FISHERY BULLETIN: VOL. 75. NO. 2 



C CAL IN 



AMPH 



CHET 



CLAD 



COPD 



S BAJ OF . S BAJ IN 55 56 57 58 59 



55 56 57 58 59 55 56 57 58 59 



YEAR 



FIGURE 8. — Graphs, for each CalCOFI standard zone, of princi- 

 pal components of annual fluctuations in biomass. See text for 

 the method of selection of the components, see also the legend to 

 Figure 6. 



- 3 u - y 



THAL 55 56 57 58 59 55 56 57 58 59 55 56 57 58 59 



55 56 57 58 59 



YEAR 



FIGURE 9. — Graphs, for each taxonomic group (Table 1), of prin- 

 cipal components of annual fluctuations in biomass. See text for 

 the method of selection of the components, see also the legend to 

 Figure 7. 



present within the components, and graphs of 

 these are given in Figure 10. The pattern was 

 found as the first component in all the months 

 except March and April where it was found in the 

 second component. Graphs of the first components 

 for August to December are also given in Figure 

 10. 



There is a marked similarity between the 

 pattern of year-to-year fluctuations in upwelling 

 as represented by the components for the first 7 mo 

 of each year and the fluctuations in biomass of the 

 zooplankton represented by the components 

 shown in Figures 8 and 9, and it is reasonable to 

 assume that some form of causal relationship is 



involved. As with the first component in relation 

 to the temperature range, the precise mecha- 

 nisms involved cannot be inferred from the infor- 

 mation here. Upwelling has effects on the vertical 

 temperature structure and particularly on the 

 timing of the establishment of a clear thermo- 

 cline. It can also be expected to have a consider- 

 able influence on the supply of nutrients. It is 

 probable, therefore, that the effect on the zoo- 

 plankton is an indirect one through the influence 

 of vertical stability of the water column and the 

 supply of nutrients on primary production pro- 

 cesses. Peterson (1973) has established a relation- 

 ship between year-to-year variation in upwelling 



366 



