74 
Fishery Bulletin 111 (1) 
Table 1 
Results of a 2-sample t-test and the standard difference in a 
comparison of trawlable and untrawlable populations for differ- 
ent parameters derived from the data collected with the Simrad 
ME70 multibeam echo sounder during a cruise in 2009 aboard the 
NOAA Ship Oscar Dyson. These parameters are normal-incidence 
seafloor backscatter strength (S b ), oblique-incidence S b , the slope 
of the angle-dependent backscatter within 10° of normal incidence 
(S^-slope), scintillation index (SI), and rugosity (roughness). 
Degrees of Standard 
t-statistic freedom P -value difference 
Normal-incidence S b 
6.6 
260 
2xlO- 10 
0.74 
Oblique-incidence S b 
17.2 
170 
4xl0 -39 
1.89 
S 6 -slope (0-10°) 
9.9 
287 
5xlO- 20 
1.12 
SI 
2.1 
216 
0.04 
0.25 
Rugosity 
3.6 
418 
0.0004 
0.25 
floor, the error rate did not change apprecia- 
bly except in the case of a combination of the 
oblique-incidence S b , the normal-incidence S b , 
and the SI, in which case the class error rate 
was reduced to 3.8%; similar error rates were 
found with 4 classes separated by a best-fit 
hyperplane. 
Because only marginal improvements in 
class error rate were achieved when multiple 
parameters were combined and maintenance 
of simplicity in the interpretation of the re- 
sults was desired, the oblique-incidence S b 
was chosen as the sole discriminator between 
the trawlable and untrawlable seafloor at the 
study site. The classifications of trawlable 
and untrawlable seafloor classifications area 
shown in Figure 2 for both the from the Sim- 
rad ME70 and the data from the SDC and 
ROV. The classification based on the data from 
the Simrad ME70 is accurate throughout most 
