42 



Fishery Bulletin 104(1) 



40 60 



Heave (cm) 



15 

 12 



Q 

 CO 



oa 



Aft) 



-8-9° 



0° 



ifipt 



0% 



I il Oo 



On o 



ti_^ 



-30 



-20 



-10 







10 



20 



30 



Current parallel to tow direction (cm/s) 



Figure 6 



Comparison of regression lines illustrating the relationship between the standard deviation (SD) of the footrope distance 

 off-bottom and environmental variables for locked winches (L), symmetry (S), and tension (T) treatments. Treatments in 

 which the environmental variable had a statistically significant effect on the SD are identified with an asterisk (*). 



-30 



-20 



-10 







10 



20 



30 



Current parallel to tow direction (cm/s) 



Figure 7 



Comparison of regression lines illustrating the relationship 

 between the symmetry of the footrope distance off-bottom and 

 current parallel to the direction of the tow for locked winches 

 (L), symmetry (S), and tension IT) treatments. Treatments 

 in which the current had a statistically significant effect on 

 the symmetry are identified with an asterisk (*). 



ing performance of the footrope, and bottom-tending 

 performance of the lower bridles. 



Trawl geometry 



Because wing and door spread and net height vari- 

 ability all influence catchability of a trawl (Rose and 

 Nunnallee, 1998), surveys would stand to benefit 

 from autotrawl systems if variances in the trawl 

 geometry features were reduced. Our study showed 

 that neither autotrawl system improved trawl geom- 

 etry over the conventional locked-winches towing 

 mode. 



Footrope 



Previous studies have demonstrated that escape- 

 ment under the footrope is an important factor 

 determining the catchability of the 83-112 Eastern 

 survey trawl (Somerton and Otto 1999; Munro and 

 Somerton, 2002; Weinberg et al., 2004). Periodic 

 separation between the footrope and the bottom 

 contribute to variability in catchability and have 



