The major table in this report 

 contains both the standardized wet 

 plankton volume for each sample taken 

 on routine cruises off the Pacific 

 coast during 1958 (columns 9 and 10) 

 and the basic information on each haul, 

 including station number (column 1), 

 location (columns 2 and 3), date and 

 time of collection (columns 4, 5, and 6), 

 volume of water strained (column 7) 

 and the estimated depth of haul (col- 

 umn 8). 



The average plankton volume at 

 each station during the year is shown 

 in figure 3. The distribution and abun- 

 dance of the smaller organisms on 

 each survey cruise are shown in fig- 

 ures 4 through 15. For maximum 

 contrast, five categories of abundance 

 are used: (1) light, 0-33 cc. of plank- 

 ton, (2) moderate, 34-100 cc. of plank- 

 ton, (3) average, 101-300 cc. of plank- 

 ton, (4) fairly heavy, 301-900 cc. of 

 plankton, and (5) heavy, more than 

 900 cc. of plankton. 



Only data collected from 1951 to 

 1957 are used in computing long-term 

 averages for comparative purposes. 

 The tows of 1949 and 1950 are not 

 included in averages because they cov- 

 ered only half the depth range of sub- 

 sequent tows, i.e., 70 meters to the 

 surface. 



The area most consistently occu- 

 pied lies between station lines 80 and 

 137 (fig. 1). For convenience in com- 

 paring 1958 plankton volumes with 

 those of earlier years, this area has 

 been divided into two roughly equal 

 parts (lines 80-107 and lines 110-137). 

 The northern area (lines 80-107) was 

 occupied at monthly intervals from 

 January through July, and October 

 through December. The southern area 

 (lines 110-137) w^as occupied at monthly 

 intervals from January through 

 October. 



The average monthly plankton vol- 

 umes for the area encompassed by 

 lines 80-107 during 1951 through 1958 

 are given in table 3. The months of 



August and September are not included 

 in this table, since cruises were not 

 made in the area during these months 

 in recent years. Except for July and 

 December, the monthly averages during 

 1958 were smaller than during any of 

 the preceding years. Similar informa- 

 tion for the southern area (lines 110- 

 137) is given in table 4. Because 

 coverage of this area during November 

 and December was discontinued after 

 1955, these months have been omitted 

 from the table. 



A comparison of plankton volumes 

 in 1958, by month and area, with the 

 average volume of the 6-year period, 

 1951-56, and also with 1957, is graph- 

 ically presented in fig. 2. The transi- 

 tion from the high volume year to low 

 volume year is best shown by treating 

 both 1957 and 1958 volumes separately. 



In the northern area (lines 80-107) 

 volumes during the 6-year period 

 (1951-56) built-up to a peak in July 

 and then receded. During 1957, volumes 

 obtained during February through April 

 ■were unusually large for these months 

 but markedly declined thereafter giving 

 the appearance of a summer minimum. 

 The pattern during 1958 was similar 

 to the 6-year period, but on a very 

 reduced scale, since plankton volumes 

 averaged only one-third as large. The 

 peak month was again July. 



The seasonal pattern of plankton 

 abundance in the southern area (lines 

 110-137) has been somewhat similar, 

 but the peak month has been more 

 variable. The volumes during 1958 

 were fairly uniform throughout the 

 year and were the smallest on record 

 for the months of May through October. 



The author acknowledges with 

 pleasure the cooperation given by 

 Scripps Institution of Oceanography 

 in the collection of data at sea. Most 

 personnel of the Bureau of Commer- 

 cial Fisheries, Biological Laboratory, 

 La JoUa, California, contributed to the 

 collection, standardization and proc- 

 essing of plankton material. 



