248 



Fishery Bulletin 100(2) 



transit. According to this technique, mean daily growth 

 was about 0.18 mrn/d and 0.02 g/d. 



Because we aged only a subset of fish from each sam- 

 pling location, mean age of all fish obtained at each site 

 could be estimated with the FL-on-age regression equa- 

 tion for age (Fig. 2B). Results of that computation revealed 

 close agreement with measured ages at all locations ex- 

 cept the Gulf of the Farallones (Fig. 3C), where calculated 

 age was 189 ±8 d. Both methods of age determination in- 

 dicated that juveniles caught in coastal waters were from 

 the same year class. 



The average migration rate through the estuary was es- 

 timated at 1.6 km/d on the basis of the difference between 

 mean ages of juvenile salmon sampled at the estuary en- 

 try and exit (i.e. 65 km/[176 d at km 3 -136 d at km 68 ]). 

 Data from coded-wire-tagged fish caught within the estu- 

 ary and the Gulf of the Farallones revealed a wide range 

 of migration rates (Table 1). For those captured within the 

 estuary (17 of 24), the mean migration rate was 4.0 ±0.9 

 km/d. Most tagged-recaptured salmon had rates <2.6 km/d 



105 

 100 

 95 

 90 

 85 

 80 

 0- 



70 



60 



50 



40 



30 20 



km 



10 



GF 



Figure 3 



Mean l±SE) fork lengths i A), weights (B), and ages (Oof juve- 

 nile chinook salmon collected from locations in the San Fran- 

 cisco Estuary (km 68, km 46. km 26, km .3) and the Gulf of the 

 Farallones (GF). Open circles and dashed line in (C) represent 

 calculated ages of all fish at each location from regi'ession of 

 fork length on age from Figure 2(B). Numbers near means are 

 sample sizes. 



but were from two releases within the estuary, thus rep- 

 resenting migration rates in the lower estuary only. Juve- 

 niles released farther upstream in the rivers and caught 

 in the lower estuary had somewhat faster migration rates 

 (.r=9.1 ±2.5 km/d, 72=4). 



Not only did juvenile chinook salmon gi'ow slowly while 

 in the estuary, their condition declined as they proceeded 

 to the Golden Gate (Fig. 4). There was a significant de- 

 crease in Fulton's condition factor (K) between fish enter- 

 ing the estuary and those departing (P<0.001). Once the 

 fish were in coastal waters, however, their condition im- 

 proved markedly 



Body constituents and energy reserves varied little 

 while migrating fish were in the estuary, but total lipid 

 was depleted in fish from the Gulf of the Farallones (Fig. 

 5A). Total body protein concentrations were approximate- 

 ly 150 mg/g, wet weight, in fish from all locations, and did 

 not vary significantly. Total lipid also did not vary in fish 

 within the estuary but was significantly lower in salmon 

 caught in the ocean (P<0.0005). Mean lipid concentration 

 for fish in the estuary was about 30 mg/g, or IS'^f of dry 

 weight, and decreased to 17.7 ±1.6 mg/g in the ocean. 

 The decline in lipids in fish from the Gulf of the Faral- 

 lones was attributed to decreased concentrations of tri- 

 acylglycerols (TAG), the dominant lipid class (Fig. 5B). 

 TAG levels increased from 14.8 ±2.5 mg/g in fish en- 

 tering the estuary to about 18 mg/g in estuarine salm- 

 on and were depleted to 4.3 ±1.4 mg/g in coastal fish. 

 The concentration of polar lipids, composed primarily of 

 phospholipids, remained unchanged through the estu- 

 ary and in the ocean. Other lipid classes — cholesterol 

 and nonesterified fatty acids — were found at much low- 

 er concentrations and did not vary significantly during 

 the emigration. Steryl or wax esters were absent or at 

 very low levels in most individuals and showed no dif- 

 ferences related to location. 



We examined feeding and prey selectivity in juvenile 

 chinook salmon migrating through the estuary and in 

 coastal waters. A lesser proportion of fish leaving the 

 rivers contained food items compared with those with- 

 in the estuary. Fifty percent of juvenile salmon had 

 stomach contents at Chipps Island (km 68, 21 of 42 

 sampled). In contrast, more than 80'^f from Carquinez 

 Strait (km 46, 8 of 10 samples) and San Pablo Bay (km 

 26, 20 of 23 samples) had prey in their stomachs. A low- 

 er percentage KlWc) from the Central Bay (km 3, 9 of 

 13) had fed recently, but in the Gulf of the Farallones, 

 82'^^f (23 of 28) of the juveniles contained food. 



The relative importance of prey items varied as juve- 

 nile salmon migrated through the estuary and entered 

 the ocean (Table 2). Stomachs of juveniles leaving the 

 rivers contained primarily gammaridean amphipods 

 Corophnim sp., and lesser amounts of crab megalopae, 

 dipteran insects, other malacostracan crustaceans, and 

 other insects. After the salmon passed through Suisun 

 Bay (km 46), their stomachs contained mostly the he- 

 mipteran Hesperocorixa sp., the calanoid copepod Eu- 

 calanus califoniiciis, the mysid Acanthoryiysis sp., fish 

 larvae, and other insects. Cumaceans were clearly dom- 

 inant in juvenile salmon in San Pablo Bay (km 26), but 



