Anadromous Sockeye Salmon ( Oncorhynchus nerka) Derived from Nonanadromous Kokanees: Life History in Lake Toro. Abstract.

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1 Scientific Reports of the Hokkaido Salmon Hatchery No. 46: , 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 two life-history patterns: anadromous sockeye and nonanadromous kokanee types. Their growth curves fit periodic von Bertalanffy s curves, but sockeyes grew lineally more than kokanees. Seasonal change in growth rate of sockeye showed a constant periodicity, but that of kokanee showed extreme fluctuations and gradually decreased with time. Life history patterns of sockeye salmon may be influenced by the genetics 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 other members 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 of sockeye 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 in several lakes. Recently, sockeye salmon have been produced by artificial releases of smolts 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 -%?Ak8) -157-

2 I Irf - %T&@fR SCI. REP. HOKKAIDO SALMON HATCHERY, NO. 46, 1992 population. Nordeng (1983) also demonstrated that both anadromous and nonanadromous forms of Arctic char (Saluelinus alpinus) can produce anadromous and nonanadromous progeny, the propensity to do so depending on parental form and environmental 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 by assortative 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 out 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 E 144E I I I 44N I_,km AREKINAI R. 0 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 a location (St. T) where water temperature was recorded every hour at a depth of 1 m, respectively

3 KAERIYAMA ET AL. - LIFE HISTORY OF SOCKEYE SALMON Origin and rearing of juvenile releases A total of 60 thousand juvenile sockeye salmon (age 0.0) was released in Lake Tor0 of the Kushiro River System, with 20 thousands released on November 22, 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 were incubated and reared untii release. Eggs of the 1989 brood stock were stripped and fertilized from adult sockeye (age 1.1) running to the Nishibetsu River in November, Eggs were held in Nijibetsu Hatchery until eyed egg stage. Subsequently, they were transferred 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 weight in the autumn of 1988, and 103 mm in fork length and 12.8 g in the body weight in autumn of 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 * a 16 Id \ \ 1ol- I: \ \ \ t \ " ' ~ ~ ' ' ' ' ' ' ' ' ' ' ' ' ' ' " ' ' ' ' ' ' ' " " ' 1 ' ' - ulluuuuuuuuuu J F M A M J J A S O N D Month Fig. 2. Seasonal changes in average water temperature at St. T at depth of 1 m in Lake Toro

4 d kf * 2*&@$$ XI. REP. HOKKAIDO SALMON HATCHERY, NO Water temperature was measured at three stations (Sts. 1-3) for seasonal isotherms, and was recorded 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 a plankton net (#NXX13 bolting nylon (aperture 94 pm) with 30-cm diameter net opening) from bottom 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. Water temperature TC) st.1 St.2 Fish samples Fish were collected by a seine net that was m long and had openings 3 m wide by 1.5 m with 5-mm square mesh, some set nets that were made of 13-mm square mesh and funnelled into a 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 mea sured (fork length, body depth, body weight, liver somatic weight, gonad somatic weight and stomach 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 SW 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 the Kushiro River System were captured by gill nets made of 45-mm square mesh in Lake Tor0 and a V-throated trap in the lower area of Kushiro River, and were immediately frozen. Afterward, b 1 1 L :: ::: : :! : :: :: : :! : : : or (51/ St I ' " " " ' I L Water temperature (t) Fig. 3. Seasonal isotherms at three stations in Lake Toro, Numerals show months. m 0 SI ' ' ' ' ' ' ' ' ' ' ' J F M A M J J A S O N Month Fig. 4. Seasonal change in standing crops of zooplankton in Lake Toro, x I \ I, b

5 KAERIYAMA ET AL. - LIFE HISTORY OF SOCKEYE SALMON Table 1. Frequency (%I of zooplankton taken in Lake Toro, R: rare (< 1%). Species Jan. Mar. Apr. May Jun. Jul. Sep. Nov. Cladocera LXaphanosoma branchyrum - - R R R 1 4 R Daphnia galeata R - R - R 1 R R Bosmina coregoni R - R 2 2 R Leptodora kindtii - - R - - R - - Copepoda Cyclops vicinus R - 7 Thermocyclops hyalinus R Nauplii Brachionidae Number (thousands/ma) Table 2. Estimated relative abundance of fish species caught in Lake Tor0 (+, rare; + +, common; + + +, abundant; *, only recorded). Species 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) Relative abundance * * * *

6 IM * ~?A@$$?L SCI. 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 was almost 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 C in early June, and C from mid-june to July, and reached a peak of 22 C in 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 ( g/m3) in September. A minor peak was observed in April or May ( g/m3). Zooplankton taken by net were mainly composed of two species of Copepoda, four species of Cladocera, and Brachinoidae (Table 1). Copepods were most abundant: dominant species was the larger 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 are whitespotted 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 were observed to jump on the surface to feed winged insects along the lake shore. More juveniles were caught in June than in other seasons. A few smolt-like juveniles were caught near the outlet of the lake in midjune. Juveniles were widely distributed until

7 KAERIYAMA ET AL. ~ LIFE HISTORY OF SOCKEYE SALMON 1988 Nw Nov N= (Po n \n OF * n FORK LENGTH (mm) Fig. 5. Seasonal changes in the fork length frequency distribution of juvenile sockeye salmon captured in Lake Tor0 during 1988 and Arrow heads indicate average fork length. Open columns show the fork length frequency distribution at release

8 Skf 0 '2?A@f% SCI. REP. HOKKAIDO SALMON HATCHERY, NO July, but in August they moved to a cold water area (less than 15"C), supplied by spring water of the Omoshironbe River. Some fish looked thin in the body and secreted a lot of mucus. In autumn, juveniles migrated around the lake again. Growth and morphological changes. Length frequencies indicated an unimodal pattern until August (Fig. 5). Thereafter, small thin fish were frequently observed. Average fork lengths of juveniles (age 1.0) attained 137 mm in June, achieved 160 mm in August, but did not increase in the following autumn. One fish was caught at age 2.0 and 210 mm in fork length in December, 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.Ol). The condition factor decreased immediately after the fish were released, remained constant until early summer, and declined markedly after summer because of high water temperatures. Similarly, the ratio of body 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 body weight fluctuated between 1.0 and 1.4 except for lower ratio in spring (Fig. 7). The GSI of male juveniles remained at a low 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 of 1989 and 2 individuals (9.1%) in July and August of They had larger body size, 0.~ L W I : a Q W a m o 1 I MONTH Fig. 6. Seasonal changes in average and standard deviation (bars) of specific growth rate for fork length of sockeye salmon captured in Lake Tor0 during 1988 and N D J F M A M J J 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 as a percentage of body weight (LW/BW) of juvenile sockeye salmon captured in Lake Toro

9 KAERIYAMA ET AL. - LIFE HISTORY OF SOCKEYE SALMON I MONTH 6 AGE D J F M A M J J A S O N -0.o.l 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. 9 N D J F M A M J J A S O N D l l l l l l l 1 i D Mysid Pisces Eggs of Pisces Other animals Fig. 9. Seasonal changes in appearance rate of prey in stomach contents of juvenile sockeye salmon captured in Lake Toro

10 3~ - *3..L@PS; SCI. REP. HOKKAIDO SALMON 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 L 0 October than in other months (P < cr 0.051, although it varied considerably among individuals (Fig. 8). 5 = During winter and early spring, the dominant food components in the stomachs of juveniles were the larger cope- 30-2o.ar - 00,*? OO //; /* A0-- fl- I I I I Adult sockeye salmon in Lake Tor0 Age, number, and morphology. We caught 16 adult sockeye salmon of the 1988 brood stock (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 than females (P < The proportions of head length, kype length, and upper jaw length to the fork length in male was also higher than in female (P < There was no size difference between age 1.1 and age 2.1 adults

11 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. Month Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov * k k k % k k 1988 brood stock 1989 brood stock Male Female Male Female (17)* (20) ( 4) ( 8) ( 3) (25) 0.082? (13) k (26) k ( 2) k ( 6) k (13) k (36) k (11) 0.034? ( 9) k ( 7) * (20) k ( 2) (89) ( 4) 0.078? (69) k (11) ? (10) 0.325? (12) ( 9) t (11) k (18) ( 4) 0.194? ( 3) * averageisd (number of fish examined) k (19) k (20) 0,109? (11) 0.096? (18) 0.130? ( 9) k (12) k (23) Table 4. Cornparision of measurements between precocious maturing and immature male sockeye salmon (age 1.0) captured in Lake Tor0 on June in FL, fork length; BD, body depth; BW, body weight; LW, liver weight; NS, P > 0.05; *,P < 0.05; * *,P < 0.01; * * *,P < 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 Mann-Whitney U-test 138? k k ? ? k k k 10 ** t *** ? * k *** k NS k NS 1.444? *** 3 Scale pattern. The number of freshwater circuli on the scales of 1988 brood adult sockeye salmon (age 1.1) averaged 26.7 (range 24-30> circuli, which corresponded with that of juveniles captured from late June to early July of 1989 (Figs. 12 & 13). The formula (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 or 2.0 and returned as anadromous sockeye salmon from the ocean to Lake Tor0 one or two years later, whereas other individuals spent at least two winters in the lake as nonanadromous

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13 KAERIYAMA ET AL ~ LIFE HISTORY OF SOCKEYE SALMON captured in ihe Kushiro River on Sepiember 18, Fork length and body weight were 520 mm and 1,245 g. respectively. Fig. 12. Scales 01 a juvenile at seaward migration (June 14, 1989) and an adult at returning (July ) from sodteye salmon caplured in Lake Toro. An arrow indicates the period 01 seaward migration. Bars = 0.1 mm

14 S M * bt&@ffp6i SCI. REP. HOKKAIDO SALMON HATCHERY, NO I I 1 I I I I I NUMBER OF ClRCULl Fig. 13. Frequency distribution in number of circuli at the seaward migration time of adult sockeye salmon (age 1.1) returning to Lake Toro I- I A a.6765 SOCKEYE 1 J / KOKAN E E K = T,= T = A = n U t/vvv\ SOCKEYE,.. $ I 8 L',---. KOKANEE YEAR (t) Fig. 14. Comparisons of growth curves and growth rate between anadromous sockeye and nonanadromous kokanee salmon in Lake Toro. Growth curves were fitted into the periodic von Bertalanffy's curve (Akamine 1986): Lt = Lax[l-exp( -K((1+a)(t-to)/2) + (1- a)(sin21r(t-tl)-sin2n(to-t,))/4n}], where & is the estimated fork length (cm) at age t, Lax is the 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) and amplitude of growth rate, and t is the age (years)

15 KAERIYAMA ET AL. ~ LIFE HISTORY OF SOCKEYE SALMON kokanee salmon. Their growth curves fit periodic von Bertalanffy s curves (Akamine 1986). 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 of 1988 showed two types of life history pattern: the anadromous sockeye type and the nonanadromous kokanee type. The sockeye type migrated seaward in late spring through early summer at age 1.0 or 2.0, remained in the ocean for one or two years, and subsequently homed to the Kushiro River System. Whereas, the kokanee type resided in Lake Tor0 for more than two years. Anadromous sockeye salmon lineally grew more than nonanadromous kokanee salmon. Change in growth rate of sockeye showed a periodical 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 the seaward migration period (Thorpe, 1977; Kubo, 1980; Hirata et al., 1986). These results indicate that life history pattern of sockeye salmon may be not affected by growth pattern. Burgner (1991) reported that there is a geographical cline from south to north in timing of the smolt migrations at lake outlets in American sockeye populations, and that size at seaward migration is influenced by lacustrine environment, climate and population density. Juveniles were widely distributed, and showed active feeding behavior in most 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 that all 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 the lake 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 , and was geographically landlocked in Lake Shikotsu for more than 15 generations. The present results estimate that some sockeye juveniles migrated seaward between late June and early July at a fork length of about 140 mm. This period corresponds with the seaward-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 genetics of the stock of origin as well as by the lacustrine-limnological environment. Thus, both

16 SV - I-$.&@f% SCI. REP. HOKKAIDO SALMON HATCHERY, NO. 46, 1992 anadromous and nonanadromous types of Oncorhynchus nerka can be produced from both sockeye and kokanee salmon. In conclusion, life-history patterns of juvenile sockeye salmon may be decided by a conditional strategy, concerned with a quantitative genetic model that sums genetic and lacustrine-environmental effects, involving trade-offs to obtain the optimum energy. Another example of this type of strategy is the prior migration of larger individuals in juvenile 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, 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 temperature and ration size. J. Fish. Res. Bd. Can., 26, Burgner, R. L. (1991): Life history of sockeye salmon (Oncorhynchus nerka). In Pacific salmon life histories (edited by Groot, C. and L. Margolis). UBC Press, Vancouver. pp 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 of sockeye salmon and kokanee, the anadromous and nonanadromous forms of Oncorhynchus nerka. Can. J. Fish. Aquat. Sci., 46, 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, 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, (In Japanese with English summary.) Kaeriyama, M. (1985) : Adaptation and differentiation of Oncorhynchus. Aquabiology, 7, (In Japanese with English summary.) Kaeriyama, M. (1986): Ecological study on early life of the chum salmon, Oncorhynchus

17 KAERIYAMA ET AL. - LIFE HISTORY OF SOCKEYE SALMON keta (Walbaum). Sci. Rep. Hokkaido Salmon Hatchery, (401, (In Japanese with English summary.) Kaeriyama, M. (1989): Aspects of salmon ranching in Japan. Physiol. Ecol. Japan, Spec. VO~. I, Kaeriyama, M. (1991): Dynamics of the lacustrine sockeye salmon population in Lake Shikotsu, Hokkaido. Sci. Rep. Hokkaido Salmon Hatchery, (451, (In Japanese 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) (In Japanese with English summary.) McCart, P. J. (1970): A polymorphic population of Oncorhynchus nerka Babine Lake, British Columbia. Ph. D. Thesis, University of BritGh Columbia, Vancouver, B.C. (cited from Foote et al. 1989). Nordeng, H. (1983): Solution to the "Char Problem" based on Arctic char (Salvelinus alpinus) in Norway. Can. J. Fish. Aquat. Sci., 40, Thorpe, J. E. (1977): Bimodal distribution of length of juvenile Atlantic salmon (Salmo salar L.) under artificial rearing conditions. J. Fish Biol,, 11, Urawa, S. (1991): A review of sockeye salmon production in the Nishibetsu River in eastern Hokkaido. Tech. Rep. Hokkaido Salmon Hatchery, (1601, (In Japanese 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, (In Japanese 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), (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 Wood, C. C. and C. J. Foote (1990): Genetic differences in the early development and growth of sympatric sockeye salmon and kokanee (Oncorhynchus nerka), and their hybrids. Can. J. Fish. Aquat. Sci., 47,

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