Table 3o Summary of certain statistics calculated for the 

 24-hour series of oblique hauls to three depths 

 made on cruise 9, John Ro Manningo 



Number of samples 

 Mean sample volume (cCo/lOOO mo^) 

 Standard deviation (s) of mean volume 

 Coefficient of variation (C) of mean volume 

 Night/day ratio 



Depth of haul (meters) 



200 



8 

 25o6 



6„4 

 24o8?J 



i 



lo72 



Coefficient of regression (b) of zooplankton i 



volume on sine fimction 0ol379 



't" value for significance of the regression I 8o673 



300 



500 



19o5 

 5„4 



lo58 



8 

 15 „4 

 4„9 



lo67 



0ol456 '■ 0„1306 

 4o853 ' 2„902 



: < OoOOl < OoOl 



> Oo05 



Correlation coefficient (r)^ for zooplankton j 



volumes and sine functicn O086I 



Coefficient of determinaticaa (r^) 



0o924 



0o891 ; 0„764 



0,794 ; 0c584 



i 



The experiment showed that the 200-meter oblique haul pro- 

 duced larger zooplankton volumes per unit of water strained than did the 

 300-meter or 500-meter hauls j, thus indicating that within the range of 

 depths sampled the largest amounts of zooplankton were found between 200 

 meters and the surface during both day and night periods. Judging from 

 the night/day ratios (table 3), the volumes of the deeper hauls were as 

 much affected by the diurnal variation as were the 200-meter hauls. In 

 view of these circumstances, together with the saving in vessel time for 

 the shallower hauls, we believe that of the three depths tested, the 200- 

 meter oblique haul provides the most satisfactory method for estimating 

 the abundance of zooplankton in the upper level of the ocean - the en- 

 vironment of the tunas , 



An important source of variation in quantitative measurements 

 of zooplankton abundance is related, therefore, to the time of day of 



14 



