244 



Abstract— Juvenile chinook salmon, 

 Oncorbyncluis tshawytscha. from natal 

 streams in California's Central Valley 

 demonstrated little estuarine depen- 

 dency but grew rapidly once in coastal 

 waters. We collected juvenile chinook 

 salmon at locations spanning the San 

 Francisco Estuary from the western 

 side of the freshwater delta — at the con- 

 fluence of the Sacramento and San Joa- 

 quin Rivers — to the estuary exit at the 

 Golden Gate and in the coastal waters 

 of the Gulf of the Farallones. Juveniles 

 spent about 40 d migrating through the 

 estuary at an estimated rate of 1.6 km/d 

 or faster during their migration season 

 (May and June 1997) toward the ocean. 

 Mean growth in length (0.18 mm/d) 

 and weight (0.02 g/d> was insignificant 

 in young chinook salmon while in the 

 estuary, but estimated daily growth of 

 0.6 mm/d and 0.5 g/d in the ocean was 

 rapid (PsO.OOll. Condition (A' factor) 

 declined in the estuary, but improved 

 markedly in ocean fish. Total body pro- 

 tein, total lipid, triacylglycerols (TAG), 

 polar lipids, cholesterol, and nonesteri- 

 fied fatty acids concentrations did not 

 change in juveniles in the estuary, 

 but total lipid and TAG were depleted 

 in ocean juveniles. As young chinook 

 migrated from freshwater to the ocean, 

 their prey changed progressively in 

 importance from invertebrates to fish 

 larvae. Once in coastal waters, juve- 

 nile salmon appear to employ a strat- 

 egy of rapid growth at the expense of 

 energy reserves to increase survival 

 potential. In 1997, environmental con- 

 ditions did not impede development: 

 freshwater discharge was above aver- 

 age and water temperatures were only 

 slightly elevated, within the species' 

 tolerance. Data suggest that chinook 

 salmon from California's Central Valley 

 have evolved a strong ecological pro- 

 pensity for a ocean-type life history. 

 But unlike populations in the Pacific 

 Northwest, they show little estuarine 

 dependency and proceed to the ocean to 

 benefit from the upwelling-driven, bio- 

 logically productive coastal waters. 



Physiological ecology of juvenile chinook salmon 

 iOncorhynchus tshawytscha) at the southern end 

 of their distribution, the San Francisco Estuary 

 and Gulf of the Farallones, California* 



R. Bruce MacFarlane 



Elizabeth C. Norton 



Santa Cruz Laboratory 



Southwest Fisheries Science Center 



National Marine Fisheries Ser^/lce, NOAA 



110 Shaffer Road 



Santa Cruz, California 95060 



E-niail address (for R B MacFarlane) Bruce MacFarlane a noaa gov 



Manuscript accepted 23 August 2001. 

 Fish. Bull. 100:244-2.57 (2002). 



Estuaries are considered important in 

 the development of juvenile salmon. In 

 the Pacific Northwest, estuaries have 

 been shown to provide nursery and 

 rearing conditions for juveniles emigrat- 

 ing from streams of birth to the ocean 

 (Reimers, 1973; Healey, 1982; Levy and 

 Northcote, 1982; Myers and Horton. 

 1982; Simenstad et al, 1982; McCabe et 

 al, 1986). The San Francisco Estuary is 

 the largest estuary on the West Coast 

 and is a segment in the migration corri- 

 dor for chinook salmon (Onc-orhyru'luis 

 tshawytscha ) from natal streams in the 

 watersheds of the Sacramento and San 

 Joaquin Rivers, known as California's 

 Central "Valley The Central Valley is 

 unique by having four runs of chinook 

 salmon which constitute a significant 

 socioeconomic resource. Ocean harvest 

 south of Pt. Arena (estimated as 85-95% 

 from Central Valley stocks) and spawn- 

 ing escapement range between 0.5 and 

 1.3 X 10'' chinook salmon per year 

 ( 1970-98) and represent about $60 mil- 

 lion (U.S.) in personal income annually 

 (PFMCM. Beyond the direct value of 

 Central Valley chinook salmon, their 

 demography and welfare significantly 

 affect the financial and societal aspects 

 of water rights decisions. 



Chinook salmon populations migrat- 

 ing through the San Francisco Estuary 

 are at the southern limit of the species' 

 geographical range and are subject to 

 the impacts of a highly urbanized, in- 

 dustrialized, and agricultural freshwa- 

 ter and estuarine system (Nichols et al., 

 1986).A11 chinook salmon runs originat- 

 ing in the Central Valley are in jeopar- 



dy. Before 1900, spawning runs were es- 

 timated at 2 X 10« adults (Fisher, 1994), 

 but in 1998 only an estimated 0.25 

 X 10'' returned of which about 30% 

 were of hatchery origin (PFMCM. The 

 Sacramento River winter-run chinook 

 was the first Pacific salmonid species 

 listed under the U.S. Endangered Spe- 

 cies Act of 1973 (ESA). Originally cat- 

 egorized as threatened in 1989, its sta- 

 tus was changed to endangered in 1994. 

 Chinook salmon of the Central Valley 

 spring run, once forming the dominant 

 chinook race in California (Clark, 1929). 

 were listed as threatened in 1999. Even 

 the fall run, by far the dominant run to- 

 day ( 92% of all Central Valley spawn- 

 ers, 1990-98 IPFMC'l), has uncertain 

 status and is an ESA candidate. Hatch- 

 ery production supports the natural fall 

 run, and the other runs to a much lesser 

 degree. Annually, about 35 million chi- 

 nook salmon are produced by state and 

 federal hatcheries in the Central Val- 

 ley; the fall run comprises 95% (Mills et 

 ai, 1997). 



California and federal water develop- 

 ment projects, such as dams and water 

 diversions, have clearly played a role 

 in the decline of Central Valley salmon 

 (Movie, 1994). but other factors may al- 



* Contribution 114 of Santa Cruz Labora- 

 tory National Marine Fisheries Service, 

 NOAA. Santa Cruz, CA 95060. 



' PFMC (Pacific Fishery Management Coun- 

 cil). 1999. Review of 1998 ocean salmon 

 fisheries. Pacific Fisheries Management 

 Council, Portland, OR, 65 p. PFMC, 2130 

 SW Fifth Ave., Suite 224, Portland, OR 

 97201. 



