382 EIGHTH PACIFIC SCIENCE CONGRESS 



In operation the 1 -meter net was hauled obliquely from about 150 

 meters to the surface with 200 meters of wire out. It was retrieved at a 

 rate of 10 m. per minute, giving a 20-minute haul. The towing angle 

 was maintained as nearly as possible to 45°. A few deeper hauls were 

 made with 600 m. of wire out. In these hauls the retrieving time was 

 20m/min. 



The amount of water filtered was calculated on the basis of per- 

 formance of identical nets provided with flow meters and towed under 

 similar conditions. 



The relatively small volumes obtained in the deep hauls with 

 600 m. wire out (Fig. 3) would indicate that the major concentra- 

 tion of zooplankton is in the upper layers, for while the net strained 

 much more water during the deep hauls, the time spent- in the upper 

 presumably more concentrated layer was one-half that spent there dur- 

 ing the shallow hauls. 



The No. 20 net was lowered and raised vertically by hand, sampling 

 from 50 meters to the surface. 



Results: The volume of zooplankton caught by the 1-meter net was 

 measured by displacement in cc. and is graphically shown for each sta- 

 tion in Figure 3. 



The noteworthy feature is the marked increase in plankton at both 

 crossings of the equatorial current system especially at the eastern cross- 

 ing where a greater number of samples were taken. The volumes of the 

 1-meter net hauls in the current system are made up primarily of cope- 

 pods, but chaetognaths were also abundant. Euphausiids and sipho- 

 nophores, while common, did not add materially to the bulk. 



The volumes of microplankton are similar in geographic distribu- 

 tion to those obtained by the 1-meter net (Fig. 4). In each haul 

 there is a mixture of phyto and zooplankton, but at the eastern cross- 

 ing the phytoplankton constituted about 3/4 of the settling volumes. 

 The pictures presented in Figures 3 to 6 are not materially influenced 

 by diurnal migration of the plankton for most of the samples were 

 taken during daylight hours. In Table I, the beginning time of sampling 

 is shown for the 1 -meter net hauls. 



In the eastern crossing of the equatorial current system only one 

 station (at 01° OS'S) was sampled during darkness with the No. 20 net. 



In Figure 5 is shown the thermal structure of the water at the west- 

 ern crossing of the equator together with the corresponding microplank- 

 ton volumes at eleven stations along the section. There is a moderately 

 high even plankton concentration from about 02 °S to 03 °N, between 

 which at about 01°-02°N there is some indication of upwelling. 



