228 
Fishery Bulletin 115(2) 
Table 3 
Statistics of the size structure of the species caught during longline sets conducted in the southwest Indian Ocean between 
November 2013 and March 2014 and results of the permutation (perm) tests for statistical comparison of mean sizes (in 
cm) for the 2 leader materials tested, 2.5-mm monofilament nylon and 1.2-mm multifilament stainless wire. Also provided 
are the number of specimens measured (no.) as well as the range and mean, with standard deviation (SD), of the sizes in 
the catch for each species or species group. Size measurements refer to the length (in centimeters): lower-jaw fork length for 
billfishes, fork length for all other fishes, and total carapace curve length for marine turtles. 
Monofilament Wire 
Group and species 
No. 
Range 
Mean 
SD 
No. 
Range 
Mean 
SD 
Perm test 
P 
Billfish 
Istiompax indica 
1 
227-227 
227.0 
0.0 
1 
235-235 
235.0 
0.0 
- 
- 
Makaira nigricans 
4 
245-277 
264.5 
13.9 
3 
236-258 
245.7 
11.2 
18.83 
0.11 
Kajikia audax 
13 
175-228 
194.2 
18.4 
8 
175-217 
192.3 
13.9 
1.90 
0.83 
Istiophorus platypterus 
2 
210-211 
210.5 
0.7 
5 
184-219 
205.6 
13.4 
- 
- 
Tetrapturus angustirostris 
2 
155-165 
160.0 
7.1 
6 
146-163 
155.3 
7.2 
- 
- 
Xiphias gladius 
519 
64-249 
151.9 
30.6 
499 
67-251 
149.9 
29.3 
2.00 
0.28 
Tuna 
Thunnus alalunga 
7 
98-109 
103.3 
3.7 
3 
98-102 
100.0 
2.0 
3.29 
0.25 
Thunnus obesus 
6 
76-162 
121.3 
38.2 
14 
76-164 
127.2 
22.9 
-5.88 
0.67 
Thunnus albacares 
11 
80-165 
137.8 
22.6 
8 
132-172 
148.5 
15.7 
-10.68 
0.29 
Other bony fishes 
Alepisaurus brevirostris 
3 
68-92 
77.3 
12.9 
3 
64-100 
81.3 
18.0 
-4.00 
0.78 
Alepisaurus ferox 
37 
71-139 
102.3 
18.2 
54 
45-152 
102.5 
23.5 
-0.24 
0.97 
Sphyraena spp 
- 
- 
- 
- 
4 
94-132 
118.8 
17.7 
- 
- 
Centrolophidae 
- 
- 
- 
- 
1 
76-76 
76.0 
0.0 
- 
- 
Coryphaena hippurus 
66 
67-130 
101.7 
13.5 
71 
65-121 
96.9 
12.4 
4.77 
0.03 
Gempylus serpens 
37 
78-155 
105.9 
15.0 
51 
77-149 
107.6 
14.1 
-1.78 
0.58 
Lampris guttatus 
- 
- 
- 
- 
1 
106-106 
106.0 
0.0 
- 
- 
Lepidocybium flavobrunneum 
24 
64-132 
104.1 
17.5 
36 
51-136 
97.6 
21.7 
6.49 
0.23 
Ruvettus pretiosus 
4 
49-60 
55.5 
4.8 
2 
54-55 
54.5 
0.7 
- 
- 
Regalecidae 
- 
- 
- 
- 
1 
171-1 
171.0 
0.0 
- 
- 
Acanthocybium solandri 
1 
141-141 
141.0 
0.0 
5 
100-140 
119.2 
17.3 
- 
- 
Sharks 
Prionace glauca 
318 
127-281 
190.6 
35.3 
433 
108-279 
198.2 
38.1 
-7.64 
0.00 
Alopias superciliosus 
5 
115-192 
171.0 
31.6 
1 
162-162 
162.0 
0.0 
- 
- 
Carcharhinus longimanus 
- 
- 
- 
- 
3 
88-148 
108.3 
34.4 
- 
- 
Lamna nasus 
- 
- 
- 
- 
1 
247-247 
247.0 
0.0 
- 
- 
Pseudocarcharias kamoharai 
- 
- 
- 
- 
1 
88-88 
88.0 
0.0 
- 
- 
Isurus oxyrinchus 
10 
152-228 
204.3 
23.1 
14 
138-227 
186.4 
26.9 
17.87 
0.10 
Sphyrna zygaena 
- 
- 
- 
- 
3 
169-179 
173.3 
5.1 
- 
- 
Turtles 
Caretta caretta 
- 
- 
- 
- 
1 
65-65 
65.0 
0.00 
- 
- 
lower catch rates of sharks, particularly blue shark. 
Other authors have reported similar results in the At¬ 
lantic (Afonso et al., 2012) and Pacific oceans (Ward et 
al., 2008; Vega and Licandeo, 2009). However, earlier 
studies in the Atlantic Ocean, by Branstetter and Mu- 
sick (1993) and Stone and Dixon (2001), showed the 
opposite result for the blue shark. Differences in the 
length of wire leaders, diameter of monofilament lead¬ 
ers and target species may account for the differences 
in catches rates among studies. For example, in the 
Stone and Dixon (2001) study the lower section (leader) 
of both gangion types was monofilament nylon and the 
upper section varied between tarred and no-tarred ny¬ 
lon material. Additionally, in our study the wire lead¬ 
ers were 2 to 3 times longer than those used in earlier 
studies and this change could have contributed to some 
of the observed differences. 
As with our study, other authors have also reported 
similar trends in rates of bite-offs and that most of 
these events occurred when the use of nylon leaders 
(e.g., Ward et al, 2008; Afonso et al., 2012). However, 
the level of bite-off rates varies considerably between 
the fishing grounds and fisheries. We found rates simi¬ 
lar to those reported by Afonso et al. (2012) for a Bra¬ 
zilian swordfish fishery in the Atlantic Ocean (about 
30% of shark catches), but much lower rates (by one 
order of magnitude) than those reported by observers 
on a tuna longline off northeastern Australia (Ward 
et al, 2008). Among the captured species, sharks are 
most likely to be responsible for the majority of bite- 
