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Fishery Bulletin 117(3) 
on benthic crustaceans (Gomez et ah, 2003; Navia et al., 
2007; Moreno-Sanchez et al., 2012). The sicklefin smooth- 
hound is a placental viviparous species (Compagno, 1984) 
that reaches a maximum total length (TL) of approxi¬ 
mately 170 cm (Compagno, 1984). Mature females and 
males typically have TLs of approximately 103.2 and 
91.5 cm, respectively (Perez-Jimenez and Sosa-Nishizaki, 
2010), and the TL at birth is 32-35 mm (Compagno, 
1984). Despite its abundance, little is known about the 
biology and ecology of the sicklefin smoothhound. Studies 
on the trophic ecology of sharks are scarce in Ecuador, 
and no research on the sicklefin smoothhound has been 
undertaken. Therefore, this study is the first to address 
the trophic ecology of this shark species in this region. 
The objectives of this study were 1) to collect quantita¬ 
tive dietary information for sicklefin smoothhounds, 2) 
to test for ontogenetic shifts in diet between stages of 
sexual maturity and size classes, and 3) to estimate the 
relative trophic position of sharks. Because of the rapid 
decline in the populations of several shark species (Bor- 
natowski et al., 2014b), it is critical that we build our 
understanding of these patterns and processes to develop 
appropriate conservation strategies. 
The prey were identified to the lowest taxon possible 
(on the basis of the digestion state of prey), counted, and 
weighed in grams. The prey species (i.e., complete organ¬ 
isms, skeletons, and otoliths) were identified according to 
Clothier (1950), Fischer et al. (1995), Chirichigno and Velez 
(1998), and Garcia-Godos (2001). The cephalopod species 
were identified by using their beaks (mandible) according 
to Wolff (1984) and Clarke (1986), and crustacean species 
were identified by their exoskeleton by using the keys from 
Garth (1973) and Fischer et al. (1995). 
Cumulative prey curve 
To determine whether the number of stomachs was suffi¬ 
cient to adequately describe the diet of sicklefin smooth- 
hounds, a cumulative prey curve was constructed. The 
observed number of each prey item in the stomachs was 
used to estimate the value of the Shannon-Wiener diver¬ 
sity index for each stomach, and the samples were random¬ 
ized 500 times with a sample-based rarefaction routine by 
using the software Estimates, vers. 9 (Colwell, 2013). The 
coefficient of variation (0.05) was the basis for determining 
whether the number of stomachs was sufficient. 
Materials and methods 
We analyzed the stomach contents of 314 specimens of 
the sicklefin smoothhound. All sharks were caught by the 
artisanal fishery in Ecuador with gill nets and longlines 
in depths of 80-90 m along the continental platform and 
were landed in the port of Manta in Manabi, Ecuador, 
between November 2003 and October 2004 (Fig. 1). 
For each specimen, natural TL (Francis 2006) was mea¬ 
sured in centimeters and sex was determined before the 
digestive tract was extracted. Stomach contents were 
removed and filtered through a 1.5-mm mesh sieve, stored 
in plastic bags, and preserved on ice for transportation to 
the laboratory. 
Dietary analyses 
To assess the importance of the different prey taxa in the 
diet of sicklefin smoothhounds (overall and by sex, stage 
of sexual maturity, size class, and trimester), the prey- 
specific index of relative importance ( PSIRI ; ) (Brown et al., 
2012), a modification of the index of relative importance 
(IRI) proposed by Pinkas et al. (1971) was used, according 
to this equation: 
PSIRI = %FO t x (%PN l + %PW t ) (1) 
1 2 
where %FO^ is the percent frequency of occurrence of a 
specific prey in all samples and %PN { and %PW { are the 
substitution of IRI’s prey percent num¬ 
ber and prey percent weight with their 
corresponding prey-specific abundances. 
Unlike the IRI, the PSIRI is cumulative 
with respect to taxonomic levels. The 
PSIRI of a major taxon is equal to the 
sum of the PSIRI of the items belonging 
to that taxon (Brown et al., 2012). 
Stages of sexual maturity were deter¬ 
mined on the basis of Perez-Jimenez 
and Sosa-Nishizaki (2010), who report 
that the average size of sicklefin smooth¬ 
hounds at sexual maturity in their study 
was 103.2 cm TL for females and 91.5 cm 
TL for males. The specimens caught were 
between 63 and 142 cm TL. They were 
grouped into 3 size classes (of both sexes) 
with a constant length range: 60-90 cm 
TL (Size I), 90-120 cm TL (Size II), and 
120-150 cm TL (Size III). 
95°W 93°W 91 °W 89°W 87°W 85°W 83°W 81 °W 79°W 
Figure 1 
Map of the study area showing the port of Manta, Ecuador, where sicklefin 
smoothhounds (Mustelus lunulatus) were collected from landings of an arti¬ 
sanal fishery between November 2003 and October 2004. The fishing area of 
the artisanal fishery and depth zones are also indicated. 
