fish (fig. 5). A lens cover is placed over 

 the glass window to prevent damage to the 

 Image Orthicon pickup tube from prolonged 

 high light intensity. 



When the equipment is used for studies 

 other than the specific one described above, 

 certain modifications in handling procedure 

 are necessary. The basic points discussed, 

 however, are generally applicable to any 

 operation that requires the attachment of 

 the camera to a trawl net. 



In addition to the cod-end observa- 

 tions described above, we have mounted the 

 underwater television camera on top of the 



i^M^a?:. 





cod-end frame in order to observe, from 

 outside the cod end, the behavior of fish 

 passing through the meshes (fig. 6). No 

 important additional problems arose with 

 this technique except that some additional 

 floats were required to help maintain the 

 frcuae in its proper orientation and so pre- 

 vent the cod end from rolling. Rolling 

 could have serious consequences with the 

 cEimera outside the cod end. 



Other Operations 



Preliminary studies of fish behavior 

 in the forward pjirts of the trawl required 

 an entirely different method 

 of rigging the camera unit. 

 For this work, the camera was 

 suspended from adjustable 

 chain bridles fastened to the 

 upper belly of the net (fig. 

 7) and depended mostly on the 

 rigidity of the netting under 

 tow for vertical orientation. 

 We also added floats for addi- 

 tional support and reinforced 

 the top belly with rope 

 stringers laced across and 

 along the netting. The cam- 

 era attached in this position 

 enabled us to observe the be- 

 havior of fish near the ground 

 line and lower belly of the 

 net and also on the bottom 







■'-''•"/Mr- 



FIGURE 5. --HAULING THE COD END UNIT ABOARD. 



slightly ahead of the net. 2/ 



Attempts to study fish 

 behavior in otter trawls by 

 towing the camera free in the 

 water from a second vessel 

 proved unsatisfactory, mainly 

 because low visibility during 

 the work made it impossible 

 to approach the moving net 

 properly. The net appeared 



1/ Results of these prelimi- 

 nary studies and those of 

 the cod-end work described 

 above are shown in the film , 

 "Underwater television 

 studies of fish behavior," 

 produced by the Bureau of 

 Commercial Fisheries Bio- 

 logical Laboratory, Woods 

 Hole, Massachusetts, 



