assumed that the effect of the small submersible was 

 negligible compared with the overall effects of the trawl. 



To distinguish between the herding described here from 

 herding patterns described in the literature we have used the 

 terms active and passive herding. Active herding is defined 

 as occurring when flatfish maintained continuous swimming 

 without settling on the substrate. Passive herding occurs 

 when the flatfish have the opportunity to move away from a 

 disturbance and settle back to the substrate before being 

 disturbed again. 



RESULTS 



Flatfish, Rock Sole ( Lepidopsetta bilineata ) , Alaska 

 Plaice ( Pleuronectes quadrituberculatus ) , longhead dab 

 ( Limanda proboscidea ) , and Yellowfin Sole ( Limanda aspera), 

 were observed during capture by trawl gear. A total of 61 

 fish, ranging in size from 6 to 24 inches, were observed to 

 determine behavior during herding and trawl entry. Fish 

 could not be identified to species on the video tapes; 

 consequently, no species specific behavioral information is 

 reported. 



The large rubber disks on the footrope produced a 

 significant sediment cloud behind the footrope during 

 trawling operations. The extent of this cloud was not 

 determined; however, webbing in the belly of the net was 

 obscured within approximately 1.5-2 feet of the footrope. 

 The height of the sediment cloud increased rapidly, reaching 

 a height of approximately 3 feet above the webbing at about 

 20 feet behind the footrope. 



All flatfish observed leaving the substrate were 

 positioned with the long axis of the fish oriented in the 

 direction of tow. Under undisturbed conditions it would be 

 expected that the fish would be oriented in a random pattern 

 or, if current or other physical factors determined 

 orientation, they would be oriented in a direction not 

 necessarily that of the tow. It is assumed the fish have 

 either experienced passive herding, or non-herding 

 orientation has taken place using visual or other sensory 

 perceptions outside the visual range of the camera. 



The distribution of flatfish during herding and trawl 

 entry is shown in Figure 1. Flatfish reacted to the footrope 

 of the trawl at relatively close range and for short time 

 periods. Flatfish initially reacted to and were actively 

 herded at a distance less than 48 inches from the footrope. 

 After leaving the substrate the fish tended to drop back 

 towards the footrope and attempted to maintain station with 

 it. The majority of fish maintained a distance of 



408 



