separated and moving down the screens. The 

 screen frame and the catch box located beneath 

 the screens were made with 19-mm marine ply- 

 wood. One end of the screen frame was hinged 

 and could be set at the slope providing maximum 

 sorting efficiency. To accommodate excess water, 

 six overflow windows around the top edge of the 

 catch box were screened with fine-mesh netting. 

 The catch box drain emptied into a 145-gal fiber 

 glass holding tank having screened overflow win- 

 dows (Figure 3). 



The 54- by 51-cm screens were constructed 

 of brass welding rods and flat stock aluminum. 

 The rods were cemented in place at both ends 

 along the aluminum strips with liquid solder ce- 

 ment. Excess cement was ground off, and an- 



FiGURE 4. — End view of sorting box. 



other aluminum strip was bolted to each enci, 

 thus sandwiching the brass rods between alu- 

 minum strips. Three layers of screens were in- 

 stalled in the frame with each layer having three 

 screens fitted end-to-end so that the rods ran 

 parallel with the long axis of the frame. The 

 average openings between rods for the screen 

 layers were 3, 2, and II/2 mm. 



Water-jet pipes were inserted through the 

 walls of the screen frame 5 cm below each screen 

 with two pipes per screen (Figure 3). The pipes 

 were perforated with 2-mm holes spaced 25 mm 

 apart to form the water jets. The force of the 

 jets, which was supplied with water by a 25-mm 

 gasoline-driven centrifugal pump, was controlled 

 by a PVC ball valve on the discharge line of the 

 pump. 



Operation of System 



After anchoring the vessel, the outriggers 

 were extended, the suction hoses and cones put 

 overboard, and the nets and frames were low- 

 ered into the water. A rope was then passed 

 around the bow, and the ends were attached to 

 the bridle of each net. When the nets were sub- 

 sequently slacked back, the rope bridles became 

 taut, and tidal flow forced the frames into the 

 water (Figure 2). The solids-handling pump 

 and the water-jet pump were then engaged and 

 the jet heights adjusted. When the sorting box 

 was full of water, the valve on the bottom was 

 opened allowing the catch to flow into the hold- 

 ing tank. 



Evaluation of System 



The number of brown shrimp postlarvae 

 caught per cruise was estimated by periodically 

 taking 5-sec samples from the pump discharge. 

 Twenty collection cruises were made on flood 

 tides between March 17 and June 2, 1971 (Table 

 1). Numbers of postlarvae caught during indi- 

 vidual cruises ranged from to about 106,000, 

 and the total estimated catch for all cruises was 

 about 411,600. Mortalities associated with 

 catching, pumping, and sorting brown shrimp 

 postlarvae were less than 3%. 



During evaluation of the system, large num- 

 bers of larval fishes and crustaceans other than 

 postlarval brown shrimp were collected. The 



1301 



