182 
Fishery Bulletin 113(2) 
Figure 1 
Depiction of the area swept between trawl wing tips with a restrictor line attached to the warps for 
constraining door spread. 
tact sensors and used in our calculation of footrope per- 
formance (Somerton and Weinberg, 2001). Sensors were 
placed in 5 positions along the footrope: one at the cen- 
ter and one each at both port and starboard corners 
of the trawl mouth (located 3 m to either side of the 
center) and at both wing ends (located 1 m aft of the 
wing end). Similarly, 4 sensors were used to measure 
lower bridle performance, with 1 sensor suspended at 
each of 2 positions, 30 and 40 m forward of the wing 
end, on both (the port and starboard sides, according 
to Somerton (2003). Bottom contact sensors are self- 
contained units consisting of an analog tilt meter ca- 
pable of measuring angle to the nearest 0.5° and a data 
logger housed in a watertight stainless steel container 
that fits inside a steel sled. Fluctuations in the dis- 
tance of the footrope or bridle from the bottom produce 
changes in the recorded tilt angle. Tilt angles were con- 
verted to distances from the bottom for each sensor by 
using separate quadratic functions derived from previ- 
ous calibrations (Somerton and Weinberg, 2001). 
Experimental design 
Three independent experimental towing sites were 
selected spanning the range of trawling depths cov- 
ered by the survey. The shallow depth site (59°17'N, 
165°37'W) was located at a depth of 21 m, the middle 
depth site (56°38'N, 167°25'W) at 104 m, and the deep 
site (54°55'N, 166°24'W) at 150 m. Depths were deter- 
mined by the ship’s echosounder. 
Towing was conducted according to standardized 
survey procedures: a 3-kn tow speed over ground with 
a fixed amount of warp as called for by the survey 
scope table (137 m at the shallow site, 274 m at the 
middle site, and 457 m at the deep site). The codend 
remained open to eliminate variable effects of changes 
in catch size on trawl geometry. With the codend open, 
the total number of possible tows was increased and 
time was saved because the codend did not need to be 
emptied after each treatment. Experimental hauls con- 
sisted of 3 towing treatments: 
1) No restrictor line and use of the standard survey 
scope ratio (control treatment); 
2) Restrictor line and use of the standard survey scope 
ratio; and 
3) Restrictor line and use of a modified scope ratio. 
Tow duration for each treatment was 10 min, after 
a 5-min stabilization period. Treatments were random- 
ized at each site to reduce biases introduced by sea 
state, wind, and tidal currents on trawl performance. 
Determining position of the restrictor line and target wire 
angle 
En route to the first study site, we conducted a lim- 
ited number of test tows at an opportune depth of 71 
