Figure 24. --Film titler in operation. 



The formula can also be used to find the 

 size of an object when the distance is known. 



Footage of a large high-speed midwater 

 trawl showed undulations of loose webbing. 

 These undulations, previously undetected were 

 the chief contributors to insignificant catches 

 of fish. Studies showed that, although the 

 basic design of the trawl was sound, the towing 

 vessel was unable to reach a speed that would 

 enable the trawl webbing to fill out. 



Fish Behavior Observations : 



Differences in fish behavior annong species 

 were graphically demonstrated. Schools of 

 butterfish (Poronotus sp.) were observed vig- 

 orously swimming with the trawl. In contrast 

 schools of anchovies passed down the trawl 

 showing little escape reaction. Silver eels 

 (Trichiurus lepturus) were seen drifting pas- 

 sively toward the codend of the trawl. 



Turbid Water Difficulties : 



Turbidity was an ever-present problem 

 during the studies that led to this report. 

 Most of the studies were carried out off the 

 Mississippi River Delta, and several thousand 

 feet of film were a total loss due to zero 

 visibility. Although some areas of highly 

 turbid water were encountered, much of the 



turbidity resulted from the trawl doors and 

 footrope skimming the muddy bottom and 

 throwing up large clouds of sediment when 

 the trawl was operated too close to the bottom. 



TV MONITORING 



The original system called for a closed- 

 circuit TV chain, coupled to an underwater 

 motion picture camera. A desired sequence, 

 on the TV monitor, would be permanently 

 recorded by the motion picture camera. This 

 would have permitted higher quality motion 

 pictures (black and white, or color) than 

 could be photographed from a TV monitor. 

 Problems such as turbidity, camera align- 

 ment, fish reaction, and changes in the trawl 

 could have been observed and changed at sea. 



A TV chain, previously purchased by the 

 Base for another project, was adapted for 

 underwater operation by the design and con- 

 struction of a lightweight underwater housing, 

 which is highly Satisfactory and relatively 

 inexpensive (figure 25). Waterproof electrical 

 connectors for underwater TV application are 

 available. 



The TV system was not used in the mid- 

 water trawl camera studies because of me- 

 chanical difficulties concerned with handling 

 the 18-conductor cable required for that par- 



14 



