Mendez-Madas et al.: Trophic ecology and ontogenetic shift in the diet of Mustelus lunulatus in the southeastern Pacific Ocean 
251 
Other prey 
Fish remains 
Pilumnus fernandezi 
Euphylax robustus 
Acanthocarpus delsolari 
lliacantha spp. 
Calappa saussurei 
L (Loliolopsis) diomedeae 
Squilla panamensis 
Crustacean remains 
Achelous iridescens 
Figure 3 
Diet composition of sicklefin smoothhounds (Mustelus lunulatus ) caught in 
the southeastern Pacific Ocean between November 2003 and October 2004, by 
stage of sexual maturity (juvenile and adult). 
well as for the different stages of sexual 
maturity (Table 4), size classes (Table 5), 
and trimesters. The B i values were 0.50, 
0.18, 0.06, and 0.05 for Trimesters I, II, 
III, and IV, respectively. 
The trophic overlap index revealed 
high dietary overlap between the sexes 
(CX= 0.92, global i?=0.009, P=0.072). When 
applied to the stages of sexual maturity 
this index showed that the diet of adult 
females significantly overlaped with 
that of juveniles, both females and males 
(Table 4). However, there was little trophic 
overlap between size classes (Table 5). 
The estimated trophic position (3.59 
[standard deviation (SD) 0.24]) indi¬ 
cates that the sicklefin smoothhound 
is a secondary consumer. Also, by sex, 
maturity stage (Table 4), and size class 
(Table 5), this species is a secondary 
consumer. 
Discussion 
Size I 
Size II 
Size 
O Achelous iridescens 
HI Squilla panamensis 
103 Calappa saussurei 
H L. (Loliolopsis) diomedeae 
H Fish remains 
L| Crustacean remains 
lJ lliacantha spp. 
E5 Euphylax robustus 
[•« Acanthocarpus delsolari 
|I] Other prey 
Figure 4 
Diet composition of sicklefin smoothhounds (Mustelus lunulatus ) caught in 
the southeastern Pacific Ocean between November 2003 and October 2004, 
by size class. The size classes are 60-90 cm in total length (TL, Size I, re=100), 
90-120 cm TL (Size II, n=183), and 120-150 cm TL (Size III, n=32). 
Dietary niche breadth, overlap, and trophic position 
The standardized niche breadth index showed that the 
sicklefin smoothhound is a selective predator. This was the 
case for both females (f? A =0.06) and males (B A = 0.05), as 
The few studies on the trophic ecology 
of the sicklefin smoothhound mention 
that its diet includes crustaceans (e.g., 
shrimps, blue crabs, and other crabs), 
small fishes (e.g., anchovies and sardines), 
and, occasionally, mollusks (Fernandez, 
1975; Gomez et al., 2003; Navia et al., 
2006; Navia et al., 2007), with crustaceans 
being the most important prey group. 
These results are in line with those of 
this study, allowing the sicklefin smooth¬ 
hound to be classified as a carcinophagous 
predator. 
Dietary studies of other members of 
Mustelus have shown that this taxon pre¬ 
fers crustaceans. The humpback smooth¬ 
hound (M. whitneyi), for example, eats 
crabs of the families Calappidae and 
Portunidae and shrimps of the family 
Squillidae and consumes small propor¬ 
tions of seaweed, annelids, mollusks, and 
fishes (Samame et al., 1989). The brown 
smoothhound (M. henlei) feeds mostly 
on crabs, shrimps (Squillidae), isopods, 
tunicates, cephalopods, and small fishes 
(e.g., Fischer et al., 1995; Gomez et al., 
2003). These similarities in the diet of 
Mustelus species indicate that they prey 
on benthic crustaceans. 
We found that the crabs A. iridescens and lliacantha 
spp. were the main prey of sicklefin smoothhounds, simi¬ 
lar to what was reported by Gomez et al. (2003) and 
Bohorquez-Herrera (2006) for Gorgona Island, Colombia. 
Our results are also consistent with those of studies 
