Rudershausen et al.: A comparison between circle hook and J hook performance in the troll fisheries off North Carolina 
159 
and gaff fish), but instead do these activities them- 
selves. Before each charter trip, the captain and first 
author determined which non-billfish species would be 
targeted and adjusted the tackle class, leader, and rig 
type accordingly; the first author made this determina- 
tion for the recreational trips. This determination was 
based on water temperature, time of year, and fish- 
ing reports that indicated which species we would be 
most likely to interact with. We fished monofilament, 
fluorocarbon, and wire leaders a total of 6, 12, and 18 
days on the charter vessels, and 18, 7, and 14 days on 
the recreational vessel. There were not equal numbers 
of days fished between the two user groups. At most, 
one boat trip was taken per day. 
On each of the two charter vessels we fished pairs 
of standing rods (held by fixed rod holders) from four 
positions. These four pairs were flat lines, short outrig- 
gers (riggers), long riggers, and bridge poles. On windy 
days, rods were not fished from the bridge because of 
increased likelihood of tangles in the lines. On days di- 
rected for wahoo, we used in-line planers on the flat-line 
rods in order to fish baits deeper in the water column 
and elicit a greater number of interactions with this 
species. We randomly selected which side of the boat 
(port or starboard) would receive the circle and J hook 
treatment on each day of charter fishing. 
We fished two pairs of lines simultaneously aboard 
the research vessel. These pairs were flat lines and 
poles fished from rod holders on a canopy “t-top.” For 
each day of fishing on the recreational vessel, we stag- 
gered hook types so that a hook type on a flat line was 
on the side of the boat opposite that same hook type 
on the t-top. 
The three vessels used to collect data trolled at be- 
tween six and seven knots (regardless of species tar- 
geted). Chains of combined artificial lures consisting 
of four 23-cm long squids ending with a blue and white 
Hand Lure® (L&S Bait Company, Inc., Largo, FL)- 
ballyhoo bait combination were deployed as teasers (no 
hooks) from each vessel during the collection of data. A 
chain of pink squids was deployed on the starboard side 
of the boat and a chain of green squids was deployed on 
the port side of the boat. Baits were medium ballyhoo 
that were replaced upon washout. 
We recorded fish total length (mm) when it was pos- 
sible to associate a fish length with a hook type. This 
was not always possible because of multiple fish being 
caught and placed in fish box at nearly the same time. 
Hooking location was recorded for all captured fish. 
Data analysis 
Four response variables were measured: numbers 
caught, numbers of strikes, proportion hooked up, and 
proportion retained. Numbers of fish caught reflected 
the cumulative results for the strike, hook-up, and reten- 
tion levels. A fish interacting with the gear in a manner 
such that the line was pulled from the outrigger clip or 
that engaged the reel clicker when no clip was used was 
considered a strike (Prince et al., 2002). A fish that had 
been hooked for 10 seconds after striking was considered 
a hook-up. A retained fish was one where the leader was 
touched or the fish put into the boat (“boated”). The 
proportion of fish that hooked up was relative to the 
number that struck (Prince et al., 2002); similarly, the 
proportion of fish that were retained on the hook was 
relative to the number that hooked up. 
Strikes and hook-ups for fish not caught or visually 
identified were included in the analysis. When the ap- 
pearance of a struck bait (e.g., bite marks), water tem- 
perature, time of year, fishing location, fish behavior 
(jumping), and order of fish landed each day indicated 
a particular species, we attributed these interactions 
to that species. When these six factors did not com- 
bine to indicate a particular species, these interactions 
were considered to be from an unidentified species. We 
allocated strikes and hook-ups from unidentified fish 
to each species in the same proportion as that for fish 
boated for that day of fishing. At each level of interac- 
tion we found similar best fitting models for data that 
excluded or included unidentified fish (Rudershausen 
et al., 2010). 
Generalized linear models (GLMs) were used to deter- 
mine the effects of hook type (circle or J), leader type 
(monofilament, fluorocarbon, or wire), species (dolphin- 
fish, yellowfin tuna, or wahoo), user group (recreational 
or charter), wave height, and potentially important 
interactions on the numbers of fish caught and each 
of three mechanisms leading to a caught fish. We con- 
structed a sequence of Poisson GLMs for the numbers 
caught and numbers of strikes data sets. For hook-up 
and retention data, we used binomial GLMs to repre- 
sent the conditional nature of the hook-up and retention 
processes (e.g., the number of fish that hooked up in a 
given trip was conditional on the number that struck). 
In each case, hook type, leader type, species, and user 
group were treated as categorical variables, whereas 
wave height was treated as a continuous variable. Spe- 
cies caught on days where they were not the main tar- 
get were included in all analyses and are referred to as 
“nondirected” species. At each level of interaction, plots 
were constructed to help better visualize the relative ef- 
fectiveness of circle and J hooks on directed leader types. 
We collected the same response variable data for 
other species that have feeding styles similar to those 
of yellowfin tuna and wahoo to provide additional data 
to clarify trends in relative hook-type effectiveness. 
The four model sets described above were also fitted 
to data sets that included blackfin tuna (Thunnus at- 
lanticus), skipjack tuna (Euthynnus pelamis), and false 
albacore ( Euthynnus alletteratus), which were combined 
with yellowfin tuna data to form a “tuna” group (fam- 
ily Scombridae, tribe Thunnini), and king mackerel 
( Scomberomorus cavalla) and Spanish mackerel ( Scomb - 
eromorus maculatus ), which were combined with wahoo 
data to form a “mackerel” group (family Scombridae, 
tribe Scomberomorini). This additional model fitting 
kept dolphinfish as a single-species group. 
We adopted an information-theoretic perspective to 
compare the parsimony of relatively simple models 
