Scientific Reports of the
Hokkaido Salmon HatcheryN o . 46: 157-174, March 1992

Anadromous Sockeye Salmon ( Oncorhynchus nerka) Derived from
Nonanadromous Kokanees: Life History in Lake Toro
Masahide KAERIYAMA*,
Shigehiko URAWA*,and Toshiya SUZUKI*

Abstract .
Life history of sockeye salmon (Oncorhynchus nerka) derived from kokanee
salmon was investigated in Lake Toro of the Kushiro River System. Juvenile
sockeyes released to Lake Tor0 as underyearlings (age 0.0) in late fall showed twolife-history patterns: anadromous sockeye and nonanadromous kokanee types.
Their growth curves fit periodic von Bertalanffy’s curves, but sockeyes grew lineallymore than kokanees. Seasonal change in growth rate of sockeye showed a constantperiodicity, but that of kokanee showed extreme fluctuations and gradually decreased with time. Life history patterns of sockeye salmon may be influenced b y thegenetics of the original stock as well as by the lacustrine environment.

Introduction
Sockeye salmon (Oncorhynchus nerka) exhibit a greater variety of life history patterns, and make more use of lake rearing habitat in juvenile stages compared with othermembers of the genus Oncorhynchus. Although sockeye are primarily anadromous, there
are distinct populations called kokanee that remain in fresh water throughout their life
period (Foerster, 1968; Burgner, 1991). Juveniles typically rear in lakes for one or more
years before seaward migration (”lake-type”), but particularly in northern populations,some individuals go to sea immediately after emergence (”sea-type”) or inhabit river
channels for at least one year (”river-type”) (Wood et al., 1987).
In the western North Pacific Ocean and Bering Sea, the spawning distribution ofsockeye salmon extends northeastward along the Far Eastern coast to the Anadyr River,southward to Iturup Island of Kuril islands, and westward to the Okhota and Kukhtuy
rivers on the northwest coast of the Sea of Okhotsk (Burgner, 1991). In Japan, wild
sockeye salmon are not found, although landlocked kokanee salmon are distributed inseveral lakes. Recently, sockeye salmon have been produced by artificial releases ofsmolts derived from the kokanee salmon in Lake Shikotsu (Kaeriyama, 1989; Urawa,1991).
McCart (1970; cited from Foote et al., 1989) concluded that sockeye and kokanee
spawning in the small tributaries of Babine Lake were part of the same panmictic
Contribution A No. 334 from the Hokkaido Salmon Hatchery* Research Division, Hokkaido Salmon Hatchery, Fisheries Agency of Japan, 2-2 Nakanoshima,
Toyohira-ku, Sapporo 062, Japan (!SLl%% iSfj%LIfaEQ %%@i%,%&gS M - % ? A k 8 )

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I Irf %T&@fRSCI. REP. HOKKAIDO S A L M O N H A T C H E R Y , NO. 46, 1992

population. Nordeng (1983) also demonstrated that both anadromous and nonanadromous forms of Arctic char (Saluelinus alpinus) can produce anadromous andnonanadromous progeny, the propensity to do so depending on parental form andenvironmental conditions. On the other hand, it is believed that anadromous sockeye
and nonanadromous kokanee salmon are genetically-distinct sympatric populations(Foote et al., 19891, and that the differentiation of sockeye and kokanee is promoted byassortative mating, and by selection against hybrid progeny owing to great selective
differences between the marine and lacustrine environments, and the special adaptations required for anadromy (Wood and Foote, 1990).
The present study was carried o u t to clarify the life-history pattern of sockeye
salmon derived from kokanee salmon.

Materials and Methods
Geographical character of Lake Tor0
Lake Toro, tributary of the lower Kushiro River, is situated in northern Kushiro
approximately 15 km inland from the coast. It is a small lake (area 637 ha) at low
elevation (8 m) with a maximum depth of 7 m, lies in the Kushiro Moor, and is almost
always covered with ice in winter (Fig. 11.

140E
I

I

144E
I

44N

I
_
,km
0

AREKINAI R.

42N

Fig. 1 . Map showing Lake Tor0 in the Kushiro River System. Solid and open circles
indicate stations (Sts. 1-3) where the limnological environment was investigated and alocation (St. T) where water temperature was recorded every hour at a depth of 1 m,
respectively.
-

158

KAERIYAMA E T AL. - LIFE HISTORY O F SOCKEYE SALMON

Origin and rearing of juvenile releases
A total of 60 thousand juvenile sockeye salmon (age 0.0) was released in Lake Tor0of the Kushiro River System, with 20 thousands released on November 22, 1988. from
Nijibetsu Hatchery (the 1988 brood stock) and 40 thousands on November 22, 1989,
from Kenebetsu Hatchery (the 1989 brood stock). Both groups of juveniles were first
filial (F-1) progeny of sockeye salmon that originated from kokanee salmon in Lake
Shikotsu. No records are known for prior occurrence of sockeye or kokanee salmon in
Lake Toro. Eggs of the 1988 brood stock were stripped and fertilized from adult sockeye(age 1.1) running to the Abira River in November, 1987, and were incubated at Chitose
Hatchery. Eyed eggs were transferred to Nijibetsu Hatchery, where hatched salmon wereincubated and reared untii release. Eggs of the 1989 brood stock were stripped andfertilized from adult sockeye (age 1.1) running to the Nishibetsu River in November,1988. Eggs were held in Nijibetsu Hatchery until eyed egg stage. Subsequently, they weretransferred to Kenebetsu Hatchery, and hatched fish were incubated and reared there.
Average sizes of released juveniles were 107 mm in fork length and 14.8 g in body weightin the autumn of 1988, and 103 mm in fork length and 12.8 g in the body weight inautumn of 1989. Juvenile sockeye salmon released into Lake Tor0 in the autumn of 1988
were marked with an excised adipose fin.
Environmental survey in Lake Tor0
Limnological environments were investigated in Lake Tor0 between 1988 and 1990.

*---•

1990
1989

a 16
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I d

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\
\

I:

1ol-

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3 6

01
-

" ' ~ ~ ' ' ' ' ' ' ' ' ' ' ' ' ' ' " ' ' ' ' ' ' ' " " ' 1 ' 'uLluuuuuuuuuu

J

F

M

A

M

J
J
A
Month

S

O

N

D

Fig. 2. Seasonal changes in average water temperature at St. T at depth of 1 m in LakeToro.
- 159 -

d kf * 2*&@$$X I . REP. HOKKAIDO SALMON HATCHERY, NO. 46. 1992

Water temperature was measured at three stations (Sts. 1-3) for seasonal isotherms, and wasrecorded at one-hour intervals with a temperature sensor memory ("Kadec-U", Kona System
Co.) at depth of 1 m at Station T (St. T in Fig.
1). Zooplankton were collected by towing aplankton net (#NXX13 bolting nylon (aperture
94 pm) with 30-cm diameter net opening) frombottom to surface. They were preserved in about
5%-formalin solution, and were equally separated into two samples for estimating standing crop
(wet-weight, mg/m3) and zooplankton fauna.
Fish samples
Fish were collected b y a seine net that was 50
m long and had openings 3 m wide by 1.5 m
with 5-mm square mesh, some set nets that weremade of 13-mm square mesh and funnelled intoa cod end of 5-mm mesh, and some gill nets
made of 28-mm square mesh. Samples were
preserved in a 10%-formalin solution, and m e a
sured (fork length, body depth, body weight,
liver somatic weight, gonad somatic weight andstomach content weight). Scales were taken for
counting the number of circuli. Condition factor(CF), gonad somatic index (GSI), and stomach
content index (SCI) were calculated by following
formulas, respectively: CF = W/(L3) X 1000,
GSI = GW/Wx100, and SCI = SW/WXlOO,
where W is the body weight (g), L is the fork
length (cm), GW is the gonad somatic weight (g),and S W is the stomach content weight (g). Specific growth rate for fork length (SGR) was calculated as follows: (In(L/L,))/tx 100, where Lo
and L are fork lengths at the release and t days
after release, and t is number of days after
release.
Adult sockeye homing from the ocean to theKushiro River System were captured by gill nets
made of 45-mm square mesh in Lake Tor0 and aV-throated trap in the lower area of Kushiro
River, and were immediately frozen. Afterward,- 160 -

Water temperature TC)
10
20

0

st.1

St.2

b

1

L1 : : : : : :: :! : :: : : : :! :: : :
or

St.3

(51//

2
1

I

0

'

"

"

"

'

I

L

10
20
Water temperature (t)Fig. 3. Seasonal isotherms at three stations in Lake Toro, 1989. Numerals
show months.

0 SI.1

x

51.2

I \

51.3

m

I

,

b
01'

'

J

F

'

M

'

A

'

M

'
J

'

J

'

'

'

'

A

S

O

N

Month

Fig. 4. Seasonal change in standing cropsof zooplankton in Lake Toro, 1989.

KAERIYAMA E T AL. - LIFE HISTORY O F SOCKEYE SALMON

Table 1. Frequency (%I of zooplankton taken in Lake Toro, 1989. R: rare (< 1%).
Species
Cladocera
LXaphanosoma branchyrum
Daphnia galeata
Bosmina coregoni
Leptodora kindtii
Copepoda
Cyclops vicinus
Thermocyclops hyalinus
Nauplii
Brachionidae
Number (thousands/ma)

Jan. Mar. Apr. May Jun. Jul. Sep. Nov.

R
R

-

5

4
R
1

-

-

R

-

-

R

-

-

8

69
2

4 4 4
10
94
44
2
1

10
77
3

8
12
76
2

R
20
57
19

11
42
38

14
35
24

3.8

6.6

2.7

1.3

4.8

19.0 25.3 0.1

-

29

R

R
R
R

R
2

-

R
R
2

1
1
R

R
R
9

7

Table 2. Estimated relative abundance of fish species caught in Lake Tor0(+, rare; + +, common; + + +, abundant; , only recorded).

*Species

Relative abundance

Lampetra reissneri (Dybowski)
Hucho perryi (Brevoort)
Salvelinus leucomaenis (Pallas)
Oncorhyncus masou (Brevoort)
Oncorhyncus nerka (Walbaum)
Oncorhyncus keta (Walbaum)
Oncorhyncus gorbuscha (Walbaum)
Hypomesus nipponensis McAllister
Hypomesus olidus (Pallas)
Tribolodon hakonensis (Gnuther)
Tribolodon ezoe Okada et Ikeda
Moroco percnurus sachalinensis (Berg)
Carassius auratus
Cyprinus carpi0 LinnC
Misgurnus anguillicaudatus (Cantor)
Noemacheilus toni (Dybowski)
Gasterosteus aculeatus aculeatus (Linnaeus)
Pungitius pungitius pungitius (Linnaeus)
Tridentiger obscurus (Temminck et Schlegel)
Rhinogobius brunneus (Temminck et Schlegel)
Chaenogobius urotaenia (Hilgendorf)
Chaenogobius laevis (Steindachner)
Platichthys stellatus (Pallas)

-

161 -

*

*

++
+
+

+++
+

+++
*
+++
++

+
+
+
*
*
++
+++
++
++
++
+++
*

I M * ~?A@$$?LSCI. REP. HOKKAIDO SALMON HATCHERY, NO 46, 1992
they were defrosted and measured.

Results
Environment in Lake Tor0
Water temperature. Seasonal changes in water temperature at a depth of 1 m (St. T)
are shown in Fig. 2. During winter (from January to March), water temperature wasalmost constant at 4°C because of ice-cover. The water temperature immediately increased after ice-melt (early April), attained 8°C in early May, 15°Cin early June, and 16-20°Cfrom mid-June to July, and reached a peak of 22°Cin August. Thereafter, it rapidly
decreased to about 5°C in November, and reached a minimum of about 2°C just before
ice-cover formation (late December).
Seasonal isotherms indicate similar thermal structure at each station (Fig. 3 ) . A
weak thermocline occurred at a depth of 2-3 m from June to July, and was broken down
by higher air temperatures and strong winds until autumn. In winter, water temperature ascended with increase in depth, and fluctuated at about 5°C near the bottom.
ZoopZankton. Seasonal changes in the standing crop of zooplankton in Lake Tor0 are
presented in Fig. 4 . Zooplankton were most abundant (1.6-3.5 g/m3) in September. A
minor peak was observed in April or May (0.5-1.2 g/m3). Zooplankton taken by net
were mainly composed of two species of Copepoda, four species of Cladocera, andBrachinoidae (Table 1). Copepods were most abundant: dominant species was thelarger copepod CycZops vicinus in winter and spring and the smaller copepod Thermocyclops hyalinus in summer and autumn. The epibenthonic mysid Neomysis intermedia
might be dominant along the lake shore in spring.
Fish species. Seventeen fish species were caught in Lake Toro, and an additional six
other species are known to occur in this lake (Table 2). Common fish species arewhitespotted charr (Salvelinus leucomaenis), juvenile chum salmon (Oncorhynchus keta),
Japanese smelt (Hypomesus nipponensis) , Japanese dace ( Tribolodon hakonensis) , ninespine stickleback (Pungitius pungitius pungitius), and Juzukake-haze (Chaenogobius
laevis). Japanese smelt is very important for fisheries, and is artificially propagated in
Lake Toro.
Life history of juvenile sockeye salmon in Lake Tor0
We caught 361 juveniles of the 1988 brood stock from December 1988 to December
1990, and 185 juveniles of the 1989 brood stock from December 1989 to October 1990 in
Lake Toro.
Lktribution and migration. In winter, most juveniles were captured near the bottom
layer where water temperature was highest (about 5°C)in the lake. They seemed to move
to upper layers after ice-melt (early April). In June and July (16-20°C in water temperature) juveniles were captured around most layers and areas of the lake, and wereobserved to jump on the surface to feed winged insects along the lake shore. Morejuveniles were caught in June than in other seasons. A few smolt-like juveniles werecaught near the outlet of the lake in midJune. Juveniles were widely distributed until- 162 -

KAERIYAMA E T AL.

~

LIFE HISTORY O F SOCKEYE SALMON

1988
N w . 1988
100

150

Nov. 1989

50

N=79

200

50

150

200

100

150

200

100

150

200

100

150

200

100

150

200

100

150

200

100

150

200

50
100

150

200

50

50

1(Po

150

200

50

50

n
\n
OF

*

100

150

200

50

50

0
2

100

150

200
50

n

50

50
100

150

200

50

50
100

150

200

100

150

200

100

150

200

100

150

200

100

150

200

100

150

200

50

50

50

FORK LENGTH (mm)Fig. 5. Seasonal changes in the fork length frequency distribution ofjuvenile sockeye salmon captured in Lake Tor0 during 1988 and 1990.
Arrow heads indicate average fork length. Open columns show the fork
length frequency distribution at release.
- 163 -Skf

0

'2?A@f% SCI. REP. HOKKAIDO SALMON HATCHERY, NO. 46. 1992

July, but in August they moved to a cold
1988
water area (less than 15"C), supplied by
01989
spring water of the Omoshironbe River.
0.41
1 - L
Some fish looked thin in the body and seW
creted a lot of mucus. In autumn, juveniles +2 03
migrated around the lake again.
I
Growth and morphological changes.
0 0.2
Length frequencies indicated an unimodal aQpattern until August (Fig. 5). Thereafter, 0
small thin fish were frequently observed. 0 0.1
Average fork lengths of juveniles (age 1.0) Wa
attained 137 mm in June, achieved 160 mm m oIin August, but did not increase in the followMONTH
ing autumn. One fish was caught at age 2.0 -0.1
and 210 mm in fork length in December, Fig. 6. Seasonal changes in average and stan-

0. ~ 1

:
-

1

1990.

The SGR of juveniles at age 1 . 0 increased slightly in winter (0.151, ascended
considerably in spring (0.281, and decreased from late summer to autumn (0.04)(Fig. 6). The SGR was considerably higher
in May (0.35 k 0.02) and July (0.37 f 0.02)
than in other months ( P < O . O l ) .
The condition factor decreased immediately after the fish were released, remained
constant until early summer, and declined
markedly after summer because of highwater temperatures. Similarly, the ratio ofbody depth to fork length was high in winter, decreased slightly in spring, and declined substantially in summer and autumn.
The ratio of liver somatic weight to bodyweight fluctuated between 1.0 and 1.4
except for lower ratio in spring (Fig. 7).
The GSI of male juveniles remained at alow level (less than 0.02%) during winter,and rose gradually from spring to summer(Table 3). Precocious maturing males (age
1 . 0 , GSI > 1%)were captured: 3 individuals (3.4% of total fish captured) in June of1989 and 2 individuals (9.1%) in July andAugust of 1990. They had larger body size,- 164 -

dard deviation (bars) of specific growth rate
for fork length of sockeye salmon captured
in Lake Tor0 during 1988 and 1990.

- +
N D
0.0

J

F

M

A

M

J

J

1.0

A

S

O

N

D
\

MONTH & AGE

Fig. 7. Seasonal changes in average and standard deviation (bars) of condition factor(CF), body depth as a percentage of fork
length (BD/FL), and liver somatic weight asa percentage of body weight (LW/BW) of
juvenile sockeye salmon captured in Lake
Toro.

KAERIYAMA E T AL. - LIFE HISTORY O F SOCKEYE SALMON

D J-0.o.l.
I

F

M

A

M

J

J

A

S

O

1.0

MONTH 6 AGE

MONTH 6 AGE

Fig. 8. Seasonal changes in rate of empty stomach occurrence and average stomach content
index with standard deviation (bars) in juvenile sockeye salmon captured in Lake Toro.

4

1988

0.0

-1

N

D
1

-

J
1

F

1

M

1

A

1

1.0

M

l

J
l

9

J
l

A
l

S
l

O
l

N
l

D
1

i

D

Mysid
PiscesEggs of Pisces

Other animals

Fig. 9. Seasonal changes in appearance rate of prey in stomach contents ofjuvenile sockeye salmon captured in Lake Toro.

-

165 -

N

.

3~

- *3..L@PS; SCI. REP. HOKKAIDOSALMON HATCHERY. NO. 46, 1992

Feeding behauior. Many juveniles
had empty stomachs except in January,
February, May and October (Fig. 8).
The stomach content index was higher
in January, February, May, June, and

A0--

30-

flL

/*

0

October than in other months ( P < cr
0.051, although it varied considerably
among individuals (Fig. 8).
During winter and early spring, thedominant food components in the stomachs of juveniles were the larger cope-

5=

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-

00

,*?.ar

O O

//;
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Adult sockeye salmon in Lake Tor0Age, number, and morphology. We caught 16 adult sockeye salmon of the 1988 broodstock (composed of 13 age 1.1, 2 age 1.2. and 1 age 2.11, and 2 individuals (both age
1.1) of the 1989 brood stock in the Kushiro River System during 1990 and 1991 (Fig. 11).
In addition, two marked sockeye adults were caught offshore of Hamanaka in the Pacific
Ocean.
Table 5 shows size and morphological characters of adult sockeye salmon captured
in the Kushiro River System. Adults captured in 1991 may be thinner than those in 1990
due to their later seasonal capture after summer. Males were strikingly larger thanfemales ( P < 0.011. The proportions of head length, kype length, and upper jaw length
to the fork length in male was also higher than in female ( P < 0.011. There was no size
difference between age 1.1 and age 2 . 1 adults.
- 166 -

KAERIYAMA ET AL.

~

LIFE HISTORY OF SOCKEYE SALMON

Table 3. Seasonal changes in the gonad somatic index (GSI) of sockeye salmon captured in
Lake Toro.
1988 brood stock

1989 brood stock

Month

Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.

Male

Female0.015
0.019 (17)*0.009
0.002 (20)0.010
0.003 ( 4)0.013 k 0.007 ( 8)0.007 k 0.003 ( 3)0.077 k 0.234 (25)0.082 ? 0.014 (13)0.077 k 0.030 (26)0.092 k 0.010 ( 2)0.089 k 0.038 ( 6)0.103 k 0.028 (13)0.106 k 0.128 (36)

*
*
*

-

-

Male
0.012 k 0.012 (11)Female0.034 ? 0.041 ( 9)0.080 k 0.018 (19)0.067 k 0.026 (20)0.015 k 0.011 ( 7)0.010
0.007 (20)0,109 ? 0.027 (11)0.096 ? 0.019 (18)*0.013 k 0.001 ( 2)0.063 % 0.262 (89)0.045 k 0.034 ( 4)-0.078 ? 0.044 (69)0.098 k 0.036 (11)-0.073 k 0.022 ( 9)0.099 2 0.100 ( 4)0.204 -t 0.063 (11)0.337 ? 0.932 (10)0.325 ? 0.809 (12)-0.130 ? 0.041 ( 9)0.144 k 0.037 (12)-0.069 k 0.030 (18)-0.150 k 0.065 (23)0.194 ? 0.118 ( 3)* averageiSD (number of fish examined)

Table 4. Cornparision of measurements between precocious maturing and immature male
sockeye salmon (age 1.0) captured in Lake Tor0 on June in 1989. FL, fork length; BD, body
depth; BW, body weight; LW, liver weight; NS, P > 0.05; * , P < 0.05;* , P < 0.01;* * * , P < 0.005.

*

Fork length (mm)Body weight (g)Condition factor
BD/FL (%>
LW/BW (%>
Stomach content index (%>Gonad somatic index (%>Number of sample

Immature male

Precocious male

138 ? 626.798 k 3.950
10.223 k 0.615
19.090 ? 0.958
0.719 ? 0.188
0.184 k 0.393
0.015 k 0.017
86

151 k 1038.057 -t 5.207
11.125 ? 0.731
21.224 k 0.334
0.858 k 0.441
0.712 k 1.051
1.444 ? 0.226
3Mann-Whitney U-test

**
***
*
***
NS
NS

***

Scale pattern. The number of freshwater circuli o n the scales of 1988 brood adultsockeye salmon (age 1.1) averaged 26.7 (range 24-30> circuli, which corresponded withthat of juveniles captured from late June to early July of 1989 (Figs. 12 & 13). T h eformula (1) indicated that their size at seaward migration may be 141 mm in fork length.
Life history pattern and growth curve. Of the juvenile sockeye salmon released in Lake
Toro, some individuals migrated seaward as smolts in spring at age 1 . 0 o r 2.0 a n d
returned as anadromous sockeye salmon from the ocean to Lake Tor0 one o r two years
later, whereas other individuals spent at least two winters in the lake as nonanadromous- 167 -

3 kf

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HOKKAIDO SALMON HATCHERY, NO. 46, 1992

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KAERIYAMA E T AL~

LIFE HISTORY OF SOCKEYE SALMON

captured in ihe Kushiro River on Sepiember 18, 1991. Fork lengthand body weight were 520 mm and 1,245 g. respectively.

Fig. 12. Scales 01 a juvenile at seaward migration (June 14, 1989) andan adult at returning (July 18. 1990) from sodteye salmon capluredin Lake Toro. An arrow indicates the period 01 seaward migration.
Bars = 0 . 1 mm.

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I

I

1

I

24

25

26

I

I

27

28

I

30

29

I

NUMBER OF ClRCULl
Fig. 13. Frequency distribution in number ofcirculi at the seaward migration time of adultsockeye salmon (age 1.1) returning to Lake
Toro.
60

SOCKEYE

40-

1

A a.6765

I-

I

J

/

KOKANEE
K = 0.6323
T,=-0.0739
T = 0.7429
A = 0.1674

n

U

2

1

3

4

-t/vVv\
SOCKEYE,---. KOKANEE

, .
.$

I8

L'

2

1

YEAR

3

4

(t)

Fig. 14. Comparisons of growth curves and growth rate between anadromous sockeye andnonanadromous kokanee salmon in Lake Toro. Growth curves were fitted into theperiodic von Bertalanffy's curve (Akamine 1986): Lt = Lax[l-exp(-K((1+a)(t-to)/2) + (1a)(sin21r(t-tl)-sin2n(to-t,))/4n}],where & is the estimated fork length (cm) at age t, Laxisthe asymptotic length, K is the growth coefficient, to is the hypothetical age when length
would by zero, both tl and a are the parameters determined phase (topology) andamplitude of growth rate, and t is the age (years).
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KAERIYAMA E T AL.

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LIFE H I S T O R Y O F SOCKEYE SALMON

kokanee salmon. Their growth curves fit periodic von Bertalanffy’s curves (Akamine1986). Anadromous sockeye grew lineally more than nonanadromous kokanee. Seasonal change in growth rate of sockeye showed a periodical fluctuation, however, that of
kokanee showed extreme fluctuations, and gradually decreased with time (Fig. 14).

Discussion
Juvenile sockeye released in Lake Tor0 as underyearlings (age 0.0) in the late fall of1988 showed two types of life history pattern: the anadromous sockeye type and thenonanadromous kokanee type. The sockeye type migrated seaward in late springthrough early summer at age 1.0 or 2.0, remained in the ocean for one or two years, andsubsequently homed to the Kushiro River System. Whereas, the kokanee type resided in
Lake Tor0 for more than two years. Anadromous sockeye salmon lineally grew morethan nonanadromous kokanee salmon. Change in growth rate of sockeye showed aperiodical fluctuation; however, fluctuations in the growth rate of kokanee were more
extreme than those of sockeye and gradually decreased with time. On the other hand,juvenile sockeye salmon showed unimodal frequency distribution in fork length until
summer at age 1 . 0 . This may be different from those of Atlantic (Salmo salar) and masu
(0.masou) salmon, whose length frequency distribution showed a bimodality in theseaward migration period (Thorpe, 1977; Kubo, 1980; Hirata et al., 1986). These results
indicate that life history pattern of sockeye salmon may be not affected b y growth
pattern.
Burgner (1991) reported that there is a geographical cline from south to north intiming of the smolt migrations at lake outlets in American sockeye populations, and thatsize at seaward migration is influenced by lacustrine environment, climate and population density. Juveniles were widely distributed, and showed active feeding behavior inmost layers and areas of the lake during June and July. However, water temperature (16-20°C) in this period exceeded apparently the optimum range (5515°C) for sockeye
salmon (Brett et al., 1969; Goodlad et al., 1974; Burgner, 1991). At first, we expected thatall juveniles should migrate seaward before summer due to high water temperatures(more than 20°C) in the lake. Despite our assumption, many juveniles remained in thelake over the summer, although their growth was impaired by high water temperatures.
The Lake Tor0 populations were derived from the kokanee salmon in Lake Shikotsu.
Kaeriyama (1991) estimated that the Lake Shikotsu kokanee population was transplanted
from sockeye population in Lake Urumobetsu on the Iturup Island during 1925-1940,
and was geographically landlocked in Lake Shikotsu for more than 15 generations. The
present results estimate that some sockeye juveniles migrated seaward between late Juneand early July at a fork length of about 140 mm. This period corresponds with theseaward-migration timing of juvenile sockeye salmon in Lake Urumobetsu (Watanabe,1965). In uther lakes where Lake Urumobetsu sockeye salmon were transplanted, juveniles also migrated downstream in late June and early July (Watanabe, 1959; Kaeriyama,1991). These indicate that the life history of sockeye salmon is influenced by the geneticsof the stock of origin as well as by the lacustrine-limnological environment. Thus, both
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SCI. REP. HOKKAIDO SALMON HATCHERY, NO. 46, 1992

anadromous and nonanadromous types of Oncorhynchus nerka can be produced fromboth sockeye and kokanee salmon.
In conclusion, life-history patterns of juvenile sockeye salmon may be decided by aconditional strategy, concerned with a quantitative genetic model that sums genetic andlacustrine-environmental effects, involving trade-offs to obtain the optimum energy.
Another example of this type of strategy is the prior migration of larger individuals injuvenile chum salmon (Kaeriyama, 1986).

Acknowledgments
We gratefully acknowledge Dr. William R. Heard, Auke Bay Laboratory, National
Marine Fisheries Service, Ms. Katherine W. Myers, Fisheries Research Institute, University of Washington, and Dr. Koji Maekawa, National Research Institute of Fisheries
Science, for improving an early draft of manuscript. Thanks are also extended to Mr.
Yoshinori Tosa and Ms. Kozue Yoshiyama , Tor0 Cooperative Fisheries Association,and staffs of Tokachi Branch, Hokkaido Salmon Hatchery for their assistance of investigation in Lake Toro. This work was supported in a part by a Grant-in-Aid (Bio Cosmos
Program) from the Ministry of Agriculture, Forestry and Fisheries (BCP 91-IV-B-2).

References
Akamine, T. (1986): Expansion of growth curves using a periodic function and BASIC
programs by Marquardt's method. Bull. Jap. Sea Reg. Fish. Res. Lab., (361, 77107.
Brett, J. W., J. E. Shelbourn, and C. T. Shoop (1969): Growth rate and body composition of fingerling sockeye salmon, Oncorhynchus nerka, in relation to temperatureand ration size. J. Fish. Res. Bd. Can., 26, 2363-2394.
Burgner, R. L. (1991): Life history of sockeye salmon (Oncorhynchus nerka). In Pacificsalmon life histories (edited by Groot, C. and L. Margolis). UBC Press, Vancouver. pp. 1-118.
Foerster, R. E. (1968) : The sockeye salmon, Oncorhynchus nerka. Bull. Fish. Res. Bd. Can.,
162, 422p.
Foote, C. J., C. C. Wood, and R. E. Withler (1989): Biochemical genetic comparison ofsockeye salmon and kokanee, the anadromous and nonanadromous forms of
Oncorhynchus nerka. Can. J. Fish. Aquat. Sci., 46, 149-158.
Goodlad, J. C., T. W. Gjernes, and E. L. Brannon (1974): Factors affecting sockeye
salmon (Oncorhynchus nerka) growth in four lakes of the Fraser River System. J.
Fish. Res. Bd. Can., 31, 871-892.
Hirata, T., A. Goto, and K. Hamada (1986): Bimodal length frequency distribution in 0'
aged masu salmon, Oncorhynchus masou, in a natural stream of southern Hokkaido. Japan. J. Ichthyol., 33, 204-207. (In Japanese with English summary.)
Kaeriyama, M. (1985) : Adaptation and differentiation of Oncorhynchus. Aquabiology, 7 ,426-432. (In Japanese with English summary.)
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keta (Walbaum). Sci. Rep. Hokkaido Salmon Hatchery, (401, 31-92. (In Japanesewith English summary.)
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Shikotsu, Hokkaido. Sci. Rep. Hokkaido Salmon Hatchery, (451, 1-24. (InJapanese with English summary.)
Kubo, T. (1980): Studies on the life history of the "masu" salmon (Oncorhynchus masou)in Hokkaido. Sci. Rep. Hokkaido Salmon Hatchery, (34). 1-95. (In Japanese withEnglish summary.)
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alpinus) in Norway. Can. J. Fish. Aquat. Sci., 40, 1372-1387.
Thorpe, J. E. (1977): Bimodal distribution of length of juvenile Atlantic salmon (Salmosalar L.) under artificial rearing conditions. J. Fish Biol,, 11, 175-184.
Urawa, S. (1991): A review of sockeye salmon production in the Nishibetsu River ineastern Hokkaido. Tech. Rep. Hokkaido Salmon Hatchery, (1601, 3-10. (InJapanese with English summary.)
Watanabe, M. (1959): Some studies on the young fish of the "Hime-masu" (Oncorhynchus nerka) in Toya Lake. Sci. Rep. Hokkaido Salmon Hatchery, (141, 5-14. (InJapanese with English summary.)
Watanabe, M. (1965): On the smolts of the red salmon (Oncorhynchus nerka) at
Urumobetsu, Etorof I., Kuril Islands. Sci. Rep. Hokkaido Salmon Hatchery, (19) ,11-23. (In Japanese with English summary.)
Wood, C. C., B. E. Riddell, and D. T. Rutherford (1987): Alternative juvenile life histories
of sockeye salmon (Oncorhynchus nerka) and their contribution to production in
the Stikine River, Northern British Columbia. In Sockeye salmon (Oncorhynchus
nerka) population biology and future management (edited by H. D. Smith, L.
Margolis, and C. C. Wood). Can. Spec. Publ. Fish. Aquat. Sci., 96. pp. 12-24.
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さけ・ますふ研報 SC1.

REP,HOKKAIDOSALMONHATCHERY,NO

46. 1992

塘路湖におけると メマス起源べ二ザケの 生活史パターン

帰山雅秀 ・浦和茂彦 ・鈴木俊哉

1988 年と1989 年の晩秋に釧路川水系
塘路湖へとメ マス起源のへ
二 ザケ当歳魚 CO ． 0歳) が放流され，その生活史が調べられた，
べ二ザケの生活史。ターンは，降侮型と淡水残留型の2 型に分かれた． べ

二ザケの成長は，周期型関数を用いて拡張された von&rta@anffyの成長曲線に適合し 降梅型が残留型に比べ直線的に著しく成長した．成長曲線から得られた成長速度は降侮型が―定の周期を持って変動するのに
対し残留型のそれは 変動幅が著しく，時間の経過とともに減少した．塘路湖へ放流されたべ二ザケの生活史，，タソは，湖沼環境と共に原産地におけるべ
二ザケ個体群の遺伝的特性によっても影響を受げることが示唆された― 174 ―