FISHERY BULLETIN: VOL. 84, NO. 4 



122°30" 



122 c 

 i 



38°- 



37°30- 



SAN FRANCI 

 GULF OF THE 

 FARALLONES 



Miles 



L 



5 



_L_ 



Kilometers 



10 



10 



_L_ 



1 r 



SAN FRANCISCO BAY 



Figure 1.— Locations of stations and the areas represented by each station sampled monthly May 1978-April 



1979. 



ern end of South Bay. The tidal prism is 27% of the 

 Bay volume. Maximum tidal currents occur in the 

 channels and may be 225 cm/s (4.5 kn) at the Golden 

 Gate. More than 90% of the freshwater entering San 

 Francisco Bay enters North Bay from the Sacra- 

 mento and San Joaquin Rivers. Less than 10% 

 enters South Bay from small tributary streams and 

 sewage. Because of the difference in freshwater in- 

 flow the northern and southern reaches are very dif- 

 ferent types of estuary. North Bay is partially-to- 

 well-mixed with true two-layer estuarine circulation. 

 South Bay, dependent for water exchange on tidal 

 circulation and occasional incursions of freshwater 

 from the north during wet winters, resembles a 

 coastal lagoon. 



The heterogeneous nature of San Francisco Bay 

 requires that stations be representative of the 

 diverse areas of the Bay. The stations (Fig. 1) were 

 located in the channel adjacent to the shoals in the 

 South Bay in 5-6 m of water (stations 1 and 2); just 

 north of San Bruno Shoal in 3 m of water (station 

 3); east of Treasure Island over a dredge borrow pit 

 in 10 m of water (station 4); in midchannel just south 



of the Richmond-San Rafael Bridge in 10-13 m of 

 water (station 5); and north of Lime Point just in- 

 side the Golden Gate Bridge in 25-35 m of water 

 (Station 6). These sites were near those of a previous 

 trawl study (Aplin 1967) and they represented loca- 

 tions from South Bay, Central Bay, the outflow from 

 North Bay, and the Pacific Ocean entrance to the 

 Bay. 



All South Bay stations were sampled in one day, 

 all Central Bay stations were sampled on another 

 day, usually the day following the South Bay sam- 

 pling. This schedule and the pattern of tidal flow in 

 the Bay (Tidal Current Chart, San Francisco Bay 

 1973) enabled all stations to be sampled before noon 

 at approximately slack tide, low water. This sched- 

 ule controlled for the effects of time of day, tide, 

 and currents which can affect catches of ichthyo- 

 plankton (Eldridge 1977). Additional samples were 

 taken in October 1978 and April 1979 at station 3 

 and over the shoals adjacent to this station. 



Duplicate oblique ichthyoplankton tows and dupli- 

 cate surface microzooplankton tows were made 

 monthly at six stations for one year, May 1978-April 



880 



