Figure 7. — Cod end (left) — (see Table 1 for source of specifications) used to concentrate plankton collected by 

 net, detached from plankton net (right). Both are fastened with hose clamps to an adapter made of polyvinyl 

 chloride (PVC) pipe. The pipe is approximately 4 inches (127 mm) long, 3-1/2-inches (95 mm) O.D. with 1/4- 

 inch (6.5 mm) -thick wall. It is turned down about 3/32 inch (2.5 mm) along its length leaving flanges at each 

 end to keep hose clamps from slipping off during tow; dimensions are not critical when turning the pipe. 



Flowmeters. — When the data on plankton are 

 processed, plankton volumes are calculated as 

 ml/1,000 m' of water strained (see section on 

 standardizing data). Water strained through 

 the net is measured by a flowmeter suspended in 

 the mouth of the net (Figs. 6 and 13) — see Table 

 1 for type of meter used and source of supply. 

 The meters are calibrated according to the meth- 

 ods described below in the section on standardiz- 

 ing data. 



Inclinometers. — The CalCOFI standard plank- 

 ton tow is taken by lowering the net(s) to the 

 desired depth and retrieving it at a given rate 

 while the ship maintains a speed that keeps the 

 tow wire at an angle of 45°. The instrument 

 that measures the angle of stray, the "wire 

 angle," is a quadrant called the inclinometer 

 (Fig. 8) which, when hung on the wire (Fig. 3) , 

 can be monitored to record the wire angles and 

 to regulate the ship's speed to keep the desired 

 angle. 



Two kinds of inclinometers have been used. 

 The one shown in Figure 8 (see Table 1 for 

 source of specifications) is equipped with a tele- 

 metering device developed by Charles Forester, 

 Master of the research vessel Jordan. When 

 equipped for telemetering, the angle of stray can 

 be controlled from the bridge or engine room 

 where wire angles are indicated in microamperes 

 (Fig. 9) . Wire angles on the quadrant (Fig. 8) 

 are recorded on the tow sheet by an observer on 

 deck. The second kind of inclinometer is simply 

 one without the telemetering device. In this 

 case, an ofl^cer of the watch or the recorder ob- 

 serves the wire angles during the tows and sig- 

 nals the bridge or engine room if the desired 

 angle is not being maintained. 



PROCEDURE FOR PLANKTON TOW 



The data sheet. — When the gear is assembled 

 as shown in Figure 6 and the data sheet for the 

 plankton tow is prepared, the tow is ready to 



