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Fishery Bulletin 88(2). 1990 



Figure 1 



Chinook salmon spawning streams and fish facihties of California's 

 Central Valley. CNH = Coleman National Hatchery; RBDD = Red 

 Bluff Diversion Dam; FRH = Feather River Hatchery; NH = Nim- 

 bus Hatchery; MRFI = Mokelumne River Fish Installation; MRFF 

 = Merced River Fish Facility; SWP = State Water Project pump- 

 ing plant: CVP = Central Valley Project pumping plant. 



variables and recruitment or abundance of Pacific sal- 

 monids through correlation analysis. Many of these 

 studies have focused on chinook salmon (e.g., Van Hyn- 

 ing 1973, Barton 1980), and a few have dealt with the 

 stock of chinook salmon that spawns in California's 

 Central Valley. Most of these studies have detected en- 

 vironmental influences on recruitment; but in the case 

 of Central Valley chinook salmon, reasonably long time- 

 series of recruitment data have been lacking. Some 

 analysts have therefore used estimates of spawning 

 escapement as a proxy for past recruitment (Dettman 

 et al. 1986, Dettman and Kelley 1986, Reisenbichler 

 1986, USFWS 1987). In general, these studies have 

 reported positive correlations with flow variables and 

 negative correlations with temperature during the 

 period when the spawners were migrating downstream 

 as smolts. Because of a negative correlation between 

 flow variables and temperatures (Dettman et al. 1986), 

 it is impossible to distinguish between effects of 

 temperature and effects of flow using existing data. 



Stevens and Miller (1983) used two time-series of smolt 

 estimates based on smolt catches in the delta (Fig. 1), 

 and showed a positive correlation with flows in the 

 previous winter. The most convincing studies used 

 estimates of mortality based on the difference in sur- 

 vival between tagged fish released above the delta and 

 tagged fish released below the delta to show a positive 

 influence of flow rates in the delta and negative in- 

 fluences of temperature and diversions (Kjelson and 

 Brandes 1989, Kjelson et al. 1981, USFWS 1987, Dett- 

 man et al. 1986). 



In contrast to those of freshwater, potential marine 

 influences on Central Valley chinook stocks have not 

 been explored. Oceanographic conditions off the Cali- 

 fornia coast vary dramatically providing potentially 

 important interannual differences in predators, prey, 

 transport, and ocean temperature during the marine 

 phase of chinook salmon life. The normal pattern of cir- 

 culation in the northeastern Pacific involves north- 

 westerly winds of varying strength along the coast of 

 California in the spring and summer months which rein- 

 force the geostrophic flow of the California Current and 

 transport surface waters offshore (Mysak 1986, Hickey 

 1989). This causes varying degrees of upwelling of 

 deeper water and longshore advection of subarctic 

 water along the coast of California and Oregon, which 

 are associated with colder temperatures and depressed 

 sea level heights. The amount of upwelling is estimated 

 by an upwelling index based on winds computed from 

 measured atmospheric pressure gradients (Bakun 

 1975). Occasional El Nino-Southern Oscillation (ENSO) 

 events, characterized by a warming of equatorial 

 Pacific waters, have a dramatic effect on California 

 coastal waters. These effects may result from either 

 coastal trapped waves which propagate poleward from 

 the Equator, or an atmospheric teleconnection between 

 the Equator and midlatitudes (Emery and Hamilton 

 1985, Mysak 1986). The former would cause higher sea 

 surface temperatures and sea level heights, but would 

 not necessarily affect Bakun's upwelling index (Enfield 

 and Allen 1980, Emery and Hamilton 1985, Mysak 

 1986). The latter involves an increase in strength of 

 the Aleutian low-pressure system and a weakening of 

 the north Pacific high-pressure system. Changes in the 

 atmospheric pressure gradients, associated with ENSO 

 events, weaken the northerly winds which results in 

 less upwelling, warmer sea temperatures, higher sea 

 level, and a lower upwelling index (Norton 1987, Mysak 

 1986). ENSO events and anomalous strengthening of 

 the Aleutian low pressure system may occur at the 

 same time, but each also occurs alone (Emery and 

 Hamilton 1985, Mysak 1986). 



Marine and freshwater influences on California Cen- 

 tral Valley chinook salmon could be confounded. Large- 

 scale oceanographic and meteorological conditions in 



