300 
Fishery Bulletin 106(3) 
or that EMs are based on neighboring EMs. Without 
standardization of these correlated EMs, the amount of 
variance explained by the first three PCs is artificially 
inflated. The inclusion of sums of variables in a PCA, 
such as the 15 sums of variables in the third (EMs 
40-70) and fourth (EMs 71-101) groups, also artificially 
inflates the amount of variance explained in a PCA. 
Inclusion of a variable that is a complement of another 
variable (EM 41 or EM 56) in a PCA does not improve or 
impair the results and one of these complements could be 
excluded, along with the three invariant variables. 
Assumption two: first echo 
The 251 sampling envelope used with the QTC IMPACT 
software may be a mismatch for the actual length of the 
first echo. In the FV Gladiator 2003 shallow and deep 
data sets (both <200 m), the 251 sampling intervals of 
Sand-sand 
Sand-boulder 
Bedrock-boulder 
1.00 
0.98 
0.96 
0.94 
0.92 
0.90 
0.88 
0 2 4 6 8 10 12 14 16 
Degrees of seafloor slope 
Figure 4 
Significant linear regressions (P<0.05) between low seafloor slopes <5° 
(•) and QTC (Quester Tangent Corporation, Sidney, British Columbia, 
Canada) IMPACT™ echogram measurement 1, with observations 
from greater slopes (O) excluded from the regression analysis, for 
the three most common substrate types found during the FV Gladi- 
ator 2005 cruise. Only data values to the left of the 5° mark (dashed 
vertical line) were included in the regression analysis. 
977 Hz or 0.001024 s translated into an 
excessive and unnecessary 192.8 m analysis 
depth range below the start of the first sea- 
floor reflection, a fact not realized during the 
collection of the echosounder data. However, 
the recording of most of the *.raw files were 
truncated before the full 192.8 m distance, 
before any second echo, and also before the 
full 251 samples; therefore most of the echoes 
needed padding (extended repetition of the 
last sound sample in the echo). The second 
echo was recorded in the *.raw file and it fell 
within the 251 sample requirement in 19 of 
the 68 shallow sites (25-100 m) and four of 
the 19 deep sites (100-200 m). These same 
pings were exported from EchoView® to 
QTC IMPACT with and without the second 
echo, and our analyses demonstrated that 
QTC IMPACT treated the second echo as if 
it were part of the first echo. The acciden- 
tal inclusion of the seafloor spike from this 
second echo reduced the values of the first 
23 EMs (except EM 16) and had the greatest 
effect when the seafloor spike of the second 
echo occurred at the edge of the export 
window, where it was repeated to fulfill the 
251 sample requirement (see Haul 206, Fig. 
6). There was less of an effect when more of 
the second seafloor spike was included, so 
that the padded value was of lower sound 
intensity (see Haul 124, Fig. 6). Thus sig- 
nificant differences in some of the echogram 
measurements can be created for the exact 
same substrate type if users are not careful 
about ensuring that the 251 sample window 
of QTC IMPACT matches up well with the 
first echo length. 
Discussion 
Although this analysis demonstrated that 
there are several strong advantages (gain 
adjustment, bottom picking, bad data exclu- 
sion, and stacking) in using the partially 
automated echogram classifying software 
(QTC IMPACT), there are also several 
potential pitfalls (dependencies among 
the 166 EMs, lack of standardization, cor- 
relation with depth, influence of seafloor 
slope, and mismatch between 251 sample 
