286 
Fishery Bulletin 106(3) 
165°20'W 165°10'W 165°0'W 
Spatial pattern in seasonal percent change (6) for the three study 
years. Refer to Figure 1 for general location of the study area. 
Symbols show study stations. The arc in the middle of the stations 
is the Cape Sarichef notrawl zone boundary. Symbol shape and 
size indicate the size of the percent change in Pacific cod ( Gadus 
macrocephalus ) catch between “before” (early January) and “after” 
(immediately after the main trawl harvest in late March) surveys 
in each year: (A) 2003, (B ) 2004, and (C) 2005. 
but not always in the same direction. In 2003, the aver- 
age catch rate decreased 55% from January to March, 
and nearly all of the individual station changes (6) were 
less than 1.0. In 2004 and 2005, the average catch rate 
increased by 73% and 26%, respectively, from January 
to March. These differences were presumably the result 
of interannual differences in the timing of seasonal 
migration and spawning aggregation 
A check of spatial pattern in the raw data and final 
6’s verified the independence of the experimental study 
stations and the absence of any strong spatial patterns. 
There was no consistent spatial pattern in raw catch 
data, either between trawled and untrawled areas or 
from southwest to northeast within the study area. 
There was some evidence of serial correlation between 
adjacent pots within each fishing day; we believe this 
correlation to be a result of similarities in timing of 
pot launches within tidal and diel cycles rather than 
spatial correlation in fish abundance. There was no 
spatial correlation in the calculated average catch at 
each station over a cruise. Although there was some 
evidence of serial correlation between days within a 
cruise, averaging the catch at each station over the 
days within a cruise eliminates this correlation. Maps 
of percentage change values (6) also showed no discern- 
ible spatial pattern (Fig. 3). Distance-based variograms 
(both isotropic or anisotropic) were reviewed for the 
final 6’s and we found no significant spatial correlation 
as a function of distance between pots. Correlation of 
pairs of 6’s at all distances of 0.11 km or more were not 
significant, verifying the assumption of independence 
between stations. 
Implementation of the study design was generally suc- 
cessful, and good replication was obtained. The excep- 
tion was the January cruise in the first year of the ex- 
periment (2003), where severe weather and mechanical 
problems severely curtailed the field effort. Sample size 
from this cruise (160 pots fished) was small (Table 1). 
The March “after” cruise in 2003 was, however, success- 
ful; a total of 475 pots were fished and full replication at 
all 80 experimental stations was obtained. Both before 
and after cruises in 2004 and 2005 achieved full cover- 
age of the 80 stations and good replication. Because of 
the very low sample size in January 2003, 6’s could be 
calculated for only 48 of the study stations, and some 
before values were based on only a single measure- 
ment. In 2004 and 2005, 6’s at all 80 study stations 
were calculated from the averages for over three to five 
replicate fishing days within each cruise. The resulting 
values ranged from negative numbers, representing a 
net seasonal decrease at a station, to fairly large posi- 
tive values, indicating a substantial seasonal increase. 
In 2004, there was a particularly large outlier (6>4) at 
one station which had very low catches in January. The 
shift to overnight soaks in 2005 resulted in not only 
smaller variance of the raw catch data but in smaller 
