Herding and maintaining station with the gear has been 

 shown to be an optomotor response. Considerable research has 

 documented the optomotor responses of fish to moving 

 backgrounds (Harden Jones, 1963; Arnold, 1974). These works 

 have pointed out that the basic condition for optomotor 

 reaction is the presence of moving orientation points in the 

 visual field. In addition, it was shown that when responding 

 to these orientation points the most frequently observed 

 behavior was the full optomotor reaction, in which fish swam 

 parallel to the moving background and at approximately the 

 same speed. 



Entry sequences appear to be positional and can be 

 considered as escape, sequence A, or avoidance, sequence B, 

 responses. It is unclear whether the two entry sequences 

 observed are also directly related to swimming ability. The 

 most common entry pattern, in which the fish flips onto its 

 back during the entry, is initiated closer to the footrope 

 than those exhibiting sequence B. However, it has also been 

 shown that these sequences are not size dependent, therefore 

 it can be concluded, not dependent upon swimming ability. 



Initiating entry by turning the large flat ventral 

 surface towards the direction of travel, sequence A, 

 effectively accomplishes three things. First, the fish's 

 forward momentum is reduced significantly and rapidly. In 

 several instances the fish's forward momentum was reduced so 

 rapidly fish were unable to avoid being struck by the 

 footrope. Secondly, this maneuver effectively redirects the 

 fish's momentum without significantly reducing speed. Third, 

 the maneuver allows the fish to maintain close eye contact 

 with the disturbance. By turning onto its back the fish is 

 able to observe the disturbance, and in the case of the 

 trawl, this disturbance continues away from the direction the 

 fish is now traveling and appears to offer no further threat. 



It is interesting to note that fish exhibiting sequence 

 A behavior which crossed the footrope at a lower level 

 righted themselves closer to the footrope than those crossing 

 at a higher level. It is speculated that the visual field, 

 in particular, the field of binocular vision, influences the 

 point at which this maneuver is executed. Flatfish closer to 

 the footrope would lose binocular contact, and depth 

 perception, with the footrope sooner than flatfish crossing 

 at a higher level. 



Fish exhibiting entry sequence B initiated entry farther 

 from the footrope and crossed at a higher level than those 

 exhibiting sequsnce A. Those fish exhibiting this sequence 

 also swam in a much more leisurely manner without exhibiting 

 any rapid change in direction. The fish rose above the 

 footrope to a height that kept maximum distance between the 



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