NOTE Stone and Dixon: A comparison of catches of Xiphias gladius and other pelagic species with longline gear 
211 
backline and a lower monofilament leader 
to which the hook was attached. The mono- 
filament leader made up one half (-1.8 
m) of the overall length of the gangion 
( —3.6 m) and was considered to yield bet- 
ter catch rates because it was assumed to 
be less visible to swordfish and other pe- 
lagic species. This innovation also effec- 
tively reduced shark damage to the gear 
because only the monofilament leader had 
to be replaced if it was bitten off. In the 
late 1980s, fishermen began to use mono- 
filament nylon for both sections of the gan- 
gion and for the backline on the assump- 
tion that this would further improve catch 
rates by decreasing overall visibility of the 
gear. 
Canadian pelagic longline fishermen 
have been using monofilament gangions 
for over a decade now and generally agree 
over its ability to outperform the older 
tarred multifilament nylon gangions in 
terms of swordfish catchability, although 
this theory has never been tested scien- 
tifically. In this note, the results of a col- 
laborative science and industry study involving the Cana- 
dian Department of Fisheries and Oceans and the Nova 
Scotia Swordfishermen’s Association are presented. Our 
study was designed to compare the catchability of sword- 
fish and other pelagic species on commercial longline gear 
configured with alternate monofilament and tarred mul- 
tifilament nylon gangions. It was based on the premise 
that some species can avoid capture on the tarred multi- 
filament gangions which are thicker, darker, and possibly 
more “visible” than the monofilament nylon gangions. 
Materials and methods 
The study was conducted aboard the 19-m fishing vessel 
Nova Blue from 22 July to 2 August 1999, along the edge 
of Georges Bank (depth to bottom: 360-1400 m) from Cor- 
sair Canyon to the Northeast Peak (Fig. 2). This area is 
closed annually to commercial longlining operations from 
1 January to 1 August to reduce bycatches of bluefin tuna 
and small swordfish. Therefore, no other vessels were fish- 
ing in this closed area at the time this experiment was 
conducted. The gear was deployed each evening between 
1800-2300 h in surface waters following the 20-22°C iso- 
therm from south to north, allowed to soak overnight, 
and hauled back from north to south beginning at day- 
break (-0600 h) the following morning. Haulback opera- 
tions generally required 10 hours — occasionally exceeding 
12 hours when the gear parted off or became entangled. 
Ten surface longline sets were completed with stan- 
dard commercial longline gear configured with alternately 
spaced monofilament and tarred multifilament nylon gan- 
gions. It was assumed that this approach would minimize 
the variability in catches between gangion types resulting 
from the different depth and temperature regimes over 
the length of the set (i.e. up to 64 km). Generally, 20 sec- 
tions of gear were deployed for most sets (one section=72 
hooks and 23 buoys), yielding a total of 1440 hooks per set 
(for sets 4-10), although there was some variation in hook 
number for the first three sets (set 1: 1008 hooks; sets 2-3: 
1656 hooks). Although the 1:1 ratio of gangion types was 
not maintained in some gear sections owing to gear dam- 
age and subsequent replacement, the overall ratio for the 
entire set remained at 1:1. 
Monofilament gangions consisted of two 3.6-m sections 
of 400-lb test, 2-nun diameter monofilament nylon at- 
tached together with stainless steel crimps, with the lower 
section or leader attached to a no. 9 Mustad J-hook (Fig. 
3). Multifilament gangions had a 3.6-m upper section of 
tarred braided nylon (400 lb test, 5-nun diameter), and a 
lower 3.6-m monofilament leader (400-lb test, 2-mm diam- 
eter) to which a no. 9 Mustad J-hook was attached. There- 
fore, the lower section (leader) of both gangion types was 
monofilament nylon and the upper section varied between 
multifilament and monofilament nylon material. With this 
configuration, only the leader section had to be replaced 
if damaged by sharks. Each leader also had three lumi- 
nous green beads and one in 20 had a green lightstick at- 
tached 1 m above the hook (Fig. 3). When the gear were 
set, gangions were clipped onto a monofilament backline 
(730 lb test) at intervals of 36 m after baiting the hooks 
with whole Atlantic mackerel ( Scomber scombrus). Styro- 
foam buoys with 2-4 m droplines were clipped to the back- 
line after every third hook, and a highflyer attached to the 
backline at the end of each section. Fishing depth during 
each set was estimated to vary between 9 and 1 1 m from 
the surface. 
The catch (in numbers) of all pelagic species was record- 
ed by gangion type for each section of gear within a set. The 
curved lower jaw fork length (LJFL, cm) was obtained for 
