SOME OUTLINES OF PLANKTON CONCENTRATION IN THE 

 EASTERN AND TROPICAL PACIFIC * 



By Martin W. Johnson 



Sorip-ps Institution of Oceanography 



University of California 



La JoUa, California, U.S.A. 



Introduction 



In recent years, especially following World War II, there has been 

 a marked increase in research involving marine plankton along part of 

 the west coast of North America and in parts of the tropical Pacific. 

 While much of this work was undertaken to elucidate fisheries problems, 

 the results will doubtless prove of much wider application in general 

 marine biology and oceanography. 



From these studies there is emerging in broad outlines a picture 

 of relative plankton concentrations and of pelagic communities that 

 characterize different areas, water masses, or current systems. It is rea- 

 sonable to believe that the relative concentration of plankton (a fun- 

 damental source of food) will be reflected in the type and distribution 

 of the benthic communities. 



Figures 1 and 2 for the eastern Pacific are from one of several cruises 

 made jointly by Scripps Institution of Oceanography, the U.S. Fisn and 

 Wildlife Service, the California Fish and Game and the California 

 Academy of Sciences— all in connection with the California Cooperative 

 Sardine Research Program. (Progress Report 1950 and 1952.) 



Figures 3-6 for the tropical Pacific are based on collections made 

 during Scripps Institution's "Capricorn Expedition" 1952-53. 



West Coast^ North America 



The area of routine study varies somewhat with season but in total 

 it extends over a thousand miles along the coast of California and Baja 

 California and seaward up to 350 miles. Three oceangoing vessels par- 

 ticipated in each monthly cruise. 



Methods. The tow nets employed were approximately 5 meters in 

 length with a mouth opening of one meter in diameter, and constructed 

 of No. 30xxx grit gauze (mesh opening 0.65 mm). A flow meter 

 provided a measure of the water strained. 



•Contribution from the Scripps Institution of Oceanography (new series), Number 658. 



379 



