PEARCY ET AL.: JUVENILE CHUM SALMON 



mm and over 4 g wet weight. Fish averaged over 

 60 mm and 2 g by the end of May in all years 

 (Table 2). Many juvenile chum salmon appar- 

 ently stayed in shallow water in Netarts Bay 

 beyond the size of 45-55 mm, the length at which 

 they are thought to migrate from shallow estu- 

 arine waters into open neritic waters of other 

 estuaries (Kaczjinski et al. 1973; Healey 1980a, 

 1982b; Simenstad and Salo 1980; Myers and 

 Horton 1982). Large chum salmon apparently 

 did not aggregate in the deep channels of 

 Netarts Bay but emigi'ated directly out of the 

 bay into open coastal waters. 



The average size of juvenile chum salmon in- 

 creased during their residence in Netarts Bay, 

 as well as in Tillamook Bay (Forsberg et al. 

 1977), Yaquina Bay (Myers and Horton 1982), 

 and Grays Harbor (Herrmann 1970). This in- 

 crease suggests growth. Since large chum 

 salmon are thought to emigrate more rapidly 

 than small chum (Healey 1982a) and recruit- 

 ment of downstream migrants may be pro- 

 longed, these estimates based on size-frequency 

 distributions probably underestimate growth 

 rates. The gi'owth rates for marked chum salmon 

 in Netarts Bay, 0.4-0.6 mm/d and 1.6-2.3% body 

 weight (BW)/d, may also be underestimates if 

 rapidly growing fish exit the bay sooner than 

 slow growing fish. Growth rates of juvenile 

 chum salmon in Netarts Bay are considerably 

 less than the 1 mm/d and 6% BW/d estimated 

 from marked juvenile chum in the Nanaimo 

 Estuary (Healey 1979, 1982a) and the 8.6% 

 BW/d for marked chum in Hood Canal (Bax and 

 Whitmus 1981), but they are more similar to the 

 0.8 mm/d and about 4.2% BW/d for unmarked 

 juvenile chum salmon in the Fraser River and 

 Gulf Islands (Phillips and Barraclough 1978; 

 Healey 1982b), the 2.7% BW/d for unmarked 

 chum in Nitinat Lake, and the 0.4 mm/d found 

 for unmarked chum in Steamer Bay, south- 

 eastern Alaska (Murphy et al. 1988). They are 

 also similar to the gi'owth rates of juvenile chum 

 reared in saltwater aquaria at daily rations of 

 6-10% BW/d (Volk et al. 1984). 



The cumulative biomass of juvenile chum 

 salmon in Netarts Bay (13.6, 6.2, and 11.2 x lO'^ 

 kg) was generally lower than the 14—66 x 10^ kg 

 estimated for natui'ally reared chum salmon in 

 the similarly sized Nanaimo Estuary by Healey 

 (1979). Total production of juvenile chum in the 

 Nanaimo Estuary during the two years studied 

 was 1,100-2,400 kg (or 0.2-0.4 g/m" of intertidal 

 area), over an order of magnitude higher than 

 that estimated in Netarts Bay (0.01-0.03 g/m^ of 



intertidal area). This suggests that the carrying 

 capacity of Netarts Bay for juvenile chum is lim- 

 ited. However, we found no evidence for den- 

 sity-dependent growth. Growth rates and resi- 

 dence times were about the same among years 

 with several-fold differences in numbers of fry 

 released and estimated biomass of juvenile chum 

 salmon in the estuary (Tables 1, 2, 3). Production 

 may be limited by the short residence times of 

 large hatchery fish released late in the spring as 

 well as by environmental factors other than 

 direct competition for food. 



Elevated water temperatures may affect 

 growth of juvenile chum salmon, especially since 

 Netarts Bay is at the southern extremity of the 

 spawning range of this species in the north- 

 eastern Pacific Ocean. Kepshire (1971) reported 

 an optimum temperature of 13°C for growth of 

 juvenile chum salmon, and at 15°C, a tempera- 

 ture often recorded in Netarts Bay, food con- 

 sumption was higher than at lower tempera- 

 tures, but food conversion efficiency and growth 

 were low. Irie (1984) found that ocean tempera- 

 tures where juvenile chum salmon were found 

 along the coast of Hokkaido were below 14°C. 

 Juvenile chum salmon in Netarts Bay may also 

 be excluded from the best foraging habitat by 

 high temperatures. Densities of crustacean prey 

 were highest in the intertidal areas of the upper 

 bay (Chapman unpubl. data) where highest tem- 

 peratures occuiTed. Costs of metabolism, food 

 conversion, prey capture, and swimming may 

 hmit allocation of energy to growth when tem- 

 peratures are above optimal (Brett 1979; 

 Wissmar and Simenstad 1988). 



Growth efficiencies may also be influenced by 

 the quality and quantity of available prey. Small 

 harpacticoid copepods (viz., Harpacticus 

 uniremis) have been found to predominate the 

 diet of juvenile chum salmon in estuaries (Healey 

 1979; Sibert 1979; Simenstad and Salo 1980; 

 Simenstad and Wissmar 1984) where growth 

 rates are high, whereas large amphipods pre- 

 dominated the diet in Netarts Bay (Chapman, 

 unpubl. data), and mollusk larvae, hyperiid 

 amphipods, and larvaceans were important prey 

 for juvenile chum salmon in Steamer Bay, AK 

 (Murphy et al. 1988) where growth was slower. 

 Large prey, such as amphipods, may require 

 more energy to capture because of highly devel- 

 oped escape responses (Volk et al. 1984), may be 

 digested less efficiently because of theii' thick 

 chitinous exoskeletons (Pandian 1967; Brett and 

 Groves 1979), and may have lower per unit 

 weight caloric value (Cummins and Wuycheck 



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