MdcFdrlane and Norton: Physiological ecology of Oncorhynchus tshawytscho 



245 



38'13'N 



Delta 



Ns% 



12r45'W 



Figure 1 



The northern portion of the San Francisco Estuary and nearshore Gulf of the Farallones. Juvenile salmon col- 

 lection locations are denoted as km (e.g. km 26) from the estuary exit at the Golden Gate. Juvenile salmon 

 were collected throughout the nearshore area in the Gulf of the Farallones, not at specific locations. 



so be involved. Migration through the highly impacted 

 San Francisco Estuary and early residence in a marine en- 

 vironment at the southern margin of the species' distribu- 

 tion may impair physiological development that could lead 

 to direct mortality or, indirectly, to reduced survival poten- 

 tial during the oceanic phase. 



Although some data exist on abundance, growth, and 

 feeding for chinook salmon migrating through estuaries in 

 southeastern Alaska and British Columbia ( Healey, 1980b, 

 1982; Levy and Northcote, 1982; Landingham et al., 1998); 

 Washington and Oregon (Reimers, 1973; Myers and Hor- 

 ton, 1982; Simenstad, et al. 1982; McCabe et al.,1986; 

 Fisher and Pearcy, 1996); and the Klamath River estuary 

 in northern California (Wallace and Collins, 1997), the on- 

 ly data available for Central Valley emigrants are those 

 of Kjelson et al. (1982). In that paper, life history descrip- 

 tions were presented for fall-run juveniles, but the empha- 

 sis was on fry (<70 mm fork length) in the freshwater delta 

 at the head of the estuary. Almost nothing is known of ju- 

 venile chinook biology in the larger saline portions of the 

 San Francisco Estuary. 



Knowledge of juvenile chinook salmon biology during 

 their first year in the marine environment is even more 

 limited, and nonexistent for the area south of the Cali- 

 fornia-Oregon border. Healey (1980a) presented distribu- 

 tion, growth, and feeding information on first ocean-year 

 chinook salmon in the Strait of Georgia, British Colum- 



bia. Similar data have been presented for juvenile chi- 

 nook from the Columbia River drainage off the Oregon 

 and Washington coasts (Miller et al., 1983; Brodeur and 

 Pearcy, 1990; Fisher and Pearcy, 1995). 



The purpose of this study was to describe juvenile chi- 

 nook salmon physiological development during their em- 

 igration through the San Francisco Estuary and early 

 residence in the coastal waters of central California. Resi- 

 dence time, age, growth, condition, lipid classes and pro- 

 tein concentrations, and feeding data are presented to 

 characterize the significance of habitat utilization at the 

 southern limit of the species' distribution. The information 

 presented here can serve as a basis for comparison with 

 other year classes from the Central Valley and with popu- 

 lations from more northerly estuaries, as well as for as- 

 sessments of the influences of natural and anthropogenic 

 perturbations on salmon habitat. 



Methods 



Study area 



Juvenile salmon leaving California's Central Valley pass 

 through the San Francisco Estuary, a series of embayments, 

 before entering the ocean in the Gulf of the Farallones (Fig. 

 1 ). The delta, a freshwater network of channels and leveed 



