Rudershausen et at: A comparison between circle hook and J hook performance in the troll fisheries off North Carolina 
169 
Table 4 
Candidate models fitted to hook-up data for three species (dolphinfish [ Coryphaena hippurus], yellowfin tuna [ Thunnus alba- 
cares I, 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. /C=number of parameters 
for each model; w=Akaike weight. Base models included all predictor variables with exception of hook and any hook interactions; 
see Methods section for a full description of base models. AQAIC values ~<4 were considered models with reasonable support. 
Interaction Data type Distribution 
Model 
K 
QAIC 
AQAIC 
U) 
Hook-up: Proportion Binomial 
base + hook 
11 
-1159.03 
0.00 
0.38 
species 
base + hook + hook*user 
12 
-1158.16 
0.88 
0.25 
base + hook + hook*species 
13 
-1156.75 
2.29 
0.12 
base + hook + hook*leader 
13 
-1156.53 
2.51 
0.11 
base + hook + hook*species + hook*user 
14 
-1155.07 
3.96 
0.05 
base + hook + hook*user + hook*leader 
14 
-1154.81 
4.23 
0.05 
base + hook + hciok*species + hook*leader 
15 
-1154.75 
4.28 
0.04 
base + hook + hook*species + hook*leader 
+ species*leader + hook*species*leader 
23 
-1148.53 
10.51 
0.00 
base 
10 
-1134.22 
24.81 
0.00 
Hook-up: Proportion Binomial 
base + hook 
11 
-1393.91 
0.00 
0.40 
taxa 
base + hook + hook*taxa 
13 
-1392.58 
1.33 
0.21 
base + hook + hook*user 
12 
-1392.17 
1.74 
0.17 
base + hook + hook*leader 
13 
-1390.90 
3.00 
0.09 
base + hook + hook*taxa + hook*user 
14 
-1390.48 
3.43 
0.07 
base + hook + hook*user + hook*leader 
14 
-1388.80 
5.11 
0.03 
base + hook + hook*taxa + hook*leader 
15 
-1388.72 
5.19 
0.03 
base + hook + hook*taxa + hook*leader 
+ taxa*leader + hook*taxa*leader 
23 
-1385.27 
8.64 
0.01 
base 
10 
-1368.17 
25.74 
0.00 
and Horodysky (2010) did not report hook-up percentage 
data for blue marlin and therefore it is unknown what 
hook-up rates would be for this aggressive feeder that 
is hooked upon strike. 
One rigging tactic when trolling is to rig the circle 
hook so that it is completely external to the bony or 
fleshy portions of the bait to maximize the exposed 
gap width (e.g., the hook is placed on top of the bait’s 
head; Prince et ah, 2002). This placement is thought 
to work best for “dropping back” to fish because the 
fish have enough time to swallow the bait and the 
hook (dolphinfish and billfish trolling) and turn their 
body, while the exposed gap width of the circle hook 
is maximized. We did not employ the external rig- 
ging technique on days when yellowfin tuna or wahoo 
were targeted. Hooks were rigged internally for these 
two species because these species hook themselves 
upon striking; drop-backs are not typically required by 
charter or recreational fishers targeting these species. 
An additional reason for embedding hooks in baits was 
so that we could fish “combo” baits (lure and natural 
bait combinations) because colored lures (skirts) elicit 
more strikes than plain ballyhoo on most days for 
yellowfin tuna and wahoo. The cooperating mates on 
charter trips embedded the hook as close to the tail 
as possible without compromising the swimming ac- 
tion of the bait. Using larger circle hooks would have 
increased the gap width between the point and the 
point shank, potentially making hook-ups more likely, 
but this change could have compromised the strike 
rate by making the hook more visible to the fish or 
causing the bait to wash out faster. 
There was little to no hook effect at the propor- 
tional retention level (caught once hooked) for dol- 
phinfish, yellowfin tuna, and tunas, although there 
was increased retention of wahoo and mackerels on 
circle hooks and yellowfin tuna on circle hooks in the 
recreational fishery. The latter result is consistent 
with the findings of Prince et al. (2002) when trolling 
dead baits with circle and J hooks for sailfish. The 
increased retention on circle hooks relative to J hooks 
has been used as a selling point for circle hooks, but 
we did not find this result for the majority of species 
that we caught. 
The procedure for assigning interactions with un- 
identified fish to a particular species is not ideal. For 
instance, if individuals of one species generate behav- 
ioral cues or are landed more readily than individuals 
for another species, species assignments may be biased 
toward more readily identified fish. In general, this 
approach decreased our ability to detect species effects 
on landing probabilities and hookup rates. However, 
we expected the reduction in statistical power to be 
relatively small and to affect only inferences about 
