MacFarlane and Norton: Physiological ecology of Oncorhynchus tshawytscha 



249 



insects were still important. In the Central Bay, the final 

 embayment before the estuary exit, fish larvae were the 

 dominant forage item. Ampelisca abdita, a gammaridean 

 amphipod, and cumaceans were important as well. Fish 

 larvae continued to be the most important prey of juvenile 

 chinook salmon in the coastal waters of the Gulf of the 

 Farallones, but euphausiids and decapod early life stages 

 were also consumed in significant numbers. 



Discussion 



Chinook salmon from California's Central Valley streams 

 have a largely ocean-type life history although perhaps a 

 few spring and late-fall run juveniles overwinter in fresh- 

 water and migrate to the ocean as yearlings (Fisher, 1994; 

 Myers et al., 1998). Fry (<70 mm FL) are abundant in the 

 freshwater delta from February to April. They leave as 

 smolts (>70 mm FL) and enter the San Francisco Estuary, 

 primarily in May and June. Kjelson et al. (19821 reported 

 that few juveniles were present in the delta or estuary 



Figure 4 



Changes in mean (±SE) Fulton's condition factor (K") of juve- 

 nile chinook salmon from locations in the San Francisco 

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

 Farallones (GFl. Numbers above means are sample sizes. 



