isotherm (-.vhich occurs within the thermocline in this region), and one just below the surface. 

 A bathythermograph (BT) cast was made at each station before the plankton haul to determine the 

 depth of the 70 F. isotherm. A 150-pound streamlined weight was attached to the end of the tow- 

 ing cable. The hauls were of about 1 hour's duration with a ship's speed of approximately 2 knots. 

 The samples were preserved in 8 to 10 percent formalin neutralized with borax. The samplers 



were calibrated before and after the 

 cruise, and the average of these 

 calibrations was used to compute 

 the cubic meters of water strained 

 for each haul. 



160° 



155° 



20° 



0° 



:^CHff/srA/>s 



160° 



150° 



145° W 



Figure 1. 



.-Locations of stations 1-30 occupied by Hugh 

 M. Smith, cruise 16, July-August 1952. 



Estimating Sampling Depth 



Throughout the cruise-- 

 for lack of exact information- -the 

 spacing of samplers on the towing 

 wire was in accordance with the as- 

 sumption that during the tow the 

 wire described a straight line in the 

 water; thus the cosine of the angle 

 of stray of the towing wire from the 

 vertical was used in calculating the 

 amount of wire to pay-out to reach 

 a desired depth. For example, an- 

 ticipating a final wire angle of 60 

 and intending to have the naiddle 

 sampler operate at the 70 isothernn 

 located at 100 meters, the proce- 

 dure would be: (1) attach the 150- 

 pound weight to the end of the tow- 

 ing wire; (2) have the winch opera- 

 tor pay-out 10 meters of wire; (3) 

 attach sampler No. 1; (4) pay-out 

 200 meters of wire; (5) attach 

 sampler No. 2; (6) pay-out an addi- 

 tional 200 meters of wire; (7) attach 

 sampler No. 3; (8) pay-out wire 

 until the last sampler was just be- 

 low the surface; (9) then begin the 

 1-hour tow, measuring the wire 

 angle at 5-minute intervals and 

 attempting to nnaintain a wire angle 

 of about 60 by varying the vessel's 

 speed. 



In operating the samplers, 

 however, it was found that the wire 

 angle increased steadily with the in- 

 crease in the amount of wire out and 

 we doubted that the assumption of a 

 straight wire provided a good esti- 

 mate of the depth of the samplers. 

 In order to obtain a closer approxi-. 

 mation of the true sampling depth, 

 four test hauls were made following 

 the cruise essentially duplicating 

 the procedure outlined above except 



