Conners and Munro: Effects of commercial fishing on local abundance of Gadus macrocephalus in the Bering Sea 
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1 65°20'W 1 65° 1 0’VV I65°0’W 
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165°I0 r W 1 65°0'W 
Figure 3 (continued) 
variance of the <5’s. Although the small sample size in 
January 2003 limited the power of statistical testing in 
this year, the overall consistency of the results persuad- 
ed us to include the 2003 data set in final analyses. 
Analysis of the raw data foreshadowed the overall 
results of the study. We examined the catch data from 
individual pots, using standard linear model analysis. 
The best-fit linear model accounted for only 30% of the 
variability in the data, reflecting the importance of oth- 
er sources of variability not included in the model. The 
treatment effect (trawled vs. untrawled zone) was not 
significant for the raw data, indicating only slight dif- 
ferences in baseline abundance between the two zones. 
The interaction term for treatment and season (which 
is the term that would reflect a substantial localized 
depletion in the trawled zone) was strongly not sig- 
nificant. As pointed out in discussions of simple BACI 
analysis (Hurlbert, 1984; Stewart-Oaten et al., 1986; 
Underwood, 1991), the interaction term from the stan- 
dard ANOVA does not provide the correct error term for 
a true test of impact; for testing the presence or absence 
of localized depletion we used the analysis of <5’s. 
Final results of the study clearly indicated very simi- 
lar values of seasonal change in Pacific cod abundance 
(d) in both the trawled and untrawled portions of the 
study area. We did not see the differences in slope that 
we would have expected to result from strong localized 
depletion in the trawled zone. When we used the rank- 
based Wilcoxon test to look for differences in mean d 
between the trawled and untrawled regions, P-values 
