FISHERY BULLETIN: VOL. 84, NO. 4 



peak abundance tracked the seasonal temperature 

 cycle closely. Temperature stratification was most 

 pronounced in June-October when spawning was 

 greatest, especially at station 5 where salinity 

 stratification was also most noticeable. 



Offshore transport of eggs and larvae is believed 

 to be one of the environmental hazards to anchovy 

 reproductive success (Bakun and Parrish 1982). 

 Peak spawning in the Bay took place in June- 

 August, the months of greatest offshore directed 

 Ekman transport at the latitude of San Francisco 

 (Parrish et al. 1981). Larvae, retained in San Fran- 

 cisco Bay by estuarine circulation or behavior, would 

 not be subject to offshore drift into areas of low 

 plankton density. Therefore, they may have a higher 

 probability of survival than larvae in the California 

 Current and they might survive during bad years 

 for oceanic larvae. 



Within San Francisco Bay there were apparent 

 differences between spawning habitat and larval 

 habitat. Eggs and small larvae were more abundant 

 in warm, clear, thermally stratified water with 

 relatively less plankton; large larvae were found in 

 shallow, warm, less stratified, plankton-rich water 

 with reduced light penetration. Negative correla- 

 tions between zooplankton and the eggs of zooplank- 

 tivorous fishes were attributed to predation on the 

 zooplankton by de Ciechomski and Sanchez (1983). 

 Cannibalism on larvae by adult northern anchovies 

 and competition between adults and juveniles are 

 two reasons why separate habitats would be adap- 

 tive. Because spawning and nursery habitats differ 

 in location and environmental properties, it is not 

 surprising that multiple regression variables mea- 

 sured in the spawning habitat did not predict lar- 

 val abundance. It may be that spawning areas are 

 selected by adults, perhaps for feeding (Brewer 

 1978) or for water clarity, while larger larvae seek 

 different conditions where their survival is deter- 

 mined by other factors than those which affect first- 

 feeding larvae. If variable mortality on the larger 

 larvae determines eventual recruitment, then 

 recruitment may be largely decoupled from spawn- 

 ing and first-feeding conditions. This could explain 

 why predictions of recruitment from larval surveys 

 (which do not adequately sample large larvae and 

 juveniles) have not been reliable. 



The conditions where larvae were more abundant 

 are more characteristic of shallow nearshore water 

 than of the California Current. Juveniles and young 

 of the year are also relatively more abundant near- 

 shore in California (Parrish et al. 1986). In 1978, 

 when spawning was restricted to nearshore areas, 

 apparent recruitment was high relative to 1979 



when spawning was offshore (Hewitt and Methot 

 1982). The 1978 spawning season for California Cur- 

 rent anchovy was not typical; storms prevented 

 favorable conditions for larvae until March in south- 

 ern California (Lasker 1981). Nearshore areas might 

 be refugia during anomalous years and they could 

 contribute a disproportionate number of recruits 

 every year (Brewer and Smith 1982). 



It might be argued that the 20-30 mm larvae found 

 nearshore in the Southern California Bight (Brewer 

 and Smith 1982) merely avoided the nets in stan- 

 dard CalCOFI tows, but I found a similar pattern 

 with respect to length frequencies when comparing 

 samples taken in the channels and in shallow water 

 in San Francisco Bay. That is, larger larvae were 

 found in shallower zooplankton-rich areas. Estuaries 

 and nearshore areas may provide conditions favor- 

 able enough for survival of larvae and juveniles to 

 compensate for low mean food density and for occa- 

 sional years of unfavorable oceanographic conditions 

 in the California Current. 



San Francisco Bay northern anchovy larvae, 

 especially those which overwinter, are subject to dif- 

 ferent ecological conditions than those in the Califor- 

 nia Current, thus they may have slightly different 

 morphology and meristics (Hempel and Blaxter 

 1961; Blaber et al. 1981). The San Francisco Bay 

 subspecies Engraulis mordax nanus Hubbs (1925) 

 may be an ecotype of E. mordax. 



A female northern anchovy has enough energy 

 stored as fat for 17 of its 20 annual batches of eggs, 

 but protein for egg production must come from 

 feeding during the spawning season (Hunter and 

 Dorr 1982). The primary food of northern anchovy, 

 zooplankton, was abundant in the Bay. I found a 

 mean density of 1 zooplankter/L with a 0.308 mm 

 mesh net, but this is an underestimate of cope- 

 podites and small copepods because of the relative- 

 ly large mesh size. By comparison, Hutchinson 

 (1981) found at least order of magnitude greater 

 densities at nearby stations over the same time 

 period using 0.080 and 0.064 mm mesh nets. An- 

 chovy feed by biting individual organisms or by 

 filter-feeding if particle density is high enough. The 

 laboratory-determined threshold for filter-feeding 

 is 5-18 particles (0.236 mm wide) per liter (Hunter 

 and Dorr 1982). My zooplankton density estimate, 

 which was biased conservatively, is of the order of 

 magnitude required to stimulate filter-feeding. 

 Therefore, I conclude that zooplankton prey for 

 adult northern anchovies were abundant in the Bay 

 during this study. 



For the Bay to be a good larval nursery area it 

 should have abundant microzooplankton prey for lar- 



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