250 



Fishery Bulletin 100(2) 



after June. Our findings concur: the smallest salmon 

 we caught was 68 mm FL, and we caught no fish after 

 27 June. Juveniles were approximately 4.5 months old 

 (after hatching) when they entered the San Francisco 

 Estuary. They spent about 40 days there, migrating at 

 1.6 km/d, based on mean age differences of fish enter- 

 ing the estuary and fish leaving at the Golden Gate. 

 This is probably a minimum estimate of migration rate, 

 because data from tagged fish caught within the estu- 

 ary showed rates of 1.70 to 13.55 km/d, representing 

 residence times of 38 to 5 days. A previous mark-recap- 

 ture study also found higher migration rates ( 10 to 18 

 km/d), although the data were for passage through the 

 upstream delta (Kjelson et al.. 1982). 



Studies in the Pacific Northwest suggest that juve- 

 niles of ocean-type chinook salmon make extensive use 

 of estuaries, spending as much as 6 to 9 months in 

 them feeding and gi'owing (Myers and Horton, 1982; Si- 

 menstad et al., 1982: Healey, 1991). In the Columbia 

 River estuary, subyearling chinook salmon were present 

 throughout the year, although most abundant in May 

 to September (McCabe et al., 1986). Fall-run juveniles 

 entered the Sixes River estuary in the spring and were 

 abundant from June through August (Reimers, 1973). 

 Juvenile chinook salmon resided in Washington estuar- 

 ies for 6 to more than 29 weeks, but some individuals 

 were present for up to 189 d (Simenstad et al., 1982). 

 Even in northern California's Klamath River estuary, 

 juvenile fall-run chinook salmon remained from June to 

 September (Wallace and Collins, 1997). The relatively 

 short period of abundance in the San Francisco Estuary 

 and emigration rates presented here suggest that juve- 

 nile chinook from the Central Valley may derive less 

 benefit from estuarine residence than do more northerly 

 populations. 



Juvenile chinook salmon grew little while in the San 

 Francisco Estuary. Though growth was not statistically 

 significant, on average they increased in size by 7 mm 

 FL and 0.9 g, representing daily growth of 0.18 mm/d 

 and 0.02 g/d. These estimates indicate slower growth than 

 has been reported for juvenile chinook in most estuaries 

 to the north. In five estuaries on Vancouver Island and the 

 Eraser River, juveniles grew 0.21 to 0.62 mm/d (Levy and 

 Northcote, 1982; Healey, 1991). Growth measurements 

 from population sampling and from following marked fish 

 produced similar results in the Sixes River estuary, where 

 daily growth ranged from 0.07 mm/d in summer to 0.9 

 mm/d in spring (Reimers, 1973). Reimers speculated that 

 the very slow gi-owth during summer was due to food limi- 

 tation caused by high salmon abundance. 



Growth can also be inferred by the change in size offish 

 collected at the same locations from the beginning to the 

 end of the emigi'ation period. We found no significant in- 

 crease in size at given locations within the estuary durhig 

 the May^une emigration season. Kjelson et al. ( 1982) al- 

 so found no change in smolt size in the delta from April to 

 June. In contrast, the mean size of juvenile chinook salm- 

 on in the Columbia River estuary increased from March to 

 December, suggesting substantial growth or immigration 

 of larger fish during the season. 



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Figure 5 



(A) Protein and total lipid concentrations, and (B) lipid class 

 concentrations (triacylglycerols [TAG], polar lipids [PL], cho- 

 lesterol IChol], and nonesterified fatty acids |NEFA|) in juve- 

 nile chinook salmon from locations in the San Francisco 

 Estuary (km 68, km 46, km 26, km 3) and the Gulf of the Far- 

 allones (GFi. Concentrations are mg/g wet weight. 



Although little gi'owth occurred during estuarine resi- 

 dence, growth was rapid in the coastal waters of the Gulf 

 of the Farallones. Juvenile ocean cohorts were 10% longer 

 in mean FL and 90% heavier than those from the estu- 

 ary, although size varied more in ocean residents than in 

 chinook salmon within the estuary. Faster growth rates 

 of juvenile chinook salmon in coastal waters than in estu- 

 aries have been reported from British Columbia (Healey, 

 1980a), and Oregon and Washington (Miller et al., 1983; 

 Fisher and Pearcy, 1995), with rates of 1 mm/d and more. 

 Daily growth rates of juveniles in the Gulf of the Faral- 

 lones were difficult to determine because the mean age of 

 the subset aged by otolith analysis was less than the mean 

 age offish at the estuary exit. But if the calculated age of 

 ocean juveniles (from the regi'ession of age on FL) is used, 

 during the calculated 13 d of ocean residence they gi-ew at 

 about 0.6 mm/d and 0.5 g/d, well above rates while in the 

 San Francisco Estuary. 



Growth rate estimates from the regressions of FL or 

 weight on age for all juveniles from both the estuary and 

 gulf were 0.16 mm/d and 0.029 g/d. These results agree 



