FISHERY BULLETIN: VOL. 69, NO. 3 



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SMALL COPEPODS 

 LARGE COPEPODS 

 CHAETOGNATHS 

 EUPHAUSIIDS 



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10" 



10' 



IC^ 10" 



MEDIAN (no/m') 



Figure 5. — The relation of sampling block range to sampling block median for the four species groups combined. 



1000, which is obviously responsible for the gen- 

 erally higher day-period densities shown else- 

 where, may indicate an upward and a downward 

 movement in the morning. 



The spread of block medians tended to be as- 

 sociated with the time-interval medians for 

 euphausiids but not for the other siiecies groups. 

 The euphausiids showed both high and low block 

 medians at night Imt only low medians during 

 the middle of the day. Large copepods showed 

 a similar distril)ution excei)t that three of the 

 highest four block medians in the series occurred 

 between 1000 and 1S(K) hr. Small copepods and 



chaetognaths showed high and low medians in 

 all time periods. 



CORRELATIONS BETWEEN DENSITIES 

 OF THE FOUR SPECIES GROUPS 



The data were examined for association be- 

 tween the densities of species groujis over the 

 area by calculating rank-difference correlation 

 coefficients (Tate and Clelland, 1957) for the 

 nighttime block medians of each cruise (Table 

 (■)) . Daytime blocks were excluded to reduce the 

 component of correlation that would result from 



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