Stiansen et al.: Efficiency and catch dynamics of square and conical crab pots 
43 
Table 1 
Catch data from the comparative fishing experiment with square and conical red king crab ( Paralithodes camtschaticus) pots. 
Total catch and catch by sex of red king crab (Paralithodes camtschaticus ) at different soak times is shown. Within-string catches 
of red king crab for square and conical pots were compared by using a Wilcoxon paired comparisons test. n p is number of pot set- 
tings for each type of pot, and N is the number of strings with nonzero catch. SE = standard error. 
Number of crabs caught 
Square pots Conical pots Paired comparisons 
Soak time 
(days) 
n P 
Median 
Mean 
SE 
Median 
Mean 
SE 
N 
P value 
Males 
2 
122 
12.0 
14.9 
0.86 
2.0 
3.5 
0.37 
61 
<0.001 
3 
60 
14.0 
13.9 
1.04 
5.0 
6.2 
0.66 
30 
<0.001 
4-5 
16 
10.0 
10.9 
1.26 
5.0 
6.0 
0.90 
8 
<0.05 
7-8 
26 
13.0 
14.0 
1.68 
9.0 
9.7 
1.43 
13 
>0.05 
Females 
2 
122 
15.0 
16.1 
1.02 
5.0 
6.2 
0.53 
61 
<0.001 
3 
60 
18.0 
17.4 
136 
12.0 
11.5 
1.08 
30 
<0.001 
4-5 
16 
20.5 
19.6 
3.57 
11.0 
10.6 
1.10 
8 
>0.05 
7-8 
26 
20.0 
21.2 
1.56 
18.0 
17.8 
1.69 
13 
>0.1 
Total catch 
2 
122 
29.0 
31.0 
1.66 
7.5 
9.7 
0.79 
61 
<0.001 
3 
60 
32.0 
31.3 
1.81 
15.5 
17.6 
1.43 
30 
<0.001 
4-5 
16 
29.0 
30.5 
3.90 
15.5 
16.6 
1.33 
8 
<0.05 
7-8 
26 
34.0 
35.2 
2.83 
26.5 
27.5 
2.54 
13 
<0.05 
pared by means of the Mann-Whitney U - test for each 
soak time. 
A Wilcoxon test was used to test for differences be- 
tween the pot types in thq proportion of male crabs and 
males that were larger than 160 mm CL (the smallest 
commercial size in the Norwegian RKC fishery). In or- 
der to reduce the effect of small sample size (Zar, 1999), 
proportions equal to zero were replaced by 1/4 n (where 
n is the denominator in the calculation of the original 
proportion) and proportions equal to one were replaced 
by l-(l/4n). Only observed data on strings with catches 
in both types of pots were included in these analyses. 
All statistical tests were performed with Statistica, 
vers. 8.0 (StatSoft Inc., Tulsa, OK). 
Results 
The square pots caught significantly more crabs than 
the conical pots at all soak times (Table 1). At the short- 
est soak times, the catch ratio of square to conical pots 
exceeded 3:1, whereas the mean ratio (squarexonical) 
for the two longest soak times was close to 3:2. Except 
for the longest soak time, the square pots caught more 
of both male and female crabs (Table 1, Fig. 5). Total 
catches and the catches of both male and female crabs in 
the conical pots increased with increasing soak time (P< 
0.001), but catches in the square pots did not increase 
beyond two days of soak time. 
The percentage of male crabs in the catch was higher 
in the square than in the conical pots after the two, 
three, and four to five days of soak time (Table 2). The 
difference was greatest for the shortest soak times be- 
cause the proportion of female crabs in the square pots 
increased with increasing soak time (P<0.05). No sig- 
nificant changes were found in the percentage of female 
crabs taken in conical pots over time. 
The overall percentages of male crabs larger than 160 
mm were 60% (SE = 3) and 50% (SE = 3) in the square 
and conical pots, respectively. At all soak times, the 
proportion of male crabs larger than 160 mm was sig- 
nificantly higher in the square pots (P<0.001, Fig. 5). 
The median length of males was larger in the square 
pots for all but the longest soak time tested (Table 3). 
There were no differences between the types of pots 
with respect to the size of female crabs caught. 
Discussion 
The square pots caught up to three times more red king 
crab than the conical pots, but the difference decreased 
with increasing soak time. Provided that the two types 
of pots attracted equal numbers of crabs (identical bait 
was used), the differences in catches must be due to dif- 
ferent rates of entry versus exit. Because escape rates 
from the conical pot have been shown to be low (Godpy 
et al., 2003), the low catch rate for the conical pot was 
