254 
Fishery Bulletin 117(3) 
Table 3 
Contribution of prey to the similarity of diet, by sex, stage of sexual maturity, and size class, for sicklefin smoothhounds (Mustelus 
lunulatus) caught in the southeastern Pacific Ocean during November 2003-Oetober 2004, based on similarity percentage analy¬ 
sis. The maturity stages are juvenile (J.) and adult (A.), and the size classes are 60-90 cm in total length (TL, Size I), 90-120 cm 
TL (Size II), and 120—150 cm TL (Size III). A dash indicates that data were not available because the prey species was not shared 
between categories. 
Combination 
Prey 
J. female vs. 
A. female 
J. male vs. 
A. male 
J. female 
vs. J. male 
A. female 
vs. A. male 
J. female 
vs. A. male 
A. female 
vs. J. male 
Size I vs. 
Size II 
Size I vs. 
Size III 
Size II vs. 
Size III 
Dissimilarity (%) 
86.28 
84.00 
80.40 
88.48 
82.67 
85.23 
82.37 
89.30 
90.92 
Achelous iridescens 
34.52 
39.24 
45.82 
27.29 
33.46 
39.00 
38.46 
28.78 
25.35 
Lolliguncula (Loliol- 
opsis) diomedeae 
9.19 
— 
8.52 
5.36 
5.66 
8.38 
5.67 
11.73 
10.87 
Squilla panamensis 
8.43 
- 
7.11 
5.25 
5.34 
7.11 
5.41 
10.16 
9.11 
Iliacantha spp. 
7.76 
10.47 
8.97 
9.46 
10.93 
7.38 
9.99 
- 
6.20 
Calappula saussurei 
5.61 
8.94 
5.69 
8.71 
9.29 
- 
7.61 
- 
5.22 
Mursia spp. 
- 
6.97 
- 
9.17 
6.31 
- 
- 
9.66 
9.67 
Euphylax robustus 
- 
- 
- 
- 
- 
- 
- 
6.39 
6.54 
Ethusa spp. 
- 
- 
- 
- 
- 
- 
- 
- 
5.17 
Mollusks 
13.16 
5.98 
11.69 
8.09 
8.98 
11.43 
7.86 
16.78 
17.3 
Crustaceans 
82.18 
90.2 
84.48 
87.21 
85.72 
85.34 
87.63 
77.16 
77.49 
Fishes 
4.66 
3.82 
3.84 
4.70 
5.30 
3.33 
4.51 
6.06 
5.21 
Table 4 
Dietary overlap between stages of sexual maturity, dietary niche breadth (.B A ), and trophic position (TP) 
for sicklefin smoothhounds (Mustelus lunulatus) caught in the southeastern Pacific Ocean during Novem¬ 
ber 2003-October 2004. An asterisk (*) indicates high overlap. n=number of stomachs analyzed. 
Maturity stage and sex 
Juvenile 
male (n= 54) 
Adult male 
(n= 90) 
Juvenile 
female (n= 90) 
Adult female 
(n=81) 
b a 
TP 
Juvenile male 
_ 
0.03 
3.86 
Adult male 
0.34 
- 
0.15 
3.49 
Juvenile female 
0.02 
0.31 
- 
0.03 
3.85 
Adult female 
0.60* 
0.47 
0.56* 
- 
0.29 
3.30 
almost exclusively of A. iridescens to one including other 
crustaceans, cephalopods, and fishes. This diet change 
may be related 1) to hunting ability and skill and 2) to 
the morphology of the mouth and jaw (Luczkovieh et a!., 
1995). In addition, this change in diet is reflected in the 
narrow trophic niche and the low dietary overlap between 
organisms of different size classes of sicklefin smooth¬ 
hounds considered in this study (Table 5). 
Because sharks exhibit characteristics typical of top- 
level predators, they are thought to regulate prey commu¬ 
nities through top-down control (e.g., Ferretti et ah, 2010; 
Navia et al., 2010; Bornatowski et a!., 2014b), together 
with habitat structure and ecosystem productivity (Estes 
et ah, 2011; Ripple et ah, 2014). Consequently, they are 
regarded as a key functional group (Frisch et ah, 2016). 
Sharks are attributed important roles in marine food 
webs; however, few studies have provided evidence of the 
presumably high trophic positions of some shark species 
(Cortes, 1999). 
Nonetheless, it is worth noting that not all sharks are 
top-level predators in a given ecosystem because the 
potential ecological functions of the species are related to 
a variety of factors, such as feeding habits, maximum body 
length, geographic and environmental range, the extent to 
which they are omnivorous, and vulnerability to predation 
by other sharks. Hence, the results of the study by Roff 
et al. (2016) indicate that sharks can exercise functions as 
high-level predators (maximum TL >300 cm, geographic 
