of silk bolting which acts as a sieve; and a metal collecting bucket at 

 the cod end of the net. 



This sampler is easy for one man to rig and operate and will 

 capture a greater number of macroplankton than nets of smaller 

 aperture. For qualitative work of a reconnaissance type, this net is 

 rapid and effective. However, this net has a limited usefulness since no 

 quantitative studies can be made without some modification, or the addi- 

 tion of a flow meter. It must be towed very slowly to eliminate backwash 

 caused by small mesh size or clogging in the net. Deep tows and 

 simultaneous collections are not considered practical with this sampler. 



2. Clarke-Bumpus plankton sampler 



The Clarke-Bumpus plankton sampler overcomes some of the 

 serious limitations of the ordinary meter or half-meter samplers. 

 The principle features are: a brass tube five inches in diameter and 

 six inches long; a straining sleeve of silk bolting cloth attached to the 

 tube by means of a ring with a bayonet-type lock, and a collecting 

 bucket at the cod end; a propeller mounted in the tube, geared to a 

 counter which registers the number of revolutions, and with calibration, 

 the volume of water sampled; and two vanes, one on each side of the 

 tube, which assist in holding the tube in a horizontal position. This 

 apparatus may be opened or closed at desired depths by means of a 

 messenger- actuated trigger. 



The Clarke-Bumpus sampler has the obvious advantage of measur- 

 ing the volume of water passing through the net. Clogging of the net 

 and overspill or backwash caused by speeds between 5 and 10 knots 

 are infrequent problems. Two or more of these samplers may be 

 operated simultaneously at different depths on the same cable. 



This sampler is limited to the collection of net plankton; macro- 

 plankton are able to avoid capture because of the small opening in the 

 tube. It will not sample efficiently at high speeds (10 to 15 knots) or 

 over long distances; nor will it withstand the added stresses of such 

 speeds. 



3. Hardy continuous plankton recorder 



The Hardy continuous plankton recorder can be towed for long 

 distances behind any ship at speeds to 15 knots. It is fitted with fixed 

 planes which enable it to be towed at constant depths which are deter- 

 mined by the amount of towing cable payed out. Water enters a small 

 hole in the front and passes through a tunnel and out the back. The 

 plankton are sieved out by a continuously moving band of silk gauze 



IX- 2 



