disturbance and the fish before turning and entering the 

 trawl. Eye contact was maintained with the disturbance and 

 when no threat was offered the fish entered the trawl in a 

 leisurely swimming manner. 



In both behavior sequences the visual field plays an 

 important role. In sequence A the field of binocular vision 

 appears to be the critical factor in determining the response 

 sequence. Preliminary observations of pacific halibut 

 ( Hippoglossus stenolepis ) , rock sole ( Lepidopsetta 

 bilineata ) , and yellowfin sole ( Limanda aspera ) indicate 

 these flatfish have a visual angle directly rearward of 

 between 145° and 165° in the ventral eye and between 130° and 

 150° in the dorsal eye. Downward visual angles, measured 

 from the optical axis, ranged from 40° to 50° for the ventral 

 eye and 80° to 95° for the dorsal eye (Bublitz, C. G. , 

 unpublished data). These figures indicate that rearward 

 binocular vision is accomplished between 10 and 50 inches 

 behind the eye, dependent upon each eye's visual field and 

 eye rotation. 



The point at which rotation from inverted to normal 

 swimming takes place after crossing the footrope, sequence A, 

 was observed to be between 130° and 160°. These figures 

 compare favorably with the preliminary observations of visual 

 angles stated above and support the theory that the limit of 

 binocular vision may determine the point of rotation. Fish 

 which are higher and farther back in the net may also be 

 reacting to the loss of visual contact with the footrope. 



Wardle (1983) showed that when viewed from above, 

 objects are contrasted against a darker background than when 

 viewed from below or at the same level. Consequently, the 

 dark roller and cookie gear of the trawl would not present as 

 high a contrast image from above as when viewed from in 

 front. This reduction in contrast would likely reduce the 

 visual distance at which flatfish could detect the footrope 

 and thus react to it. 



Flatfish exhibiting capture sequence B also maintained 

 eye contact with the disturbance; however, in this case, 

 contact appears to be maintained mainly through monocular 

 vision. The visual angle within which this behavior was 

 initiated ranged between 152° to 164°. The preliminary 

 observations of flatfish visual field indicate flatfish may 

 be initially reacting near the limits of binocular vision; 

 however, once flatfish begin to rise above the substrate 

 binocular vision is soon lost. The downward visual angles 

 reported above indicate monocular eye contact is probably 

 maintained throughout the behavior sequence. The distance at 

 which fish rise above the substrate and at which they cross 



421 



