Note: Experience will teach the readers what a 

 normal meter reading should be for a standard tow. 

 If meter readings are not normal, the net tow may 

 have to be repeated. A very high reading may 

 have been caused by too great a ship's speed — 

 check for many high wire angles. A low reading 

 may have been due to too slow a ship's speed — 

 check for many low wire angles. Another reason 

 for low meter readings may be clogging of the nets. 

 This may be cumulative if a net is not rinsed pro- 

 perly or it may occur at a single station. If a 

 meter shows a trend toward lower and lower read- 

 ings, it is not malfunctioning, and the net should 

 be washed (see below). The net tow need not be 

 repeated if it is obvious that heavy clogging is the 

 reason for low readings (it will only clog again) 

 or if the ship's speed has caused low or high angles. 

 If wire angles are normal, the net clean, the towing 

 time routine but the meter reading is low, the cause 



Figure 16.— Installation of 5-gal (18.91 liters) heavy- 

 gauge plastic carboys (see Table 1 for source of supply) 

 of concentrated formaldehyde aboard R/V David Starr 

 Jordan — carboy, upper right is reserve supply. Metal 

 straps are hinged to release carboys and locked at oni; 

 corner by metal pin through the hinge. Screw-top plastic 

 cap is holed to allow siphon action. Siphon is started by 

 pulling formaldehyde with action of automatic double 

 valve on 50-ml syringe, bottom right (see Fig. 17). At 

 middle right is 20-mm plastic syringe with cannula (see 

 Table 1 for source of supply) and a 1-quart jar con- 

 taining saturated solution of sodium borate in seawater 

 (see text for buffering plankton samples). 



could be that a bit of detritus, a fish, or even a large 

 jelly or salp had become entangled in the meter 

 blades for a portion of the tow. Under these con- 

 ditions, the tow should be repeated. If the reading 

 is again very low and it is obvious that the flow- 

 meter is not functioning properly, replace the 

 meter and repeat the tow. Do not oil or grease 

 any meter or make any repairs that might alter 

 the rotation of the blades. Repairs of this type 

 would seriously aifect the calibration of the meter. 



14. The tow sheet is completed as follows: 



a. Towing time — the time at which the 

 watch was stopped when the meter (s) 

 broke water, is recorded at item 9. 



b. Total towing time — recorded in item 10, 

 is the sum of items 8 and 9. In a 300-m 

 tow, total time should be about 21'30" — 

 6' sinking time -f 15'30" towing time. 

 If total time is off by 15 to 20 sec, it must 

 be explained in the Remarks section. 

 The most usual variation will be in the 

 sinking time, caused by a slightly faster 

 or slower rate in paying out the wire 

 than the recommended 50 m/min. In 

 certain conditions, such as poor control 

 of the ship, countercurrents below the 

 sea surface adversely controlling the net 

 as it falls, etc., the winch operator may 

 have to depart from the sinking-time 

 procedures to slow the falling net in 

 order to keep, it from becoming tangled. 

 Such departures from normal proced- 

 ures must be recorded in the Remarks 

 section. 



c. Total towing time is added, in minutes 

 and seconds, to item 6 to record the hour, 

 minutes and seconds at item 7. This is 

 actually the time the net comes out of 

 the water. 



d. Number of jars per sample — lower left 

 hand section of sheet. 



e. Inches of plankton — this gives approx- 

 imate volume before water is added. 



f. Formalin and borate added — the person 

 who adds the preservative and buffer 

 should initial this box for each net — 

 after the Formalin and borate are added. 



g. Sample labelled — the person who labels 

 the sample (s) should initial this box - 

 after the sample{s) is labelled. 



h. Depth, wind, sky, sea swell — should be 

 given by a crew member to the observer 

 who is recording the angles while the 

 tow is being taken. 



17 



