166 
Fishery Bulletin 1 10(2) 
Table 3 
Candidate models fitted to strike data for three species (dolphinfish \Coryphaena hippurus], yellowfin tuna [ Thunnus albacares], 
and wahoo 1 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. /f=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 
hQAIC 
w 
Strike: Count 
Poisson 
base + hook 
15 
979.96 
0.00 
0.36 
species 
base 
14 
980.17 
0.21 
0.33 
base + hook + hook*user 
16 
981.89 
1.93 
0.14 
base + hook + hook*leader 
17 
983.42 
3.46 
0.06 
base + hook + hook*species 
17 
983.81 
3.86 
0.05 
base + hook + hook*user + hook*leader 
18 
985.40 
5.44 
0.02 
base + hook + hook*species + hook*user 
18 
985.75 
5.79 
0.02 
base + hook + hook*species + hook*leader 
19 
987.85 
7.89 
0.01 
base + hook + hook*species + hook*leader 
23 
996.39 
16.43 
0.00 
+ hook*species*leader 
B. Strike: Count 
Poisson 
base + hook 
15 
1050.57 
0.00 
0.40 
taxa 
base 
14 
1051.09 
0.52 
0.31 
base + hook + hook*user 
16 
1052.66 
2.08 
0.14 
base + hook + hook*taxa 
17 
1054.54 
3.97 
0.05 
base + hook + hook*leader 
17 
1054.56 
3.99 
0.05 
base + hook + hook*taxa + hook*user 
18 
1056.59 
6.01 
0.02 
base + hook + hook*user + hook*leader 
18 
1056.64 
6.07 
0.02 
base + hook + hook*taxa + hook*leader 
19 
1058.92 
8.34 
0.01 
base + hook + hook*taxa + hook*leader 
23 
1067.40 
16.83 
0.00 
+ hook*taxa*leader 
rate of tunas on circle hooks over that for J hooks has 
been observed in other longline studies (Falterman and 
Graves, 2002). It is unclear what the mechanism is that 
leads to higher tuna catches on longline circle hooks, 
but lower tuna catches on trolled dead baits rigged with 
circle hooks; it is likely that tuna ingested the bait and 
hook more deeply in comparison to the actively trolled 
bait in our study. Actively trolling hooks (versus passive 
fishing on a longline) may be the mechanism contribut- 
ing to these hook-type differences. 
Most comparative studies of hooks in the dead bait 
troll fishery have been designed to estimate catch- 
and-release mortality in billfishes (Prince et al., 2002; 
Horodysky and Graves, 2005; Graves and Horodysky, 
2010). The species that we examined in this study are 
not generally released; therefore, our focus was on the 
influence of hook type on catch rates and the potential 
mechanisms responsible for similarities or differences 
in catch by hook type, rather than on postrelease mor- 
tality. This was our focus because many charter boat 
captains suspect that circle hooks negatively impact 
catches of dolphinfish, tunas, and mackerels in the 
North Carolina dead-bait troll fishery. Our results con- 
firm this suspicion. Model-averaged estimates suggest 
a strong negative effect of hook type on catch rates for 
all three species; however, examination of the raw data 
for individual species suggests that the effect of hook 
type on wahoo catch may be minor. Future studies with 
increased sample sizes would help to refine estimates 
of species by hook-type interactions, providing greater 
resolution of the importance and magnitude of hook ef- 
fects for individual species. Thus, this is the first study 
to find that catch rates in a dead bait troll fishery can 
be negatively impacted by circle hooks. Horodysky and 
Graves (2005) and Graves and Horodysky (2010) did 
not provide comparisons of catch data between circle 
hooks and J hooks in their hook comparative studies 
on billfish. 
Differences in strike, hook-up, and retention rates be- 
tween hook types all have the potential to contribute to 
differences in catch rates. There was little evidence for 
a hook effect on strike rate; therefore, J and circle hook 
rigged baits were equally attractive to these three fish 
groups. Other studies that have compared hook types 
in the dead bait troll fishery have not reported data on 
strike rate by hook type; we recommend that this in- 
formation be collected so that the specific mechanisms 
responsible for potential differences in catch rate can 
be determined. 
The greater effectiveness of J hooks at hooking fish 
once they struck generally held across the three species 
and dolphinfish and the two taxa groups. Circle hooks 
