WILLASON ET AL.: ZOOPLANKTON IN CALIFORNIA CURRENT 



I Southern Nearshore 



II Northern Nearshore 



III Southern Offshore 



IV Northern Offshore 



San 

 Francisco 



~&Sjii: Monterey Bay 



II J 



\ > 



v oj £///. Point Conception 



San 

 Diego 



38 c 



36 ( 



34° 



32° 



124< 



122< 



120° 



118' 



Figure 1.— Sampling grid. Open circles are day stations and closed circles are night stations. 

 Arrows show the sampling sequence The first station, adjacent to San Diego, was occupied on 

 7 April 1981. The last station, just north of San Francisco, was occupied on 27 April 1981. 



ed inside the mouth of each net to measure the 

 volume of water filtered. An oblique net tow was 

 made to a depth of about 210 m at each station (bot- 

 tom depth permitting); each net filtered about 400 

 m 3 of water. Ship speed during the net tows was 1.5 

 to 2.0 kn. Thirty-six stations were occupied at night 

 (after sunset and before sunrise) and 45 were oc- 

 cupied during the day. 



The euphausiids, Euphausia pacifica and Nema- 

 toscelis difficilis, and the copepod, Calanus pacificus, 

 were separated from the catch of net 1 immediately 

 after collection. Adult euphausiids were sorted for 

 males and females and copepods sorted for females 

 and stage V copepodites. Specimens of E. pacifica 

 and N. difficilis were considered adults if they were 

 larger than 11 mm and 15 mm, respectively (Brin- 

 ton and Townsend 1981). Fifty undamaged animals 

 of each species and sex (or stage) were saved from 

 each net tow if adequate numbers were captured. For 



C. pacificus, which were very abundant, 50 females 

 and stage V's were saved from 72 and 75 of the 81 

 stations, respectively. Two replicate groups of 50 

 females of C. pacificus were taken from 7 stations 

 and two replicate groups of 50 stage V copepodites 

 from 9 stations. After sorting, animals from each 

 net tow were wrapped in parafilm in groups (5 to 

 50 animals of each sex or stage) and frozen at -20°C 

 for biochemical analyses in the laboratory. Catches 

 from net 1 that could not be sorted on the ship (10 

 of the 81 stations sampled) were frozen whole at 

 -20°C and sorted in the laboratory after the cruise. 

 The entire catch of net 2 was preserved in Formalin 

 immediately after collection. 



The abundances (numbers per 1,000 m 3 ) of adult 

 euphausiids at each station were estimated by count- 

 ing all adults captured in net 1 and dividing by the 

 volume of water filtered. Copepod abundances (num- 

 bers per 1 m 3 ) were estimated by counting all 



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