Rudershausen et al A comparison between circle hook and J hook performance in the troll fisheries off North Carolina 
163 
Table 2 
Candidate models fitted to catch-per-trip data for three species (dolphinfish | Coryphaena hippurus 1, yellowfin tuna I Thunnus 
albacares], and wahoo \Acanthocybium solandri], and taxa (dolphinfish, tunas, and mackerels]) when trolling circle and J hooks 
in Gulf Stream waters off North Carolina. Quasi-Akaike information criterion (QAIC) was used to evaluate model performance, 
with the lowest value indicating the most parsimonious model. Categorical predictor variables included hook type (hook), leader 
type (leader), species or taxa, and user group (user). Wave height was used as a continuous predictor variable. K= number of param- 
eters for each model; ic=Akaike weight. Base models included all predictor variables with exception of hook and any hook interac- 
tions; see Methods section for a full description of base models. 4QAIC values ~<4 were considered models with reasonable support. 
Interaction Data type Distribution Model 
K 
QAIC 
AQAIC 
w 
Catch: species Count Poisson base + hook 
13 
356.77 
0.00 
0.54 
base + hook + hook*user 
14 
358.42 
1.65 
0.23 
base + hook + hook*leader 
15 
360.49 
3.72 
0.08 
base + hook + hook*species 
15 
360.90 
4.14 
0.07 
base + hook + hook*user + hook*leader 
16 
361.98 
5.21 
0.04 
base + hook + hook*species + hook*user 
16 
362.54 
5.77 
0.03 
base + hook + hook*species + hook*leader 
17 
364.91 
8.15 
0.01 
base + hook + hook*species + hook*leader 
21 
373.59 
16.83 
0.00 
+ hook*species*leader 
base 
12 
385.14 
28.37 
0.00 
Catch: taxa Count Poisson base + hook 
13 
477.17 
0.00 
0.55 
base + hook + hook*user 
14 
479.11 
1.94 
0.21 
base + hook + hook*leader 
15 
480.63 
3.46 
0.10 
base + hook + hook*taxa 
15 
481.14 
3.97 
0.07 
base + hook + hook*user + hook*leader 
16 
482.54 
5.37 
0.04 
base + hook + hook*taxa + hook*user 
16 
483.16 
5.99 
0.03 
base + hook + hook*taxa + hook*leader 
17 
485.11 
7.94 
0.01 
base + hook + hook*taxa + hook*leader 
21 
493.60 
16.43 
0.00 
+ hook*taxa*leader 
base 
12 
501.35 
24.18 
0.00 
charter trips. This trend was most pronounced on 
charter trips for all leader types (Fig. 6). The excep- 
tion was a slightly greater hook-up rate for yellowfin 
tuna on circle hooks than on J hooks when fishing 
fluorocarbon leaders on recreational trips. For the 
taxa analysis, trends in model fitting to proportional 
hook-up data were similar to three species (Table 
4; Fig. 7); hook was a main effect in the best fit- 
ting model and it was a main effect and interaction 
term in models receiving lesser support. The base 
model received no support (Table 4). The addition of 
mackerel data on recreational trips strengthened the 
trend of greater effectiveness of J hooks in hooking 
up these taxa on wire, the directed leader type for 
that group (Fig. 7). 
The third mechanism contributing to catch was 
retention. Hook type did not appear to have a pro- 
nounced effect on proportion of fish retained (Fig. 8). 
For models fitted to species data, the base model re- 
ceived majority support (Table 5). A base model with a 
hook effect was the only other model receiving support, 
but it was minor. The proportion retained on circle 
hooks generally equaled (dolphinfish and yellowfin 
tuna) or slightly exceeded (wahoo) those retained on J 
hooks on directed leader types (Fig. 8). Proportional 
retention data for the taxa also showed that retention 
was high, with little to no difference between hook 
types (Table 5; Fig. 9). The base model received major- 
ity support and the base model with hook as a main 
effect received less support. Two other models that 
received minor support had hook-species and hook-user 
interactions (Table 5). 
Estimates of effect size on catch rates determined 
from model-averaged predictions showed that J hooks 
were more effective than circle hooks. This trend held 
across the species and taxa levels. For the three spe- 
cies, mean predicted effect size (± standard deviation 
[ SD] ) for dolphinfish, yellowfin tuna, and wahoo on 
directed leader types was 0.60 (0.05), 0.60 (0.07), and 
0.65 (0.09), respectively (Fig. 10), meaning that circle 
hooks were roughly 60% as effective as J hooks. For 
the taxa groups, mean predicted effect size (±SD) for 
dolphinfish, tunas, and mackerels was 0.62 (0.05), 
0.62 (0.06), and 0.67 (0.08), respectively (Fig. 10). 
There were no significant between-hook differences 
in the distribution of lengths for dolphinfish (^ 2 = 0.973, 
P=0.324), yellowfin tuna (^ 2 =0.003, P=0.958), or wahoo 
(^ 2 = 0.068, P=0.795). Thus, hook type was not size selec- 
tive within a species. 
The effect of hook type on deep hooking was species 
dependent. Rates of deep hooking were significantly 
less for dolphinfish caught on circle hooks than J hooks 
(Table 6). However, there was no effect of hook type on 
proportion of deep-hooked wahoo or blackfin tuna. Rates 
