FISHERY BULLETIN: VOL. 74, NO. 4 







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Body Length (mm) Of Ovigerous Females 



Figure 3.-Number of mature eggs in ripe spermatophore-bear- 

 ing Euphausia pacifica in relation to body length. Numbers of 

 individuals examined are indicated. 



found to be immature at time of counting, either 

 in ripe or other females, mature in time to con- 

 tribute to the monthly spawn. The egg estimates 

 are therefore regarded as only relative, month to 

 month. 



The production of eggs and larvae in each year 

 (Figure 4c) was considered in relation to four 

 parameters: 1) annual upwelling cycle in the 

 southern California area inferred from atmo- 

 spheric parameters (Figure 4a) and from min- 

 imum water temperatures (Figure 4b), 2) size 

 structure of the spawning stock (Figure 4d), 3) 

 zooplankton biomass (Figure 5a), and 4) E. pacifica 

 biomass (Figure 5b). 



1953 



Upwelling began early (February, cruise 5302) 

 with above-average intensity, accompanied by 

 spawning in February and April. The February 



740 



spawn, mainly by females of medium length 

 (12.6-16.5 mm), led to discernable recruitment of 

 larvae in March. The April spawn, mainly by large 

 females (16.6-21.5 mm) led to the year's maximum 

 recruitment in May-June. Upwelling peaked in 

 June, and diminished to an unseasonably low 

 intensity thereafter (Figure 4a), accompanied by 

 local variability in water temperature through 

 October (Figure 4b). 



Substantial egg production during June- 

 August, by medium-sized and small (10.6-12.5 mm) 

 spawners, led to less recruitment than in April 

 when spawning was of similar intensity. April was 

 the start of the general spring zooplankton bloom 

 (Figure 5a), presumably a response to the greater 

 availability of phytoplankton food in the spring. 

 Spawning diminished after August although lar- 

 vae were evident in September and November. 

 Small females became predominant after Sep- 

 tember when they became important contributors 

 to the production of eggs. 



These estimates of relative spawning are sup- 

 ported by a consistent relationship of egg peaks to 

 larva peaks. Three of the four egg peaks in 1953 

 were followed by larva peaks a month later. Under 

 conditions of laboratory hatching and rearing, 

 euphausiids live as larvae for about 29 days 

 (Gopalakrishnan 1973). 



1954 



Upwelling commenced in March (Figure 4a), a 

 month later than in 1953. Local temperature 

 minima, however, showed that this process was 

 not obvious until April (Figure 4b). By both 

 criteria, spring upwelling in 1954 was the least 

 intense to be observed during 1953-56. (According 

 to Bakun (1973), it was the least observed during 

 1953-71, though substantially greater than during 

 1947-52.) Production of eggs was initiated in March, 

 evidently by a stock of large females derived from 

 the September 1953 recruitment (see sections on 

 growth and survival below, and Figure 9). 

 Recruitment became intense only during June- 

 July, associated with the one peak in spawning 

 observed during 1954. 



1955 



As in 1954, upwelling started in March 

 (following Bakun 1973, Figure 4a) or in April 

 (using temperature minima. Figure 4b). There 

 was a gradual increase in egg production begin- 



