Table 1. --Number of plankton samples obtained with different 

 types of hauls on the Hugh M. Smith EASTROPIC cruise 



3 -Net Hauls 



On EASTROPIC the multiple -net haul 

 consisted of 1 open net and 2 closing nets, each 

 operating obliquely within a rather narrow depth 

 range. The initial objective was to divide the 

 depth sampled by the "standard. "0-200 m. haul 

 into 3 parts and thus obtain a more detailed pic- 

 ture of the vertical distribution of the zooplank- 

 ton, diurnally and in respect to the thermal 

 structure. The plan was to have the 3 nets 

 sample obliquely in the depth ranges 0-60 m. , 

 70-130 m. , and 140-200 m. They were attached 

 to the towing wire at intervals in accordance 

 with an anticipated wire angle and with the as- 

 sumption that during the haiil the towing wire 

 described an essentially straight line in the 

 water. We knew that the latter assumption was 

 not entirely correct but, prior to the cruise, 

 exact information was lacking on the curvature 

 of the towing wire with 3 nets attached. By 

 means of the depth gauge we learned that the 

 towing wire curved downward so that the lower 

 nets fished deeper than assumed from the wire 

 angle measured at the surface. Utilizing the 

 data obtained with the depth gauge on 11 hauls 

 on EASTROPIC, and with additional observations 



Figure 2. --Diagram of the flowmeter- 

 mounting in the mouth of the closing net. 



Figure 3. --Diagram of flowmeter showing 

 the design of the propeller -blocking de- 

 vice (in cutaway section), p - pressure 

 plate; r - propeller -blocking rod activa- 

 ted by water pressure on the plate (p). 



made on a later test cruise, correction factors 

 were calculated for the upper and lower limits 

 of each net. The corrected depths, given in 

 table 3, show that, on the average, the upper 

 net operated between the surface and 52 meters, 

 the intermediate net between 66 and 134 meters, 

 and the lower net between 147 and 272 meters. 



The straining surface of the closing nets 

 was similar to that of the open nets; they differed 

 in certain other respects, however. Each 



closing net was essentially a standard net to the 

 forward end of which was added a cylinder of 

 10-ounce canvas 44 inches in length. A pursing 

 line encircled the net passing through brass 

 rings attached to the outside of the canvas about 

 30 inches from the mouth of the net. The flow- 

 meter was mounted off-center along the rim of 

 the net (fig. 2) in such a manner that it did not 

 interfere with the opening and closing of the net. 



