Conners and Munro: Effects of commercial fishing on local abundance of Gadus macrocephalus in the Bering Sea 
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1 65°30'0"W 165°0'0"W 164°30'0"W 
Location of the study to determine localized depletion of Pacific cod ( Gadus 
macrocephalus) in the southeast Bering Sea. The large arc shows the regula- 
tory notrawl zone around the Steller sea lion ( Eumetopias jubatus ) haulout 
at Cape Sarichef on Unimak Island. The small triangles indicate station 
locations for the experiment. Depth contour lines and light shading show 
the region of 70 to 100 m depth. 
At the tunnel openings there was a modified Hilti-style 
stainless-steel trigger, a variation of a fish retention 
mechanism commonly used in cod-pot fishing. Research 
pots were fished individually with buoy lines, buoy con- 
figurations, and other tackle configured similarly to 
that deployed in commercial pot fishing. 
Experimental design 
We used an experimental design similar to the class 
of designs referred to as “before/after control/impact” 
(BACI). The capabilities and limitations of B AC I study 
designs have been discussed extensively in the ecological 
literature (e.g., Osenberg and Schmitt, 1994; Hewitt et 
al., 2001). We used many of the components of a BACI 
design, but the final design differed substantially from 
the paired designs of Stewart-Oaten et al. (1992). In 
our study, the measured quantity was not the difference 
between treatment and control stations replicated over 
time, but the percentage difference over time at each sta- 
tion, replicated over space. In this sense, our design was 
similar to the ANOVA-type designs of Underwood (1994). 
Our design allowed for expected seasonal and small- 
scale spatial variability in fish abundance, and provided 
the necessary replication for hypothesis testing. 
The experiment was conducted in 2003, 2004, and 
2005. In each year, data were collected during two 
separate cruise legs: in early January (before the trawl- 
ing season) and immediately after the main trawl har- 
vest in late March. Sampling was balanced between a 
treatment area subject to intensive trawl fishing and a 
control area inside the Cape Sarichef notrawl zone. A 
total of 80 sampling stations were set along 10 parallel 
transects intersecting the notrawl zone boundary, and 
each transect contained four stations inside and four 
outside the boundary (Fig. 1). Although it was not pos- 
sible to match treatment and control stations exactly 
with respect to depth, habitat, bottom currents, etc., 
this layout provided a similar range of habitats within 
the two zones. 
The quantity of interest for each station was the ratio 
of the mean pot catch (in numbers or weight of Pacific 
cod) at that station during the March survey (X A f ter ) to 
the average catch during the January survey (X Before ). 
This ratio reflects the percentage change in abundance 
between the two surveys at a particular station. The 
seasonal percentage change is referred to as the delta 
(6) for the station: 
5 
The ratio is expressed so that <5 will be near zero if the 
catch is the same at a given station during both the 
before and after surveys, positive if the catch increases, 
_ After ' 
X 
Before J 
_ ^ After 
L Before 
x 
l. 
Before 
