SEA-FISHERIES LABORATORY. 201 



May and June (the months when phytoplankton pre- 

 dominates), and compare the total with that for Copepoda 

 (both young and adult) in July and August (months of 

 the zooplankton maximum) the contrast is obvious. 



Phytoplankton. Zooplankton. 



May + June 28,046,330 98,333 



July + August 30,684 238,215 



These are, moreover, not the largest hauls in any of 

 the cases, but only monthly averages; and in the right- 

 hand column it is only the Copepod zooplankton that is 

 taken into account. Still the dilt'erences are quite 

 sufficient to show the changes in the nature of the pre- 

 dominant plankton in passing from the one period to the 

 other. 



It is always necessary to analyse the total numbers 



for the days, or nets, whenever a sudden change is seen, 



in order to determine what has caused the change. For 



example, in 1911, on April 21st the total catch in the 



coarse net went up to 225 c.c. from an average of about 



40 c.c. during the previous gatherings of the same net 



that month. The gathering immediately before, on 



April 18th, was 4"5 c.c. Now this great increase in bulk — 



about five-fold — was not due to any increase in numbers 



in any one of the more important groups, as the following 



figures will show : — 



Diatoms. Dinoflag- Copepoda. Copepod 

 ellates. nauplii. 



April 18 4-5 c.c. 238,000 3,000 7,651 7,000 



AprU21 22-5 c.c. 194,000 2,403 4,800 



It is evident that these figures for Diatoms, 

 Copepoda, etc., do not account for the rise in volume of 

 April 21st. 



It is necessary, then, to examine the specific details, 

 when we find that an increase in the number of Medusae, 

 polychaet larvae, fish eggs, and a few other larger 



