawning populations. Scale measurements presented of four-
year-old adult salmon, 1953 year class, have indicated that growth during
the initial year achieved by salmon originating in other 'Wood River lakes
was much superior to that obtained in Lake Aleknagik (Fig. 25). This,
however, is exactly the reverse of the relation found by Koo {1962) for
adults of the 1948 year class returrJng to spawn in 1952 and 1953, and by
the writer for scale measurements made of adults of the 1946 year class
returning to spav,'n in 1950. The first year's growth in those two year
classes was better in Aleknagik than in the Beverley-Kulik area. Fol-
288 AJ.aska Red Salmon
lowing the hypothesis of population pressure, an explanation of this re-
versal in rates of early growth lies in relative population sizes of young
salmon present in the two areas during the years in question. Referring
again to Table 19, the spawners were relatively much more numerous
in the Beverley-Kulik area than in the AleknagLlt-Agulowak area in the
years 1946 through 1948. In the years to follow, the Aleknagik-Agulowak
area population increased greatly in relative imp:>rtance, overshadowing
that of the Beverley-Kulik area in eight out of nine years, particularly
in the years 1953, 1955, and 1956, which produced the bimodality of
smolt sizes seen in 1955, 1957, and 1958, respectively.
The relation discussed above between magnitude of adult populations
and growth of smolts produced is surprisingly consistent. In view of
the very large changes in relative magnitude of adult spawning popula-
tions between the areas under discussion, it appears that spawning popu-
lation estimates were a sufficiently sensitive index of relative size of
fry p:>pulations produced within the major divisions of the lake system;
and, therefore, that intraspecific competition of the young does play a
determining role in growth achieved during the first year of lake life.
In view of other possibilities, yet unmeasured, the relation found be-
tween initial populations and smolt size in Wood River lakes must be
further tested. The very real possibility of interspecific competition
should not be overlooked, for a prominent competitor, rivaling the young
reds in abundance, exists in the threespine stickleback fow1d in the Wood
River lakes. This species is closely associated with young red salmon
in the lakes and was found by the writer to feed on the same organisms.
It will be shown in a later report that r1eduction in growth of sticklebacks
also occurs when p:>pulation density of young salmon is high. Increase or
decrease in ge.1erallevel of abundance of sticklebacks or annual fluc-
tuations in their abundance would be expected to influence growth of young
salmon if competition for food is indeed responsible for a major share
of the size fluctuations observed.
Relation of Growth Rate to Survival
Fresh-water Survival
Young red salmon that grow more slowly are probably subject to greater
mortality from a number of sources. Ricker and Foerster (1948) have
suggested that lacustrine predation is gnatest while the sockeye are
small, and that if this vulnerable stage is, passed through rapidly the
chances for survival are increased.
It is likely that slower-growing young salmon may also suffer more
damage from parasites. In Bristol Bay, the cestode, Triaenopho·rus
crassus, was found by the writer to be. a common parasite of red salmon
(Lawler and Scott, 1954). The plerocercoid stage of this cestode has been
found on occasion to be detrimental to other species of fish, and may
.....
Smolts from Wood River Eakes 289
affect young red salmon. At the fish culture station at Kalerna, s~ eden,
plerocercoids of T. crassus were reported to ha,ve caused a widespread
mortality of young rainbow trout, brook trout, and Atlantic salnon in
the years 1921 through 1923 (Bergman, 1924; Scheuring, 1930). Ji'liller
(1945) reported the cestode to havl~ affected growth and condition of com-
mon whitefish (Coregonus clupeaformis) and tullibee (Leucichth: 1s sp .)
at Lesser Slave Lake.
In young red salmon the plerocercoids of T. eras sus destroy c 1nsid-
erable tissue during' development and encystment in the museu .ature.
The plerocercoids first appear in the flesh of red fry in late su .nmer.
Weakening of young salmon is likely to be severe or even letha i if the
fish is very small, since a high proportion of the musculatt1.re is then
destroyed by a single plerocercoid. While direct proof is lacking that
the cestode is a serious mortality factor in young salmon, the p uasite
is prevalent enough to be wo:rthy of attention. Average annual in· !idence
of parasitism by T. eras sus in red smolt samples collected at M Jsquito
Point "'aS found to be 66.0 per cent for the years 1948 through 195S (Table
20).
TABLE 20. PERCENTAUES OF WOOD RIVER RED SALMON SMOLTS PARASITIZED BY THE PLEROCKRCOID S rAGE OF
THE CESTODE TRIAENOPHORUS CRASSUS IN THE YEARS 1948 THROUGH 1958* , ,
j
Average Per Cent Range Total Number Number of I
Year C1f .Fish Samples ...... ·;~·········· Samples
E:~:aminec Examined All Samples Para
1948 100 2 48~ 52 88 8
1949 504 8 50-112 81 7
1950 350 7 so . 76 e
1951 423 8
I
so-73 82 e
1952 31::0 7 50 82 7
1953 393 8 32-78 78 6
1954 445 7 50-110 63 5
1955 810 7 99-152 63 3
1956 400 4 100 74 6
1957 263 3 76-104 23 2.
1958 276 ., 74-111 16 . ~ --
M~an annual percentage = 6J
betwe-l!n
n Per Cent
itized
·-90
1•92
1-94
1-96
t-:30
1~90
-76
-80
-86
-25
-22
----------------
*Only samples taken between dates of lake breakup and July 31 are included,
Delay in seaward migration is another probable cause of mort a.lity in
slower-growing ycung salmon. The tendency for smaller fish to remain
an additional year or more in the lake before migrating seaw~ ~rd has
been well established (Foerster, 1937; Barnaby, 1944; Koo, 1962; l(rogius
and Krokhin, 1956a; Krogius, 1957). The additional mortality s .tffered
by those fish residing an extra year .in the lakes is not apt to bE offset
by increased ocean survival gained through their greater size at S•!award
migration. This view is shared by Krogius and Krokhin (1956c: ), who
emphasized the need to understand causes of difference in age at down-
stream migration in order to develop means of management to •educe
length of residence in fresh water.
In summary, slower growth of young in fresh water is believed to
result in greater over-all mortality during fresh-water stages .. \.ctual
290 Alaska Red Salmon
proof that such is the case is lacking for red salmon of Wood .l.tive:r lakes.
Marine Survival
It i..,:; generally accepted that marine survival rates vary dii'ectly with
sh!:e of anadromous salmonoids at time of seaward migration. In fin-
clipping experiments on Karluk Lake red salmon smelts; higher marine
survival values were obtained in four of five years for the older (and
larger) of the two major cmolt age groups (Barnaby, 1944). However,
it must be noted that siza alone at seaward migration may not have been
responsible for these results. A close exam:ination uf the Karluk data
indicates that differential S11rvival m the ocean was probably influenced
by at least three distinct factors oi unknown re.lrative importance: (1) size
and age at seaward migration, older smolts being larger in size; (2)
timing of entry into .I!'.arine environment, older smolts tending to migrate
earlier in the season; and (3) length of stay in the ocean, older smolts
having a greater tendency to remain only two years at sea, but at the
same time ter.rHng to return later in t:hot=.! season in the year of return.
Strong evidence that size of smolts at time of seaward migration is
actually an important qualitative factor in survival during seaTVard mi-
gration and ocean residence was presented by Foerster (1954) for Cultus
Lake sockeye. Data were presented gi ring numbers and mean size of
smolts in the 1927 through 1944 seaward migrations, and the number of
adults in return spawning escapements t0 the lake. Through analysis
of these data by multiple-correlation treatment, Foerster concluded
that the negative correlation between magnj:ude of smolt migration and
percentage return of adult spawners to the lake. was related principally
to size nf smolts at time of seaward migration.
Krogius ~nd Krokhin (1956a) did not find a relation between size and
marine survival of Lake Dalnee sockeye smoits, but considered that
this lack of coincidence with Foerster's findin;;ri;; may be explained by
the larger size of Dalnee smolts and less size varlaoility between years
than at Cultus Lake.
Distinct bimodality of sizes at Wood; iver in the 1955 vearling mi-
gration presnnted a unique opportunity to study the effeci: o~· a jifference
in smolt size on marine survival and length of stay in the t ...... ean, for in
this instance ~he size difference existed within a single year class en-
tering the nl:iu:lne environment in the same season. Peretmtages of small
and large migrants found in the 1955 seaward migration were compared
wlth percentages of returning adults in catch and escapement possessing
the fresh-water scale pattern characteristic of small and of la.1'ge sea-
ward migrants. Small smolts, originating in the Aleknagik.-Agulowak
area, were calculated to have totaled 29 per cent of the 1955 yearling
seaward migration, and were produced by a parent escapement calculated
at approximately 49 ,r,ar cent of the Wood River lakes total. Adult returns
in catch and escapement in 1957 and 1958 provided evidence that stunting
Smolts from Wood River Lakes 291
of young reds in fresh water had affected both marine survival and age
at return (Table 21 ).
TABLE 21. RATIOS OF SMALL A.~D LARGE YEARLINGS IN 1955 SEAWARD
MIGRATION A..~D IN RETURN AB ADULTS IN 1957 A.lffi 1958
Small Large
Yearlings Yearlings
1955 seaward migration 29 71
1957 adult return 7 93
1958 adult retm"n 18 82
Tbtal adult return 15 85
The ratio of small to large yearlings in the 1957 adult return was cal-
culated to be 7:93 and in the 1958 adult return, 18:82, for a total weighted
ratio of 15:85. This indicates that survival of small Aleknagik yearlings
was about half that of large yearlings from the remainder of the Wood
River system, and that there was a definite tendency for smaller smolts
to rc,main an extra year at sea.
It should be noted that the computations involve determinations of
smolt age composition, spawning population estimates, age analysis
of catch al!ld escapement, and an assumption as to percentage of Wood
River fish in the entire Nushagak red salmon cat\!h. Return ratios may
also have been affected by differential fishing mortality from the Japanese
high-seas fishery. Selection by the Bristol Bay fishery may conceivably
have had an effect, although tagging conducted by Bureau of Commercial
Fishf'ries personnel has in·li.cated that tirr.t.ing of the Aleknagik run through
the fishery does not differ hom the remainder of the Wood River race.s.
There was also no indicathm from length frequencies that Aleknagik
adult fish differed in size from those of the same age group in there-
mainder of the system. Although confidence intervals of the ratios pre-
sented cannot be determined, the trend of results is strongly suggestive.
Further, the 1959 and 1960 :.:·eturns of adult red salmon from the 1S57
seaward migration again indicated a lower survival of sh,nted smolts
from Lake Aleknagik.
Effect of Smolt Size on Adult Popu:i.ation Size
The above discussion touches on possible effects of changes in la-
c.ustrine growth conditions on fresh-water and marine survival of red
salmon. The inverse '!'elation observed between population size and smolt
size in subdivisions of tr1e Wood River lakes system may explain the
mechanism of some fluctuations in population level that have occurred.
When spawning· populations produce numbers of young beyond the capacity
of a lake rearing area, stunting of yc,ung, low survival, and delay in
return from the o~ean may follow. With low survival, the return runs
d:rop in numbers and fry production may decrease, again permitting
292 Alaska Red Salmon
good growth. Individual rearing areas may thus tend to fluctuate in popu-
lation level somewh&t 1Gdependently of other rearing areas in the lake
system. This sequen~e of events appears to have held in recent years
in the Wood River la...l{es.
SUMMARY
1. The early life history studies discussed in this paper are an integral
part of the Fisheries Research Institute program on red salmon runs of
the Nushagak District in Bristol Bay, Alaska. The research described
deals with smolts in ·wood River seaward migrations of 1951 through
1959.
2. A smolt enumeration system adaptable to large rivers was estab-
lished in 1951 at the outlet of Lake Aleknagik. A winged fyke net was
fished throughout the migration seasons: 1951 through 1958, its catch
furnishing the annual migration index. A comparison of catches made
by two nets fished simultaneously during the same period as well as
indirect evidence attest to reliability of the index method.
3. Smolts used for length frequency study were measured alive under
anesthesia. Those fish preserved in 10 par cent formalin undergo shrink-
age in length. Shrinkage is greater in percentage for smaller fish. A
correction of +5 mm in length was determined necessary to convert
lengths of pr9served yearling smol1:s to correspond to measurements
of live fish.
4. Size selectivity of the index fyke net was tested by comparison of
smolt samples taken simultaneously at Mosquito Point by beach seine
and fyke net. Heterogeneity between schools in size composition was
made evident by the tests. There was no indication that larger yearling
smolts are less likely to be caught by tr.e fyke net than smaller fish.
5. A pattern of decrease in size of yearling smolts during evening
migration was established. Net selectivity was ruled out as a causa.
It is proposed that the phenomenon of diurnal change in size was due to
difference in swimming speed or migration .stimulus related to fish size,
and that schools of larger fish tended to reach the outlet earlier in the
evening from the daytime milling area.
6. Agr. determination of smolts was based on a combination of length-
frequenc,:ll' a.11d scale study. In determining age it was necessary to pre-
serv,e for scale study only those fish of lengths which fell in the range
of overlap between age I and age II fish.
7, No definite relationship was found between magnitudes of parent
escapement of red salmon :.n Wood River lakes and seaward migrants
produced for the year classes 1S49 through 1955 .. Rates of survival of
young in fresh water varied as mu~h as 19 times.
8. Climate was determined to be a dominant factor in over-a~l1 timing
Smolts from Wood River Lakes 293
of seasonal migration. Timing of early season migration was closely
associated with breakup of lake ice, and termination of migration with
rise of lake surface temperatures above 50° F.
9. Seasonal increase in new ~ummer growth on scales of yearling
smolts was demonstrated, and differences between years in amount
of new growth attained by a given calendar date during the season was
shown to be related to time of breakup and subsequent lake tempera-
tures.
10. The pattern of seasonal changes in smolt length frequency at Wood
River, 1954 through 1957, suggests that L~e first smolts to migrate were
from the lowest lake in the Wood River chain, and that in certain years
these fish were smaller in size at time of migration than were those
from lakes above. Delay in migration of smolts from the upper lakes is
attributed to delay in ice oreakup and distance between lake of origin
and Wood River.
11. Length-frequency and age studies reveal a distinct bimodality
in size of yearling smolts in the 1955, 1957, and 1958 seaward migra-
tions. Smaller yearlings were first to begi1.1 migration. The origin of size
groups,was studied by comparison of scale measurements of 1955 year-
ling smolts with measurements of fresh -water scale grmvth in adults of
the same year class returning to the spawning grounds in 1957 and 1958.
The small smolts were found to h.ave originated in Alek.rmgik, confirming
the hypothesis based on the seasonal smolt size sequence observed at
Mosquito Point.
12. In Lake Nerka, scale measurements of adult fish of the 1953 year
class established the existence of significant differences in fresh -water
growth between fish spawning in upper and lower arms of the lake. This
indicated limited circulation of young and difference between lake areas
in conditions for growth. Significant differences in fresh-water growth
were a.1so found between adult samples from different spawnL11g grounds
in Lower Lake Nerka.
13. Small size attained by Lake Aleknagik smolts migrating in 1955,
1957, and 1958 was related to heavy density of parent spawning popula-
tions in the Lake Aleknagik-Agulowak River area. Differences between
lakes in degree of competition between fry for food were apparently a
major source of differences in growth attained. The possibility of com-
petition between age classes as well as interspecific competition with
threespine sticklebacks is discussed.
14. Change in smolt size, hence in fresh-water and marine sur·. ~val
rate, is suggested as one cause of fluctuations in relative spawning pop-
ulation levels among the rearing area divisions in the Wood River lakes.
The low returns of adults in 1957 and 1958 from the small-size group
of smolts migrating sBaward in 1955 .;:,1~strate the effect of smoh: size
on marine survival and age at return.
294 Alaska Red Salmon
ACKNOWLEDGMENT
It is a pleasure to express my sincere appreciation toW. F. Thomp-
son, who, as the first director 7 organized and developed the Fisheries
Research lnstltute. It was he who foresaw the need for the early life his-
tory studies as a part of the basic program of research on red salmon in
Bristol Bay. His constant encouragement, inspiration, and helpful advice
are gratefully acknowledged.
During the course of the studies I received valuable cooperation and
assistance from other memberto:. oi the staff working on closely integrated
problems. These included {)!".v:i.tcularly, Ted S. Y. Koo, Ole A. Mathisen,
and John R. Gilbert. Wilb1..l~ A. Church gave competent assistance in the
conduct of the sampling pr•Jg;ram at Lake Nerka.
I also wish to thank Miss Pea;rl Mooney, Institute librarian, for her
assistance in preparation C!f my original thesis, and William F. Royce
for his review and criticism of the revised manuscript.
This study was financed by the Bristol Bay salmon canning industry.
LITERATURE CITED
Alaska Department of Fish and Game. 1959. Annual Report for 1957.
Juneau. 124 p.
Babcock, J. P. 1904. Fisheries Commissioner's Report for 1903, British
Columbia Dept. of Fisheries, Victoria. 15 p.
-----. 1905. Fisheries Commissioner's Report for 1904. BriUsh Co-
lumbia Dept. of Fisheries, Victoria. 12 p.
Barnaby, J. T. 1944. Fluctuations in abundance of red salmon, Onco-
rlz;,nchus nerka (Walbaum), of the Karluk River, Alaska. U.S. Fish
and Wildl. Serv., Fishery Bull., 50(39):237-95.
Bergman, A. M. 1924. Larven von Triaenoplzor.ts robustus Olsson und
einer Dibothriocephalusart als Ursache eines Massensterbenr.; unter
jungen Lachsfischen. Deutsche tiedirztliche Wochschr., 32(21):292-~a;
32(22):311-16.
Brett, J. R., and J. A. McConnel. 1950. Lakelse Lake sockeye survival.
J. Fish. Research Board Canada, 8(2):103-10.
Canada, Fisheries Research Board. 1957. Annual Report for 1955. Ot··
tawa. 182 p.
-----. 1957a. Annual Report for 1956/1957. Ottawa. 195 p.
-----. 1958. Annual Report for 1957/1958. ottawa. 195 p.
Chamberlain, F. M. 1907. Some observations on sa1mon and trout in
Alaska, 112 p, In Rept. U.S. Commissioner of Fisheries for 1906.
Clutter, R. I., and L. E. Whitesel. 1956. Collection and interpretation
of sockeye salmon scales. Int. Pacific Salmon Fisheries Comm., Bull.
9, 159 p. New Westminster, B. C.
Smolts from Wood River Lakes 295
Dombroski, E. 1952. Sockeye smolts from Babi!te Lal~e· in 1951. Fish-
cries Research Board of Canada, Pacific Biol. Sta. Progr. Rept.,
(91):21-26.
-----. 1954. The sizes of Babine Lake sockeye salmon smolt emi-
grants, 1950-1953. Fisheries Research Board of Canada, Pacific Biol.
Sta. Progr. Rept., (99):30-34.
Duncan1 D. B. 1955. Multiple range and multiple F tests. Biom~trics,
11(1):1-42.
Dunlop, H. A. 1924. The growth-rate of the scales in the sockeye salmon,
Oncorhynchus n.erka. Contrib. Canaclian BioL, 2(10):151-59.
Fisheries Research Institute .. 1959. Report of Operations, 1958. Univ.
Washington. 24 p.
Foerster, R. E. 1937. The relation of temperature to the seaward mi-
gration of young sockeye salmon (0nc(;rhynchus nerka). J. Bioi. Board
Canada, 3(5):421-38.
------. 1938. An investigation of the relative efficiencies of natural
and artificial propagation of sockeye salmon (Oncorhynchus nerka)
at Cultus Lake, British Columbia. J. Fish. Research Board Canada,
4(3):151-61.
-----. 1944. The relation of lake population density to size of young
sockeye salmon (Oncorhynchus nerka). J. Fish. Research Board Can-
ada, 6(3):267-80.
-----. 1952. The seaward-migrating sockeye and coho oalmon from
Lakelse Lake, 1952. Fisheries Research Board of Canada, Pacific
Bioi. Sta. Progr. Rept., (93):30-32.
-----. 1954. On the relation of adult sockeye salmon (Oncm~hynchus
nerka) returns to known smolt seaward migrations. J. Fish. Research
Boat'd Canada, 11(4):339-50.
-----. 1955. The Pacific salmon (genus Oncorhynchus) of the Canadian
Pacific coast, with particular reference to their occurrence in or
near fresh water. Int. North Pacific Fisheries Comm. Bull., (1):
1-56.
Gilbert, C. H. 1914. Contributions to the life-history of the sockeye
salmon. (:No. 1) p. 53-57 . .Jn Fisheries Commissioner's Report for
1913. British Columbia Dept. Fisheries. Victoria.
-----. 1915. Contributiong to the life-history of the sockeye salmon.
(No. ?.) p. 45-75. In Fisheries Commissioner's Report for 1914. Brit-
ish Columbia Dept. Fisheries. Victoria.
-----. 1916. Contributions to the life-history of the sockeye s~lmon.
(No. 3) p. 27-64. Jn Fisheries Commissioner's Report for 1915. Brit-
ish Columbia Dept. Fisheries. Victoria.
-----. 1918. Contributions to the life-history of the sockeye salmon.
(No.4) p. 33-80. In Fisheries Commissioner1 s Report for 1917. Brit-
ish Columbia Dept. Fisheries. Victoria.
Gilbert, C. H., and W. H. Rich. 1927. Investigations concerning the red
Alaska Red Salmon
salmon runs tn the Karluk River, Alaska. Bull. U.S. Bur,. Fisheriess
43(Pl. 2):1-69.
Goldman, C. R. 1960. Primary productivity and limiting factors in three
lakes of the Alaska Peninsula. Ecol. Monographs, 30:207-30.
Hile, R. 0. 1936. Age and growth of the cisco Leu.cichthys artedi (Le
Sueur), in the lakes of the northeastern highlands, Wisconsin. Bull.
U.S. Bur. Fisheries, 48(19):211-317.
Holmes, H. B. 1934. Natural propagation of salmon in Alaska. Fifth Pa-
cific Science Congress, Victoria and Vancouver, B. C., Proc. for 1933,
5:3585-92.
Johnson, W. E. 1956. On the distribution of young sockeye salmon (On-
corhynchus nerka) in Babine and Nilkitkwa Lakes, B. C. J. Fish. Re-
search Board Canada, 13(5):695-708.
-----. 1958. Density and distribution of young sockeye saimon (On-
corh:ynchus nerka) throughout a multibasin lake system. J. Fish. Re-
search Board Canada1 15(5):961-82.
Koo, T. S. Y. 1959. Red salmon smolt enumeration in the Wood River
system. Report of field operations and results, 1958. Univ. Wash-
ington, Fisheries Research Inst. Circ. 103. 11 p.
-----. 1960. Abundance, size and age of red salmon smolts from the
Wood River system, 1959. Univ. Washington Fisheries Research Inst.
Circ. 118. 9 p.
----. 1962. Age and growth studies of red salmon scales by graphical
means. See elsewhere in this volume.
Krogius, F. V. 1951. 0 dinamike chislennosti krasnoi. [Oncorhynchus
nerka (Walbaum)]. !zvestiia Tikhookeanskovo Nauchno-issledovatel-
skovo Inst. Rybnovo Khoziaistva i Okeana~., 35:1-16. [On the dynamics
of abundance of the sockeye salmon Oncorhynchus nerka (Walbaum) .]
Fisheries Research Board of Canada, Transl. Ser., No. 101, 1957.
ottawa.
Krogius, F. V., and Eo M. Krokhin. 1948. Ob urozhainosti molodi kras-
noi (Oncorhynchus nerka Walb. ). Izvestiia Tikhookeanskovo Nauchno-
issledovatelsiwvo Inst. Rybnovo Khoziaistva i Okeanog. 28:3-27. [On
the production of young sockeye salmon Oncarhym:h~t.s nerka (Wan· .:.urn).]
Fisheries Research Board of Canada, Transl. Ser., No. 109, 1958.
Ottawa.
-----. 1956. Rezultaty issledovanii biologii nerki-krasnoi, sostoianiia
ee saposov i kolebanii chislennosti v vodakh Kamchatki. Voprosy Ikhtio-
logii. (7):3-20. [Results ~fa study of the biology of sockeye salmon,
the conditions of the stocks and the fluctuations in numbers in Kam-
chatka waters.] Fisheries Research Board of Canada, Transl. Ser.,
No. 176, 1958. Ottawa.
-----. 1956a. Priehiny kolebanii chislennosti krasnoi na Kamchatke.
Trudy Problemnekh i Tematicheskikh Sovesbchanii ZIN, (6): 144-49.
[Causes of the fluctuations in abundance of sockeye salmon in Kam~
Smolts from Wood River Lakes 297
chatka.] Fisheries Research Board of Canada, Trans!. Ser., No. 92,
1959. Ottawa.
Kroki1in, E. M. 1957. Istochiki obogashcheniya nerestovykh ozer bio-
gennymi elementami. Izvestiia Tikhookeanskovo Nauchno-issledova-
telskovo Inst. Rybnovo Khoziaistva i Okeanog., 45:29-35. [Sources of
enrichment of spawning lakes in biogenic elements.] Fisheries Re-
search Board of Canada, Trans!. Ser., No. 207, 1959. Ottawa.
Lawler, G. H., and W. B. Scott. 1954. Notes on the geographical distri-
bution and the hosts of the cestode genus Triaenophorus in North Amer-
ica. J. Fish. Research Board Canada, 11(6):884-93.
Mathisen, 0. A. 1962. The effect of altered sex ratios on the spawning of
red salmon. See elsewhere in this volume.
Mertie, J. B., Jr. 1938. The Nushagak District, Alaska. !r S. Geol.
Survey, Bull. 903. 96 p.
Miller, R. B. 1945. Effects of Triae1Wphorus on growth of two fishes.
J. Fish. Research Board Canada, 6(4):334-37.
Nelson, P. R. 1958. Relationship between rate of photosynthesis and
grmvth of juvenile red salmon. Science, 128(3317):205-7.
Nelson, P. R., and W. T. Edmondson. 1955. Limnological effects of
fertilizing Bare Lake, Alaska. U.S. Fish and Wildl. Serv., Fishery
Bull. 56(102):415-36.
Parker, R. R. , and R. E. Vincent. (1956]. Progress report on research
studies at the Kitoi Bay Research Station, p. 25-67. In Alaska Depart-
ment of Fisheries Ann. Rep:. for 1955.
Ricker, W. E. 1937. The food and the food supply of sockeye salmon
(Oncorhynchus nerka Walbaum) in Cultus Lake, British Columbia. J.
Biol. Board Canada, 3(5):450-68.
Ricker, W. E. , and R. E. Foerster. 1948. Computation of fish production.
Bull. Bingham Oceanog. Collection, 11(7):173-211.
Rounsefell, G. A. 1958. Factors causing decline in sockeye salmon of
Karluk River, Alaska. U.S. Fish and Wildl. Serv., Fishery Bull.,
58(130):83-169.
Scheuring, L. 1930. Beobachtungen zur Biologie des Genus TriaeJwfthm'US
und Betrachtungen iiber das Jahreszeitliche Auftreten von Bandwiirm-
ern. Z. Parasitenkunde, 2:157-77.
Shetter, D. S. 1936. Shrinkage of trout at death and on preservation.
Copeia, (1}:60-61.
SWrdson; G. 19.55. Salmon stock fluctuations in the Baltic Sea. Drott-
ningholm, Sweden. Statens undersoknings-och forsoksanstalt for
sotvattensfisket. Ann. Rept. and Short Papers for 1954. (36): 226-62.
Thompson, W. F. 1950. Some salmon research problems in Alaska; pre-
pared for the meeting held by the National Research Council on scien-
tific research in Alaska. Washington; D. C., November 9, 1950. Univ._
Washington Fisheries Research Inst., Circ. 11. 19 p.
-----. 1951. An outline for -salmon research in Alaska; prepared for
298 Alaska Red Salmon
the meeting of the International Council for the Exploration of the Sea
at Amsterdam, October 1-9, 1951. Univ. Washington Fisheries Re-
search Inst., Circ. 18. 49 p.
U.S. Army Corps of Engineers. 1957. Harbors and rivers in southwest-
ern Alaska. U.S. GO",;i:. Printing Office, Washington. 89 p. (House
Document No. 390]
Ward, H. B. 1932. The origin of the landlocked habit in salmon. Proc.
Nat. Acad. Sci. 18(9):569-80.
Withler, F. C. 1952. Estimation of the size of the sockeye smolt run,
Babine Lake, 1951. Fisheries Research Board of Canada, Pacific Bioi.
Sta. Progr. Rept., (91):17-19.
1
N
WOOD RIVER LAKE SYSTEM
BIUSTOL BAY, ALASKA
01.2345
fA I LE 5
Fig. 1. Wood River lake system1 Bristol Bay, Alaska.
Fig. 2. The fyke net used at Mosquito Point index site, Wood
River, for smolt sampling. (Photo by W. F. Thompson)
Fig. 3. The outlet of Lake Aleknagik, showing fyke-net
location (arrow) in the river current at Mosquito Point; Wood
River is in the foreground. (Photo from color transparency
by Ole A. Mathisen)
25
20
IS
10
s
0
25
3)
IS
~
"'10 " w a
~ 5 .. ...
0
25
20
15
1?
s
0
!-
!-
!-
i-
r--
-
2100-
2200
r--
r---
2200-
2300
I '1 S ~
1956
-
1957
-
2300-
2400
Houu
r---
r--
2~-
0100
r--
:---']
0100-
0lOO
I
I
I
I
I
Fig. 4. Mean percentage distribution of hourly
fyke-r.et catches during daily fishing period,
2100-0200 hours, at Mosquito Point smelt-
enumeration site 1955-57.
.. -;.
s
Tttn•
-21J5
""''2150
leoeb-tebt.,mpl..,
I L ~-->-<:-z..., I
0 Tim•
·-2135
10 ...... ..,2150
s s
0 . l'yke-oet .,mpl.,,
dmull<ultollll wltb above
!:
~ ...
~ol ..d ~ I .. ..
s
Compudtt, alloampl.,, Jun• IS
(i sample1
907 flab
0 1 1 L r 1 •' • 1 I
70 80 90 100 I I 0 I 20
Longth Ia mllllm•tort
Fig. 5. Length-frequency samples of red smolts taken
at Mosquito Point, June 15, 1954. (All fish measured
alive. All frequencies smv..>thed by moving averages of
threes. Frequencies at each millimeter interval graphed
as per cent of total sample.)
10
5
IO
~ -g., s
tl
"' -tl ... 5 Q .. ....
0 ... = Ill
u ..
Ill 0 II.
10
5
... ......
Time
-2205 June 16
--2238 June 16
·-·-2214 Jun~ l7
•••••••• 2240 June 17
Beach-teine samplea
Time
-2~5June 16
---2238 June 16
·-·-~214 June 17
•••••••• 2240 Junt-17
Fyke-net samples, simultaneo1.11
~-~will>abm
~~~--~~ ~
Composiee, all samples, Junr 16-17
10 samples
1132 fiah
Length in millimeters
120
Fig. 6. Length-frequency samples of red smolts taken at Mos-
quito 1?oint1 June 16 and 17, 1954. (All fish measured alive. All
frequencies at each millimeter interval graphed as per cent of
total sample.)
Ill ... p.
E
tl
"' ....
0 ...
~
(lj
0 ..
(lj
ll.,
5
5
10
5
5
0
10
s
0
10
5
5
Fyke net
Beach seine
Xf= 88.72 mm
"'ib • 88.99 mm
2135, June 15
Xf= 87.94 mm
xb•93.70 mm
2150, Junf" IS
~fm84.76 mm
xb= 82.62 mm
2205, June 16
Xf• 85.23 mm
Xb=86.19 mm
2238, June 16
~=85.77 mm
xb ""'86.60 mm
2214, June 17
xf= 84.44 mm
xb=85.07 mm
2240, June 17
Xf:::r 86.07 mm
xb =86.95 mm
Composite of above liamples,
June 15-17
140
Fig. 7. Comparison of pairs of length-frequency samples taken
simultaneously by beach seine and fyke net at Mosquito Point,
Lake Aleknagik, June 15-17, 1954.
.. -0. s.
0 .. ...
0 ... = ..
u .. ..
g.
lO
5
0
10
5
5
0
10
5
0
L~ngth in millimeters
t.., 2100-2106
D • 152
w=5.-97
1 .. 88.50
D .157
'il. 5. 78 r. 87.87
D • 170 w c 5.34
T. ss.n
t & 2358-2400
n • 183
w-4.95 r-83.04
t • 0058 -QlOO
n • 178
w •5.10
T • 84.17
t. 0158-0m<l
D • 179
1f -5.07
i = 84.65
Fig. 8. Length frequencies of red smolts in samples captured by fyke
net at Mosquito Point at hourly intervals during evening of June 8 and early
morning of June 9, 1954. (All fish under 95 mm are yearlings. Measured
under anesthesia. Frequencies smoothed by moving averages of threes.}
t = fishing period w = mean weight in g
n = sample size l = mean length in mm
.. -Q, s a
n
0 ...
0 ... ...
0 ...
n ..
u ..
" 0:.
10
s
t ... 2·1oo-2·104
n = 125 w. 6.45
T = 90.34
0~--L-----~L-------~----~~~-----L--~
10
5
0
5
0
10
5
0
10
5
0
70 80
length in millimeters
t = 2159-2200
n • 157
w: 5.78
T • 88. ·14
t = 2259-2300
n • 164 • w = 5.53 r = 86.81
t :: 2359-2.(00
n • 157
w :11:5.78 r. 87.99
t = 0059-Q 100
n • ·134
w. 5.27 r = 85. 1s
100 110
Fig. 9. Length frequencies of red smolts in st~.mples ca¢ured by fyke
net at Mosquito Point at hourly intervals during evening of June 12 and
early morning of June 13, 1954. (Measured under anesthesia. Fre-
quencies smoothed' by moving averages of threes. All fish under 100
mm were yearlings.)
t = fishing period
n = sample size
w = mean weight in g
l = mean length in mm
80
c 60 ..
u
" .. c. .. > ~ 40 :;
E
" u
zo
May
1000
j
.5
~ 500 ..
E
~
0 ...
Ill
0
1949 1950
Index of smolts produced
fZ1Zl Agr II
D Ag .. I
Parent escapement
1951 1953 !954
Year af escaprment
1955
Fig. 10. Wood River escapement countpr and indexes of smolts
produced.
June
I
i
195Z j
,.~
I ,. . ../
11956 .. ...
July
Fig. 11. Cumulative daily fyke-net catches, Mosquito Point, ir>
per cent of season's total.
Fig. 12. Daily lake-surface temperatures: Lake Nerka station,
June-Septennber, 1952-57.
1954
1953
1957
1956
195Z
1955
--Fniod brtwun lGlc~ hrt>ekup and
wormlo.g of tm.,_. aurfac~ to so• F
utntnua ?rriod brtw~rn date-s then S cmd 90
pPr c:rnt of the ucucus'• cumulatlvr
indtx; catch orr frocbtd.
1111111111111111111
IIIIIIIIIIIIIIIIIIIIIIIIUIIUII
11111111 ,. ...................... .
II IIIIIIIIIIIIIIIIIIIIIIIUIIIIIIIIIIIIIIIII
tlllllllllllllltlillllllltllllllltlll"'''''''"'''''
111111111111111 f:,!lllll I IIIII .....
S 10 IS a.
July
Fig. 13. Relationship between spring climate and timing of the
red smolt migration, Wood River lakes, 1952 through 1957.
(Years arranged in sequence of breakup dates at Lake Aleknagik.)
Fig. 14. Scale of a red salmon yearling 99 nun long, collected
at Mosquito Point on July 5, 1954, showing new summer growth
beyond the narrow rings of the annulus. Magnification 113x.
30
.c ..
3:
0
~
C'l
~ .. a 20
E
:I
w ..
r:; ..
u
~
" 10 ...
Jun.-July
Fig. 15. Changes during 1953 migration season in amount of
new summer growth on scales of yearling smolts sampled at
Mosquito Point, Lake Aleknagik. (Summer growth is shown as
percentage of total anterior scale radius.)
25
t~
fi s 15
il
~ i 10
u
J! 5
Oj I L! I I I
10 20 3D •n
25
~ 20
G.
ll e 15 ~
lt
:! 10
i ..
t
c>. s
Number of dayt Irom date of lee breakup to date of mmple.
1953 /
• ~1957 ·19~
OL-------~--~~--~--------~------~~----~ 0 200 800
Number of aJ.r TU11 accumulated from date ~ lee breakup
to date of ~ample
Fig. 16. A. Relation between time of ice breakup,
Lake Nerka, and percentage new summer growth on
scales of red yearlings in above samples. B. Relation
between cumulative air temperature following ice
breakup and percentage of new summer growth on
scales of red yearlings in samples collected on or
about July 5 in the years 1952-57.
" w
0 s
"
"' 0 -..
.a s
" ~
~
>
w
" -" ..:
60 80
Length In mllllmet•n
-ngrl
---a~~ U
May 2!1-Jun~ 2
\ "
Juu• 8-12
June 18-22
Jun• 23•July l
120
Fig. 17. Length frequencies of red smolts, i.n
1954 Wood River seaw, rd migration, weighted
by magnitude of 2100-2300 catches in index fyke
net and grouped by five-day periods. (Frequen-
cies smoothed by moving averages of threes.)
0
li ...
0
M . ...
E
~
~
u ..
~ . ..:
Jun• 1-22
--Agd
---Ag•ll
July 8-12
60 120
Lfl'ngth ln mllllmco~cra
Fig. 18. Length frequencies of red smolts in
1955 Wood River seaward migration, weighted
by magnitude of 2100-0200 catches in index fyke
net and grouped by five-day periods. (Frequen-
cies smoothed by moving averages of threes.)
-·c--·-----~------~v-----. ---•-.• ~--.,_.,r---~-----_,....,.._....,.
''\
,! ' I \
/ \
' ' I ' ..
--Age[
---Agel&
Ju,. 1 -12
Juue 13 ... 17
June 18-22
June 23-U
E I ' , I ... ........,...,.. 1 d I
0
li ...
0
: 1 t 4"
u ... e
~
A ..
>
~ a ..
..:
60
June 28 -July 2
July 3-7
July 8-12
July 13 -Augwt 8
so 120
Length In mUUmcters
Fig. 19. Length frequencies of red smolts in
1956 Wood River seaward migration, we ... ghted
by magnitude of 2100-0200 catches in index fyke
net and grouped by five-day periods. (Frequen-
cies smoothed by moving averages of threes.)
~
N
0
May 29 -1""• 2
,_, ... "-. -~ .... ~~-'---
]oUle 3-7
]uoe8-12
...... _
! I ,J,t1t ,..,____ 'CI..., I ---....--. __ , I !
...
0 .. ]1111< 18-22
= I ......,..... ,Q ..,_...__.,,=+-~ -I I
.. . ...
N
! . a:
!50
-Agel
---·AgeD
]liDO 2l • 27
]tme 28 • July 2
July 3-28
80 100 120
Length In m11Umoten
Fig. 20. Length frequencies of red smolts in
1957 Wood River seaward migration, weighted
by magnitude of 2100-0200 catches in index fyke
net and grouped by five-day periods. (Frequen-
cies smoothed by moving 2.verages of threes.)
r-6~ (\ -Aoe 1
4
~ ---·Age II
1954
2
19!5!5
2
0
4
....... t:l 19!56 .... ~ 2 ..,
~ 0
~ 4
~
'II) 1957
..... 2
(l
1958
4
19!59
2
0 6'0 120
Fig. 21. Season composite length frequencies
of red salmon smolts, 1954-57, Wood River.
A B
Fig. '22. Photomicrographs of scales from small and large
yearling smolts in the 1955 seaward migration, and of nuclear
areas of scales from adults in the 1957 return escapement, Wood
River lakes (magnification 43x): A. Scale from smolt 72 mm long;
B. Nuclear area of scale from adult female, Hansen Creek, Lake
Aleknagik, showing small amount of growth to first annulus;
C. Scale from smolt 90 mm long; D: Nv.clear area of scale from
adult female, Fenno Creek, Lake Nerka, showing good growth
to first annulus.
1 ...
0
5 u
ll
""
Length In mllUmetm
Fig. 23. Season composite length frequency of red salmon year-.
ling migrants, Wood River, 1955, showing length groups from
which scale radius measurements were taken, and number of
scale measurements made.
_______ .,.. _____ _...•~M,09tW4¥V ;u:w;a:::az 144 az.s:;::t:U.,tWii$~4}$lW¥f.., ... 4iPfMt£Ji.?h¥!¢.k:H*$,.~;;)!CJi'Xjtid4?ftW'!.l;%::i;;l\6ZpUtJ;Q;t:E)il;i;%i!IAljifll'f>K1&Jj.._ff~,.*ifMfk .. Ui'JJt\ti:;;:;JiM1Ilk_:cg::;:}MUJ£Q44JAifU4JVWQ4MRWii4f.~
" :z:
a)
10
A
·--Aleknagik adults
-Small yrarllngs
n•29
D"S6
o~ ~ I
B
20
10
----adults Jram lakrs above
Alrknaglk n=29Z
-l.Grgr yearlings ll"lZ2
t-, I , __ \ , \
I \
I ' . \
I \
I \ ' \ I \
I \
I \
I ' I l
I \
' ' I
' I
0 I 'rrC"?C:' :( • • I ' 'I ,...,.
SO 6S 80 95 110 1ZS 140
Magnlflrd seal., radius to first annulus, In mllUmrtrrs
Fig. 24. Comparison betwr-en scale radius
measurements of yearling smolts ancl of four-
year-old adult red salmon (scale formula 1.2)
from 1953 year class, Wood River lakes: A.
Modal group of small yearlings, 1955, com-
pared with adult fish from Lake Aleknagik
spawning grounds, 1957; B. Modal group of
large yearlings, 1955, compared with adult fish
from Wood River lakes above Lake Aleknagik,
1957.
..
w
0 .. e .. ..
" ..
0
" e ..
" .,
0 .. ...
0 .. ..
.0 e
" :z:
3-L. Nrrka
Frnno Crerk
4-t. Nrrka
Allah Beach
S-L. Nerka
Stovall Crrrk
1 6-L. Nerka
N-4 B~ach
I 7-L. N~rka
Pick Crrei<
I 8-Llttlr Togiak l.Gke
West end
I 9-L. Nrrka
Anvil Boy
I 10-L, Nerka
Krma Crrek
13-L. Beverley
SllvnHorn
14-L. Kulik
Crant Rlv<r
no:29
..,.zs
.,.zs
...... zs
naZS
n-ZS
,.,zs
n•ZS
n•ZS
nmZS
no<ZS
...... zs
n•ll
n•ll
SO 65 80 95 110 IZS 140
Magnlflrd scalr radius to flm annulus, In mllllmrtrn
Fig. 25. Frequencies of radius measurements
of scales from four-year-old adult 1·ed salmon,
year class 1953, scale formula 1.2. (Measure-
ments from focus to edge of fresh-water annulus
x 230, grouped in 5 mm-class intervals. Scales
taken from spav.'!led-out fish.)
Fig. 26. Spawning grounds represented in the
study of first-year growth attained by adults,
1953 year class, returning 1957. (See Figure 25
for names of numbered areas.)
10
40
10
10
Ulwn LGiol' Nrrkcaad
UttlrTogiak Lak•
....
•• 170
50 65 95 110 125 140
Ma!Jillfird seal .. tad.ha lD fint ~~~U~Ullll, la miWmrcm
Fig. 27. Difference between lake areas in
scale radius measurements of four-year-old
adult red salmon, scale formula 1.2, 1953 year
class.