366 
Fishery Bulletin 114(3) 
- 1.5 - 1.0 - 0.5 0.0 0.5 1.0 
ln{Cf)-ln(Cs) 
Figure 3 
Normal distribution curve fitted to a histogram of the differences in \n{catch) of 
large Pacific cod (Gadus macrocephalus) between fast and slow towing speeds 
(goodness-of-fit: x25.2.i=1.226, P=0.54) from this study conducted in 2013 in the 
eastern Bering Sea. ln(cf)=catch at the fast towing speed of 2.1 m/s; ln(cs)=catch 
at the slow towing speed of 1.5 m/s. 
Table 3 
Power of /-test (probability of rejecting Hq when 
it is false) for the mean difference d between 
In(cf) (cr=catch of fast tows) and InCcg) (Cs=catch 
of slow tows), where Hq: d=0, against one-sided 
H^: d>0 alternative hypothesis. The /-distribution 
was used with a degree of freedom of 23 and a 
significance level (a) of 0.05. 
d 
e^=Cf/Cs 
Power 
0.1 
1.1 
0.21 
0.2 
1.2 
0.53 
0.3 
1.3 
0.83 
0.4 
1.5 
0.97 
0.5 
1.6 
0.99 
1.0 
2.7 
1.00 
large Pacific cod (>55 cm FL) were caught with 
the 83-112 eastern trawl. Therefore, we surmise 
that if the dome-shaped selectivity estimated in 
recent stock assessments (Thompson^’^.^) is due to 
a decrease in trawl efficiency for large Pacific cod, 
that decrease is not attributable to fish outswim- 
ming the net. We are unaware of other direct 
studies on the swimming behavior of Pacific cod 
in relation to trawling activity. Consequently, to 
make inferences, we must draw upon the conclu- 
sions from research conducted on other, similar 
species. 
Of the many species studied for their swim- 
ming capabilities, the Atlantic cod is most close- 
1 
0.9 
0.8 
0 7 
0.6 
0 5 
04 
0 3 
Both vessels 
Figure 4 
Boxplot indicating the proportion of demersal fish backscat- 
ter, in all depth layers examined (0.25-16.0 m above the 
sounder-detected bottom echo), found below the average hea- 
drope height but above the 0.25-m dead zone (0.25-2.0 m; 
n=20 tows), for this study conducted in August 2013 in the 
eastern Bering Sea. The line within the shaded box indicates 
the median value, the shaded box indicates the first and third 
quartiles, the horizontal lines outside the shaded box indicate 
a distance of 1.5 times the interquartile range above the third 
quartile and below the first quartile, and the plus marks in- 
dicate outliers outside these lines. 
j- 0) 
Is 
(D^ 
I J 
C 0 
CO 
I- 
d:« 
ly related to Pacific cod. Winger et al. (2000) performed a 
comprehensive tank study on the swimming stamina of At- 
