which is slowly wound across the tunnel and into a storage tank of 

 formalin by a system of rollers geared to a propeller on the outside 

 of the instrument. The propeller is turned as it moves through the 

 water, and the gauze is moved in direct proportion to the distance 

 the recorder travels through the water. Sections of the gauze are 

 marked to correspond with previously determined distances, depending 

 on the size or pitch of the propeller. For most collections, two inches 

 of gauze for each mile sampled are recommended. The spools hold as 

 much as 500 inches of gauze which allownearly 250 miles of continuous 

 data collection. As the gauze leaves the tunnel, it is at once joined by 

 a second gauze strip which winds with it onto the storage spool in the 

 formalin tank. This second strip prevents the plankton from being 

 rubbed from one part of the roll to another. 



This sampler has the advantage of being able to sample continuously 

 for over two hundred miles and will indicate horizontal distribution or 

 "patchiness 11 in plankton populations. It is possible to collect a very 

 large amount of somewhat restricted data with this instrument with 

 little effort or expense. 



This instrument has an even smaller aperture than the Clarke- 

 Bumpus sampler, and consequently most macroplankton will avoid 

 capture. It is restricted to near- surface sampling and crushes some 

 of the larger zooplankton. 



4. Issacs high-speed sampler 



A high-speed sampler has been developed by the Scripps Insti- 

 tution of Oceanography that fulfills many of the requirements mentioned 

 above. It is a streamlined tube containing a net and a depth registering 

 flow meter. Water enters the sampler through a one-inch opening, is 

 filtered by the net, passes around and activates the meter, and is 

 ejected astern. The sampler has been constructed so that it precedes 

 the cable by about a third of its length, thereby more readily capturing 

 everything in its path. A depressor- vane is used to sample at depth. 



This instrument is reputed to capture macroplankton, be useful at 

 depths to 60 meters, perform well at high speeds (8 to 12 knots), give 

 a record of both depth and flow, be useful over considerable distances, 

 and be used in series alignment. 



5. Midwater trawl 



The midwater trawl is used for collecting some of the larger and 

 more active marine forms (nekton). The net of 2 1/2-inch stretch forms 



IX- 3 



