In order to compare concentrations of plank- 

 ton, five categories of abundance are used: 

 (1) very light, 0-33 cc. of plankton per 1,000 

 m. 3 of water strained, (2) light, 34-100 cc. of 

 plankton, (3) moderate, 101-300 cc. of plank- 

 ton, (4) heavy, 301-900 cc. of plankton, (5) very 

 heavy, more than 900 cc. of plankton. The 

 average plankton volume at each station during 

 the year is shown in figure 3. The distribution 

 and relative abundance of plankton on each 

 survey cruise are shown in figures 4 through 

 15. 



The author gratefully acknowledges the co- 

 operation given by Scripps Institution of Ocea- 

 nography in the collection of data at sea. Most 

 personnel of the Bureau of Commercial Fisher- 

 ies Biological Laboratory, La Jolla, California, 

 contributed to the collection and processing of 

 the plankton material. 



LITERATURE CITED 



Service, Special Scientific Report — 

 Fisheries No. 125, 54 p. 



1954b. Zooplankton volumes off the Pacific 

 coast, 1953. U.S. Fish and Wildlife Serv- 

 ice, Special Scientific Report — Fisher- 

 ies No. 132, 38 p. 



1955. Zooplankton volumes off the Pacific 

 coast, 1954. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 161, 35 p. 



1956. Zooplankton volumes off the Pacific 

 coast, 1955. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 177, 31 p. 



THRAILKILL, JAMES R. 



1956. Relative areal zooplankton abundance 

 off the Pacific coast. U.S. Fish and 

 Wildlife Service, Special Scientific Re- 

 port — Fisheries No. 188, 85 p. 



STAFF, SOUTH PACIFIC FISHERY INVESTI- 

 GATIONS. 



1952. Zooplankton volumes off the Pacific 

 coast, 1951. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 73, 37 p. 



1953 Zooplankton volumes off the Pacific 

 coast, 1952. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 100, 41 p. 



1954a. Zooplankton volumes off the Pacific 

 coast, 1949-50. U.S. Fish and Wildlife 



1957. Zooplankton volumes off the Pacific 

 coast, 1956. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 232, 50 p. 



1959. Zooplankton volumes off the Pacific 

 coast, 1957. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 326, 57 p. 



1961. Zooplankton volumes off the Pacific 

 coast, 1958. U.S. Fish and Wildlife 

 Service, Special Scientific Report — 

 Fisheries No. 374, 70 p. 



