245 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
n* established in 1881 •<?> 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Trophic ecology and ontogenetic shift in the diet 
of the sicklef in smoothhound (Mustelus lunulatus) 
in the southeastern Pacific Ocean 
Jose S. Mendez-Macias 1 
Vanessa M. Velazquez-Chiquito 1 
Colombo Estupinan-Montaho (contact author ) 2 
Felipe Galvan-Magarta 3 
Email address for contact author: goliathcem@gmail.com 
Abstract— The feeding habits of the 
sicklefin smoothhound ( Mustelus lunula¬ 
tus) were studied on the basis of 
analysis of stomach contents of 314 
specimens, allowing the diet of this 
species to be determined by sex, size, 
and stage of sexual maturity and for 
changes in the dietary ontogeny to be 
identified. The prey-specific index of 
relative importance revealed that the 
sicklefin smoothhound is a crab preda¬ 
tor. Female and male sicklefin smooth- 
hounds consumed a swimming crab 
species, Achelous iridescens, in similar 
proportions. Adults and juveniles of 
both sexes complemented their diets 
with the Panama mantis shrimp ( Squil- 
la panamensis), the dart squid, Lolli- 
guncula (Loliolopsis) diomedeae, and 
the crab species Euphylax robustus, 
indicating behavioral and habitat seg¬ 
regation. Ontogenetic changes in diet 
were identified, with juveniles feeding 
almost exclusively on A. iridescens and 
adults having a more varied diet. The 
diet of sicklefin smoothhounds also 
changed with size: sharks <90 cm in 
total length (TL) consumed more A. iri¬ 
descens, and sharks >90 cm TL fed on 
a wider variety of prey. These results 
indicate that the sicklefin smooth¬ 
hound is a selective mesopredator in 
the coastal marine food chain, having a 
significant influence on populations of 
benthic crustaceans in the southeast¬ 
ern Pacific Ocean. 
Manuscript submitted 31 October 2018. 
Manuscript accepted 21 August 2019. 
Fish. Bull. 117:245-257 (2019). 
Online publication date: 30 August 2019. 
doi: 10.7755/FB.117.3.11 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
1 Facultad Ciencias del Mar 
Universidad Laica "Eloy Alfaro" de Manabi 
Avenida Circunvalacion, Via a San Mateo 
Manta, Manabi, Ecuador 
2 Fundacion Alium Pacific 
Carrera 26 No. 5C-13 
Santiago de Cali, Valle del Cauca, Colombia 
3 Centro Interdisciplinario de Ciencias Marinas 
Institute Politecnico Nacional 
Avenida Institute Politecnico Nacional s/n 
Colonia Playa Palo de Santa Rita 
23096 La Paz, Baja California Sur, Mexico 
Sharks generally occupy high positions 
in the food chain (Cortes, 1999), and 
some play an important role as regula¬ 
tors of lower trophic positions (Stevens 
et al., 2000; Heithaus et al., 2008; Fer- 
retti et al., 2010). Such top-down control 
can be key to maintaining the health of 
the marine ecosystem because a decline 
in top-level predator populations can 
lead to trophic cascades, thereby chang¬ 
ing the abundance of lower trophic-level 
populations (Ferretti et ah, 2010). For 
example, some authors have hypoth¬ 
esized that the removal of sharks can 
cause a significant increase in the bio¬ 
mass of smaller sharks (mesopreda- 
tors), sea turtles, sea birds, and fishes 
(Heithaus et ah, 2010). 
Understanding the ecological role 
of a species in an ecosystem depends 
mostly on knowing its trophic relation¬ 
ships (Braga et al., 2012). The trophic 
ecology of a species can in turn provide 
the information required for studies on 
resource sharing, competition, energy 
transfer, and food web dynamics (Navia 
et al., 2010; Bornatowski et al., 2014a). 
These more complex approaches rely 
on basic diet descriptions and are 
affected by the lack of basic knowledge 
of the diet of fish species (Bornatowski 
et al., 2014b). Understanding the tro¬ 
phic interactions and positions of large 
predators within food webs is a crucial 
step toward unraveling the dynamics 
of marine communities and the effect 
of sharks on different food web compo¬ 
nents (Lucifora et al., 2009; Heithaus 
et al., 2013). 
The sicklefin smoothhound ( Mus¬ 
telus lunulatus) is an abundant spe¬ 
cies in warm temperate and tropical 
waters of the eastern Pacific Ocean 
(Compagno, 1984). This species typi¬ 
cally inhabits muddy bottoms (Fernan¬ 
dez, 1975) of the continental shelf 
and offshore areas (Compagno, 1984; 
Fischer et al., 1995) and feeds mainly 
