gradually moving the fish into the capture zone of the net. 

 At the footrope fish would turn and swim with the net before 

 entering. 



Wardle (1983) described the behavior of flatfish to the 

 ropes of the Danish seine. He observed two types of behavior 

 and related these to rope configuration during initial and 

 final stages of the tow. During initial stages, when rope 

 configuration is U shaped, he found the majority of fish 

 tended to swim in the direction of tow. During latter 

 stages, when rope configuration is V shaped, the majority of 

 fish tended to swim towards the mouth of the net. As in Main 

 and Sangster's observations, fish near the footrope tended to 

 swim in the direction of tow keeping station with the net. 



All observations of flatfish made during this study were 

 near the footrope of the trawl gear. From these 

 observations, the mechanism by which flatfish first orient 

 themselves to the trawl is indeterminable. However, the fact 

 that all fish were oriented away from the advancing gear 

 prior to leaving the substrate indicates that some stimulus, 

 or combination of stimuli, has produced this orientation. 



Two major factors, vision and sound, have been shown to 

 influence fish behavior during fishing operations. 

 Considerable evidence is available which indicates visual 

 stimuli is the major factor in determining behavioral 

 responses in close proximity to trawl gear. However, it is 

 also well established that sound transmission underwater is 

 detectable by fish at distances beyond visual capabilities. 

 It seems likely, therefore, that audio stimuli may be a more 

 important factor in determining initial orientation to the 

 gear than visual stimuli. An additional factor, the fish's 

 swimming ability, is critical in determining reaction 

 distances to various stimuli, especially visual. 



Kiselev (1968), observing fish schools from a manned 

 submersible, indicated that cod and haddock became agitated 

 by noise and all the fish oriented instantly in one 

 direction. He did not indicate what the relative orientation 

 to the sound was, however. Chapman (1976) reported 

 consistent avoidance responses by gadoid fish to low 

 frequency narrow bandwidth noise. The ability of herring to 

 detect the direction of sounds and take evasive or selective 

 action without visual input has been reported by Blaxter and 

 Batty (1985), Blaxter and Hoss (1981), and Schwarz and Greer 

 (1984). 



The ability to discriminate between sounds varies with 

 species. Most fish appear to be able to detect frequencies 

 between 50 - 500 Hz; whereas, they are insensitive to 

 frequencies above 2-3 kHz (Schwarz 1985 and Hawkins, 1986). 



417 



