ZOO PLANKTON VOLUMES OFF THE PACIFIC COAST, 19^9-50 



This is the third report on zooplankton volumes off the Pacific coast. 

 The first, titled "Zooplankton Volumes Off the Pacific Coast, 195l", 

 appeared in this series as Special Scientific Report; Fisheries No. 73 j 

 the second, covering zooplankton volumes for 1952, was issued as Special 

 Scientific Report? Fisheries No. 100. The data for zooplankton volumes 

 for 19U9 and 1950 are presented in the name form as that followed in the 

 1952 report. 



The zooplankton collections were taken on the survey cruises of the 

 California Cooperative Oceanic Fisheries Investigations. The survey cruises 

 were made at monthly intervals between March and November 19^9 (cruises 1-9), 

 and b etween February and September 195>0 (cruises 11-18) . Cruises numbered 

 10 (January 1950), 19 (October 1950) , and 20 (November 1950) were special- 

 purpose cruises, and the plankton samples obtained on those cruises are not 

 included in this report. 



Vessels of three agencies participated in the cruises. These included 

 the Crest (all cruises), Horizon (cruises 1-Lu) , and Paolina T. (cruises 

 12, 15-18) of the Scripps Institution of Oceanography, the N.~B. Scofield 

 (cruises 1-3) of the California Department of Fish and Game7~aiid the Black 

 Douglas (cruises 5-18) of the U. S. Fish and Wildlife Service. 



The nets employed in collecting the plankton samples were constructed 

 of No. 30xxx grit gauze, and were 1 meter in diameter at the mouth, by 

 about 5 meters in length. They are identical with those being used in the 

 Pacific Oceanic Fisheries Investigations (King and Demond, 1953). 



A similar procedure for taking plankton hauls was followed during both 

 19^9 and 1950. The hauls were made obliquely from approximately 70 meters 

 deep to the surface (100 meters of wire out at greatest depth). 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; these are given as a group following cruise 18. The method of 

 standardizing hauls is discussed in Special Scientific Report: Fisheries 

 No. 100. 



The plankton measurements are of "wet" volume. The plankton was sepa- 

 rated from its preserving liquid and allowed to drain for a few minutes 

 before a determination was made of its displacement volume. For compara- 

 bility, all hauls are given in the same unit - the volume present in 1,000 

 cubic meters of water strained. Two measurements are given for each samples 

 (1) the total displacement volume, which includes all organisms taken in 

 the haul, and (2) the volume of the "smaller" organisms only, from which 

 jelly masses, large salps, larger Crustacea (such as Pleuroncodes) , larger 

 mollusca, and juvenile and adult fish were removed. 



