The depth of haul has not been uniform throughout the period covered by 

 the charts. In 1949 and 1950, hauls were taken to depths of about 70 meters 

 (100 meters of towing wire were payed out); since 1951, the hauls have been 

 made to depths of about 140 meters (200 meters of towing wire were payed out) . 

 On the average, the upper 70 meters is richer in plankton than the zone from 70 

 to 140 meters. Based on information obtained from closing hauls (1940 survey 

 off southern California), the average plankton volume in the 70 to 140 meter zone 

 is about 60 percent as great as that of the upper level. If a similar relationship 

 held over the entire California Cooperative Oceanic Fisheries Investigations area, 

 the standardized volumes in 1949 and 1950, based on to 70 meter oblique hauls, 

 would average 25 percent larger than the volumes based on deeper hauls. 



In both instances, plankton volumes have been standardized to the amount 

 in 1,000 cubic meters of water strained. The procedure for determining the volume 

 of water strained during each plankton haul is discussed in Special Scientific Report -- 

 Fisheries No. 136, p. 2, and will not be repeated here . 



The system of numbering cruises was changed in 1953, in order to identify 

 cruises more readily. Originally, cruises were numbered consecutively, No. 1 

 being the March cruise of 1949. Under the new system of numbering, each cruise 

 is designated by four digits -- the first two numerals refer to the year, and the 

 next two numerals refer to the month. Thus, cruise 4903 refers to the March 

 cruise of 1949; and cruise 5112 is the December cruise of 1951. 



Table 1 presents a chronological listing of California Cooperative Oceanic 

 Fisheries Investigations cruises through 1955, with information on the area covered 

 and the number of stations occupied on each cruise. It will be noted that the station 

 line designations for 1949 are different than those used subsequently. The equivalents 

 of the 1949 stations in the current numbering system have been given in "Station 

 Positions of the California Cooperative Sardine Research Program", 1952, S10 

 reference 52-64, prepared by the Scripps Institution of Oceanography and the Fish 

 and Wildlife Service. They are also given in "Zooplankton Volumes off the Pacific 

 Coast, 1949-1950", Special Scientific Report -Fisheries No. 125, p. 3. 



Since 1950, the same method of numbering stations has been followed, 

 although the number of stations occupied per cruise has been changed with season 

 and time. The intensity of coverage has gradually increased from year to year, 

 especially during the months of heavy spawning of the Pacific sardine (March 

 through June) . 



