This report contains data on the volume of zooplankton collected on 

 the monthly survey cruises of the California Cooperative Sardine Research 

 Program during 1951 o The cruises were numbered XXI through XXXII, Two 

 to four vessels participated in each cruise Participating vessels in- 

 clude the Horizon (Cruises XXI, XXIII through XXVI, XXXII), the Crest 

 (Cruises XXI through XXXI), and the Paolina T. (Cruises XXVII through 



XXX) of the Scripps Institution of Oceanography j the N„ B, Scofield 

 (Cruise XXI) and the Yellowfin (Cruises XXVI, XXXII) of the" California 

 DeDartment of Fish and Game, and the Black Douglas (Cruises XXII through 



XXXI) of the U, S. Fish and' Wildlife Service. 



The plankton samples are being collected for the twofold purpose 

 of studying pilchard or sardine, Sardinops c aerulea , "recruitment" and 

 the productivity of pilchard spawning areas „ The "recruitment 1 * research 

 is being carried out by the U. S. Fish and Wildlife Service;; the pro- 

 ductivity studies by the Scripps Institution of Oceanography. Roth 

 facets of the research are directed toward determining the factors 

 affecting the survival rates of pilchard eggs and larvae. 



The nets employed in collecting the plankton samples were constructed 

 of No. 30xxx grit gauze, a heavy-duty grade of silk bolting clotho The 

 opening between meshes of this grade of grit gauze is approximately 0„65 mm 

 The nets were conical in shape, l o meter in diameter at the mouth by 

 approximately 5> meters in length,, 



A similar procedure for taking plankton hauls was followed on all 

 vessels. The hauls were made obliquely from approximately lUo meters 

 deep to the surface (200 meters of wire out at greatest depth) whenever 

 the depth of water permitted,, Hauls taken at shallower depths are so 

 indicated in the tables. At all stations, a current meter was used in 

 the mouth of the net to register the flow of water into the net 



At a moderate number of stations, deeper tows were made in addition 

 to the routine ones. Usually at such stations, 600 meters of wire was 

 payed out and retrieved. The data for such hauls are grouped together 

 on the last page of the following tables. 



In determining plankton volume, the plankton was separated from its 

 preserving liquid by filtering, allowed to drain, and then its volume 

 was determined by displacement. Consequently, the volume measured is 

 "wet" volume o 



In the following tables the plankton volume is given under four 

 headings s (1) Total displacement volume of plankton taken, (2) volume 

 of "smaller" organisms remaining when jelly masses, large mollusc a, fish, 

 larger squid, and the like, were removed, (3) total volume standardised 

 in the amount present in 1000 cubic meters of water, and (a) a similar 

 value for the smaller organisms. 



